Brunner's gland adenomas in two cats.

Case series summary: Two cats, aged 13.5 and 14 years, presented with duodenal masses ultimately diagnosed as Brunner's gland (BG) adenomas. In the first cat, the lesion was a firm, pale tan, proximal duodenal polyp adjacent to the major duodenal papilla that was composed histologically of a well demarcated, expansile mass of well-differentiated BGs separated by fibrovascular septa and few adipocytes. This patient was euthanized for otitis-related vestibular signs, and the clinical significance of the duodenal polyp is unknown. The second cat presented with a 6-month history of vomiting. This cat had a mural duodenal mass in the region of the major duodenal papilla of approximately 2 cm, which was histologically composed of a dense population of variably ectatic BGs expanding the submucosa and lamina propria. This patient's mass was non-resectable, but the vomiting resolved after palliative gastroenterostomy loop surgery to allow ingesta to flow past the mass. The patient survived 35 months after the procedure. Relevance and novel information: BG adenoma is a rare, typically benign tumor in humans with non-specific clinical manifestations and no clear etiopathogenesis. This lesion, and the related condition BG hyperplasia, has been documented rarely in animals (one dog, two horses, and in mice and rats). This is the first description of the lesion in the cat. The comparative pathology, differential diagnoses and possible significance of these lesions are discussed.