Peripheral nerve sheath tumors of the gastrointestinal tract: a multicenter study of 58 patients including NF1-associated gastric schwannoma and unusual morphologic variants.

The frequency and morphological spectrum of gastrointestinal peripheral nerve sheath tumors (PNSTs) from consecutive case material has not been studied in the c-KIT era. We reviewed all mesenchymal gastrointestinal (GI) lesions at our departments according to current diagnostic criteria. PNSTs formed the third commonest group of mesenchymal GI tumors with a lower frequency (< or =5%) compared to gastrointestinal stromal tumors (GISTs; approximately 50%) and smooth muscle neoplasms ( approximately 30%). Granular cell tumors (GCTs; n = 31) and schwannomas (n = 22) were the most common types of PNSTs encountered. Rare tumors included neurofibromatosis 1 (NF1)-associated PNSTs (n = 5) and gastric perineurioma (n = 1). Thirteen schwannomas (including also some recent cases) were initially diagnosed as GIST, leiomyoma, or neurofibroma. Unusual histological variants included sigmoid GCT with prominent lipomatous component (n = 1), reticular-microcystic schwannoma of small (n = 1) and large (n = 1) bowel, NF1-associated gastric schwannoma (the first case to date), and psammomatous melanotic colonic schwannoma unrelated to Carney complex (n = 1). PNSTs coexisted with GIST in four patients (three had definite NF1). In conclusion, PNSTs of the GI tract are rare uniformly benign neoplasms that may show schwannian, perineurial, fibroblastic, or mixed differentiation. Most of them (92%) occurred sporadically unassociated with NF1 or NF2. Gastrointestinal PNSTs are still underrecognized by general pathologists. Awareness of their diverse morphology will help to avoid confusing them with smooth muscle neoplasms and GIST that they may closely mimic.