Arterio Venous Malformations

Arterio-venous (AV) malformations of the liver are rare and are caused either iatrogenically in liver biopsy and liver surgery, or are distributed diffusely in patients with hereditary hemorrhagic teleangiectasia (HHT; "Osler's disease") [23]. In general, AV-malformations may occur between the hepatic artery and the hepatic vein, as well as between the hepatic artery and the portal-venous system.

Typical findings on dynamic MR images of the liver for singular AV-malformations post-biopsy or surgery include a dilatation of the draining hepatic vein and early enhancement of the hepatic veins (Fig. 21). Shunts between the hepatic artery and the portal-venous system typically lead to increased portal-venous pressure and thus to the usual findings of portal hypertension [21].

In contrast, AV-malformations in Osler's disease are diffusely distributed throughout the liver and may be associated with enlargement of the hepatic artery and increased tortuousity of the vessels in the liver hilum and in the central portions of the liver lobes. In Osler's disease, increased arterial perfusion of the liver tissue leads frequently to secondary nodular hypertrophy that may be misinterpreted as a malignant hepatic tumor. These pseudotumors, as in focal nodular hyperplasia (FNH), represent a localized overgrowth of hepatocellular tissue and are not real liver tumors. Dynamic MRI reveals that these lesions show strong arterial phase enhancement and subsequent isoin-tensity with the surrounding liver tissue in the portal-venous and equilibrium phases. Normal enhancement of the affected tissue in the hepatobil-iary phase can be noted with the use of contrast agents with hepatocellular properties such as Gd-BOPTA [71] (Fig. 22).

Severe cases of AV shunting in Osler's disease may lead to right heart failure and, at present, the only curative treatment is liver transplantation [6].

Fig. 21a-f. AV shunt of the liver. Unenhanced Tl-weighted images (a, b) reveal dilatation of the draining hepatic veins in AV shunting (arrows). The corresponding T2-weighted image (c) again reveals flow void in the vessels. Early enhancement of the draining liver veins indicating an AV malformation can be depicted clearly on early arterial phase images (d-f) after intravenous injection of paramagnetic contrast agent

Fig. 21a-f. AV shunt of the liver. Unenhanced Tl-weighted images (a, b) reveal dilatation of the draining hepatic veins in AV shunting (arrows). The corresponding T2-weighted image (c) again reveals flow void in the vessels. Early enhancement of the draining liver veins indicating an AV malformation can be depicted clearly on early arterial phase images (d-f) after intravenous injection of paramagnetic contrast agent

Fig. 22a-r. Diffusely distributed AV-malformations in a patient with Osler's disease and development of hyperplastic nodules. Flow sensitive gradient echo images (a-c) reveal enlarged tortuous vessels in the liver hilum and in the more centrally located liver parenchyma (arrows), indicating increased flow in the hepatic artery. On contrast-enhanced MRA (d), the dilatation of the hepatic artery is even more obvious. Again, the tortuous vessels and diffusely distributed small AV malformations in the liver are observed. On T2-weighted images (e-g) areas of flow void in the liver can be noted, indicating increased flow in branches of the hepatic artery (arrows). Additionally, some nodular-appearing liver lesions (arrowheads) in the right liver lobe can be seen. On pre-contrast Tl-weighted images (h-j) these liver tumors show an almost isointense SI compared with the surrounding liver tissue. However, in the arterial phase after injection of Gd-BOPTA (k-m) these liver lesions (arrows) are clearly hypervascular. On portal-venous phase images (n, o) the lesions are isointense with the surrounding liver tissue. In the hepatobiliary phase one hour after injection of Gd-BOPTA (p-r), the lesions appear hyperintense compared to the surrounding liver tissue due to uptake of Gd-BOPTA into hepatocyctes. These liver lesions correspond to a localized overgrowth of hepatocellular tissue similar to that which occurs in FNH. The lesions appear hyperintense in the hepatobiliary phase due to the delayed excretion of the contrast agent into the newly formed bile ductules ^

Fig. 22a-r. Diffusely distributed AV-malformations in a patient with Osler's disease and development of hyperplastic nodules. Flow sensitive gradient echo images (a-c) reveal enlarged tortuous vessels in the liver hilum and in the more centrally located liver parenchyma (arrows), indicating increased flow in the hepatic artery. On contrast-enhanced MRA (d), the dilatation of the hepatic artery is even more obvious. Again, the tortuous vessels and diffusely distributed small AV malformations in the liver are observed. On T2-weighted images (e-g) areas of flow void in the liver can be noted, indicating increased flow in branches of the hepatic artery (arrows). Additionally, some nodular-appearing liver lesions (arrowheads) in the right liver lobe can be seen. On pre-contrast Tl-weighted images (h-j) these liver tumors show an almost isointense SI compared with the surrounding liver tissue. However, in the arterial phase after injection of Gd-BOPTA (k-m) these liver lesions (arrows) are clearly hypervascular. On portal-venous phase images (n, o) the lesions are isointense with the surrounding liver tissue. In the hepatobiliary phase one hour after injection of Gd-BOPTA (p-r), the lesions appear hyperintense compared to the surrounding liver tissue due to uptake of Gd-BOPTA into hepatocyctes. These liver lesions correspond to a localized overgrowth of hepatocellular tissue similar to that which occurs in FNH. The lesions appear hyperintense in the hepatobiliary phase due to the delayed excretion of the contrast agent into the newly formed bile ductules ^

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Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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