Attenuation of Ascites Following Surgical Ligation of a Congenital Caudal Mesenteric Arteriovenous Fistula in a Dog.

A 1-year-and-9-month-old intact female Pembroke Welsh Corgi (10.5 kg) was referred for abdominal distension, intermittent diarrhea, and ascites. Abdominocentesis yielded 1200 mL of transudate (specific gravity, 1.008). Serum biochemistry showed hyperammonemia (NH3, 163 μg/dL), increased bile acids, and mild hypoalbuminemia. Abdominal ultrasonography suggested a vascular anomaly, and contrast-enhanced computed tomographic angiography confirmed an arteriovenous communication between the caudal mesenteric artery and vein with marked venous dilation and multiple acquired portosystemic shunts, consistent with portal hypertension secondary to a congenital caudal mesenteric arteriovenous fistula. Surgical ligation was performed via ventral midline celiotomy. Portal venous pressure measured via a mesenteric vein decreased from 23/20 (21) mmHg to 19/16 (17) mmHg after occlusion; a 5-min test occlusion caused no gross intestinal congestion. Liver biopsy revealed portal vein hypoplasia with reduced portal triads. Ascites resolved by Postoperative Day 3, and the dog was discharged on Postoperative Day 6 (Day 22). Ascites recurred on Day 868, but follow-up computed tomography on Day 1191 confirmed persistent occlusion of the fistula. Under adjunct medical management, the dog remained clinically stable with only mild hyperammonemia (NH3, 132 μg/dL). This case suggests that surgical ligation can reduce portal hypertension and resolve ascites in dogs with caudal mesenteric arteriovenous fistulas, although long-term monitoring may be required.