Azygos Continuation of the Caudal Vena Cava Complicated by Thrombophlebitis in a Dog.

A 4.5-month-old female intact Doberman was referred for acute on chronic gastrointestinal signs and acute lethargy, polyuria, and polydipsia. Abdominal ultrasonography revealed marked focal dilatation, thrombosis, and suspect phlebitis of the caudal vena cava (CVC; renal segment). The prehepatic CVC was not identified; however, an enlarged azygos vein was identified as cranial to the dilated vessel. The patient was humanely euthanized, and a necropsy confirmed congenital segmental aplasia of the prehepatic CVC with azygos continuation complicated by thrombophlebitis. While this vascular malformation has been documented in canines, this is the first reported case of concurrent thrombophlebitis.