Multiple peripheral nerve sheath tumors in the small intestine of a horse.

Multiple neurofibromas, schwannomas, and hyperplastic enteric plexuses were observed in the distal jejunum and ileum of a 6-year-old pinto gelding. The animal was presented because of an acute episode of colic. Three meters of distal small intestine, partially incarcerated in the epiploic foramen, were surgically removed. Numerous tumor nodules up to 10 mm in diameter were found adjacent to a Meckel's diverticulum, predominantly located in the subserosa of a hypertrophic segment. Histologically, tumors were well demarcated and composed of interlacing fascicles formed by spindloid cells. Adjacent enteric plexuses were hyperplastic. Immunohistochemically, all tumors were positive for vimentin and S-100. Desmin immunoreactivity was only observed in larger tumors (> 500 microns). Glial fibrillary acid protein was demonstrated nearly exclusively in smaller ones. Immunostaining for neurofilament was restricted to entrapped ganglion cells. Based on conventional light microscopic examination and immunohistochemical evaluation, the lesion was diagnosed as multiple benign peripheral nerve sheath tumors in the small intestine.