They may also increase the risk of seizures, as would any abnormal tissue in the brain. Finally, hemorrhage from an AVM may lead to intracerebral hemorrhage (bleeding into the brain), which causes any of the symptoms of stroke such as weakness in part of the body or difficulty speaking. If the bleeding occurs into the subarachnoid space (subarachnoid hemorrhage), there is usually a severe, sudden headache and decreased level of consciousness and often weakness in part of the body. Other problems
A very small proportion (those affected by SMAD4 (MADH4) mutations, see below) have multiple benign polyps in the large intestine, which may bleed or transform into colorectal cancer. A similarly small proportion experiences pulmonary hypertension, a state in which the pressure in the lung arteries is increased, exerting pressure on the right side of the heart and causing peripheral edema (swelling of the legs), fainting and attacks of chest pain. It has been observed that the risk of thrombosis (particularly venous thrombosis, in the form of deep vein thrombosis or pulmonary embolism) may be increased. There is a suspicion that those with HHT may have a mild immunodeficiency and are therefore at a slightly increased risk from infections. Genetics
HHT is a genetic disorder with an autosomal dominant inheritance pattern. Those with HHT symptoms that have no relatives with the disease may have a new mutation. Homozygosity appears to be fatal in utero.Five genetic types of HHT are recognized.
Surgical excision has now essentially been abandoned due to the success of embolotherapy.Those with either definite pulmonary AVMs or an abnormal contrast echocardiogram with no clearly visible lesions are deemed to be at risk from brain emboli. They are therefore counselled to avoid scuba diving, during which small air bubbles may form in the bloodstream that may migrate to the brain and cause stroke. Similarly, antimicrobial prophylaxis is advised during procedures in which bacteria may enter the bloodstream, such as dental work, and avoidance of air bubbles during intravenous therapy. Liver AVMs
Given that liver AVMs generally cause high-output cardiac failure, the emphasis is on treating this with diuretics to reduce the circulating blood volume, restriction of salt and fluid intake, and antiarrhythmic agents in case of irregular heart beat. This may be sufficient in treating the symptoms of swelling and breathlessness. If this treatment is not effective or leads to side effects or complications, the only remaining option is liver transplantation. This is reserved for those with severe symptoms, as it carries a mortality of about 10%, but leads to good results if successful. The exact point at which liver transplantion is to be offered is not yet completely established. Embolization treatment has been attempted, but leads to severe complications in a proportion of patients and is discouraged.Other liver-related complications (portal hypertension, esophageal varices, ascites, hepatic encephalopathy) are treated with the same modalities as used in cirrhosis, although the use of transjugular intrahepatic portosystemic shunt treatment is discouraged due to the lack of documented benefit.