Jejunal stromal tumor with skeinoid fibers or myenteric plexoma: a case report.

Small intestinal stromal tumors with 'skeinoid fibers' are uncommon stromal tumors with an associated controversial histogenesis. Although their microscopic appearance is suggestive of a smooth muscle nature, they lack specific smooth muscle features, as evident by electron microscopy and immunohistochemistry. They also appear to lack features of neurogenic origin because they fall to react with neural/neuroendocrine markers such as S-100 protein, neuron-specific enolase and chromogranin. It is interesting, nonetheless, to note that the ultrastructural examination of these tumors may show structures reminiscent of neural differentiation, such as cytoplasmic projections, containing occasional membrane-bound, dense-core, neurosecretory-type granules, which mimick the long cytoplasmic processes seen in tumors of neural origin. Moreover, the association of these tumors with Von Recklinghausen's neurofibromatosis, as well as the presence of 'skeinoid fibers' in proven neurogenic spindle cell neoplasms such as gastrointestinal autonomic nerve tumors and schwannomas, suggests that these tumors might also be neurogenic in origin and enhances the diagnostic value of 'skeinoid fibers' as a possible ultrastructural marker of neural differentiation. Thus, light microscopic evaluation is clearly insufficient to accurately diagnose these tumors and to determine their histogenesis, electron microscopic and immunohistochemical studies being necessary. In this article the histogenesis of small intestinal stromal tumors with 'skeinoid fibers', regarding a jejunal neoplasm in a 63-year-old patient, is reviewed. The light microscopic, immunohistochemical and ultrastructural features are described and compared with findings usually seen in all those stromal tumors which may raise a differential diagnosis, such as smooth muscle stromal tumors, gastrointestinal autonomic nerve tumors, schwannomas, paragangliomas and fibrosarcomas.