Comprehensive Management of Vestibular Schwannoma

Comprehensive Management of Vestibular Schwannoma

Comprehensive Edition by Matthew L Carlson (Editor), Michael J. Link (Editor), Colin L.W. Driscoll (Editor)

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The definitive resource on clinical management of vestibular schwannoma from world renowned experts

Although a histologically benign and relatively uncommon tumor, otolaryngologists and neurosurgeons have maintained a lasting and deep-rooted fascination with vestibular schwannoma, also known as acoustic neuroma. Advancements in microsurgical technique, radiosurgery, and radiotherapy, coupled with an increased understanding of the natural history of the disease, have made modern management of this tumor considerably more complex. Concurrently, new controversies have added to the original debates among pioneering surgeons, with the pendulum swinging between conservatism and definitive cure.

Comprehensive Management of Vestibular Schwannoma, by distinguished Mayo Clinic clinicians and renowned international contributors, is a comprehensive textbook covering all the clinical aspects of vestibular schwannoma management. Eighty-four chapters written by multidisciplinary experts including otolaryngologists, neurosurgeons, radiation oncologists, neurologists, neuroradiologists, and audiologists, ensure a balanced view of all treatment modalities for sporadic and neurofibromatosis type 2-associated vestibular schwannoma.

Key Features

Evaluation, surgical and nonsurgical approaches, rehabilitation, controversies, and long-term clinical outcomes Detailed illustrations by Robert Morreale, senior medical illustrator at the Mayo Clinic, highlight relevant anatomy and surgical approaches Chapter summary tables provide readers with a rapid clinical reference derived from the published world literature The chapter “Anatomy of Vestibular Schwannoma Surgery” by the late internationally renowned neurosurgeon Albert L. Rhoton Jr. reflects his major contributions on this subject With inclusion of fundamental principles to advanced concepts, this is a robust resource for residents, fellows, and early attending physicians, as well as mid- to later-career physicians who care for patients with vestibular schwannoma.

This book includes complimentary access to a digital copy on https://medone.thieme.com.

Vestibular evoked myogenic potentials

Vestibular evoked myogenic potentials

The vestibular evoked myogenic potential (VEMP or VsEP) is a neurophysiological assessment technique used to determine the function of the otolithic organs (utricle and saccule) of the inner ear. It complements the information provided by caloric testing and other forms of inner ear (vestibular apparatus) testing.


They are a useful and increasingly popular component of the neurootology test battery. These otolith-dependent reflexes are produced by stimulating the ears with air-conducted sound or skull vibration and recorded from surface electrodes placed over the neck (cervical VEMPs) and eye muscles (ocular VEMPs). VEMP abnormalities have been reported in various diseases of the ear and vestibular system, and VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence. However there is significant variability in the methods used to stimulate the otoliths and record the reflexes. A review discusses VEMP methodology and provides a detailed theoretical background for the techniques that are typically used. The review also outlines the common pitfalls in VEMP recording and the clinical applications of VEMPs 1).


Combined with tests of semicircular canal function, they provide a useful tool for eliciting diagnostic profiles in vestibular neuritis and Ménière’s disease. VEMPs are valuable in the pre-surgical confirmation of superior semicircular canal dehiscence and in some cases, may alert the clinician to the presence of a vestibular schwannoma in patients with symmetrical hearing 2).


Cervical vestibular evoked myogenic potential cVEMP

Ocular vestibular evoked myogenic potential oVEMP

Patients with vestibular migraine (VM) are more likely than subjects with vestibular disorders other than migraine to exhibit normal cVEMP responses in the presence of unilaterally abnormal oVEMP responses. Such a VEMP pattern may be a biomarker of VM and further supports a possible pathophysiologic relationship between the utriculo-ocular reflex and VM 3).


Bickford et al. (1964) and subsequently Townsend and Cody, provided evidence for a short latency response in posterior neck muscles in response to loud clicks that appeared to be mediated by activation of the vestibular apparatus. These authors made the additional important observations that the response was generated from EMG (muscle) activity and that it scaled with the level of tonic activation. Subsequent work led to the suggestion that the saccule was the end organ excited.

In 1992 Colebatch and Halmagyi reported a patient with a short latency response to loud clicks studied using a modified recording site (the sternocleidomastioid muscles: SCM) and which was abolished by selective vestibular nerve section. Colebatch et al. (1994) described the basic properties of the response. These were: the response occurred ipsilateral to the ear stimulated, the click threshold was high, the response did not depend upon hearing (cochlear function) per se, it scaled in direct proportion to the level of tonic neck contraction, the response was small (although large compared to many evoked potentials) and required averaging, and only the initial positive-negative response (p13-n23 by latency) was actually vestibular-dependent. It was subsequently shown to be generated by a brief period of inhibition of motor unit discharge.

VsEPA and VSEPL

VsEP assesses the non-auditory portions of the labyrinth and requires kinematic stimuli (i.e. motion) instead of sound stimuli and bear only a loose relationship to VEMPs. This kinematic stimuli needs to be well characterized, precisely controlled, consistent in amplitude, and consistent in kinematic makeup. An electromechanical shaker is a stimuli generator that is widely available. This shaker provides a transient stimuli, can generate angular or linear acceleration, and can couple to the skull directly (with skull screws) or via a stimulus platform.

The VsEP is commonly divided into two sections: angular vestibular evoked potentials (VsEPA) and linear vestibular evoked potentials (VsEPL).

VsEPA

VsEPA stimuli needs to be a brief or transient, high amplitude, angular acceleration pulse. Currently, the most effective stimuli for the best results have not yet been identified or agreed upon by researchers. The major downfall of the VsEPA response is that it also elicits a VsEPL response.

VsEPL

In contrast to VsEPA, researchers have standardized the VsEPL stimuli but many variants of this standard are being used in research laboratories today. The stimulus needs to be a transient, rapidly changing pulse (i.e. linear jerk stimulus). A rectangular jerk step/pulse is generated by an electromechanical shaker. The main downfall of the VsEPL response is the presence of electrical artifacts due to movement and touching of the wires/electrodes during testing.

Application of VEMPs

An early application was in the diagnosis of superior canal dehiscence a condition in which there can be clinical symptoms and signs of vestibular activation by loud sounds. Such cases have a pathologically lowered threshold for the sound-evoked VEMP. The test is also of use in demonstrating successful treatment.It has diagnostic applications in Ménière’s disease, vestibular neuritis, otosclerosis as well as central disorders such as Multiple Sclerosis.

Other methods of activating the vestibular apparatus have been developed, including taps to the head,bone vibration and short duration electrical stimulation.It is likely that both air-conducted and bone-conducted stimuli primarily excite irregularly discharging otolith afferents.

The two otolith receptors appear to have differing resonances that may also explain their responses.

In addition to the response in the SCM, similar reflexes can be shown for the masseter and for eye muscles (oVEMPs or OVEMPs = ocular vestibular evoked myogenic potentials).

Case series

Data were obtained from 33 patients with vestibular schwannoma. Vestibular examinations were performed preoperatively. VEMP was obtained upon stimulation with ACS (ACS cVEMP) and BCV to the forehead using a minishaker (BCV cVEMP). Vestibular function was also analyzed using the caloric test and ocular VEMP (oVEMP) testing. oVEMP was measured using bone-conductive vibration to the forehead. The results of BCV cVEMP, ACS cVEMP, and oVEMP were compared by the caloric test.

Rates of patients with abnormal ACS cVEMP, BCV cVEMP, oVEMP, and caloric test results were 78.8%, 75.8%, 78.8%, and 69.7%, respectively. BCV cVEMP did not correlate with ACS cVEMP, but correlated with oVEMP and caloric test results.

BCV cVEMP did not correlate with ACS cVEMP. Therefore, BCV cVEMP cannot be used as a substitute for ACS cVEMP 4).

References

1)

Rosengren SM, Colebatch JG, Young AS, Govender S, Welgampola MS. Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications. Clin Neurophysiol Pract. 2019 Feb 26;4:47-68. doi: 10.1016/j.cnp.2019.01.005. eCollection 2019. Review. PubMed PMID: 30949613; PubMed Central PMCID: PMC6430081.
2)

Taylor RL, Welgampola MS. Otolith Function Testing. Adv Otorhinolaryngol. 2019;82:47-55. doi: 10.1159/000490271. Epub 2019 Jan 15. Review. PubMed PMID: 30947185.
3)

Makowiec KF, Piker EG, Jacobson GP, Ramadan NM, Roberts RA. Ocular and Cervical Vestibular Evoked Myogenic Potentials in Patients With Vestibular Migraine. Otol Neurotol. 2018 Aug;39(7):e561-e567. doi: 10.1097/MAO.0000000000001880. PubMed PMID: 29912833.
4)

Ogawa Y, Otsuka K, Inagaki T, Nagai N, Itani S, Kondo T, Kohno M, Suzuki M. Comparison of cervical vestibular evoked potentials evoked by air-conducted sound and bone-conducted vibration in vestibular Schwannoma patients. Acta Otolaryngol. 2018 Oct;138(10):898-903. doi: 10.1080/00016489.2018.1490815. Epub 2018 Sep 27. PubMed PMID: 30261801.

Retrosigmoid transmeatal approach for vestibular schwannoma videos

Retrosigmoid transmeatal approach for vestibular schwannoma videos

Dorsal displacement of the facial nerve is relatively rare in patients with vestibular schwannoma. Its prediction remains difficult in patients with large tumors, even with the recent advances in preoperative radiologic assessments. Anatomic and functional preservation of the facial nerves combined with maximal tumor removal is particularly challenging in this rare anatomic variant, and surgery may lead to postoperative facial nerve paralysis, inadequate tumor removal, and/or a high retreatment rate.

The 3-dimensional video (Video 1) demonstrates a vestibular schwannoma with dorsally displaced facial nerve, which was surgically treated by the retrosigmoid transmeatal approach under continuous facial nerve monitoring. The video was reproduced after informed consent of the patient. A 46-year-old man presented with transient hearing impairmentNeuroimaging displayed a left vestibular schwannoma extending into the internal acoustic meatus. The retrosigmoid transmeatal approach was performed, and a dorsally displaced facial nerve was predicted by preoperative magnetic resonance images and confirmed during surgery. The facial nerve was accurately dissected under continuous facial nerve monitoring, and gross total resection of the tumor was achieved without postoperative facial dysfunction 1).


A case of a mid-sized vestibular schwannoma (T3b according to the Hannover Grading Scale) that was resected through a Endoscopic assisted retrosigmoid approach in semisitting position

A 52-year-old male with acute loss of functional hearing on the right side. Audiometry confirmed a loss of up to 60 dB and lost speech discrimination, there were no associated symptoms such as tinnitus or vertigo. This 2D video demonstrates positioning, OR set-up, anatomical and surgical nuances of the skull base approach and the operative technique for microdissection of the tumor from the critical neurovascular structures, especially the facial and cochlear nerves. A gross total resection was achieved and the patient discharged home after four days with unaltered function of the facial nerve (HB I). At one year follow up there was no indication of residual or recurrence. In summary, the retrosigmoid transmeatal approach is an important and powerful tool in the armamentarium for the microsurgical management of all kinds of vestibular schwannomas. Provided the necessary anesthesiological precautions and intraoperative procedures the semi-sitting position is safe and effective. If needed, the approach can be complemented by the use of an endoscope for visualization of the distal internal auditory canal. The link to the video can be found at: https://youtu.be/pPKT4_5nIn0 2).


The anterior inferior cerebellar artery (AICA) usually runs loosely within the cerebellopontine cistern; in rare cases, however, it is firmly adherent to the petrous dura mater. Recognizing this variation is particularly important in vestibular schwannoma surgery via the retrosigmoid transmeatal approach to prevent the high morbidity associated with vascular injury. This video demonstrates a surgical technique to effectively mobilize the AICA when firmly adherent to the petrous dura mater.

A 39-year-old man presented with a history of progressive right-sided hearing loss without facial weakness or other associated symptoms. Magnetic resonance imaging (MRI) demonstrated an intracanalicular lesion, suggestive of vestibular schwannoma. During follow-up, audiometryconfirmed a further slight deterioration of hearing and repeated MRI demonstrated tumor growth (T2 according to Hannover Grading Scale). Since the patient opted against radiosurgery, a retrosigmoid transmeatal approach under continuous intraoperative monitoring was performed in supine position. Following drainage of cerebrospinal fluid and exposure of the cerebellopontine cistern, the AICA was found to be firmly adherent to the petrous dura mater. Both structures were elevated conjointly and displaced medially for safe drilling of the inner auditory canal, sufficient exposure, and complete excision of the vestibular schwannoma. The patient had an excellent recovery, hearing and facial function were preserved, and no secondary neurological deficits noted.The patient consented to publication of this anonymized video 3).


Skull Base Neurosurgery – University of Colorado


George Kaptain


Paolo Regolo


Sameer A. Sheth

References

1)

Matsushima K, Kohno M, Nakajima N, Ichimasu N. Dorsally Displaced Facial Nerve in Retrosigmoid Transmeatal Approach for Vestibular Schwannoma: 3-Dimensional Operative Video. World Neurosurg. 2019 Mar;123:300. doi: 10.1016/j.wneu.2018.11.261. Epub 2018 Dec 21. PubMed PMID: 30580063.
2)

Evangelista-Zamora R, Lieber S, Ebner FH, Tatagiba M. Retrosigmoid Transmeatal Endoscope-Assisted Approach in Semi-Sitting Position for Resection of Vestibular Schwannoma: 2-D operative Video. J Neurol Surg B Skull Base. 2018 Dec;79(Suppl 5):S385-S386. doi: 10.1055/s-0038-1669985. Epub 2018 Oct 9. PubMed PMID: 30473983; PubMed Central PMCID: PMC6240135.
3)

Tatagiba MS, Evangelista-Zamora R, Lieber S. Mobilization of the Anterior Inferior Cerebellar Artery When Firmly Adherent to the Petrous Dura Mater-A Technical Nuance in Retromastoid Transmeatal Vestibular Schwannoma Surgery: 3-Dimensional Operative Video. Oper Neurosurg (Hagerstown). 2018 Nov 1;15(5):E58-E59. doi: 10.1093/ons/opy052. PubMed PMID: 29617908.
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