Hereditary Haemorrhagic Telangiectasia HHT

HHT, also called Rendu-Osler-Weber disease or Osler's disease, is a vascular, hereditary, autosomic dominant disorder that occurs with a frequency of approximately 10-20 cases/100,000 [15]. HHT is characterized by the presence of mucocutaneous or visceral angiodysplastic lesions, the latter most frequently seen in the liver, lung, brain, and gastrointestinal tract. Hepatic involvement accounts for 10-40% of cases and is characterized by the presence of intrahepatic shunts (arterioportal, ar-teriosystemic, venous portosystemic), diffuse telangiectases, and vascular mass-forming lesions [3]. AVMs are usually distributed diffusely throughout the liver and may be associated with enlargement of the hepatic artery and increased tortuousity of 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 frequently leads to secondary nodular hypertrophy, which may be misinterpreted as a malignant hepatic tumor. These pseudotumors, as in focal nodular hyperplasia, represent a localized overgrowth of hepatocellular tissue and are not real liver tumors. Patients with hepatic involvement can be asymptomatic, but heart failure, portosystemic encephalopathy, cholangitis, portal hypertension, and cirrhosis have been reported [34].

Focal or diffuse changes in hepatic circulation are detectable on all of the imaging modalities. US, particularly in association with color Doppler, shows intrahepatic shunts with arterial and venous vessels frequently increased in size. However, this imaging method has comparatively low sensitivity

Fig. 33a-f. Arteriovenous malformations in a healthy young patient. An US scan (a) shows an abnormal communication (arrow) between an arterial branch and a venous vessel. On pre-contrast T1- and T2-weighted MR images (b, c) a small, hypointense area (arrowheads) is visible in the lower parts of segment VII of the liver. On the arterial phase image (d) the lesion (arrowhead shows intense and homogeneous enhancement. Early enhancement of a right portal vein branch (arrow) is also evident. The lesion shows the same signal intensity as observed in surrounding vascular structures in the portal venous (e) and equilibrium (f) phases

Fig. 33a-f. Arteriovenous malformations in a healthy young patient. An US scan (a) shows an abnormal communication (arrow) between an arterial branch and a venous vessel. On pre-contrast T1- and T2-weighted MR images (b, c) a small, hypointense area (arrowheads) is visible in the lower parts of segment VII of the liver. On the arterial phase image (d) the lesion (arrowhead shows intense and homogeneous enhancement. Early enhancement of a right portal vein branch (arrow) is also evident. The lesion shows the same signal intensity as observed in surrounding vascular structures in the portal venous (e) and equilibrium (f) phases

Fig. 34a-e. Arterioportal fistula in a cirrhotic patient. On the T2-weighted (a) and T1-weighted (b) MR images, the fistula (arrows) appears as a hypointense, round area, with a signal void close to that observed in the aorta and portal vein. In all phases of the dynamic evaluation after contrast agent administration (c-e) the enhancement of the vascular area is similar to that occurring in the aorta and the left branch of the portal vein that indicates an arterioportal fistula and spatial resolution for demonstrating small arteriovenous shunts [39].

On multidetector CT, the possibility to perform a selective, multiphase study of hepatic vascular structures permits both arterial and venous vessels to be visualized. Hence, the visualization of ar-teriosystemic shunts is improved. Compared with conventional spiral CT, multidetector CT improves image quality, and permits better multiplanar and angiographic reconstruction. Consequently, the capability to identify and characterize the vascular lesions typical of HHT is improved [8]. Thus telangiectases, which are present in more than 60% of cases of HHT, are seen as small vascular spots that are readily recognizable on reconstructed multiplanar reformatted and maximum intensity projection (MIP) images. Likewise, large confluent vascular masses, which are present in about 25% of HHT cases, are seen as large shunts or multiple telangiectases that coalesce. In a recent study, mul-tidetector CT (MDCT) was able to detect hepatic vascular alterations in about 80% of patients with a confirmed or suspected diagnosis of HHT [35]. In this study arterioportal shunts and arteriosys-temic shunts were detected as the only vascular alterations in roughly 50% and 20% of patients, respectively, while both shunt types were detected in approximately 30% of patients.

On MR imaging, telangiectases appear as small hypo- to isointense lesions on unenhanced T1-weighted images and as iso- or hyperintense lesions on T2-weighted images (Fig. 35).Whereas ar-teriovenous shunts are poorly detected on unen-hanced T1- and T2-weighted images, dilatated and tortuous vessels can usually be seen near the arte-riovenous shunts.

Dynamic MR imaging reveals strong arterial phase enhancement and subsequent isointensity with the surrounding liver tissue in the portal venous and equilibrium phases. Normal enhancement of the affected tissue in the hepatobiliary phase can be noted with the use of contrast agents with hepatocellular properties such as Gd-BOPTA (Fig. 36).

Fig. 35a, b. Hereditary haemorrhagic teleangiectasia. The pre-contrast T2-weighted fat-suppressed TSE image (a) reveals almost complete exchange of normal hepatic structure by diffuse small, round markedly hyperintense lesions. On the GRE Tl-weighted image (b) the lesions demonstrate similar hypointensity to that observed in the vessels

Fig. 35a, b. Hereditary haemorrhagic teleangiectasia. The pre-contrast T2-weighted fat-suppressed TSE image (a) reveals almost complete exchange of normal hepatic structure by diffuse small, round markedly hyperintense lesions. On the GRE Tl-weighted image (b) the lesions demonstrate similar hypointensity to that observed in the vessels

Fig. 36a-c. Hereditary haemorrhagic teleangiectasia. Diffusely distributed AV-malformations in a patient with Osler's disease. On the T2-weighted image (a) areas of flow void (arrows) in the liver can be noted indicating increased flow in branches of the hepatic artery. Additionally, some nodular-appearing liver lesions (arrowheads) in the right liver lobe can be seen. These lesions (arrow) are clearly hypervascular on the arterial phase image after injection of Gd-BOPTA (b). In the hepatobiliary phase one hour after injection of Gd-BOPTA (c), the lesions appear hyperintense compared to the surrounding liver tissue due to uptake of the contrast agent 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 Gd-BOPTA into the newly formed and malformed bile ductules

Fig. 36a-c. Hereditary haemorrhagic teleangiectasia. Diffusely distributed AV-malformations in a patient with Osler's disease. On the T2-weighted image (a) areas of flow void (arrows) in the liver can be noted indicating increased flow in branches of the hepatic artery. Additionally, some nodular-appearing liver lesions (arrowheads) in the right liver lobe can be seen. These lesions (arrow) are clearly hypervascular on the arterial phase image after injection of Gd-BOPTA (b). In the hepatobiliary phase one hour after injection of Gd-BOPTA (c), the lesions appear hyperintense compared to the surrounding liver tissue due to uptake of the contrast agent 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 Gd-BOPTA into the newly formed and malformed bile ductules

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