Extrahepatic porto-systemic shunt (PSS) in small animals can be congenital (CPSS) or acquired (APSS) as a consequence of portal hypertension (PH), and are distinguished on the bases of their anatomical pattern. A precise morphologic imaging assessment, along with clinical and histopathologic findings, is important for distinguishing patients with PH from those with congenital PSSs, which require different therapeutic approach. Expected findings in patients with PH are presence of ascites, multiple APSS, and a confirmed cause of portal flow obstruction. On the other hand, a single PSS, absence of ascites and no evidence of portal vein, caudal vena cava or hepatic disorders are typical findings of CPSS patients. This paper describes four cases of PSSs in which the combination of the computed tomographic imaging findings did not match the standards for APSS nor for CPSS: one dog had chronic hepatitis causing PH and ascites and a splenoazygos PSS, to date considered a CPSS pattern. One dog showed a left splenogonadal PSS and porto-caval varices, to date considered an APSS pattern, without ascites, portal vein obstruction, primary structural hepatic disorders nor evidence of PH. Two cats, with and without diffuse hepatic structural disorders respectively, had a single left splenogonadal PSS without ascites. Possible interpretation of such unusual haemodynamic conditions and clinical repercussion, especially for orientation of treatment choice, are discussed.