Hypoglossal Nerve Schwannoma Masquerading As A Plunging Ranula: A Diagnostic Pitfall In Submandibular Masses.

Abstract

Background:

Schwannomas are benign, encapsulated peripheral nerve sheath tumors that most commonly arise from the vagus nerve or sympathetic chain in the neck. Extracranial schwannomas of the hypoglossal nerve are distinctly rare and may be clinically silent. When cystic degeneration predominates, these tumors can radiologically mimic common cystic lesions of the submandibular region, particularly plunging ranula, and fine-needle aspiration cytology (FNAC) may be non-diagnostic due to hypocellular aspirates. Awareness of this masquerade is important for appropriate preoperative planning and nerve-preserving surgery.

Case report:

A 57-year-old man presented with a progressively enlarging, painless right submandibular swelling for 6 months. Examination revealed a well-defined, firm, mobile, non-tender mass (~3 × 3 cm) without overlying skin changes, floor-of-mouth swelling, cervical lymphadenopathy, or apparent cranial nerve deficits. FNAC was non-contributory. Contrast-enhanced computed tomography demonstrated a well-circumscribed hypodense lesion in the right submandibular space (approximately 2.7 × 6.3 × 3.4 cm) extending superiorly toward the sublingual region and compressing the submandibular gland without invasion, leading to a provisional diagnosis of plunging ranula. Surgical excision was performed with removal of the presumed ranula, sublingual gland, and right submandibular gland. Histopathology of the neck mass showed a circumscribed spindle cell neoplasm with Antoni A and Antoni B areas and Verocay bodies, with focal hyalinized thick-walled vessels. Tumor cells were diffusely positive for S100 and SOX10 and negative for CD38 and CD163, confirming schwannoma. The submandibular gland showed chronic sialadenitis.

Conclusion:

Hypoglossal nerve schwannoma should be considered in the differential diagnosis of “ranula-like” cystic submandibular swellings, particularly when FNAC is inconclusive. Definitive diagnosis relies on histopathology and immunohistochemistry, and preoperative suspicion may facilitate nerve-conscious surgical management.