GASTROINTESTINAL AUTONOMIC NERVE TUMORS - A CLINICOPATHOLOGICAL, IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY OF 10 CASES

Gastrointestinal Autonomic Nerve Tumors (GANTs) are an underrecognized group of gastrointestinal stromal tumors (GISTs) putatively arising f rom the neural plexuses of the bower wall. Approximately 24 cases have been previously reported. Their histogenesis, malignant potential, mo rphology and phenotypic features are not well defined. We present deta ils of 10 GANTs iterating features, predominantly ultrastructural, all owing distinction from other GISTs. Clinical details are: sex-7M, 3F; age range 31-79 yrs, mean 53; symptoms/signs - abdominal pain 3, GI bl eeding 3, mass 2, anemia 2. Follow-up ranged from 1-102 mths, mean 29. Seven tumors involved the smalt intestine and 3 were gastric. Tumor s ize ranged from 30-160 mm, mean 79. They were solid and cystic, often transmural and usually involved mesentery and retroperitoneum. Spindle d and epithelioid cells were ''compartmentalized'' by a branching micr ovasculature. Eosinophilic, PAS positive stromal globules were promine nt. Paraffin immunostaining results were (number positive/total): vime ntin (8/9), NSE (10/10), S100 protein (6/10), neurofilament protein (0 /9), synaptophysin (3/9), desmin (2/9, focal), smooth-muscle actin (0/ 9). Ultrastructural diagnostic features were elaborate, branching cyto plasmic processes containing microtubules, intermediate filaments and varying numbers of neurosecretory granules. Characteristic features we re elaborate smooth endoplasmic reticulum enmeshed with intermediate f ilaments, pleomorphic mitochondria with lamellar cristae, mitochondria l-RER complexes, confronting RER cisternae, and circumscribed collecti ons of stromal ''skeinoid'' fibres. There were no features of smooth m uscle, Schwannian or perineurial differentiation. We conclude that: 1) GANTs can be distinguished from other GISTs, electron microscopy bein g essential for diagnosis: 2) biological behaviour and predictors must await study of further cases with longer follow-up; our findings indi cate less aggressive behaviour than that described previously; and 3) immunohistochemistry on fixed material is of limited value without ult rastructural assessment; focal desmin positivity is not indicative of smooth muscle differentiation without other supporting evidence.