Incidental diagnosis of a spindle cell type gastrointestinal stromal tumor in a dog with ethylene glycol intoxication

A 6-year-old castrated male American Pit Bull Terrier dog was presented for evaluation of acute onset of tonic-clonic seizures, anorexia, and vomiting. On physical examination, neurologic signs, such as generalized proprioceptive ataxia, salivation, circling to the right, and absent patellar reflexes bilaterally, were noted. A complete blood cell count revealed mild hemoconcentration and an inflammatory leukogram, while a chemistry panel showed severe azotemia, marked hypochloremia, and a severe titrational metabolic acidosis, suggesting possible ethylene glycol intoxication. However, an irregularly round, small mass was identified in the large intestine on abdominal ultrasound. Additionally, bilateral hyperechoic renal cortices with medullary rim sign were suggestive of acute nephritis or tubular necrosis. The cytologic evaluation of a fine-needle aspiration biopsy of the abdominal mass revealed a large population of mesenchymal cells, suggesting the presence of neoplasia. Due to the worsening of symptoms, the dog was humanely euthanized. Necropsy confirmed ethylene glycol intoxication, and the incidental finding of a neoplastic intestinal mass was diagnosed as spindle cell sarcoma. Immunohistochemical staining showed strong, diffuse positivity for CD117, smooth muscle actin, and S-100, indicating the final diagnosis of a spindle cell type gastrointestinal stromal tumor (GIST). This report briefly discusses the classifications of nonlymphoid, nonangiogenic intestinal mesenchymal tumors, characteristics of GISTs, and the importance of the immunohistochemical classification of mesenchymal tumors of the gastrointestinal tract.