Vagal Nerve Schwannoma
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).
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 is based on clinical suspicion and confirmation obtained by means of surgical pathology.
Schwannomas of the vagus nerve must be differentiated from the carotid body and glomus vagale tumors because the distinction may influence treatment planning.
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).
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.
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 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).
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).
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).