Plexiform Schwannoma in the Duodenum of a Horse with Recurrent Colic

Abstract

Background: Intestinal neoplasia is an uncommon cause of colic in the horse. Accurate clinical diagnosis is necessary to direct rationale intervention because equine intestinal neoplasms have widely varying prognoses and treatment requirements. Case Presentation: A 23-year-old Missouri Foxtrotter gelding presented with a history of mild recurrent colic. Physical examination, abdominal ultrasound, and cytologic evaluation of peritoneal fluid were unremarkable. Upper gastrointestinal endoscopy revealed multiple tan raised masses in the duodenal mucosa. Histopathology demonstrated a well demarcated, multicentric, intramucosal spindle cell neoplasm arranged in an Antoni A pattern with no evident mitotic figures or necrosis. Immunohistochemistry was negative for desmin, smooth muscle actin, and the gastrointestinal stromal tumor (GIST) marker CD117 (c-Kit). Tumor cells were uniformly positive for neuronal specific enolase and S-100. Based on distribution, morphology and immunohistochemical markers, the tumor was diagnosed as benign plexiform Schwannoma. The horse responded well to conservative symptomatic treatment. Conclusion: Although uncommon, spindle cell tumors should be considered in cases of recurrent equine colic after more common causes have been excluded. Immunohistochemistry is necessary to definitively diagnose intestinal mesenchymal and neuroectodermal tumors. Benign tumors such as Schwannoma, neurofibroma and lowgrade GIST carry a good prognosis.