Portal hypertension

Obstruction at the pre- and postsinusoidal level may be located outside the liver for instance in portal vein thrombosis or in Budd Chiari syndrome.

The most common cause of intrahepatic increased resistance located at the sinusoidal level is liver cirrhosis. Increased pressure within the portal circulation can be due also to increased blood flow occurring in patients with splenomegaly or arterioportal fistula.

Major collateral channels in portal hypertension are numerous and include: the gastro-oesophageal veins, paraumbilical vein, coronary vein, pancreaticoduodenal veins, splenic vein, superior and inferior mesenteric veins, left renal vein, paravertebral veins, hemiazygos vein and haemorrhoidal veins.

The major clinical symptoms related to portal hypertension are: haemorrhage from gastro-oesophageal varices, splenomegaly with hypersplenism, ascites and acute or chronic hepatic encephalopathy.

Although in most cases the diagnosis of portal hypertension can be suggested on the basis of clinical and laboratory data, radiological noninvasive imaging frequently provides important ancillary information about the cause of the portal hypertension and is well suited to visualize abnormal dilatation of collateral vessels and varices.

Radiographic findings

Plain chest frontal radiography can show the following abnormalities in portal hypertension: azygos vein dilatation, lateral displacement of the left paravertebral line due to hemiazygous vein dilatation, obliteration of the lateral border of the descending thoracic aorta or mass adjacent to the aorta due to a varix in the pulmonary ligament. On the lateral chest film an enlarged paraumbilical vein may be seen as a round or tubular structure within the fatty tissue, anterior or inferior to the liver. Barium studies can demonstrate oesophageal and gastric varices.

Ultrasound

Sonographic findings in portal hypertension include ascites, splenomegaly, dilatation of and reversal of flow in portal and splenic as well as superior mesenteric veins, portal vein thrombosis and demonstration of portosystemic collaterals.

Duplex sonography and colour flow Doppler are very useful because they provide precise identification of collateral vessels, information about flow direction and allow precise measurement of the diameter of the main portal vein, which should not exceed 13 mm. It is thus possible to detect hepatofugal flow within the main portal vein and/or reversal of flow in the splenic vein, findings which are indicative for portal hypertension. However, it is accepted that Doppler ultrasound is not reliable for quantification of the blood flow in the portal vein in portal hypertension. A dilated paraumbilical vein within the fissure of the ligamentum teres may be depicted on the transverse view as an anechoic, round structure sometimes with a bulls eye appearance. In the sagittal plane the paraumbilical vein may be visible as a tubular structure coursing dorsally to the ventral abdominal wall and displaying hepatofugal flow. The coronary vein is recognized as a tubular structure running between the oesophagogastric junction and the splenoportal confluence and its diameter should not exceed 4 mm in normal individuals. Sonography is also able to assess patency and flow direction in portocaval shunts after surgery or in assessing patency of TIPS.

CT and MRI

In patients with portal hypertension CT is able to visualize ascites, splenomegaly and the exact location and extent of portosystemic collateral and varices. Portosystemic collaterals are depicted on CT as multiple round and tubular tortuous soft tissue attenuation structures in the different anatomical areas, where the collaterals are known to occur. The ability to scan the entire abdomen during peak enhancement using spiral CT can significantly improve detection of vascular channels and will allow to differentiate these vascular structures from enlarged lymph nodes. Multiplanar reconstruction results in an excellent topographic display of the portosystemic collaterals and varices. Patients with portal hypertension and portosystemic shunts have reduced hepatic enhancement on CT and conspicuity of focal liver lesions is decreased.

Collateral vessels are depicted on MRI as rounded or tubular structures with low signal intensity on T1-weighted images. In addition to anatomic delineation, MRI can also provide functional information about the flow direction and velocity of the blood in the main venous structures. MRA has the advantage over catheter angiography to display the splanchnic and portal circulation by noninvasive approach.

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