Gastric tumors in patients with pulmonary chondroma or extra-adrenal paraganglioma: an ultrastructural study.

The histogenesis of a distinctive metastasizing intramural gastric tumor found in patients with extra-adrenal paragangliomas, pulmonary chondromas, or both, is unknown. By light microscopy, it has appeared to be of smooth-muscle derivation, and it has been interpreted as being epithelioid leiomyosarcoma. For further clues to its nature, we studied three examples by electron microscopy (two obtained from patients with extra-adrenal paragangliomas and one from a patient with pulmonary chondroma). Ultrastructurally, they were characterized by interdigitating cytoplasmic processes, plasma membrane-associated dense patches, an incomplete basement membrane, junctional complexes, randomly oriented filaments without periodicity, cytoplasmic dense bodies, pinocytotic vesicles, clustering of mitochondria, and rare cilia-features of normal smooth muscle or of smooth-muscle tumors with classic histologic patterns. Thus, the findings suggest that the three tumors we studied are of smooth-muscle derivation.