Schwanomma arising from mental nerve: a rare entity

INTRODUCTION

Schwannomas or neurilemmomas are benign tumors of the nerve sheath that are single, well encaspsulated, benign and arise from the perineural schwann cells. They may arise either in central or peripheral nerves. Approximately 25–45% of all schwannomas are present in the head and neck region. In the head and neck region, the tumor mostly appears in the tongue. Lower lip is an extremely rare site with only a few similar cases reported in the literature. Here we present a case report of schwanomma of the lower lip arising from mental nerve.

CASE REPORT

A 30 year male was admitted to the department of Otorhinolaryngology with a painless lesion located in the lower lip on the right side as presented in Figure 1.

Clinical history revealed that the lesion was present since 3 months and was not associated with any pain or bleeding or any history of prior trauma. On physical examination, a smooth globular swelling was present in the lower lip on right side, 2 cm × 3 cm in size and of firm, non-tender in character with regular margins extending anteriorly up to canine and posteriorly up to first pre molar. CT revealed a fairly well defined lesion in the sublabial region measuring about 1.5 cm × 3 cm × 2.3 cm with multiple tiny vascular channels within on arterial phase and becoming homogenously enhancing on delayed phase with no obvious calcification or haemorrhage within the lesion as shown in Figure 2. Also there was no associated destruction of bone and the overlying buccal mucosa was intact. FNAC was suggestive of neurogenic tumour. The differential diagnosis consisted of minor salivary gland tumour, fibroma, neurofibroma and mucocoele. Laboratory investigations were within normal limits. The patient underwent surgery and the lesion was excised intraorally with sublabial incision as given in Figure 3. Tumour was dissected all around and complete excision was done. As seen in Figure 4. The postoperative course was uneventful. Histopathology was suggestive of encapsulated cellular mesenchymal tumour consisting of spindle cells with a uniform cellular appearance (Antoni A pattern) throughout the tumour without hypocellular areas (Antoni B pattern). The tumour cells were arranged in palisaded fashion (Verocay bodies) as in Figure 5. Final pathological diagnosis was made as “schwannoma.” Post operatively, he developed decreased sensation in the distribution of mental nerve which gradually recovered over a period of six weeks. The patient has been recurrence-free at six months of follow up.

DISCUSSION

Schwannomas or neurilemmomas are rare neurogenic tumours of the peripheral nerves, arising from the Schwann cells. It was first described by Verocay in 1910. The underlying etiology is not known. Schwannomas mostly present as asymptomatic solitary nodules, with no gender predilection. Approximately 25–45% of all schwannomas are present in the head and neck region.¹ In the head and neck region, the tumor mostly appears in the tongue. Tumour can be less likely in the palate, floor of the mouth, gingiva, buccal mucosa and parotid gland as well.² Lower lip is an extremely rare site with only a few similar cases reported in the literature.³

The age at onset varies between 20-50 years; though lately the presence of lingual schwannomas has been described in children between 10-13 years of age.⁴

Schwannomas do not arise from cranial nerves I and II as they lack schwann cells.¹ They usually arise from both peripheral and intracranial parts of cranial nerves in head and neck region. The eighth nerve is the most common intracranial site whereas peripheral cranial nerve schwannomas are mostly found in parapharyngeal space of the neck and in soft tissues such as tongue, buccal mucosa, palate and gingival.⁵ In parapharyngeal space, the most commonly involved nerves are the vagus and the cervical sympathetic chain.⁶

Das gupta et al first described schwannoma of the lip in 1969.⁷ Since then only a few number of schwannoma cases of the lip have been reported.² The overall incidence of intraoral schwanommas is 1% with most common site being tongue followed by buccal mucosa and lastly lip and gingival.^2,3

These are slow-growing and asymptomatic, and the differential diagnosis may include neuromas, neurofibromas, granular cell myoblastoma, neuro-epitheliomas, fibromas or adenomas.⁸ The tumor may mostly manifest as a painless mass or swelling developing over several years. Mostly it is asymptomatic though sometimes pain and paresthesias may be associated. The lesion may also lead to displacement and compression of surrounding normal nerve tissue.⁹ There are only a few isolated case reports of schwanommas arising from mental nerve.¹⁰ Although we did not identify the nerve of origin intra-operatively, the presence of post-operative hypoesthesia over chin and lower lip indicates the origin of tumour from mental nerve.

Imaging techniques such as computed tomography (CT) or magnetic resonance imaging may be important in demarcating tumour margins, lesion composition and whether there is any associated tumour infiltration.² However, the definitive diagnosis depends on biopsy and histological study revealing an encapsulated lesion with two characteristic tissue patterns referred to as Antoni A and Antoni B. Immunohistochemically, the lesion is positive for protein S-100 (a specific neural tissue marker), vimentin or other more specific markers such as neuron-specific enolase.¹

Treatment of choice is complete removal of the encapsulated lesion. Recurrences and development of malignancy are rare events.

CONCLUSION

High index of suspicion is required and Schwannoma should be considered as a differential diagnosis in oral cavity benign lesions. The final diagnosis is based on histopathology report and immunohistochemical analysis. The treatment of these tumors is complete resection. The prognosis of such cases is extremely good, without any recurrence.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

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