schwannoma

Olfactory groove schwannoma

Olfactory Groove Schwannoma: A Rare Intracranial Tumor – Case Studies and Review

Test

Olfactory Groove Schwannoma Test

  1. What is the primary location of Olfactory Groove Schwannomas?
    1. [ ] a) Temporal lobe
    2. [x] b) Frontal lobe
    3. [ ] c) Occipital lobe
    4. [ ] d) Parietal lobe
  1. Which of the following is NOT a common symptom of Olfactory Groove Schwannoma?
    1. [ ] a) Anosmia
    2. [ ] b) Visual disturbances
    3. [x] c) Auditory hallucinations
    4. [ ] d) Headaches
  1. What is the primary treatment option for Olfactory Groove Schwannomas?
    1. [ ] a) Radiation therapy
    2. [ ] b) Chemotherapy
    3. [x] c) Surgical resection
    4. [ ] d) Medication
  1. Which of the following statements is true regarding Olfactory Groove Schwannomas?
    1. [x] a) They often originate from Schwann cells in the olfactory groove.
    2. [ ] b) They primarily affect the optic nerve.
    3. [ ] c) They are associated with frequent auditory deficits.
    4. [ ] d) They cannot be treated surgically.
  1. Olfactory Groove Schwannomas can sometimes be confused with which other tumors?
    1. [ ] a) Glioblastomas
    2. [x] b) Olfactory groove meningiomas
    3. [ ] c) Medulloblastomas
    4. [ ] d) Astrocytomas
  1. What is the typical outcome after complete surgical resection of an Olfactory Groove Schwannoma?
    1. [ ] a) Poor prognosis
    2. [ ] b) Neurological deficits
    3. [x] c) Favorable prognosis
    4. [ ] d) Olfactory dysfunction
  1. What is the primary goal of surgical resection in treating Olfactory Groove Schwannomas?
    1. [ ] a) Complete removal of the tumor with no concern for neurological function
    2. [x] b) Partial removal of the tumor while preserving neurological function
    3. [ ] c) Eliminating olfactory function
    4. [ ] d) None of the above
  1. According to the provided information, what is the controversial aspect of Olfactory Groove Schwannoma origin?
    1. [ ] a) They always originate from the olfactory nerve.
    2. [x] b) Their origin remains unknown.
    3. [ ] c) They originate from the optic nerve.
    4. [ ] d) They develop due to hormonal imbalances.
  1. In which cranial fossa are Olfactory Groove Schwannomas predominantly located?
    1. [ ] a) Middle cranial fossa
    2. [ ] b) Posterior cranial fossa
    3. [x] c) Anterior cranial fossa
    4. [ ] d) Inferior cranial fossa
  1. Which specific cells are responsible for the formation of Schwannomas?
    1. [ ] a) Oligodendrocytes
    2. [x] b) Schwann cells
    3. [ ] c) Neurons
    4. [ ] d) Astrocytes

Abstract

Olfactory groove schwannoma is an uncommon intracranial tumor originating in the olfactory groove and is primarily associated with benign schwann cells. This review aims to provide insights into the clinical characteristics, diagnosis, treatment, and prognosis of this rare entity. Olfactory groove schwannomas are predominantly located in the anterior cranial fossa, often resulting in symptoms such as headaches, anosmia, visual disturbances, personality changes, and cognitive deficits. Diagnosis typically involves neuroimaging studies like MRI and CT scans. Surgical resection is the primary treatment option, with the goal of preserving neurological function, and sometimes complemented with radiation therapy for inoperable cases. While olfactory groove schwannomas are generally benign, each case presents unique challenges, and a multidisciplinary approach is essential for comprehensive patient care. Additionally, there is an ongoing debate about their origin, with both developmental and non-developmental hypotheses being proposed. Differential diagnosis should consider other tumors, such as olfactory groove meningiomas and esthesioneuroblastomas. This review also discusses case reports to shed light on the complex nature of olfactory groove schwannomas. Understanding the diverse aspects of this rare tumor is crucial for accurate diagnosis, management, and patient outcomes.

Keywords: Olfactory groove schwannoma, anterior cranial fossa, diagnosis, surgical resection, prognosis, differential diagnosis, case reports.

Introduction

Olfactory groove schwannoma is a rare type of tumor that arises in the olfactory groove of the skull. Schwannomas are typically benign tumors that originate from Schwann cells, which are responsible for the formation of the myelin sheath covering nerves. When a schwannoma develops in the olfactory groove, it usually arises from the olfactory nerve or its branches.

Here are some key points about olfactory groove schwannomas:

Location: Olfactory groove schwannomas are found in the anterior cranial fossa, where the olfactory bulb and tract are located. They can grow and compress nearby structures, including the frontal lobes of the brain.

Symptoms: The symptoms of an olfactory groove schwannoma can vary depending on its size and location. Common symptoms may include headaches, changes in smell (anosmia), visual disturbances, personality changes, and cognitive deficits.

Diagnosis: Diagnosis often involves neuroimaging studies, such as magnetic resonance imaging (MRI) or computed tomography (CT) scans. These tests can help visualize the tumor and its impact on adjacent structures.

Treatment: The primary treatment for olfactory groove schwannomas is surgical resection. The goal of surgery is to remove the tumor while preserving neurological function. In some cases, a combination of microsurgery and endoscopy may be used to access and remove the tumor. Radiation therapy may be considered for residual or inoperable tumors.

Prognosis: Olfactory groove schwannomas are typically slow-growing and benign, which generally results in a favorable prognosis after surgical removal. The long-term outcome depends on factors such as the extent of tumor resection and the patient’s overall health.

Differential Diagnosis: Olfactory groove schwannomas may be mistaken for other tumors, such as olfactory groove meningiomas, which are more common in this region. A precise diagnosis is essential for determining the most appropriate treatment plan.

Multidisciplinary Approach: Managing olfactory groove schwannomas often requires a multidisciplinary approach involving neurosurgeons, otolaryngologists, and neurologists to provide comprehensive care.

It’s important to note that while olfactory groove schwannomas are generally benign, each case is unique, and treatment decisions should be made in consultation with a medical team specializing in neurosurgery and neuro-oncology.

According to past reports, subfrontal schwannomas are occasionally described as olfactory schwannomas or olfactory groove schwannomas.

Epidemiology

Schwannoma arising from the olfactory system, often called olfactory groove schwannoma (OGS), is rare, as the olfactory bulb and tract, belonging to the central nervous system, should lack Schwann cells. Another rare entity called olfactory ensheathing cell tumor (OECT) has been reported, which mimics clinical and radiological characteristics of OGS.

They are very rare tumors, leaving the issue of their origin controversial.

In 94 patients with anterior skull base (ASB) and sinonasal schwannomas, 44 (46.8%) were exclusively sinonasal, 30 cases (31.9%) were exclusively intracranial, 12 (12.8%) were primarily intracranial with extension into the paranasal sinuses, and 8 (8.5%) were primarily sinonasal with intracranial extension 1).

Li et al. gathered previous literatures and reported that results in 35 cases of olfactory schwannomas (between 1974 and 2010) has shown that 14 out of 30 cases (47%) (with the exclusion of five cases due to unknown olfactory function) had preserved olfactory function, but that the remaining 16 (53%) experienced either anosmia or hyposmia. Regarding the attachment sites of the schwannomas, they summarized that 12 cases were on the cribriform plate, 10 cases were on the olfactory groove, and 5 cases were on the skull base and skull base dura. When the tumor was attached to the cribriform plate, the rate of olfaction preservation was relatively high [9 of 11 cases (82%), excluding one case due to unknown olfactory function], compared to olfactory groove attachment [2 of 7 cases (29%), excluding three cases due to unknown olfactory function].

Figueiredo et al. systematically reviewed the literature concerning the anterior cranial fossa schwannomas to understand their pathogenesis, determine their origin, and standardize the terminology. They performed a MEDLINE, EMBASE, and Science Citation Index Expanded search of the literature; age, gender, clinical presentation, presence or absence of hyposmia, radiological features, and apparent origin were analyzed and tabulated. Cases in a context of neurofibromatosis and nasal schwannomas with intracranial extension were not included. Age varied between 14 and 63 years (mean = 30.9). There were 22 male and 11 female patients. The clinical presentation included seizures (n = 15), headache (n = 16), visual deficits (n = 7), cognitive disturbances (n = 3), and rhinorrhea (n = 1). Hyposmia was present in 14 cases, absent in 13 cases (39.3%), and unreported in five. Homogeneous and heterogeneous contrast enhancement was observed in 14 and 15 cases, respectively. The region of the olfactory groove was the probable site in 96.5%. Olfactory tract could be identified in 39.3%. The most probable origin is the meningeal branches of trigeminal nerve or anterior ethmoidal nerves. Thus, olfactory groove schwannoma would better describe its origin and pathogenesis and should be the term preferentially used to name it 2).

Etiology

Because the olfactory and optic nerves lack a Schwann cell layer, these are not prone to develop into a schwannoma.

Some hypotheses about the genesis of olfactory groove schwannoma are centered on its developmental and non-developmental origins.

The developmental hypotheses suggest whether mesenchymal pial cells to transform into ectodermal Schwann cells or neural crest cells to migrate within the substance of the central nervous system .

The non-developmental hypotheses postulate that intracranial schwannomas arise from the Schwann cells normally presenting in the adjacent structures, such as the perivascular nerve plexus, the meningeal branches of the trigeminal and anterior ethmoidal nerves innervating the anterior cranial fossa and olfactory groove 3) 4).

Yasuda et al. 5) proposed the concept of an olfactory ensheathing cell (OEC) tumor in 2006. Olfactory ensheathing cells are glial cells that ensheath the axons of the first cranial nerve. Microscopically, both olfactory ensheathing cells and Schwann cells have similar morphological and immunohistochemical features. However, immunohistochemically olfactory ensheathing cells are negative for Leu7 and Schwann cells positive 6).

Differential diagnosis

Often, these tumors can be confused for other entities, especially olfactory groove meningiomas and esthesioneuroblastomas 7).

Treatment

Because most olfactory region schwannomas have a benign nature, a complete resection of the tumor is the treatment of choice, and adjunctive therapy is not usually required 8) 9).

With the recent advances in endoscopic skull base surgery, various anterior skull base tumors (ASB) can be resected successfully using an expanded endoscopic endonasal transcribriform approach through a “keyhole craniectomy” in the ventral skull base. This approach represents the most direct route to the anterior cranial base without any brain retraction. Tumor involving the paranasal sinuses, medial orbits, and cribriform plate can be readily resected. In a video atlas report, Liu and Eloy demonstrate their step-by-step techniques for resection of an ASB olfactory schwannoma using a purely endoscopic endonasal transcribriform approach. They describe and illustrate the operative nuances and surgical pearls to safely and efficiently perform the approach, tumor resection, and multilayered reconstruction of the cranial base defect. The video can be found here: http://youtu.be/NLtOGfKWC6U 10).

Endoscopic Endonasal Anterior Cranial Fossa Approach 11)

Prognosis

The prognosis after complete resection is known to be favorable 12).

When the tumor is attached to the cribriform plate, the preservation rate of olfactory function is higher compared to nearby structures 13).

Case reports

A 65-year-old male patient who presented with olfactory groove meningioma and non-functioning pituitary adenoma as a collision tumor. The patient was admitted with a headache and right-sided vision loss. The patient’s first neurologic examination was consistent with temporal anopsia in the right eye. Subsequent contrast-enhanced cranial MRI revealed a 65x55x40 mm heterogeneously contrast-enhanced lesion in the anterior skull base extending from the sellar region to the corpus callosum. Because of the tumor size, a two-staged operation was planned. First, the tumor was partially excised via a right frontal craniotomy with a transcranial approach, and the tumor in the sellar region was left as a residue. The pathology reports after the first surgery showed pituitary adenoma and meningeal epithelial type meningioma (WHO Grade I). The residual tumor tissue was resected seven months later via an endoscopic endonasal approach, except for the part that invaded the right anterior cerebral artery. The optic nerve was decompressed. The patient was then referred to the radiation oncology clinic for radiosurgery. Collision tumors should be considered in the differential diagnosis in preoperative evaluation and surgical planning when heterogeneously contrast-enhanced areas significantly localized adjacent to each other are seen on cranial MRI. On the other hand, when the surgeon encounters sudden changes in the appearance or consistency of the tumor during the surgery, they should suspect these tumor complexes. The diagnosis of collision tumors is quite challenging but is of great importance regarding the patient’s need for postoperative radiation therapy or the recurrence characteristics of tumors. However, more studies are needed on these complexes’ etiology, surgical planning, and postoperative management 14).

A 59-year-old woman who presented with a paroxysmal headache for 1 year. The tumor appeared as hypointensity on T1-weighted images, hyperintensity on T2-weighted, and exhibited strong, heterogeneous enhancement. The tumor was removed through a lateral supraorbital approach. The final pathologic diagnosis was schwannoma. The postoperative period was uneventful after 4 months, and the headache disappeared 15).

2016

Bohoun et al report two rare cases of schwannoma-like tumor in the anterior cranial fossa that showed negative staining for Leu7, but positive staining for Schwann/2E, and discuss their origin. Two cases of mass lesions in the anterior cranial fossa in a 26-year-old man and a 24-year-old woman were successfully removed. Morphological examination of these tumors was compatible with a diagnosis of schwannoma. Immunohistochemically, both cases were negative for Leu7, yielding a diagnosis of olfactory ensheathing cell tumor (OECT), but were positive for the schwannoma-specific marker, Schwann/2E. Immunohistochemical staining results in this two cases question the current assumption that OGS and OECT can be distinguished only by Leu7 staining pattern. In conclusion, the origins of OGS and OECT remain to be determined, and further studies in larger numbers of cases are needed to characterize these rare tumors in the anterior cranial fossa 16)

2015

A case of a 49-year-old woman with an olfactory groove schwannoma attached to the cribriform plate without olfactory dysfunction. She had no specific neurological symptoms other than a headache, and resection of the tumor showed it to be a schwannoma. About 19 months after the operation, a follow-up MRI showed no evidence of tumor recurrence. Surgical resection through subfrontal approach could be one of the curative modality in managing an olfactory groove schwannoma. An olfactory groove schwannoma should be considered in the differential diagnosis of anterior skull base tumors 17).

2014

Okamoto et al. report two cases of subfrontal schwannomas treated with surgical resection. In one case, the tumor was located between the endosteal and meningeal layers of the dura mater. This rare case suggests that subfrontal schwannomas may originate from the fila olfactoria 18).

A 24 year old lady presented with hemifacial paraesthesias. Radiology revealed a large olfactory region enhancing lesion. She was operated through a transbasal approach with olfactory preservation. 19).

One patient had intradural intracranial extension and required an extended endoscopic endonasal transcribriform approach with anterior skull base resection 20).

2013

A 66-year-old woman presented with a 1-year history of progressive headaches. Clinical examination revealed hypoesthesia of the nasal tip. CT-scan and MRI studies revealed a large subfrontal tumor thought preoperatively to be a meningioma. Intraoperatively, a large extra-axial tumor arising from the floor of the right frontal fossa was encountered. Histopathology identified the tumor as a schwannoma. This current case gives strong clinical presumption of an origin from the anterior ethmoidal nerve. We reviewed the literature in order to establish the epidemiology of these tumors, from which there appear to be divergent profiles depending on tumor origin and histology. Despite close similarities with olfactory groove meningiomas, patient history and radiological findings provide substantial evidence for differential diagnosis 21).

2012

Liu and Eloy demonstrate their step-by-step techniques for resection of an ASB olfactory schwannoma using a purely endoscopic endonasal transcribriform approach.

A case of schwannoma arising from the olfactory groove in a 16-year-old girl who presented with generalized seizures without olfactory dysfunction or other neurologic deficits. Computerized tomography (CT) scan showed a large mass with abundant calcification located in the olfactory groove, which was confirmed as a schwannoma by histology and totally resected via basal subfrontal approach.

The tumor was attached to the cribriform plate, and achieved gross total resection without compromising her olfactory function 22).

Latest Pubmed Olfactory groove schwannoma- Related Articles

Conclusions

In conclusion, understanding the diverse aspects of olfactory groove schwannomas is crucial for accurate diagnosis, effective management, and improved patient outcomes. This rare tumor entity serves as a reminder of the complexity of intracranial pathologies and the need for ongoing research to better comprehend its origin and pathogenesis.

References

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Kim DY, Yoon PH, Kie JH, Yang KH. The olfactory groove schwannoma attached to the cribriform plate: a case report. Brain Tumor Res Treat. 2015 Apr;3(1):56-9. doi: 10.14791/btrt.2015.3.1.56. Epub 2015 Apr 29. PubMed PMID: 25977910; PubMed Central PMCID: PMC4426280.
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Aydin MV, Yangi K, Toptas E, Aydin S. Skull Base Collision Tumors: Giant Non-functioning Pituitary Adenoma and Olfactory Groove Meningioma. Cureus. 2023 Sep 5;15(9):e44710. doi: 10.7759/cureus.44710. PMID: 37809125; PMCID: PMC10552590.
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Guo W, Liu Z, Wang Z, Tian H, Zi X. Olfactory Groove Schwannoma or Olfactory Ensheathing cell Tumor? J Craniofac Surg. 2023 Aug 29. doi: 10.1097/SCS.0000000000009705. Epub ahead of print. PMID: 37643126.
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Bohoun CA, Terakawa Y, Goto T, Tanaka S, Kuwae Y, Ohsawa M, Morisako H, Nakajo K, Sato H, Ohata K, Yokoo H. Schwannoma-like tumor in the anterior cranial fossa immunonegative for Leu7 but immunopositive for Schwann/2E. Neuropathology. 2016 Dec 7. doi: 10.1111/neup.12357. [Epub ahead of print] PubMed PMID: 27925298.
18)

Okamoto H, Mineta T, Wakamiya T, Tsukamoto H, Katsuta T, Nakagaki H, Matsushima T. Two cases of subfrontal schwannoma, including a rare case located between the endosteal and meningeal layers of the dura. Neurol Med Chir (Tokyo). 2014;54(8):681-5. Epub 2013 Dec 5. PubMed PMID: 24305023.
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Salunke P, Patra DP, Futane S, Nada R. Olfactory region schwannoma: Excision with preservation of olfaction. J Neurosci Rural Pract. 2014 Jul;5(3):281-3. doi: 10.4103/0976-3147.133600. PubMed PMID: 25002774; PubMed Central PMCID: PMC4078619.
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Sauvaget F, François P, Ben Ismail M, Thomas C, Velut S. Anterior fossa schwannoma mimicking an olfactory groove meningioma: case report and literature review. Neurochirurgie. 2013 Apr;59(2):75-80. doi: 10.1016/j.neuchi.2013.02.003. Epub 2013 Apr 13. Review. PubMed PMID: 23587626.
22)

Li YP, Jiang S, Zhou PZ, Ni YB. Solitary olfactory schwannoma without olfactory dysfunction: a new case report and literature review. Neurol Sci. 2012 Feb;33(1):137-42. doi: 10.1007/s10072-011-0573-9. Epub 2011 Apr 12. Review. Erratum in: Neurol Sci. 2012 Feb;33(1):217. PubMed PMID: 21484358; PubMed Central PMCID: PMC3275737.

Vestibular schwannoma treatment

Vestibular schwannoma treatment

Optimal decision making in new diagnosed vestibular schwannoma remains a matter of debate. For small- to medium-sized lesions (Koos grading scale I–III), the options are radiosurgery (RS), microsurgery, or a “wait and-scan” approach 1).

This is mainly based on the hospital setting, as well as surgeon’s preference. It is worth noting that comparative studies advocate that GKS compares favorably with microsurgery, with high local tumor control, much lower rate of facial nerve palsy, and much higher rate of serviceable hearing preservation 2) 3) 4) 5) 6).

Conservative treatment

see Vestibular schwannoma conservative treatment.

Fractionated stereotactic radiotherapy

see Fractionated stereotactic radiotherapy for vestibular schwannoma

Radiosurgery

see Vestibular schwannoma radiosurgery.

Surgery

see Vestibular schwannoma surgery.

Subjects presented to the Department of Otolaryngology-Head and Neck Surgery and the Department of Neurosurgery at the Johns Hopkins University, Baltimore, Maryland for management of unilateral vestibular schwannoma from 1997 through 2007, with at least two visits within the first year of presentation. The proportion of patients for whom initial management consisted of observation, surgical resection, or radiation therapy was determined, and the relative influence of study year, patient age, hearing status, and tumor size was analyzed.

RESULTS: Over the study period there was an increase in the proportion of cases that were observed with follow-up scanning (10.5% to 28.0%) and recommended for radiation (0% to 4.0%), whereas the proportion of operated cases declined (89.5% to 68.0%). There were no changes in mean age or hearing status at diagnosis, but mean tumor size declined significantly. Compared to those undergoing surgery, patients choosing observation and radiation therapy were on average 11.7 and 4.5 years older, respectively. Tumors that were surgically removed were on average 11.6 mm larger than those that were observed. The increasing frequency over time of observation relative to surgery was significant even after controlling for age, hearing status, and tumor size.

CONCLUSIONS: Among patients managed by our center, there has been a significant shift in management of vestibular schwannomas over the last decade, with increasing tendency towards observation. This trend implies changing provider philosophy and patient expectations 7).

Patients with VS completed a voluntary survey over a 3-month period. Setting Surveys were distributed online through email, Facebook, and member website. Subjects and Methods All patients had a diagnosis of VS and were members of the Acoustic Neuroma Association (ANA). A total of 789 patients completed the online survey. Results Of the 789 participants, 474 (60%) cited physician recommendation as a significant influential factor in deciding treatment. In our sample, 629 (80%) saw multiple VS specialists and 410 (52%) sought second opinions within the same specialty. Of those who received multiple consults, 242 (59%) of patients reported receiving different opinions regarding treatment. Those undergoing observation spent significantly less time with the physician (41 minutes) compared to surgery (68 minutes) and radiation (60 minutes) patients ( P < .001). A total of 32 (4%) patients stated the physician alone made the decision for treatment, and 29 (4%) felt they did not understand all possible treatment options before final decision was made. Of the 414 patients who underwent surgery, 66 (16%) felt they were pressured by the surgeon to choose surgical treatment. Conclusion Deciding on a proper VS treatment for patients can be complicated and dependent on numerous clinical and individual factors. It is clear that many patients find it important to seek second opinions from other specialties. Moreover, second opinions within the same specialty are common, and the number of neurotologists consulted correlated with higher decision satisfaction 8).

From a total of 8330 patients (average age 54.7 years, 51.9% female) were analyzed and from 2004 to 2011, there was a statistically significant decrease in tumor size category at time of diagnosis (P < .01). Overall, 3982 patients (48%) received primary microsurgery, 1978 (24%) radiation therapy alone, and 2370 (29%) observation. Within the microsurgical cohort, 732 (18%) underwent subtotal resection, and of those, 98 (13.4%) received postoperative radiation therapy. Multivariable regression revealed that surgical treatment was more common in younger patients and larger tumor size categories (P < .05). Management trend analysis revealed that microsurgery was used less frequently over time (P < .0001), observation was used more frequently (P < .0001), and the pattern of radiation therapy remained unchanged. Linear regression was used to create an equation that was applied to predict future management practices. These data predict that by 2026, half of all cases of VS will be managed initially with observation.

While the incidence of VS has remained steady, tumor size at time of diagnosis has decreased over time. Within the United States there has been a clear, recent evolution in management toward observation 9).

Immunotherapy

Rapid progression of residual vestibular schwannoma following subtotal surgical resection has an underlying immune etiology that may be virally originating; and despite an abundant adaptive immune response, T-cell immunosenescence may be associated with rapid progression of VS. These findings provide a rationale for clinical trials evaluating immunotherapy in patients with rapidly progressing VS 10)

1)

Kondziolka D, Mousavi SH, Kano H, Flickinger JC, Lunsford LD. The newly diagnosed vestibular schwannoma: radiosurgery, resection, or observation? Neurosurg Focus 2012;33(03):E8
2)

Pollock BE, Lunsford LD, Kondziolka D, et al. Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery 1995;36(01):215- –224, discussion 224–229
3)

Régis J, Pellet W, Delsanti C, et al. Functional outcome after Gamma knife radiosurgery or microsurgery for vestibular schwannomas. J Neurosurg 2002;97(05):1091–1100
4)

Myrseth E, Møller P, Pedersen PH, Vassbotn FS, Wentzel-Larsen T, Lund-Johansen M. Vestibular schwannomas: clinical results and quality of life after microsurgery or Gamma Knife radiosurgery. Neurosurgery 2005;56(05):927–935, discussion 927– 935
5)

Myrseth E, Møller P, Pedersen PH, Lund-Johansen M. Vestibular schwannoma: surgery or Gamma Knife radiosurgery? A prospective, nonrandomized study. Neurosurgery 2009;64(04):654–661, discussion 661–663
6)

Pollock BE, Driscoll CL, Foote RL, et al. Patient outcomes after vestibular schwannoma management: a prospective comparison of microsurgical resection and stereotactic radiosurgery. Neurosurgery 2006;59(01):77–85, discussion 77–85
7)

Tan M, Myrie OA, Lin FR, Niparko JK, Minor LB, Tamargo RJ, Francis HW. Trends in the management of vestibular schwannomas at Johns Hopkins 1997-2007. Laryngoscope. 2010 Jan;120(1):144-9. doi: 10.1002/lary.20672. PubMed PMID: 19877188.
8)

Moshtaghi O, Goshtasbi K, Sahyouni R, Lin HW, Djalilian HR. Patient Decision Making in Vestibular Schwannoma: A Survey of the Acoustic Neuroma Association. Otolaryngol Head Neck Surg. 2018 Feb 1:194599818756852. doi: 10.1177/0194599818756852. [Epub ahead of print] PubMed PMID: 29436268.
9)

Carlson ML, Habermann EB, Wagie AE, Driscoll CL, Van Gompel JJ, Jacob JT, Link MJ. The Changing Landscape of Vestibular Schwannoma Management in the United States-A Shift Toward Conservatism. Otolaryngol Head Neck Surg. 2015 Jun 30. pii: 0194599815590105. [Epub ahead of print] PubMed PMID: 26129740.
10)

Amit M, Xie T, Gleber-Netto FO, Hunt PJ, Mehta GU, Bell D, Silverman DA, Yaman I, Ye Y, Burks JK, Fuller GN, Gidley PW, Nader ME, Raza SM, DeMonte F. Distinct immune signature predicts progression of vestibular schwannoma and unveils a possible viral etiology. J Exp Clin Cancer Res. 2022 Oct 4;41(1):292. doi: 10.1186/s13046-022-02473-4. PMID: 36195959.

Vestibular schwannoma natural history

Vestibular schwannoma natural history

see also Vestibular schwannoma conservative treatment.

Spontaneous involution of acoustic tumors does occur. Long-term follow-up is necessary to determine this potential 1).

Systematic review

Three-dimensional volumetric assessment of VS provides a more sensitive measure of tumor growth when compared with linear diameter assessment. Through volumetric analysis, a study revealed that a significant proportion of VSs demonstrate growth during observation 2).

An extensive MEDLINE search was performed to cull studies on VS growth according to sequential imaging. The percentages of growing and regressing tumors and lesions requiring treatment during follow-up periods were calculated. Factors associated with differences among studies were identified. Twenty-six studies including 1340 patients met all inclusion criteria. The overall frequency of VS growth during a mean follow-up period of 38 months was 46% (95% confidence interval [CI] 43-48%) and that of regression was 8% (95% CI 6-10%). The mean annual tumor growth rate was 1.2 mm/year. Furthermore, the percentage of cases requiring treatment during follow up was 18% (95% CI 16-21%). According to results of a sensitivity analysis, evaluation by serial MR imaging (39%, 95% CI 35-43%) and a prospective study design (29%, 95% CI 21-37%) were associated with less frequent reported tumor growth.

Conclusions: Although their applicability may be limited to relatively elderly patients with small tumors, data revealing a limited frequency of VS enlargement and an infrequent necessity for eventual therapy should assist decision-making in the treatment of small VSs causing minimal symptoms 3)

Case series

Volumetric tumor measurements from 3,505 serial MRI studies were analyzed from unselected consecutive patients undergoing wait-and-scan management at three tertiary referral centers between 1998 and 2018. Volumetric tumor growth was defined as a change in volume ≥20%.

Among 952 patients undergoing observation, 622 experienced tumor growth with initial growth-free survival rates (95% CI) at 1, 3, and 5 years following diagnosis of 66% (63-69), 30% (27-34), and 20% (17-24). Among 405 patients who continued to be observed despite demonstrating initial growth, 210 experienced subsequent tumor growth with subsequent growth-free survival rates at 1, 3, and 5 years following initial growth of 77% (72-81), 37% (31-43), and 24% (18-31). Larger tumor volume at initial growth (HR 1.13, p=0.02) and increasing tumor growth rate (HR 1.31; p<0.001) were significantly associated with an increased likelihood of subsequent growth, whereas a longer duration of time between diagnosis and detection of initial growth was protective (HR 0.69; p<0.001).

While most vestibular schwannomas exhibit an overall propensity for volumetric growth following diagnosis, prior tumor growth does not perfectly predict future growth. Tumors can subsequently grow faster, slower, or demonstrate quiescence and stability. Larger tumor size and increasing tumor growth rate portend a higher likelihood of continued growth. These findings can inform timing of intervention: whether upfront at initial diagnosis, after detection of initial growth, or only after continued growth is observed 4).

Of the 1,818 consecutive patients, diagnosed with VS during the period from 1975 to 2005, 729 patients were allocated to observation by repetitive magnetic resonance imaging. At least two scans had been performed in 552 patients at the time of data analysis. Two hundred thirty patients had a tumor confined to the internal acoustic meatus, whereas 322 patients had a tumor with an extrameatal extension. Growth to extrameatal extension was the definition for growth in intrameatal tumors, whereas a largest diameter change of more than 2 mm was the criteria for growth/shrinkage of extrameatal tumors. The mean observation time was 3.6 years (range, 1-15 yr).

Seventeen percent of the intrameatal tumors grew, whereas significantly more of the extrameatal tumors displayed growth during the period (28.9%). Growth occurred within the first 5 years after diagnosis. No correlation could be demonstrated between tumor growth rate, sex, or age.

VS growth occurs within the first 5 years after diagnosis in a limited number of tumors, primarily in tumors with an extrameatal extension. They found no relation between tumor growth and sex or age. These findings justify primary observation of small tumors. A treatment strategy is proposed for this disease, focusing on the patient group allocated to observation 5).

The natural history of Vestibular Schwannomas (VS) is yet not totally known, but most of them have the tendency to slow growth, sometimes without any kind of symptoms during the individuals entire time. About 69% of diagnosed VS do not grow at all and 16% of these can even regress. Considering tumors that grow, about 70% have grown less than 2mm an year. Advanced radiological diagnosis, especially magnetic resonance imaging with gadolinium helps us diagnose small and less symptomatic tumors. Treatment of choice still is complete tumor resection. Surgical approaches have improved considerably and have helped preserve facial nerve function and hearing. Considering VSs natural history, there is a possibility for conservative treatment for these tumors, because their growth in the first year after diagnosis predicts tumor growth behavior in the next years. Surgery should be done in cases of tumor growth, patients desire or symptoms worsening. Moreover, in terms of postoperative sequelae, there is no difference between patients who underwent surgery immediately after diagnosis and those who underwent initial conservative treatment for these tumors 6).

1)

Luetje CM. Spontaneous involution of acoustic tumors. Am J Otol. 2000 May;21(3):393-8. PubMed PMID: 10821554.
2)

Lees KA, Tombers NM, Link MJ, Driscoll CL, Neff BA, Van Gompel JJ, Lane JI, Lohse CM, Carlson ML. Natural History of Sporadic Vestibular Schwannoma: A Volumetric Study of Tumor Growth. Otolaryngol Head Neck Surg. 2018 Sep;159(3):535-542. doi: 10.1177/0194599818770413. Epub 2018 Apr 24. PMID: 29685084.
3)

Yoshimoto Y. Systematic review of the natural history of vestibular schwannoma. J Neurosurg. 2005 Jul;103(1):59-63. doi: 10.3171/jns.2005.103.1.0059. PMID: 16121974.
4)

Marinelli JP, Schnurman Z, Killeen DE, Nassiri AM, Hunter JB, Lees KA, Lohse CM, Roland JT, Golfinos JG, Kondziolka D, Link MJ, Carlson ML. Long-term Natural History and Patterns of Sporadic Vestibular Schwannoma Growth: A Multi-institutional Volumetric Analysis of 952 Patients. Neuro Oncol. 2021 Dec 29:noab303. doi: 10.1093/neuonc/noab303. Epub ahead of print. PMID: 34964894.
5)

Stangerup SE, Caye-Thomasen P, Tos M, Thomsen J. The natural history of vestibular schwannoma. Otol Neurotol. 2006 Jun;27(4):547-52. doi: 10.1097/01.mao.0000217356.73463.e7. PMID: 16791048.
6)

Oliveira Penido N, Tangerina RP, Macoto Kosugi E, Cesário de Abreu CE, Brandão Vasco M. Vestibular Schwannoma: spontaneous tumor involution. Braz J Otorhinolaryngol. 2007 Nov-Dec;73(6):867-871. doi: 10.1016/S1808-8694(15)31189-7. PubMed PMID: 18278239.

Vestibular Schwannoma Gamma Knife radiosurgery complications

Vestibular Schwannoma Gamma Knife radiosurgery complications

Patients treated with Stereotactic radiosurgery for vestibular schwannoma can have a similar complication profile to those treated with intracranial surgery. Vestibular Schwannoma Meta-analysis from early experience showed that 44% with serviceable hearing prior to treatment retained their ability after SRS, a statistically equivalent rate to the surgical data. This evidence also suggest that 37.9% of patients have other complications 1).

In the mid-1970s, early facial weakness occurred in 38% and facial numbness in 33%. This has gradually decreased to less than 2% in the 1990s. Preservation of hearing (unchanged or almost unchanged) is currently achieved in 65 to 70%. Tinnitus is rarely changed by the treatment. The risks of intracranial bleeding, infection, and CSF leak are avoided because of the non-invasive nature of the treatment. Hydrocephalus directly induced by the tumor occurred in 9.2% of patients. On the other hand, a treatment%related peritumoral reaction sufficient to block the CSF circulation and require shunt insertion was seen in only 1.4%. Based on experiences worldwide, the incidence of secondary neoplasia seems to be 0.1%. The effectiveness of GKR together with its low complication rate makes it a suitable treatment for anyone, regardless of age and general health 2).

Malignant transformation is possible 3). , and long-term post-SRS surveillance MRI is important 4).

Patients receiving > 13 Gy were significantly more likely to develop trigeminal neuropathy than those receiving < 13 Gy (p < 0.001) 5).

Case reports

Pollack et al. described an acute facial and acoustic neuropathy following gamma knife surgery (GKS) for vestibular schwannoma (VS). This 39-year-old woman presenting with tinnitus underwent GKS for a small right-sided intracanalicular VS, receiving a maximal dose of 26 Gy and a tumor margin dose of 13 Gy to the 50% isodose line. Thirty-six hours following treatment she presented with nausea, vomiting, vertigo, diminished hearing, and a House-Brackmann Grade III facial palsy. She was started on intravenous glucocorticosteroid agents, and over the course of 2 weeks her facial function returned to House-Brackmann Grade I. Unfortunately, her hearing loss persisted. A magnetic resonance (MR) image obtained at the time of initial deterioration demonstrated a significant decrease in tumor enhancement but no change in tumor size or peritumoral edema. Subsequently, the patient experienced severe hemifacial spasms, which persisted for a period of 3 weeks and then progressed to a House-Brackmann Grade V facial palsy. During the next 3 months, the patient was treated with steroids and in time her facial function and hearing returned to baseline levels. Results of MR imaging revealed transient enlargement (3 mm) of the tumor, which subsequently returned to its baseline size. This change corresponded to the tumor volume increase from 270 to 336 mm3. The patient remains radiologically and neurologically stable at 10 months posttreatment. This is the first detailed report of acute facial and vestibulocochlear neurotoxicity following GKS for VS that improved with time. In addition, MR imaging findings were indicative of early neurotoxic changes. A review of possible risk factors and explanations of causative mechanisms is provided 6).

Pseudoprogression

see Vestibular Schwannoma pseudoprogression.

1)

Kaylie DM, Horgan MJ, Delashaw JB, McMenomey SO. A meta-analysis comparing outcomes of microsurgery and gamma knife radiosurgery. Laryngoscope. 2000 Nov;110(11):1850-6. doi: 10.1097/00005537-200011000-00016. PMID: 11081598.
2)

Norén G. Long-term complications following gamma knife radiosurgery of vestibular schwannomas. Stereotact Funct Neurosurg. 1998 Oct;70 Suppl 1:65-73. doi: 10.1159/000056408. PMID: 9782237.
3)

Yanamadala V, Williamson RW, Fusco DJ, Eschbacher J, Weisskopf P, Porter RW. Malignant transformation of a vestibular schwannoma after gamma knife radiosurgery. World Neurosurg. 2013 Mar-Apr;79(3-4):593.e1-8. doi: 10.1016/j.wneu.2012.03.016. Epub 2012 Apr 2. PubMed PMID: 22480982.
4)

Kawashima M, Hasegawa H, Shin M, Shinya Y, Katano A, Saito N. Outcomes of stereotactic radiosurgery in young adults with vestibular schwannomas. J Neurooncol. 2021 Jul 9. doi: 10.1007/s11060-021-03803-w. Epub ahead of print. PMID: 34241770.
5)

Sughrue ME, Yang I, Han SJ, Aranda D, Kane AJ, Amoils M, Smith ZA, Parsa AT. Non-audiofacial morbidity after Gamma Knife surgery for vestibular schwannoma. J Neurosurg. 2013 Dec;119 Suppl:E4. Review. PubMed PMID: 25077327.
6)

Pollack AG, Marymont MH, Kalapurakal JA, Kepka A, Sathiaseelan V, Chandler JP. Acute neurological complications following gamma knife surgery for vestibular schwannoma. Case report. J Neurosurg. 2005 Sep;103(3):546-51. doi: 10.3171/jns.2005.103.3.0546. PMID: 16235688.

Vestibular schwannoma

Vestibular schwannoma

A vestibular schwannoma (also known as acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma) is a benign, usually slow-growing cerebellopontine angle tumor that develops from the balance and hearing nerves supplying the inner ear. The tumor comes from an overproduction of Schwann cells.

They usually originate in the internal acoustic meatus, and gradually extends into the cerebellopontine cistern. Invasive growth into the petrous bone is extremely rare. This may have arisen because of an unusually peripheral site of origin on the vestibular nerve 1).

Epidemiology

see Vestibular schwannoma epidemiology.

Etiology

see Vestibular schwannoma etiology.

Classification

see Vestibular schwannoma classification.

Natural history

see Vestibular schwannoma natural history.

Pathology

Tumors are composed of Antoni A fibers (narrow elongated bipolar cells) and Antoni B fibers (loose reticulated). Verocay bodies are also seen, and consist of acellular eosinophilic areas surrounded by parallel arrangement of spindle shaped schwann cells (they are not a cell type).

Clinical

see Vestibular schwannoma clinical features.

Diagnosis

see Vestibular schwannoma diagnosis.

Scores

see Vestibular schwannoma scores.

Differential diagnosis

Cerebellopontine angle meningioma.

Cerebellopontine hemangioblastoma.

Gao S et al., reported a cerebellar glioblastoma multiforme patient, with his clinical presentations and imaging characteristics mimicking a vestibular schwannoma. To the best of authors knowledge, this is the first reported patient with cGBM mimicking a vestibular schwannoma 2).

Guidelines

see Vestibular schwannoma guidelines.

Treatment

see Vestibular schwannoma treatment.

Outcome

see Vestibular schwannoma outcome.

Meta-analysis

see Vestibular Schwannoma Meta-analysis

Case series

see Vestibular schwannoma case series.

Case reports

see Vestibular schwannoma case reports.

Books

Vestibular Schwannoma Books.

1)

Matsumura H, Matsuda M, Tabuchi K, Yamamoto T, Ishikawa E, Matsumura A. Vestibular schwannoma extending into the tympanic cavity and jugular fossa by invasion of the petrous bone. Br J Neurosurg. 2019 Mar 11:1-3. doi: 10.1080/02688697.2019.1588226. [Epub ahead of print] PubMed PMID: 30856348.
2)

Gao S, Liu X, Cheng P, Yuan X, Niu J, Bai Y, Xi B. A Primary Cerebellar Glioblastoma Multiforme Mimicking Vestibular Schwannoma. J Craniofac Surg. 2016 Aug 10. [Epub ahead of print] PubMed PMID: 27513787.

Vestibular schwannoma tinnitus

Vestibular schwannoma tinnitus

The presence of unilateral tinnitus alone is a sufficient reason to evaluate an individual for vestibular schwannoma.

Nearly two-thirds of patients with vestibular schwannoma (VS) are reporting a significantly impaired quality of life due to tinnitus. VS-associated tinnitus is attributed to anatomical and physiological damage of the hearing nerve by displacing the growth of the tumor. In contrast, the current pathophysiological concept of non-VS tinnitus hypothesizes maladaptive neuroplasticity of the central nervous system to a (hidden) hearing impairment resulting in a subjective misperception. However, it is unclear whether this concept fits VS-associated tinnitus.

An analysis of Baguley et al. does not identify any single one mechanisms for tinnitus as being the obvious culprit. In fact, even in a homogeneous group of patients such as this, there is evidence of multiple mechanisms that are not mutually exclusive. The association between increased tinnitus severity in older patients, patients with canal pareses on caloric testing, and tinnitus as a principal presenting symptom should be borne in mind by the clinician 1).

Tinnitus is attributed to partial sensory deafferentation resulting in central maladaptive neuroplasticity. Unfortunately, the agent of deafferentation is usually unknown or irreversible. In patients with unilateral vestibular schwannoma (VS), however, the auditory nerve is affected by a benign tumor. Hence, removal of the tumor can cease tinnitus. In turn, sustaining complaints after surgery indicate cortical neuroplasticity. A cross-sectional study aimed to track cortical structural changes by surface-based morphometry in 46 VS patients with sustained (i.e. centralized) or ceased (i.e. peripheral) tinnitus after surgery. A volumetric analysis of cortical and subcortical gray matter (GM) anatomy was performed on preoperative high-resolution MRI and related to the presence of hearing impairment, pre-and/or postoperative tinnitus. Patients with sustained (i.e. chronic) tinnitus showed an increased GM volume of the bilateral caudate nucleus, the contralateral superior colliculus, the middle frontal and middle temporal gyrus, the fusiform gyrus as well as the ipsilateral pars orbitalis when compared to those patients in whom tinnitus ceased postoperatively. Chronic tinnitus in VS patients is associated with characteristic structural changes in frontal, temporal, and subcortical areas. Notably, a significant GM change of the caudate nucleus was detected providing further support for the striatal gaiting model of tinnitus 2).

A study aimed to determine the clinical predictors of VS-associated tinnitus to ascertain the compatibility of both pathophysiological concepts.

This retrospective study includes a group of 478 neurosurgical patients with unilateral sporadic VS evaluated preoperatively regarding the occurrence of ipsilateral tinnitus depending on different clinical factors, i.e., age, gender, tumor side, tumor size (T1-T4 according to the Hannover classification), and hearing impairment (Gardner-Robertson classification, GR1-5), using a binary logistic regression.

61.8% of patients complain about preoperative tinnitus. The binary logistic regression analysis identified male gender [OR 1.90 (1.25-2.75); p = 0.002] and hearing impairment GR3 [OR 1.90 (1.08-3.35); p = 0.026] and GR4 [OR 8.21 (2.29-29.50); p = 0.001] as positive predictors. In contrast, patients with large T4 tumors [OR 0.33 (0.13-0.86); p = 0.024] and complete hearing loss GR5 [OR 0.36 (0.15-0.84); p = 0.017] were less likely to develop tinnitus. Yet, 60% of the patients with good clinical hearing (GR1) and 25% of patients with complete hearing loss (GR5) suffered from tinnitus.

These data are in good accordance with literature about non-VS tinnitus indicating hearing impairment as the main risk factor. In contrast, complete hearing loss appears a negative predictor for tinnitus. For the first time, these findings indicate a non-linear relationship between hearing impairment and tinnitus in unilateral sporadic VS. Our results suggest similar pathophysiology in VS-associated and non-VS tinnitus 3).

1)

Baguley DM, Humphriss RL, Axon PR, Moffat DA. The clinical characteristics of tinnitus in patients with vestibular schwannoma. Skull Base. 2006 May;16(2):49-58. doi: 10.1055/s-2005-926216. PMID: 17077869; PMCID: PMC1502033.
2)

Trakolis L, Bender B, Ebner FH, Ernemann U, Tatagiba M, Naros G. Cortical and subcortical gray matter changes in patients with chronic tinnitus sustaining after vestibular schwannoma surgery. Sci Rep. 2021 Apr 16;11(1):8411. doi: 10.1038/s41598-021-87915-3. PMID: 33863965.
3)

Naros G, Sandritter J, Liebsch M, Ofori A, Rizk AR, Del Moro G, Ebner F, Tatagiba M. Predictors of Preoperative Tinnitus in Unilateral Sporadic Vestibular Schwannoma. Front Neurol. 2017 Aug 3;8:378. doi: 10.3389/fneur.2017.00378. eCollection 2017. PubMed PMID: 28824535; PubMed Central PMCID: PMC5541055.

Vestibular schwannoma subtotal resection

Vestibular schwannoma subtotal resection

Vestibular schwannoma surgery (VS) remains controversial. Historical surgical series prioritized gross total resections (GTR); however, near total resections (NTR) and intentional subtotal resections (STR) aiming at improving cranial nerve outcomes are becoming more popular.

Hybrid strategy of STR and adjuvant SRS provides patients with large VS excellent tumor control and a good clinical outcome 1).

Reviews of the literature have revealed that in the event of partial removal, the residual VS in patients who had undergone near total resection (NTR) versus subtotal resection (STR) showed an incidence of regrowth ranging from 0.0% to 3.5% versus 18.4% to 73.9%, respectively 2) 3) 4) 5) 6) 7) 8) 9) 10)

The Ki-67 analysis results were compared with tumor regrowth to determine the presence of a correlation between this proliferative index and postoperative tumor regrowth. Study Design Seventeen adult patients (7 male, 10 female) were retrospectively reviewed. Nine (52.9%) and eight (47.1%) patients underwent NTR and STR, respectively. Postoperative clinical and radiological data associated with vestibular schwannoma growth were compared with the Ki-67 immunohistochemical analysis results. Results Evidence of clinically significant regrowth was observed in four (23.5%) patients. Patients who underwent NTR had a lower rate/incidence of tumor regrowth than did patients who underwent STR. Patients with a higher Ki-67 index had the highest tumor regrowth rates. The study indicates that assessment of the Ki-67 index may be useful for determining the probability of regrowth of vestibular schwannomas when only partial resection is accomplished 11).

The main purpose of a article was to assess the tumor control and facial nerve outcomes in VS patients treated with STR or NTR.

VS patients undergoing STR or NTR at our institution between 1984 and 2016 were retrospectively reviewed. Patient demographics, extent of tumor resection, facial nerve injury, tumor recurrence, and need for Gamma Knife radiosurgery were analyzed. Facial nerve outcomes were quantified using House-Brackmann (HB) scores. Tumor regrowth was defined by the San Francisco criteria. Results Four-hundred fifty-seven VS resections were performed in a 32-year period. Sixty cases met inclusion criteria. The mean (range) follow-up duration was 30.9 (12-103) months. The STR cohort ( n = 33) demonstrated regrowth in 12 patients (36.3%) at an average of 23.6 months. The NTR cohort ( n = 27) did not experience tumor recurrence. Risk of tumor recurrence was positively correlated with preoperative tumor size ( p = 0.002), size of residual tumor ( p < 0.001), and STR ( p < 0.001). Facial nerve outcomes of HB1-2 were observed in the majority of patients in both cohorts (74.1% NTR, 56% STR), though NTR was associated with a higher likelihood of facial nerve recovery ( p = 0.003).

GTR remains the gold standard as long as facial nerve outcomes remain acceptable. NTR achieved superior tumor control and higher likelihood of facial nerve recovery compared with STR 12).

Surgical strategy in vestibular schwannomas may require subtotal resection to preserve neurological function. Residual tumor growth pattern and contrast enhancement in the immediate post-resection period remains uncertain. Heller et al. sought to evaluate changes in the enhancement pattern and volume of vestibular schwannomas after subtotal resection in the immediate post-operative period.

Volumetric analysis of tumor size and enhancement patterns of vestibular schwannomas were measured on MRIs obtained within three days of surgery, three months after surgery, and one year after surgery.

Nineteen patients were eligible for inclusion in the study (nine males and ten females) with an average age of 47 years. Contrast enhancement was absent in 6/19 (32%) of cases on the immediate post-resection MRI with return of expected enhancement on subsequent studies. Volumetric analysis identified that tumors decreased in size by an average of 35% in the first three months (p = 0.025) after resection and 46% in the first year after resection (p<0.01).

Vestibular schwannomas that undergo subtotal resection tend to decrease in size over the first 3 months after resection. Residual tumor volume may fail to enhance on the immediate post-resection MRI. Both of these findings could lead surgeons to misinterpret degree of resection after surgery and have implications for clinical decision making and research reporting in the scientific literature for vestibular schwannomas after subtotal resection 13).

1)

Radwan H, Eisenberg MB, Sandberg Knisely JP, Ghaly MM, Schulder M. Outcomes in Patients with Vestibular Schwannoma after Subtotal Resection and Adjuvant Radiosurgery. Stereotact Funct Neurosurg. 2016;94(4):216-224. doi: 10.1159/000447520. Epub 2016 Aug 12. PMID: 27513938.
2)

Chen Z, Prasad SC, Di Lella F, Medina M, Piccirillo E, Taibah A, Russo A, Yin S, Sanna M. The behavior of residual tumors and facial nerve outcomes after incomplete excision of vestibular schwannomas. J Neurosurg. 2014 Jun;120(6):1278-87. doi: 10.3171/2014.2.JNS131497. Epub 2014 Apr 11. PMID: 24724851.
3)

Bloch DC, Oghalai JS, Jackler RK, et al. The fate of the tumor remnant after less-than-complete acoustic neuroma resection. Otolaryngol Head Neck Surg 2004; 130: 104–112.
4)

Fukuda M, Oishi M, Hiraishi T, et al. Clinicopathological factors related to regrowth of vestibular schwannoma after incomplete resection. J Neurosurg 2011; 114: 1224–1231.
5)

Schwartz MS, Kari E, Strickland BM, et al. Evaluation of the increased use of partial resection of large vestibular schwanommas: facial nerve outcomes and recurrence/regrowth rates. Otol Neurotol 2013; 34: 1456–1464.
6)

Seol HJ, Kim CH, Park CK, et al. Optimal extent of resection in vestibular schwannoma surgery: relationship to recurrence and facial nerve preservation. Neurol Med Chir (Tokyo) 2006; 46: 176–180.
7)

Vakilian S, Souhami L, Melançon D, et al. Volumetric measurement of vestibular schwannoma tumour growth following partial resection: predictors for recurrence. J Neurol Surg B Skull Base 2012; 73: 117–120.
8)

Sughrue ME, Kaur R, Rutkowski MJ, et al. Extent of resection and the long-term durability of vestibular schwannoma surgery. J Neurosurg 2011; 114: 1218–1223.
9)

Virk JS, Tripathi S, Randhawa PS, et al. Tumour resection volumes and facial nerve outcomes for vestibular schwannomas. Indian J Otolaryngol Head Neck Surg 2014; 66: 191–195.
10)

El-Kashlan HK, Zeitoun H, Arts HA, et al. Recurrence of acoustic neuroma after incomplete resection. Am J Otol 2000; 21: 389–392.
11)

Iannella G, de Vincentiis M, Di Gioia C, Carletti R, Pasquariello B, Manno A, Angeletti D, Savastano E, Magliulo G. Subtotal resection of vestibular schwannoma: Evaluation with Ki-67 measurement, magnetic resonance imaging, and long-term observation. J Int Med Res. 2017 Jun;45(3):1061-1073. doi: 10.1177/0300060516686873. Epub 2017 Apr 27. PMID: 28447494; PMCID: PMC5536425.
12)

Strickland BA, Ravina K, Rennert RC, Jackanich A, Aaron K, Bakhsheshian J, Russin JJ, Friedman RA, Giannotta SL. Intentional Subtotal Resection of Vestibular Schwannoma: A Reexamination. J Neurol Surg B Skull Base. 2020 Apr;81(2):136-141. doi: 10.1055/s-0039-1679898. Epub 2019 Mar 1. PMID: 32206531; PMCID: PMC7082167.
13)

Heller RS, Joud H, Flores-Milan G, Franzese R, Ford J, Nelson J, Decker S, Mhaskar R, van Loveren H, Agazzi S. Changing enhancement pattern and tumor volume of vestibular schwannomas after subtotal resection. World Neurosurg. 2021 Apr 22:S1878-8750(21)00600-8. doi: 10.1016/j.wneu.2021.04.059. Epub ahead of print. PMID: 33895370.

Facial nerve schwannoma

Facial nerve schwannoma

Facial nerve schwannoma may arise in any portion of the facial nerve, with a predilection for the geniculate ganglion 1) 2).

They can occur anywhere from the internal auditory canal to the parotid gland. Schwannomas arising from the greater superficial petrosal nerve are exceedingly rare 3).

Clinical

Even in these tumors, hearing loss tends to precede facial paresis. Hearing loss may be sensorineural from VIII cranial nerve compression from tumors arising in the proximal portion of VII cranial nerve (cisternal or internal auditory canal (IAC) segment), or it may be conductive from erosion of the ossicles by tumors arising in the second (tympanic, or horizontal) segment of VII. Facial palsy (peripheral) may also develop, usually late 4).

Diagnosis

Computed tomography (CT) of the temporal bone is important for evaluating the impact on the surrounding structures 5).

Treatment

Treatment for intracranial facial nerve schwannomas depends on clinical presentation, tumor size, preoperative facial, and hearing function.

Conservative management is recommended for asymptomatic patients with small tumors. Stereotactic radiosurgery may be an option for smaller and symptomatic tumors with good facial function. If tumor is large or the patient has facial paralysis, surgical resection should be indicated. If preservation of the facial nerve is not possible, total resection with nerve grafting should be performed for those patients with facial paralysis, whereas subtotal resection is best for those patients with good facial function 6).

see Middle Fossa Approach for Facial Nerve Schwannoma.

These tumors must be assessed with imaging studies, incisional biopsy is not recommended. The treatment is surgical resection in symptomatic patients with facial paralysis greater than grade III of House-Brackmann, with immediate reconstruction of the nerve 7).

Case series

Facial nerve schwannoma case series.

Case reports

Facial nerve schwannoma case reports.

References

1) , 4)

Inoue Y, Tabuchi T, Hakuba A, et al. Facial Nerve Neuromas: CT Findings. J Comput Assist Tomogr. 1987; 11:942–947
2)

Tew JM, Yeh HS, Miller GW, Shahbabian S. Intratemporal Schwannoma of the Facial Nerve. Neurosurgery. 1983; 13:186–188
3)

Sade B, Lee JH. Recovery of low-frequency sensorineural hearing loss following resection of a greater superficial petrosal nerve schwannoma. Case report. J Neurosurg. 2007 Jul;107(1):181-4. PubMed PMID: 17639892.
5)

Loos E, Wuyts L, Puls T, Foer B, Casselman JW, Bernaerts A, Vanspauwen R, Offeciers E, Dinther JV, Zarowski A, Somers T. Cochlear Erosion due to a Facial Nerve Schwannoma. J Int Adv Otol. 2019 Jul 9. doi: 10.5152/iao.2019.5304. [Epub ahead of print] PubMed PMID: 31287431.
6)

Xu F, Pan S, Alonso F, Dekker SE, Bambakidis NC. Intracranial Facial Nerve Schwannomas: Current Management and Review of Literature. World Neurosurg. 2017 Apr;100:444-449. doi: 10.1016/j.wneu.2016.09.082. Epub 2016 Sep 28. Review. PubMed PMID: 27693767.
7)

Prado-Calleros HM, Corvera-Behar G, García-de-la-Cruz M, Calderón-Wengerman Ó, Prado A, Pombo-Nava A. Tympanic-mastoid and parotid schwannomas of the facial nerve: clinical presentation related to the anatomic site of origin. Cir Cir. 2019;87(4):377-384. doi: 10.24875/CIRU.18000449. PubMed PMID: 31264987.

Vagal Nerve Schwannoma

Vagal Nerve Schwannoma

Epidemiology

Schwannoma arising from the vagus nerve is an uncommon (2–5%) benign nerve tumour.

Vagal Nerve Schwannomas are usually confined to the retrostyloid parapharyngeal space, although patients with schwannomas that extend into the posterior cranial fossa through the jugular foramen have been reported

Schwannomas arising from the vagus nerve are extremely rare in children, with only 16 cases reported in the world literature 1).

Clinical features

They usually presents as an asymptomatic slow growing mass 2).

Most cases of schwannomas manifest between the third and sixth decades of the patient’s life as a slow growing firm, painless mass in the lateral neck. Hoarseness, pain, or cough may be the presenting complaints. They displace the carotid arteries anteriorly and medially, jugular vein laterally and posteriorly. These swellings are mobile transversely but not vertically 3).

Diagnosis

Diagnosis is based on clinical suspicion and confirmation obtained by means of surgical pathology.

Differential diagnosis

Schwannomas of the vagus nerve must be differentiated from the carotid body and glomus vagale tumors because the distinction may influence treatment planning.

Treatment

Surgical excision is the treatment of choice for vagal schwannoma, with recurrence being rare.

Intermittent intraoperative neuromonitoring via selective stimulation of splayed motor fibers running on the schwannoma surface to elicit a compound muscle action potential has been previously reported as a method of preserving vagal motor fibers.

In a case report, vagal sensory fibers were mapped and continuously monitored intraoperatively during high vagus schwannoma resection using the laryngeal adductor reflex (LAR). Mapping of nerve fibers on the schwannoma surface enabled identification of sensory fibers. Continuous LAR monitoring during schwannoma subcapsular microsurgical dissection enabled sensory (and motor) vagal fibers to be monitored in real time with excellent postoperative functional outcomes 4).

Outcome

Nerve damage during surgical resection is associated with significant morbidity 5).

This tumour most often presents as a slow growing asymptomatic solitary neck mass, which rarely undergoes malignant transformation.

Literature review

In a comprehensive literature review on 197 articles reporting 235 cases of cervical vagal schwannomas. Presenting symptoms, treatment approach, and postoperative outcomes were recorded and analyzed.

Vagal schwannomas commonly present as asymptomatic neck masses. When they become symptomatic, surgical resection is the standard of care. Gross total resection is associated with higher postoperative morbidity compared to subtotal resection. Initial reports using intraoperative nerve monitoring have shown improved nerve preservation. Recurrence rates are low.

The combination of intermittent nerve mapping with novel continuous vagal nerve monitoring techniques may reduce postoperative morbidity and could represent the future standard of care for vagal schwannoma treatment 6).

Case series

Case series of three patients who underwent vagal schwannoma excision utilizing a IONM technique. The recurrent laryngeal and vagus nerves were monitored via the laryngeal adductor reflex (LAR) using an electromyographic endotracheal tube.

Three patients with suspected vagal schwannomas were treated surgically using the intracapsular enucleation approach with a combination of intermittent IONM and continuous IONM of the LAR.

This combination of continuous and intermittent IONM can be used to preserve vagal laryngeal innervation and function and may represent the future standard of care for vagal schwannoma excision 7).

Green et al. reported 36 of these rare neoplasms in 35 patients. The majority of the tumors presented as a mass in the upper cervical or parapharyngeal region. Usually the mass was asymptomatic. The following types and frequencies of neoplasms of the vagus nerve were noted: paragangliomas, 50%; neurilemmomas, 31%; neurofibromas, 14%; and neurofibrosarcomas, 6%. Surgical resection, with preservation of the vagus nerve when possible, is the treatment of choice. The clinical features, diagnosis, management, and prognosis of the tumors are presented. Special problems that occur with vagal neoplasms include postoperative dysfunction, catecholamine secretion, and intracranial or skull-base extension 8).

Case reports

In a case report, vagal sensory fibers were mapped and continuously monitored intraoperatively during high vagus schwannoma resection using the laryngeal adductor reflex (LAR). Mapping of nerve fibers on the schwannoma surface enabled identification of sensory fibers. Continuous LAR monitoring during schwannoma subcapsular microsurgical dissection enabled sensory (and motor) vagal fibers to be monitored in real time with excellent postoperative functional outcomes 9).

Keshelava et al. operated one patient for cervical schwannoma causing internal carotid artery (ICA) compression.

The patient underwent en bloc excision via transcervical approach under general anesthesia. Pathological examination demonstrated the diagnosis of schwannoma.

This case shows that VNS can cause ICA compression and therefore brain ischemia 10).

Schwam et al. reported a purely intracranial vagal schwannoma 11).

2018

A 60-year-old female patient was seen at our service for a slow-growing, 9 × 6 cm left-sided cystic neck mass. Preoperative clinical and computed tomography evaluation suggested a diagnosis of a lateral neck cyst. The surgical exploration through the lateral cervicotomy revealed a large cystic mass and clearly identified that the tumor was originating from the left vagal nerve. The histopathologic analysis confirmed the diagnosis of schwannoma. Although uncommon, vagal schwannoma with pronounced cystic component should be included in the differential diagnosis of the cystic neck swellings 12).

A 55-year-old woman who presented to the clinic complaining of throat irritation and feeling of something stuck in her throat for the past three months. On examination, a bulging left parapharyngeal mass was noted, displacing the left tonsil and uvula medially. A contrast-enhanced computed tomography (CT) scan of the neck showed a large, hypervascular soft tissue mass with splaying of the left internal carotid artery. Intraoperatively, the tumor was found to be arising from the vagus nerve. Macroscopic surgical pathology examination showed a tan-red, ovoid, and firm mass. Histopathology showed a benign spindle cell tumor with Antoni A areas with palisading cell nuclei and some degenerative change, confirming the diagnosis of vagus nerve schwannoma. CONCLUSIONS Vagus nerve schwannomas should be distinguished from other tumors that arise in the neck before planning surgery, to minimize the risk of nerve injury. Physicians need to be aware of the differential diagnosis of a neck mass, investigations required, the surgical treatment and the potential postoperative complications 13).

Sreevatsa et al. described three cases of schwannoma involving the vagus who presented differently to our unit during past 5 years 14).

A large vagal neurilemmoma in a 33-year-old man is reported. He complained of slowly progressive palsy of the tongue on the left side. Weakness of soft palate movement was also noted. Magnetic resonance imaging (MRI) revealed a tumour in the left parapharyngeal space with partial extension to the posterior cranial fossa through the jugular foramen. Carotid angiography revealed avascularity of the tumour and anterior shift of the left internal carotid artery. The venous phase showed no blood flow in the internal jugular vein. The tumour was successfully extirpated via a transmandibular transpterygoid approach. Although vagus nerve dysfunction was not observed pre-operatively, the tumour was identified as a neurilemmoma arising from the vagus nerve. The surgical approach should be selected according to the lesion in individual patients. Since neurilemmoma is benign in nature, minimal post-operative sequelae should be expected 15).

References

1)

Mierzwiński J, Wrukowska I, Tyra J, Paczkowski D, Szcześniak T, Haber K. Diagnosis and management of pediatric cervical vagal schwannoma. Int J Pediatr Otorhinolaryngol. 2018 Nov;114:9-14. doi: 10.1016/j.ijporl.2018.08.021. Epub 2018 Aug 23. PubMed PMID: 30262374.
2) , 13)

Ramdass AA, Yao M, Natarajan S, Bakshi PK. A Rare Case of Vagus Nerve Schwannoma Presenting as a Neck Mass. Am J Case Rep. 2017 Aug 21;18:908-911. PubMed PMID: 28824161; PubMed Central PMCID: PMC5574523.
3)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3227827/
4) , 9)

Sinclair CF, Téllez MJ, Sánchez Roldán MA, Urken M, Ulkatan S. Intraoperative mapping and monitoring of sensory vagal fibers during vagal schwannoma resection. Laryngoscope. 2019 Dec;129(12):E434-E436. doi: 10.1002/lary.28147. Epub 2019 Jun 18. PubMed PMID: 31211430.
5) , 7)

Sandler ML, Sims JR, Sinclair C, Ho R, Yue LE, Téllez MJ, Ulkatan S, Khorsandi AS, Brandwein-Weber M, Urken ML. A novel approach to neurologic function sparing surgical management of vagal schwannomas: Continuous intraoperative nerve monitoring of the laryngeal adductor reflex. Head Neck. 2019 Sep;41(9):E146-E152. doi: 10.1002/hed.25793. Epub 2019 May 6. PubMed PMID: 31058386.
6)

Sandler ML, Sims JR, Sinclair C, Sharif KF, Ho R, Yue LE, Téllez MJ, Ulkatan S, Khorsandi AS, Brandwein-Weber M, Urken ML. Vagal schwannomas of the head and neck: A comprehensive review and a novel approach to preserving vocal cord innervation and function. Head Neck. 2019 Jul;41(7):2450-2466. doi: 10.1002/hed.25758. Epub 2019 Apr 7. Review. PubMed PMID: 30957342.
8)

Green JD Jr, Olsen KD, DeSanto LW, Scheithauer BW. Neoplasms of the vagus nerve. Laryngoscope. 1988 Jun;98(6 Pt 1):648-54. PubMed PMID: 2836676.
10)

Keshelava G, Robakidze Z. Cervical Vagal Schwannoma Causing Asymptomatic Internal Carotid Artery Compression. Ann Vasc Surg. 2019 Oct 17. pii: S0890-5096(19)30859-3. doi: 10.1016/j.avsg.2019.09.021. [Epub ahead of print] PubMed PMID: 31629844.
11)

Schwam ZG, Kaul VZ, Shrivastava R, Wanna GB. Purely intracranial vagal schwannoma: A case report of a rare lesion. Am J Otolaryngol. 2019 May – Jun;40(3):443-444. doi: 10.1016/j.amjoto.2019.02.011. Epub 2019 Feb 18. PubMed PMID: 30799212.
12)

Cukic O, Jovanovic MB. Vagus Nerve Schwannoma Mimicking a Lateral Neck Cyst. J Craniofac Surg. 2018 Nov;29(8):e827-e828. doi: 10.1097/SCS.0000000000005006. PubMed PMID: 30320693.
14)

Sreevatsa MR, Srinivasarao RV. Three cases of vagal nerve schwannoma and review of literature. Indian J Otolaryngol Head Neck Surg. 2011 Oct;63(4):310-2. Epub 2011 Apr 8. PubMed PMID: 23024932; PubMed Central PMCID: PMC3227827.
15)

Yumoto E, Nakamura K, Mori T, Yanagihara N. Parapharyngeal vagal neurilemmoma extending to the jugular foramen. J Laryngol Otol. 1996 May;110(5):485-9. PubMed PMID: 8762326.

Cervical spinal schwannoma

Cervical spinal schwannoma

Spinal schwannoma are most frequently seen in the cervical and lumbar regions, far more frequently than in the thoracic spine.

Classification

Asazuma Classification

1).

Eden’s classification for dumbbell tumors of the spine, long considered a “gold standard,”

no longer is sufficient to determine surgical strategy in view of recent advances in computed tomography and magnetic resonance imaging.

Treatment

Cervical dumbbell spinal schwannomas with an extraspinal extension through the intervertebral foramina pose significant challenges for complete resection while avoiding injury to the vertebral artery and preserving the integrity of the cervical spine. Posterior approaches may require an extensive soft-tissue dissection and bone removal with potential spinal instability. Moreover, they offer only a limited access to an extraspinal tumor component that entails an additional anterior approach for complete resection of a dumbbell-shaped lesion.

Goga et al., used an anterolateral transforaminal approach that preserves the bony elements of the intervertebral foramen and offers a comprehensive access to the extraspinal, foraminal and intraspinal/intradural components of a cervical dumbbell tumor 2).

Outcome

Cervical spinal schwannoma is benign, and outcomes after surgical resection are generally excellent. A surgical dilemma sometimes arises as to whether to perform total tumor removal, which carries a risk of sacrificing the nerve root, or subtotal removal, where the risk can be tumor recurrence.

Case series

Chowdhury et al. reported schwannomas arising from C1, C2 and C3 spinal nerve roots were regarded as high cervical spinal schwannoma. All patients with high cervical spinal schwannomas that were consecutively operated microneurosurgically from 2006-2010 were included in the study. Postoperatively all patients were followed up regularly both clinically and neuro-radiologically (MRI of cervical spine).

Average follow up was 31.5 months. The mean age of the series was 35.8 years (range 10-61 years). There were 8 male and 7 female patients. The mean duration of symptoms at the time of presentation was 32 months (range 06 months-5 years). Two schwannomas were completely extradural, seven were intradural and rest six were interdural or hourglass type (both extra and intradural) as identified during surgery. The standard midline posterior approach was used in all patients. A C2 hemilaminectomyor C2 laminectomy with or without cutting of posterior arch of atlas was used for most intradural and large interdural C2 schwannomas. Tumor removal was complete in all cases. Preservation of the nerve root fibers was not possible in 9 cases and was possible only in 3 cases. In two patients CSF leak developed after operation. One patient who had severe myelopathic features with bed sore failed toimprove and expired 5 months after operation. Rest of the patients showed postoperative improvement in their preoperative symptoms and returned to their normal life by the end of sixth month. There was no tumor recurrence in any patient till last follow up.

Proper 3-D anatomical orientation & physiological knowledge, deep neuro-radiological observation,pathological appreciations and micro-neurosurgical skill and expertization can make the surgical management of these tumors ( in a surgically complex site) simple with gratifying result (i.e.neurological outcome) without extensive bone removal or soft tissue manipulation through a standard midline posterior approach 3).

Thirty cases of cervical schwannomas treated by Yamane et al. were retrospectively reviewed;initial symptoms, tumor location, Eden classification, surgical method, functional outcome, and tumor recurrence were investigated. All permanent motor deficits were the result of resecting functionally relevant nerve roots (i.e., C5-8). The rate of permanent sensory deficit was 11% after C1-4 nerve root resection, and 67% after C5-8 nerve root resection. Permanent neurological deficits occurred in 14% of patients younger than 40 years and 38% of those older than 40. Dumbbell tumors were associated with the need for total or ventral nerve root transection, as well as with a high incidence of tumor recurrence. The incidence of permanent neurological deficit was significantly higher in patients undergoing C5-8 nerve root resection, and tended to be higher in those over 40 4).

Forty-two patients with cervical dumbbell tumors were analyzed retrospectively using a new three-dimensional classification.

To establish optimal surgical strategies, we considered shapes and three-dimensional locations of cervical dumbbell tumors based on diagnostic images and intraoperative findings.

Forty-two cervical dumbbell tumors were characterized according to transverse-section images (Toyama classification; nine types) and craniocaudal extent of intervertebral and transverse foraminal involvement (IF and TF staging; three stages each).

Type IIIa tumors, involving dura plus an intervertebral foramen, accounted for 50% of cases. A posterior approach was used in 35 patients; 7 others underwent a combined anterior and posterior approach. A posterior approach was used for all type IIa and IIIa tumors, and for some type IIIb (upper cervical), IV, and VI tumors; a combined posterior and anterior approach was used for type IIb and the remainder of type IV and VI. Reconstruction was performed using spinal instrumentation in 4 patients (9.5%). Resection was subtotal in 6 patients (14.3%) and total in 36 (85.7%).

Systematic, imaging-based three-dimensional characterization of shape and location of cervical dumbbell tumors is essential for planning optimal surgery. The classification used here fulfills this need 5).

Case reports

Pokharel et al. reported a case of extradural cervical schwannoma in a 14-year-old boy with swelling in the posterior triangle of his neck. The radiological features suggested solitary extradural cervical schwannoma which was confirmed later by histopathological findings. There were no postoperative neurological complications 6)

Perry et al. reported in 2019 the third case of synchronously presenting primary progressive multiple sclerosis (MS) and spinal schwannoma. A 65-year-old man presented with six months of progressive weakness and pain of the right shoulder, forearm, and hand. MRI demonstrated a contrast-enhancing transforaminal lesion at C7, most consistent with a benign nerve sheath tumor. Additional history disclosed several years of worsening fatigue, accompanied by bilateral weakness and lancinating leg pain. MRI of the neuraxis demonstrated abnormalities consistent with chronic demyelinating disease intracranially and within the spinal cord; cerebrospinal fluid (CSF) analysis revealed nine oligoclonal bands and an elevated IgG index, resulting in the diagnosis of MS. Given the symptomatic C7 lesion, the patient subsequently underwent right C6-C7 facetectomy, gross total resection of the tumor, and C6-T1 posterior instrumented fusion. Postoperatively, the patient rapidly recovered normal right upper extremity function, and pathology confirmed benign schwannoma. Synchronously presenting co-morbid neurologic diagnoses are exceedingly rare. Nonetheless, the high incidence and protean nature of MS make it particularly susceptible to such confounding clinical cases. Correspondingly, MS should be considered when neurologic abnormalities are not compatible with a focal radiographic lesion, and the present report emphasizes the value of a good history and exam in unraveling similarly challenging cases 7).

References

1) , 5)

Asazuma T, Toyama Y, Maruiwa H, Fujimura Y, Hirabayashi K. Surgical strategy for cervical dumbbell tumors based on a three-dimensional classification. Spine (Phila Pa 1976). 2004 Jan 1;29(1):E10-4. PubMed PMID: 14699292.
2)

Goga C, Türe U. The Anterolateral Transforaminal Approach to a Dumbbell Schwannoma of the C3 Nerve Root. A 3-Dimensional Operative Video. Neurosurgery. 2014 Sep 24. [Epub ahead of print] PubMed PMID: 25255264.
3)

Chowdhury FH, Haque MR, Sarker MH. High cervical spinal schwannoma; microneurosurgical management: an experience of 15 cases. Acta Neurol Taiwan. 2013 Jun;22(2):59-66. PubMed PMID: 24030037.
4)

Yamane K, Takigawa T, Tanaka M, Osaki S, Sugimoto Y, Ozaki T. Factors predicting clinical impairment after surgery for cervical spinal schwannoma. Acta Med Okayama. 2013;67(6):343-9. PubMed PMID: 24356718.
6)

Pokharel A, Rao TS, Basnet P, Pandey B, Mayya NJ, Jaiswal S. Extradural cervical spinal schwannoma in a child: a case report and review of the literature. J Med Case Rep. 2019 Jul 17;13(1):230. doi: 10.1186/s13256-019-2108-6. PubMed PMID: 31311599; PubMed Central PMCID: PMC6636037.
7)

Perry A, Peters P, Graffeo CS, Carlstrom LP, Krauss WE. Synchronous Presentation of a Cervical Spinal Schwannoma and Primary Progressive Multiple Sclerosis in a 65-year-old Man. Cureus. 2019 Mar 4;11(3):e4176. doi: 10.7759/cureus.4176. PubMed PMID: 31093475; PubMed Central PMCID: PMC6502288.