Schwannomas

Schwannomas are benign tumors that arise from Schwann cells, which form the myelin sheath around peripheral nerves. They are typically encapsulated and grow adjacent to nerve fibers, often displacing them rather than infiltrating.

These tumors can occur anywhere along the peripheral nerve sheath but are most commonly found in the head and neck region and along the vestibulocochlear nerve, where they are called vestibular schwannomas. They may present as solitary lesions or, less commonly, be associated with neurofibromatosis type 2 or schwannomatosis. Most patients are adults in middle age.

Histologically, schwannomas are well circumscribed and encapsulated, with characteristic Antoni A and Antoni B areas and, in many cases, Verocay bodies. Tumor cells typically express S-100 protein on immunohistochemistry, supporting neural crest origin.

Clinically, presentation depends on location. Vestibular schwannomas commonly cause unilateral sensorineural hearing loss, tinnitus, and balance disturbance. Others may present as a painless enlarging mass or cause focal neurological deficits if a cranial or peripheral nerve is involved.

Diagnosis relies on imaging and histology. Magnetic resonance imaging is the preferred modality, usually showing an enhancing lesion along a nerve with variable cystic change. Computed tomography can help assess bone remodeling. Definitive diagnosis is confirmed by histologic examination after biopsy or surgical excision.

Treatment ranges from observation for small, asymptomatic tumors to surgical excision aimed at nerve-sparing resection. Stereotactic radiotherapy is an option for patients who are not good surgical candidates or for residual or recurrent disease. Prognosis after complete excision is generally excellent, with recurrence being uncommon.

Variants include cellular, ancient, and plexiform schwannomas, which have distinct histologic features but similar benign behavior.