Gastric schwannoma--a clinicopathological analysis of six cases.

Six gastric schwannomas found among 150 mesenchymal tumours of the gastrointestinal tract were analysed clinically, histologically and immunohistochemically. These tumours occurred in the wall of stomach in middle-aged patients, five women and one man, and measured 2-9 cm in diameter. Follow-up from 3 to 24 years showed no recurrences or metastases. Histologically, all tumours were composed of spindle cells with vague nuclear palisading and variably myxoid stroma. One case showed a multinodular pattern of growth, reminiscent of plexiform neurofibroma. In all cases, there was a peripheral cuff-like B-lymphocyte infiltration with germinal centers in two cases. None of the tumours showed mitotic activity. Immunohistochemically, the tumour cells were positive for S-100 protein and focally for GFAP and CD57 (Leu 7). They were negative for desmin and actin, unlike true leiomyomas, and negative for CD34, unlike most gastrointestinal stromal tumours that were examined for comparison. Electronmicroscopy of three cases showed complex cell processes surrounded by prominent basement membranes, while myofilaments were not present. These cases show that schwannomas can be identified as rare, benign gastrointestinal tumours which probably arise from the gastrointestinal autonomic nervous system.