Parapharyngeal space schwannomas: our experience and review of literature

INTRODUCTION

Tumours of the parapharyngeal space are an interesting group of tumours because of the origin, presentation and management. Most of these tumours are of salivary glands origin (50%, most commoly deep lobe of parotid), followed by tumours of neurogenic origin (20%). The remaining 30% includes lymphoreticular lesions, metastatic lesions and carotid body tumours. Together they account for only about 0.5% of all head and neck tumours.¹ Schwannomas are the most common tumours of neurogenic origin of which vagal schwannoma accounts for 50%.² The clinical presentation of schwannomas depends on the anatomical area involved and nerve of origin.

Accurate diagnosis and management can be very challenging and at times requires a team approach including pathologist and neuro-surgeon. Surgical excision is the standard treatment modality for parapharyngeal schwannomas and recurrence is uncommon.

In this article we present a review of 5 consecutive cases of parapharyngeal space schwannomas which we managed in the last two years.

The aim of the study was i) to determine the incidence of parapharyngeal space schwannoma among defence personnel’s and their dependents presenting to otorhinolaryngology out patients department (OPD) and

ii) to study the clinical presentation, management and outcomes of such lesion.

METHODS

Our study is a retrospective study conducted at a tertiary care centre in Western India. All new patients referred to ENT OPD at our center were included in the study. Data was collected from our OPD records. The study was conducted over two years between Jan 2015 to Dec 2016. All old cases and those with an established diagnosis on follow up, patients for periodic medical examination and medical examination of recruits were excluded from the study.

RESULTS

The total number of our OPD work load (old cases and new cases) between Jan 2015 and Dec 2016 was 30,208. Out of which the total number of new cases was 7,367. Out of these only 538 patients had a diagnosis of head and neck lesions. Out of these there were 12 cases of parapharyngeal space tumours which included 6 cases of salivary gland tumours, 5 cases of schwannomas and 1 case of lymphoma. The incidence rate of parapharyngeal space schwannoma was 0.034% out of all fresh cases reporting to otolaryngology OPD and 0.47% out of all fresh diagnosed cases of head and neck lesions at our centre.

Out of the total 5 cases of parapharyngeal space schwannomas 2 patients had vagal schwannoma and one each had hypoglossal nerve schwannoma, spinal accessory nerve schwannoma and sympathetic chain schwannoma as depicted in Table 1.

MRI was preoperatively suggestive of origin of schwannoma correctly in 4 out of the 5 cases. The 4^th case was diagnosed on imaging to be a vagal nerve schwannoma, however, intraoperatively it was noted that schwannoma was arising from cervical sympathetic chain. 3 out of the 5 cases developed post op complications in the form of nerve palsies of the nerve of origin of the schwannoma. One case of hypoglossal schwannoma which was extensive and presented with both cervical and intracranial component and brain stem compression developed multiple cranial nerve palsy.

DISCUSSION

Schwannomas are rare tumours of neurogenic origin of which about 30-40% occur in the head and neck region.³ Parapharyngeal space schwannomas are next only to vestibular schwannoma in the head and neck region.

They are usually asymptomatic and presents as a slow growing lateral neck swelling that can be palpated along the sternomastoid muscle. In our series of cases all the 5 patients presented as lateral neck swelling. Clinical diagnosis is difficult because of the rare occurrence and also because most of them do not present with neurological deficit. Often the clinician has a differential diagnosis of metastatic cervical lymphadenopathy, lymphoma, branchial cleft cyst apart from paragangliomas of the parapharyngial space.⁴

Amongst the symptomatic patients, the most common symptom is hoarseness. Occassionally patient may give a history of paroxysmal cough on pressing the mass, as was seen in one of our patient with vagal schwannoma, which is unique to vagal schwannoma.^5-7 Another patient presented with giddiness which was because of intracranial component of hypoglossal schwannoma compressing on the brainstem.

Schwannomas arising from spinal accessory nerve are uncommon tumours which may involve the cisternal, foraminal, and extracranial (spinal or intrasternomastoid) segments of the spinal accessory nerve.⁸ Schwannomas of extracranial segment of the spinal accessory nerve represent rarer forms of tumour.⁹ Our series reports a case of schwannoma of extracranial or cervical segment of spinal accessory nerve which was clinically diagnoses as carcinoma of unknown primary origin. Final diagnosis was based on intraoperative finding and histopathological report.

MRI plays a very important role pre-operatively in the diagnosis and determining the extent of the lesion. The MRI appearance of a well circumscribed non- enhancing mass should lead to the clinical suspicion of a schwannoma. Furukawa et al had reported in their paper on how to differentiate between schwannoma of the vagus nerve and cervical sympathetic chain.¹⁰ The vagal schwannomas, in fact, displace the internal jugular vein laterally and the carotid artery medially, whereas schwannomas from the cervical sympathetic chain displace both the carotid artery and jugular vein without separating them.^10-14 We had one case of cervical clinical sympathetic chain schwannoma which was diagnosed as vagal nerve schwannoma based on clinical and radiological imaging. However intraoperatively it was seen arising from the sympathetic chain and histopathological report confirmed the diagnosis of schwannoma.

The treatment of these tumours is complete surgical excision. Intraoperative these tumours appear as yellowish-white and well circumscribed masses arising from the nerve of origin and at times the nerve is stretched out and lying on the surface of the tumour. Dissecting the tumour from the nerve and preserving the neural pathway of the nerve should be primary aim of surgery. However at times it is very difficult to do so and the nerve has to be sacrificed and an end to end anastomosis may be performed if possible, especially in vagal nerve schwannoma.⁵

As an alternative to complete surgical excision, patients can be offered stereotactic radiosurgery for both newly diagnosed and residual tumour. Pollock et al in their study concluded that although the reported number of patients having radiosurgery for nonvestibular schwannomas is limited, radiosurgery appears to have less treatment associated morbidity for non-vestibular schwannomas, especially for the schwannomas involving the lower cranial nerves.¹⁵

Although the reported incidence of pre-operative vocal cord palsy is about 10-20 % in cases of vagal schwannoma, hoarseness is almost always present following surgery.⁵ Hence, vocal cord assessment is a must prior to surgery in all neck swellings. Because of the high incidence of associated morbidity and the benign nature of the disease, patient needs to be informed about the possible complications and an option of conservative approach may be given specially in elderly patients. Our entire patients were young adults and opted for surgical excision of the tumour. Only 2 out (40%) of the 5 patients did not have any postoperative cranial nerve deficit. One of the patients had multiple postoperative cranial nerve deficits because of the large size of tumour with both intracranial and cervical component which was removed in 2 stages first by the neurosurgeon and in second stage by the head and neck surgeon.

CONCLUSIONS

The aim of discussion this case series was to highlight the mode of presentation of schwannomas of parapharyngeal region. At times these lesions can be very extensive with intracranial extension and may require to be removed as a staged procedure involving the Neurosurgeon and Head & Neck surgeon. The surgery carries the risk of cranial nerve palsy and patients should be informed about it preoperatively.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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