Gastrointestinal autonomic nerve (GAN) tumor. Ultrastructural evidence for a newly recognized entity.

We describe three cases of spindle cell tumors arising in the gastrointestinal tract, each with ultrastructural features that recapitulate the ultrastructural morphology of the enteric autonomic nervous system. These features include the presence of small, dense core granules in the synthetic-secretory Golgi structures, sparsely distributed within the ample tumor-cell cytoplasm, near plasma-membrane surfaces and within axons. Tumor cells had elongated processes and axons contained small granular vesicles, clear vesicles, or large, dense vesicles. Specific features diagnostic for smooth-muscle cell, Schwann cell, or fibroblast cellular origin were absent.