Atypical azygos continuation of the caudal vena cava in a dog

Abstract

A whole-body CT scan and CT myelography were performed on a 13-year-old male neutered Pug with gait abnormality and a history of cough that had been medically managed. The CT scan revealed multiple sites of intervertebral disc disease and incidentally revealed an abnormally distended azygos vein with absent pre-hepatic caudal vena cava (CVC). The pre-renal segment of the CVC was duplicated with both common iliac veins joining to each duplicated CVC, and then cranially connected to the azygos vein (cavo-right-azygos shunt) (Fig 1A, B). Both renal veins connected and then joining to a cranially coursing tortuous shunting vessel connecting to the azygos vein in the thoracic cavity (Fig 1A, B, D). Thus, the renal veins were not directly connected to the pre-renal segment of CVC in the abdomen. The hepatic and post-hepatic segments of the CVC were present as normal. Segmental aplasia of the CVC with azygos continuation is a congenital anomaly characterised by the CVC uniting the azygos vein with partial absence of the CVC. In this case, concurrent partial duplication of the CVC was present. The duplicated pre-renal segment of CVC course dorsal to the aorta and cranially continued to the azygos vein. To the best of the authors' knowledge, the atypical azygos continuation of the CVC with concurrent segmental aplasia of the pre-hepatic CVC has not been reported. Although concomitant portosystemic shunting is common in azygos continuation of the CVC, there was no evidence of portosystemic shunting in the present case. This dog had no clinical signs related to this anomaly; therefore, it was considered incidental, similar to most cases of azygos continuation of the CVC.

The work described in this manuscript involved the use of a non-experimental (owned) animal. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed. Ethical approval from a committee was therefore not specifically required for publication in Images in Small Animal Practice in Journal of Small Animal Practice. Although not required, ethical approval was still obtained.