Segmental caudal vena cava (CVC) aplasia, also termed azygos continuation of the CVC, is a very rare congenital vascular anomaly in dogs and is similar to the segmental aplasia of the same blood vessel in humans. Four dogs between 4 and 18 months of age were diagnosed by computed tomography (CT) at the Veterinary Hospital of the ULPGC. In addition, a normal patient (N) is described first for knowledge and understanding of the normal anatomy and pathophysiology of these abnormalities. A three-phase angiographic study (arterial, portal and delayed) with manual administration of contrast and multiplanar reconstructions are performed, from the cranial aspect of the cardiac silhouette to the region of the bifurcation of the iliac veins and arteries. The images show an interruption of the caudal vena cava between the kidneys and the hepatic structure, with marked distension of the right azygos vein with continuity to the right abdominal region presenting a mild-severe aneurysm. In this study, the following diameters were measured: the azygos vein (0.9 – 1.6 cm, being equal or wider than the aorta), the dilatation produced cranial to kidneys (between 1.75 and 5.4 cm) and the portal vein (1 cm being normal or becoming less than 3 mm). Therefore, two animals were found with portal vein hypoplasia/atresia and one with a thrombus, but in no case were there porto-azygos shunts. Due to the complex vascular anatomy of these patients, it is essential to measure the diameter and insertion site of the portal vein to understand the clinical signs and to evaluate prognosis and surgical interventions if necessary. The results demonstrate that CT is the gold standard test for diagnosing vascular malformations
