Solitary solid stromal gastrointestinal tumors in von Recklinghausen's disease with minimal smooth muscle differentiation.

Neurofibromatosis (von Recklinghausen's disease) is occasionally associated with large, solid stromal tumors of the gastrointestinal tract. The authors examined by electron microscopy two such cases of cellular spindle cell neoplasms of the small bowel histologically that resembled leiomyomas, in an attempt to clarify the cell of origin of these lesions. Ultrastructurally, the tumor cells predominantly contained moderate to large numbers of intracellular filaments, small cell processes, discontinuous adherent dense basement-membrane-like material, and abundant intercellular collagen. Definite fusiform dense bodies or structures highly suggestive of them and pinocytotic vesicles were seen in rare cells of each lesion after viewing multiple blocks. While patients with neurofibromatosis are certainly at risk of developing gastrointestinal Schwann cell neoplasms, these two cases suggest that they are also at risk for developing poorly differentiated stromal tumors, resembling leiomyomas by light microscopy, which may show only characteristic cytoplasmic differentiation of smooth muscle cells after ultrastructural examination of many sections.