In our body, blood flow begins with a high pressure in arteries and it decreases gradually as it reaches the capillary beds, to end with a very low blood pressure in the veins. Lacking capillary connection between arteries and veins in many sites is an arteriovenous malformation (AVM) that allows the blood to flow through veins in a high pressure causing enlargement of the veins. Consequently, this may result in compression or irritation of adjacent tissues and frequent hemorrhages. If AVMs occur in superficial vessels of the skin and mucous membranes, which are known as telangiectases, they often rupture and bleed after slight trauma. Frequent hemorrhages in brain, liver, intestines, lungs or other organs result from large AVMs. The most common clinical feature of AVMs is epistaxis (nose bleeding) that usually initiates at 12 years of age. About 64% of AVMs are associated with hereditary hemorrhagic telangiectasia (HHT). HHT, type 1 has a less severe lung involvement which can be asymptomatic and it starts earlier than the other HHT types. Prevalence rate of all HHT types is calculated approximately at 1:5,000 to 1:10,000 people worldwide. Chest radiograph, CT scan, and MRI are useful for the diagnosis of HHT. The treatment of choice in symptomatic patients includes embolotherapy with coils and/or detachable balloons.
Hereditary hemorrhagic telangiectasia, type 1 (HHT1), or Osler-Rendu-Weber (ORW) disease, is an autosomal dominant disorder caused usually by inheriting a mutated copy of the endoglin (ENG) gene on chromosome 9.
In a large Arab family in the Sahara, Muller et al. (1978) found 87 cases of hereditary hemorrhagic telangiectasia in six generations. Because of the extensive consanguinity in the kindred, a person considered to be homozygous was identified. In the case of 4 couples indicated in the pedigree, both partners were affected. The son of one such couple had a total of 13 children by 4 different wives. All the wives were unaffected; all the children were affected. According to the Bayes theory, the probability of homozygosity was estimated to be 0.99975. The father, who was the presumed homozygote and also the proband, had severe but no exceptionally unusual manifestations of the disease. Examination of the family tree confirmed the autosomal dominant transmission of the disorder.
Khalid et al. (2005) reported a 33-year-old Bahraini male whose routine chest radiograph revealed a sharply defined lobulated soft tissue mass of uniform density in the right lower hemithorax with evidence of tubular densities radiating from the hilum. A contrast-enhanced CT scan of the chest showed subpleural nodular, lobulated masses of uniform density in the right lower lobe anteriorly, with a single feeding artery and a draining vein consistent with pulmonary arteriovenous malformation (PAVM) that could be associated with Osler-Weber-Rendu disease. Angiography was not performed due to the complete asymptomatic nature of the lesion and because no therapeutic intervention was intended.