Cavernous transformation of the portal vein

Cavernous transformation of the portal vein (CTPV) is a sequelae of portal vein thrombosis and is the replacement of the normal single channel portal vein with numerous tortuous venous channels.

For discussion of demographics and presentation please refer to article on portal vein thrombosis.

Pathology

Following thrombosis the portal vein may or may not re-canalise. Re-canalisation is seen more frequently in patients without cirrhosis or disease of liver leading to inherently increased resistance to portal flow. In patients whose portal vein does not recanalise or only partially re-canalises collateral veins (thought to be paracholedochal veins) dilate and become serpiginous. This process takes a variable amount of time, from as little as a week to a year ¹. 

These vessels drain variably into the left and right portal veins or more distally into the liver. Additional communications can also be identified with the pericholecystic veins.

Radiographic features

In addition to direct visualisation of the dilated vessels, the resultant portal hypertension results in other frequent changes: see portal hypertension. Additionally, there are changes in liver shape which are somewhat different to those seen in cirrhosis ².  Typically these changes are:

• atrophy of the left lateral segment (segments 2 and 3) c.f hypertrophy being more common in cirrhosis
• hypertrophy of segment IV c.f atrophy being more common in cirrhosis
• hypertrophy of the caudate lobe (also seen in cirrhosis)

Ultrasound

Ultrasound is able to identify a normal portal vein in almost all cases when present (97%) ³, and thus is a good first order examination. Doppler examination can be carried out at the same time to evaluate for portal hypertension. Cavernous transformation appears as numerous tortuous vessels occupying the portal vein bed. Flow is generally hepatopetal and continuous with little if any respiratory or cardiac variation ⁴. 

CT

Multiphase CT can confirm the diagnosis by demonstrating numerous vascular structures in the region of the portal vein. These enhance during the portal venous phase, and not during the arterial phase (distinguishing it from an arteriovenous malformation). 

Calcification of the previously thrombosed portal vein may be evident ⁵.

MRI

MRI is also a proven method for imaging the portal venous system and may be used as a complementary or alternative modality to CT.

Treatment and prognosis

Despite collateral formation portal hypertension is usually present (up to 90%)¹ with associated complications.

Whereas portal hypertension can in some cases be treated with TIPS, the absence of normal portal circulation usually makes this impossible.