Clinical importance of pulmonary arteriovenous malformations
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0975-2870.186080
Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu Osler Weber disease, is an inherited multisystem disorder of the vascular system characterized by recurrent epistaxis and mucosal telangiectasias.[1],[2] Pulmonary artery malformations (PAVMs) are common findings and observed in about 20% of patients with HHT.[1] These malformations are direct fistulous connections between the branches of pulmonary artery and vein without an intervening capillary bed. Furthermore, these malformations are known as pulmonary arteriovenous fistulas, pulmonary arteriovenous aneurysms, and pulmonary hemangiomas. The arterial supply of the PAVMs is usually derived from the pulmonary arterial bed in 95% of cases and lead to the right-to-left shunt.[3] On rare occasions, arterial supply may be derived from systemic arterial circulation (bronchial artery, intercostals artery, or a direct branch from the aorta). Although venous return is usually to the pulmonary veins, there may be a direct communication to the left atrium.[4] Furthermore, these vascular malformations may develop in the cerebral and hepatic circulation. The different genetic mutations are responsible for the disease. Ninety-six percent of patients with HHT have a mutation in either the endoglin (HHT Type 1) or activin receptor-like kinase gene (HHT Type 2). These two types of HHT are indistinguishable clinically, and their symptoms and complications are similar.[1] Both mutations are associated with transforming growth factor beta, which controls cellular adhesion, migration, and proliferation.[5] PAVMs may be either congenital or acquired. Congenital malformations are more frequently encountered. Acquired PAVMs are caused by cavopulmonary shunt procedure, infections, tuberculosis, schistosomiasis, hepatic cirrhosis, mitral stenosis, metastatic thyroid cancer, thoracic trauma, or iatrogenic.[6] Cavopulmonary shunt procedure has always been performed as an intermediate surgical intervention before the Fontan operation. PAVMs may develop after cavopulmonary shunt due to the exclusion of the hepatic venous blood flow from the pulmonary circulation.[7] Patients may present with symptoms such as epistaxis, hemoptysis, cyanosis, clubbing and shortness of breath. The most common symptom is epistaxis. It develops secondary to telangiectasias that localize on the nasal mucosa. However, epistaxis might not be seen in ten percent of the patients.[8] The clinical diagnosis of HHT is based on the presence of three of the four specific criteria (familial history, recurrent epistaxis, multiple telangiectasias, and arteriovenous malformation (AVM).[5] Furthermore, PAVMs are among the rare cases of massive hemoptysis and should be taken into consideration in the differential diagnosis of recurrent hemoptysis refractory to conventional medical therapy.[3] A circumscribed, lobulated density may be the characteristic finding on the chest radiogram. Contrast echocardiography can be used as the initial screening test for the presence of PAVMs.[4],[8] Furthermore, contrast echocardiography is an effective diagnostic tool to assess the efficiency of embolization treatment and useful in screening for family members.[4] However, pulmonary angiography should be performed to determine the precise location and extent of the PAVMs as reported in an article (Pulmonary arteriovenous fistula mimicking as cyanotic heart disease with shunt reversal) published in this issue of the journal. Most patients with HHT have also iron deficiency anemia due to frequent epistaxis attacks. Iron supplementation may be required in these cases.[8] Currently, the recommended treatment options of PAVMs are embolization or surgical resection (open surgery or video-assisted thoracoscopic surgery). Currently, angiographic embolization therapy has been adopted as the preferred treatment method. It can be performed by occlusion balloons or metallic coils.[4] PAVMs can be treated successfully in 95% of the cases via embolization procedure if all feeding arteries could be embolized. However, some complications may develop following the PAVM embolization such as pleurisy, air embolism, and coil migration into the systemic arterial circulation.[5] When embolization procedure is contraindicated or has failed, surgical therapy is the procedure of choice. Conservative pulmonary resections (segmental or wedge resections) are usually sufficient.[4] Rarely, lobectomy and even pneumonectomy may be necessary in cases with extensive malformations. Although the etiopathogenesis of cavopulmonary shunt-related PAVMs has not been completely understood, hepatic factor plays a crucial role in genesis as well as regression of PAVMs. Redirection of the hepatic venous flow into the affected pulmonary artery can be treatment for the PAVMs seen in the patients after cavopumonary shunt procedure.[7] Fontan operation should be completed to obtained balanced distribution of the hepatic venous blood to both right and left pulmonary arteries. Thus, embolization or pulmonary resection should not be used as an initial treatment method in patients with cavopulmonary shunt. The normal pulmonary capillary network prevents bacteria and clots from reaching the systemic arterial circulation. Brain abscess and cerebrovascular events develop due to the absence of capillary filtering system in patients with PAVMs.[8] Therefore, these patients should be evaluated by a multidisciplinary team and should be treated as soon as possible to avoid severe complications.
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