Perineurial cells and nerve axons in gastrointestinal schwannomas: a similarity with neurofibromas. An immunohistochemical study of eight cases.

Gastrointestinal schwannoma (GIS) is a distinctive and extremely rare lesion showing some differences from conventional soft tissue schwannoma and some similarities with common soft tissue neurofibroma. Soft tissue neurofibromas and schwannomas differ by contents of specific types of nerve sheath cells, such as Schwann cells, perineurial cells and CD34+ cells. To compare GIS with these soft tissue lesions, eight cases of typical GIS were studied immunohistochemically to evaluate their nerve sheath cell types. Epithelial membrane antigen (EMA) and claudin-1 as perineurial cell markers, and neurofilament protein as a marker for intratumoral axons were used. In addition, the tumors were stained for cytokeratin, CD117 (C-KIT), alpha-muscle specific actin, S100 protein and CD34. EMA- and claudin-positive cells were seen in 2 (25%) and one lesion, respectively, thus resembling cellular composition of neurofibroma. Intratumoral neurofilament protein positive axons otherwise typical of neurofibroma were found inside 4 tumors (50%). CD34 positivity was found in 6 tumors (75%) and often revealed a diffuse pattern as seen in neurofibroma and not a zonal pattern as described in schwannomas. These results show that GIS has some features that are more typical for neurofibroma than for conventional schwannoma. In surgical pathology practice, a finding of intratumoral axons and positivity for claudin-1 and especially for EMA should not preclude diagnosis of GIS.