Metaplastic Ossification of a Giant Paraprostatic Cyst in a Dog: A Case Report

A 7-year-old male Caucasian shepherd presented with a 3 month history of intermittent hematuria, penile discharge, and abdominal pain and distension. The dog had a history of prostatic hyperplasia with multiple cysts, diagnosed by the referring clinician two years prior to the case presentation. Two oral courses of antibiotics and antiandrogens were administered by the treating veterinarian without resolution. At the case presentation visit, massive swelling was present in the mid- and caudal parts of the abdomen. Abdominal ultrasound and exploratory laparotomy revealed a paraprostatic cyst (size: 25 × 20 × 18 cm) in the caudal part of the abdomen. The cyst had a bony ridge along the wall with multiple cauliflower-like lesions extending inside. Histopathologic examination revealed an intermittently epithelial-lined inner wall of the cyst, which was partially degenerated and flattened due to the pressure of the intraluminal fluid. The luminal surface of the cyst appeared markedly irregular with multiple structures made of dense, fibrous connective tissue protruding inside with metaplastic ossification foci, consistent with severe osseous metaplasia. The epithelium showed focal secretory activity. Numerous subepithelial multifocal neutrophil and mononuclear cellular infiltrates were found. The lumen of the cyst contained a reddish-brown (blood and protein-rich) fluid. Complete surgical excision of the cyst and omentalization of the capsular remnant resulted in successful resolution of the clinical signs.