A 13-year-old, 55-pound, castrated male border collie with a 4-week history of dribbling urine, pollakiuria, stranguria, and dysuria was presented. He had been treated with antibiotics for decreased appetite and apparent incontinence. A 1.5-cm, firm swelling was palpable at the level of the bulbus glandis. Fine-needle aspiration of the mass revealed large clusters of spindle-shaped cells with round to oval nuclei and a coarse chromatin pattern. The dog continued to have urinary problems, and excisional biopsy of the mass was eventually recommended. The mass was 3- × 2-cm in diameter and appeared to be removed completely along with the caudal 1 cm of the os penis. A diagnosis of ossifying fibroma of the os penis was made, and it was noted that neoplastic cells extended to the periphery on all edges. Nineteen months after the first surgery, a second procedure was performed when the dog began having a diminished urine stream. A mass associated with the urethra at the caudal aspect of the os penis was found so scrotal urethrostomy was performed, as the owner declined penile amputation. Seventeen months after the second surgery, the dog continues to urinate normally. Ossifying fibromas are relatively rare and are more commonly associated with tumors of the skull.

COMMENTARY: This case outlines steps in diagnosis and management of urethral obstruction in male dogs, which is most often caused by uro-lithiasis. When uroliths are not present, intraluminal/extraluminal neoplasia, traumatic strictures, and neurogenic urethral spasm must be considered. Careful palpation of the urethra, retrograde urethrography, endoscopy, and urethral pressure profilometry can help define location and extent of obstruction. Cytologic or histologic examination is necessary to determine the cause of the problem. Some strictures can be managed by dilatation methods and stents while others, such as this case, require urethrostomy.

Urinary obstruction secondary to an ossifying fibroma of the os penis of a dog. Mirkovic TK, Shmon CL, Allen AL. JAAHA 40:152-156, 2004.