Colonic duplication cyst with secondary septic peritonitis in a cat.

Case summary: A 5-month-old male castrated domestic shorthair cat was evaluated for acute onset of emesis. Abdominal radiographs identified a suspected colonic foreign body and abdominal-focused assessment with sonography for trauma, triage and tracking (AFAST) evaluation revealed a large amount of peritoneal effusion. Cytology of the peritoneal effusion was consistent with a septic exudate. An exploratory celiotomy identified a ruptured ileocecocolic mass and a resection and anastomosis was performed. No foreign material was identified and histopathology confirmed that the ruptured mass was a colonic duplication cyst. Recurrent septic peritonitis was diagnosed based on cytologic evaluation of fluid from a silicone bulb reservoir of a closed suction drain. No abnormalities were surgically identified, the cat recovered without complication, was discharged at 7 days postoperatively and has continued to remain healthy 8 months after surgical intervention. Relevance and novel information: To our knowledge, this is the first known instance of a histopathologically confirmed non-communicating colonic duplication cyst causing septic peritonitis in the veterinary literature.