Plexiform schwannoma of the oral/pharyngeal region: report of four cases and a review of the literature

Plexiform schwannoma represents an unusual schwannoma variant, characterized by multinodular growth grossly and/or microscopically. A review of the English language literature reveals only 30 previously reported cases involving the oral/pharyngeal region, and herein we present 4 additional cases. Among these 34 cases, the average age at diagnosis was 27 years (range 5 to 58 years), with a female-to-male ratio of 1.3:1. The most frequently involved sites were the lips (n=11) and tongue (n=11). Lesion duration prior to presentation was reported in 15 cases and ranged from 6 weeks to 26 years. The average lesion size was 2.1 cm (range 0.4 to 8.5 cm). Three tumors were described as “large” or “giant,” including one extending from the sublingual region to the mediastinum. The typical clinical presentation was a solitary/localized, painless, and slowly enlarging swelling. However, 5 patients exhibited other clinical findings (e.g., pain/discomfort, sore throat, dysphagia, dyspnea). Three cases arose in association with neurofibromatosis 2 (NF2). Other neural tumor types (e.g., conventional schwannoma, meningioma) and/or >1 plexiform schwannoma were found in 5 patients (3 with NF2 and 2 who did not fulfill diagnostic criteria for NF2). Microscopic examination typically showed a proliferation of multiple well-circumscribed tumor nodules, each surrounded by a thin capsule. Antoni A and B patterns were evident in varying proportions. Infrequent histopathologic findings included ancient change (n=1) and induction of adjacent surface epithelium/odontogenic epithelial rests (n=1). Immunohistochemical findings included reactivity for S-100 protein among the tumor cells (15/15 cases), reactivity for EMA among capsular perineural cells (3/4 cases), and no reactivity for NFP among the tumor cells (6/6 cases). Most patients (n=22) were treated by excision or enucleation. Among the 14 cases for which follow-up information was provided, 3 recurred. Unlike plexiform neurofibromas, plexiform schwannomas exhibit only a weak association with neurofibromatosis and have no known malignant potential.