Hybrid schwannoma-perineurioma of the gastrointestinal tract: a clinicopathologic study of 2 cases and reappraisal of perineurial cells in gastrointestinal schwannomas.

Soft tissue neoplasms with features of both schwannoma and perineurioma (hybrid schwannoma-perineurioma) have been increasingly recognized in recent years. To date, only a single case of this entity has been documented in the gastrointestinal tract (sigmoid colon). We herein describe 2 new cases of this entity. For comparison, we reevaluated 12 classic gastrointestinal schwannomas for the perineurial cell component. The 2 hybrid schwannoma-perineuriomas were detected incidentally in the gastric antrum and the vermiform appendix in a 50-year-old woman and a 17-year-old man during surgery for gastric GIST and appendicitis-like symptoms, respectively. None of the patients had neurofibromatosis 1 or 2. Patients were alive with no evidence of recurrence or new tumors at 8 and 12 months, respectively. The tumors measured 1.2 cm and 1.5 cm in size. Histologically, they showed prominent storiform, lamellar, and fascicular patterns. Notably, both lacked peripheral lymphoid cuffs and the trabecular pattern of gastrointestinal schwannomas. Both tumors coexpressed protein S100 (≥80%), CD34 (80%), and the perineurial cell markers (20% to 40% of tumor cells). The perineurial cell component formed alternating fascicles with S100-positive cells throughout the neoplasm. Reevaluation of 12 classic gastrointestinal schwannomas showed isolated claudin-1/epithelial membrane antigen-positive cells. However, 4 schwannomas (33%) strongly expressed glucose transporter-1 in most of the tumor cells indicating its limited specificity in this setting. Compared with gastrointestinal schwannomas, CD34 expression was stronger and more diffuse in hybrid schwannoma-perineuriomas. We conclude that hybrid schwannoma-perineuriomas are distinct from gastrointestinal schwannoma, both histologically and immunohistochemically.