GASTROINTESTINAL AUTONOMIC NERVE TUMORS AND THEIR SEPARATION FROM OTHER GASTROINTESTINAL STROMAL TUMORS - AN ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL STUDY OF 7 CASES

Gastrointestinal stromal tumours (GIST) represent a heterogeneous grou p whose classification frequently requires ultrastructural and immunoh istochemical studies. In a retrospective study of the ultrastructural findings of 24 gastrointestinal stromal tumours, whose light microscop ic study has yielded ambiguous results and in which accurate diagnosis had required ultrastructural support, seven were found to have the ch aracteristics of gastrointestinal autonomic nerve (GAN) tumours. In al l of them the diagnosis was based on the presence of dendritic process es with dense neuroendocrine granules. Immunohistochemically, the seve n tumours were negative for smooth-muscle markers. All stained positiv ely for vimentin. NSE, chromogranin, and synaptophysin were positive i n most of them, while S-100 protein was positive only in two cases. We present the ultrastructural and immunohistochemical features of seven GANT against the background of the GISTs of our series, We conclude t hat GAN tumours cannot be diagnosed by light microscopy alone but this tumour group displays characteristic electron microscopic and immunoh istochemical features and appears to represent a distinct type of GIST .