Urachal Adenocarcinoma in a Dog

An 8-year-old neutered female Labrador retriever was presented with a 3-year history of intermittent haematuria. Ultrasonographic evaluation of the urinary bladder revealed a 2 × 3 × 0.5 cm intraluminal mass arising at the dome. The mass was excised via partial cystectomy. Histopathological examination revealed neoplastic epithelial cells arranged in sheets, irregularly-branching tubules and acini within a fibrovascular stroma. Neoplastic cells were cuboidal to polygonal with abundant foamy amphophilic cytoplasm, typically with a single, large, clear intracytoplasmic vacuole and eccentric nucleus ('signet ring' cells). Neoplastic tubules were often ectatic and contained abundant mucin. Immunohistochemically, the neoplastic cells had weak, cytoplasmic immunoreactivity for cytokeratin 7 and rare, but strong, nuclear immunoreactivity for CDX2. Based on the cellular morphology, immunolabelling characteristics and anatomical location, a diagnosis of adenocarcinoma of urachal origin was made. To the authors' knowledge, this is the first reported case of urachal adenocarcinoma in a dog.