A four year old male castrated Maltese terrier was evaluated by the Internal Medicine Service at the Cornell University Hospital for Animals on January 22, 2010 for urethral obstruction. He had a history of neurologic signs, polyuria and polydipsia, urinary tract infections and urinary obstruction. He had undergone three cystotomies to remove ammonium biurate stones. In November 2007, he presented to the Surgery Service for a urinary obstruction. At that time, a CBC showed a leukocytosis (29.7 thou/uL ref. 6.2-14.4) with a mature neutrophilia (22.3 thou/uL ref. 3.4-9.7). A chemistry panel revealed elevated ALT (234 U/L ref. 25-106), AST (414 U/L ref. 16-50) and ALKP (127 U/L ref. 12-122). Urinalysis revealed an inappropriately concentrated urine (specific gravity of 1.015) with moderate proteinuria. A urine culture was negative for bacterial growth. An abdominal ultrasound revealed microhepatica with a small portal vein, mild bilateral renal cortical mineralization and cystic calculi. A cystotomy was performed and the stones were removed and submitted for analysis, which showed they were 100% ammonium acid urates. A liver biopsy was collected and revealed portal triad and lobular atrophy with portal arteriole hyperplasia and multifocal lipogranulomas. These changes are consistent with vascular malformation most likely from a portosystemic shunt or microvascular dysplasia. He recovered well post-operatively and was referred to the internal medicine service for further work-up.