Malignant transformation of a duodenal duplication cyst in a cat

A 15-year-old domestic shorthair cat presented for lethargy, vomiting and anorexia. Abdominal ultrasound showed a bi-lobed cystic duodenal mass. Based on ultrasonographic features, malignant transformation of a duodenal duplication cyst was suspected. A resection and anastomosis was performed. Histology of the mass was consistent with carcinoma and an intestinal mucosa was present along the inner surface of the mass, suggestive of a duplication cyst. The patient returned 3 months postsurgery with recurrence of clinical signs. Abdominal ultrasound showed a recurrent duodenal mass at the surgery site and body wall nodules. Fine-needle aspirates of these lesions showed epithelial neoplasia. Owing to the poor prognosis, the owners elected euthanasia.

Malignant transformation of duplication cysts in cats is rare but can be detected on ultrasound. The described ultrasonographic features can aid in prioritization of malignant transformation of duplication cysts as a differential diagnosis.