Answer: Schwannoma

Histology: The lesion is well circumscribed and features a thin fibrous capsule with focal lymphoid cuffing. The lesion is composed of bland, elongated spindled cells with wavy nuclei arranged in alternating cellular areas (Antoni A) with nuclear palisading (Verocay bodies) and less cellular areas (Antoni B). Occasional hyalinized vessels are seen. Mitotic activity is rare, and necrosis is absent.

Discussion: Schwannomas are benign neoplastic proliferations of the Schwann cells of the peripheral nerve sheath (1), and they can occur in a wide anatomic distribution. Schwannomas of the larynx are rare, but have been reported (2). Schwannomas may be sporadic or syndromic, and schwannomas of the cerebellopontine angle (CPA) are classically associated with neurofibromatosis type 2 (NF2), in which patients have bilateral CPA schwannomas, glial hamartomas, meningiomas, and ependymomas.

Grossly, schwannomas are most often solitary, well-circumscribed and encapsulated, but they can also be plexiform. Schannomas of the gastrointestinal tract often display a lymphoid cuff. Histologically, the individual cells are most often spindled, wavy, and taper to a point at both ends. However, schwannomas can display a range of morphologies, including cellular, epithelioid, and melanotic (pigmented) variants. The stroma may be occasionally myxoid, particularly in Antoni B areas. Ancient schwannomas are characterized by widespread degenerative changes including cystic degeneration, hemorrhage, and marked nuclear atypia such as nuclear enlargement and hyperchromasia; however, mitoses and necrosis are rare. Schwann cells, and thus schwannomas, are diffusely immunoreactive for the S100-protein and negative for EMA (3). Most schwannomas are negative for cytokeratins, but focal cytokeratin immunoreactivity has been described (4).

The differential diagnosis of a schwannoma includes other benign nerve sheath tumors such as neurofibroma, as well as non-neural, bland-appearing spindle cell lesions such as fibromatosis and leiomyoma, and low-grade fibromyxoid sarcoma. Immunohistochemistry can aid in the diagnosis. For instance, schwannoma is diffusely and strongly immunoreactive for the S-100 protein; fibromatosis is positive for actin and nuclear beta-catenin; leiomyoma is positive for actin and desmin.

Reference(s):
– Jessen KR, Mirsky R. The origin and development of glial cells in peripheral nerves. Nat Rev Neurosci 2005;6(9):671-682.
– Ebmeyer J, Reineke U, Gehl HB, et al. Schwannoma of the larynx. Head Neck Oncol. 2009 Jul 8;1:24.
– Fisher C. Immunohistochemistry in diagnosis of soft tissue tumours. Histopathology 2011;58(7):1001-1012.
– Fanburg-Smith JC, Majidi M, Miettinen M. Keratin expression in schwannoma; a study of 115 retroperitoneal and 22 peripheral schwannomas. Mod Pathol 2006;19(1):115-121.