section content


A neutered domestic medium hair cat, 4y 2mo, presented to the neurology service due to a history of occasional seizures, tremors, dull mentation and hypersalivation for 6 months. Physical and neurological examinations were generally unremarkable at the time of examination.

Hematology and biochemistry did not show significant abnormalities.


Brain MRI, sagittal and transverse T2w

Transverse T2-FLAIR and T1w (alternating pre- and post-contrast)

Sagittal T1w+C, transverse T2-FFE

There are bilateral and symmetrical well-defined hyperintense areas on T2W, FLAIR series and matching hypointense areas on T1W series when compared to normal grey matter. These are located at the level of the subthalamus, tegmentum and tectum of midbrain, pons, both cerebellar hemispheres and medulla oblongata.

Located in the region of the lentiform nuclei, there are bilateral and symmetrical faint hyperintense areas on T1W series, which are isointense to white matter on T2W series, without signal intensity change on T1W post gadolinium series.


Bilateral symmetrical hyperintense in T2W and FLAIR and hypointense in T1W lesions in the hypothalamus, brainstem and cerebellum when compared to normal grey matter and bilateral symmetrical faint hyperintense in T1W areas at the lentiform nuclei.

Differential diagnosis

A metabolic or nutritional encephalopathy was considered the most likely etiology and the following differential diagnosis as probable in light of the imaging findings, signalment and clinical history:

-Hepatic encephalopathy

-Thiamine deficiency

-Hypocobalaminemic encephalopathy.


Complementary tests were performed to exclude possible etiologies.

Cobalamine levels were tested to exclude hypocobalaminemia, the cobalamine concentration in blood was within normal limits:

-Cobalamin (B12):  663.0    Range: >200 ng/l

Ammonia and post prandial bile acids concentrations in the blood were markedly increased:

-Ammonia:  257     Range: 0-60 umol/l

-Bile Acids post prandial:  24.7 *   Range: 0.5 – 10 umol/l

Urine analysis showed the presence of a few urate crystals.

The presenting neurological signs, MRI findings and bloodwork indicative of hepatic dysfunction, were considered consistent with hepatic encephalopathy.

Abdominal CT, pre-contrast, arterial and venous/portal phases.

Imaging findings can vary between the different metabolic disorders, however, bilaterally symmetric signal intensity changes to deep gray matter nuclei, with or without abnormal contrast enhancement, symmetric and diffuse signal intensity changes to gray and/or (subcortical) white matter, and/or brain atrophy are common. In general, lesion symmetry should alert of the presence of a metabolic, nutritional or degenerative encephalopathy.

Hepatic encephalopathy is the result of the inability of the liver to remove toxic substances from the gastrointestinal tract and portosystemic shunts are the most common cause in dogs and cats.

Bilaterally symmetric T1 hyperintensities in the basal ganglia, specifically the lentiform nuclei, have been observed in cats and dogs with hepatic insufficiency associated with portosystemic shunts and other pathologies. In this case they were attributed to a hepatic encephalopathy in conjunction with the clinical signs and laboratory tests. The increase signal in T1W is thought to be due to an increased concentration in manganese. On top of the presence of these bilaterally symmetric hyperintensities in T1W at the lentiform nuclei, there were multiple bilaterally symmetric non-contrast enhancing areas hyperintense in T2W, and FLAIR and hypointense in T1W located at the subthalamus, tegmentum and tectum of midbrain, pons, both cerebellar hemispheres and medulla oblongata. Similar lesions were described in a case report of two West Highland White Terriers, located at the level of the brainstem and were associated to a combination of vasogenic and cytotoxic oedema, most likely secondary to ammonia exposure derived from a portosystemic shunt. Other MRI findings of hepatic encephalopathy include brain atrophy and bilateral extensive T2 hyperintense lesions along the cerebral cortex. None of these were observed in this case.

Primary hypoplasia of the portal vein (PHPV) or previously known as microvascular dysplasia, is a congenital condition that occurs rarely in cats.

The histological features are decreased portal vein diameter or absence of the portal vein and an increased number of arteriolar profiles in the portal tracts. Other diseases that share the same histological characteristics of PHPV due to a portal vein hypoperfusion are congenital portosystemic shunts, intrahepatic arteriovenous fistula, and portal vein obstruction. A combination of imaging and histological information is necessary to reach a final diagnosis of PHPV, however in this case, a histological diagnosis could not be obtained, and a presumptive diagnosis was made based in the imaging findings of markedly reduced caliber of the portal vein, presence of acquired collateral circulation and the exclusion of other conditions causative of portal vein hypoperfusion.

A large spleno-systemic shunt was detected in this patient, caudal to the left kidney and connecting the splenic and left renal vein, also known as the spleno-gonadal shunt.  Though we cannot confirm in this patient if this shunt was congenital or acquired, previous studies suggest a possible acquired origin as these shunts do not appear to share similar clinical or anatomic features with previously described congenital portosystemic shunts in cats. In a previous study, 42% of the cats in which this shunt was observed, had clinicopathological or histopathological changes that suggested hepatopathy with potential secondary portal hypertension.

Imaging findings: Computed Tomography of the abdomen

A Computed Tomography of the abdomen (aortic and portovenous angiogram, parenchymal phase) was then performed to investigate the origin of the hepatic encephalopathy; most commonly caused by portosystemic shunt and hepatic disease  in cats and dogs.

The hepatic volume is subjectively small.

The extra- and intrahepatic portions of the portal vein (PV) are not clearly observed.

Located in the cranial abdomen, left ventral to the CVC, there is a very thin vessel that receives a splenic vein branch and appears to connect to the gastroduodenal vein. It remains small in size as it continues its path cranial to the porta hepatis, where it gives a very small branch dorsally, to the right and left division of the liver where it disappears. This vessel could be consistent with a hypoplastic PV. Caudal to the insertion of the splenic vein, this vessel is not visible anymore.

At the level of the porta hepatis there are multiple small tortuous vessels (varices) that follow the usual path of the PV and seem to originate from the previously described suspected hypoplastic PV and the gastroduodenal veins, branching into the liver.

The cranial and caudal mesenteric veins converge adjacent to the cranial pole of the right kidney, and taper shortly after the convergence.

Multiple small anomalous tortuous vessels are also observed in the mid-abdomen cranial and medial to the left renal pole (gastro-phrenic varices). In the caudal abdomen, adjacent to the mesenteric aspect of the colon, there are multiple small anomalous tortuous vessels (colic varices). These vessels converge into a single vessel that inserts into the dorsal aspect of the caudal vena cava caudal to the renal veins.

A tortuous vessel is also observed caudal to the left renal pole inserting into the left renal vein (spleno-gonadal shunt), originating from multiple hilar branches of the splenic vein.

The common bile duct is slightly dilated (approximately up to 4 mm) and the previously described collateral vessels run adjacent. The gallbladder is bilobed.

The right renal cortical outline is irregular due to the presence of wedge shape non-enhancing lesions causing marked indentations of the capsule and cortex located in both the cranial and caudal pole.


Hypoplastic portal vein.

Secondary acquired portal collateral circulation: Porto-portal collaterals and multiple acquired portosystemic shunts (spleno-gonadal shunt, gastro-phrenic varices and colic varices)

Microhepatia secondary to the portal vein hypoplasia.

Mild common bile duct dilation DDX historical cholangitis, variant

Bilateral renal chronic cortical infarcts DDX: chronic renal disease, less likely nephritis/glomerulonephritis


A final diagnosis of hepatic encephalopathy secondary to congenital hypoplasia of the portal vein and associated acquired portosystemic shunts was made.


The portal hypertension is the result of increased resistance to portal blood flow. The clinical consequences of portal hypertension include the development of multiple acquired portosystemic shunts, ascites, hepatic encephalopathy, or some combination of these.

In this case, although not measured, the presence of portal hypertension was highly suspected due to the concurrent hepatic encephalopathy and portosystemic collateral vessels which are already strongly indicative of portal hypertension.

Similar findings were observed in a previous case report of a 6yo feline that presented with clinical signs late in life, like the ones of the described case, and a markedly reduced in size PV with thin and tortuous intrahepatic branches observed in CT. A tortuous vessel connecting the splenic vein with the left renal vein among acquired portal collateral vessels were also detected in this patient and the histopathology confirmed the presence of PHPV. Ascites was not detected in this patient neither.

The main difference with our case, was that in that patient, only the intrahepatic portal vein was affected, while in our case, both the intra- and prehepatic portal vein were reduced in diameter, even not observed in some segments.

Differentiation between the PHPV and the congenital absence of the portal vein (CAPV) can be challenging. CAPV is a rare condition in which the portal blood bypasses the liver and a spleno-mesenteric shunt to the systemic circulation is present. The PHPV can mimic in occasions a CAPV, as there may be a persistent small PV but it cannot be detected by CT.  In the few previously described cases of CAPV in dogs and cats, the cranial mesenteric and the splenic veins, both tributaries of the PV, drain into the inferior CVC by forming together a portal trunk or more frequently draining separately into the CVC via an anomalous paracaval vessel. Although a connection of the spleno-systemic connection was observed in this case via the left renal vein, connection between the cranial mesenteric vein and the cava could not be demonstrated. The definitive diagnosis of complete agenesis of the portal system requires additional histological analysis of the hepatic parenchyma that demonstrates the absence of hepatic portal venules within the portal triad.