Concomitant, Acquired Cavo-Azygos Shunt and Spleno-Gastroepiploic Bypass After Multiple Venous Obstruction in a Dog

A 13-year-old intact female Shih Tzu presented with anorexia, panting and pain of unknown origin. Physical examination was normal except for a systolic murmur (grade 3/6). Abdominal radiographs revealed an ill-defined area of increased opacity in the mid-abdomen. A subsequent computed tomography (CT) scan confirmed a large, heterogeneously enhancing mass near the left adrenal gland, extensively invading the adjacent caudal vena cava, portal vein and splenic vein. This was accompanied by multiple metastatic lesions affecting the abdominal lymph nodes, lungs, liver and kidneys. Two distinct vascular anomalies were identified. The first was a shunt vessel that was diverting pre-occlusive blood from the caudal vena cava to the azygos vein, causing dilation of the azygos vein and forming a cavo-azygos shunt. The second was a significantly distended left gastroepiploic vein, forming a collateral pathway that rerouted blood from the splenic vein and ultimately drained into the gastroduodenal and portal vein. These findings are clinically significant as they demonstrate the formation of unique collateral pathways, specifically a cavo-azygos shunt and spleno-gastroepiploic bypass, which play a crucial role in maintaining venous drainage and systemic circulation in the presence of multiple venous obstructions. Recognizing such vascular anomalies through advanced imaging techniques like CT provides insights into underlying pathologies and aids in better clinical decision-making for chronic venous obstructions in veterinary patients.