Definition
• Pulmonary arteriovenous malformation (PAVM) consists of a direct communication between a pulmonary artery and a pulmonary vein without an intervening capillary network
Pathogenesis
• These are almost always congenital vascular anomalies, occurring as sporadic or isolated entities in more than 60% of cases
• The most common syndromic association is with hereditary hemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu disease. About 15% of patients with this syndrome have PAVMs. This syndrome is an autosomal dominant condition with the clinical triad of epistaxis, mucocutaneous or visceral telangiectasia, and family history of the disease. Patients with ENG mutations tend to have PAVMs, while those with the less frequent ACVRL1 mutations tend to have pulmonary hypertension
• Rarely, PAVM may occur after trauma (resulting in an arteriovenous fistula)
Clinical features
Epidemiology
• Most PAVMs manifest in the second decade of life
• Females are twice as frequently affected as males
• Multiple lesions may be seen in up to a third of the cases
Presentation
• Most patients remain asymptomatic: lesions are usually incidentally detected
• The most common clinical presentation is with hemoptysis or chest pain due to bleeding
• Dyspnea may result from shunting of blood from the right to the left side of the heart
• Rare manifestations include transient ischemic attack and cerebral stroke due to paradoxical emboli (10% to 19% of patients), systemic severe infections and abscesses (including cerebral abscess in 5% to 19% of patients), and massive hemoptysis or hemothorax
• All adult patients with HHT should be screened for PAVM by contrast echocardiography or computed tomography of the chest
Prognosis and treatment
• PAVMs with feeding arteries greater than 3 mm require treatment
• Percutaneous transcatheter embolization has become the first line of treatment
• Long-term follow-up is warranted after transcatheter vasoocclusion because of frequent recanalization of treated PAVMs and development or growth of unrecognized/untreated PAVMs
• Surgical resection is the definitive treatment
Pathology
Gross
• The lower lobes are more commonly affected
• Subpleural and endobronchial lesions may appear as areas of bluish swelling
Histology
• Most PAVMs (>70% cases) have a single feeding artery and a single draining vein
• The lesions themselves show a network of thick- and thin-walled vessels. Thick-walled arteries directly drain into thin-walled veins without an intervening capillary network
• In some lesions, the vessels may be significantly dilated (“cavernous angioma”) or assume aneurysmal proportions (“arteriovenous aneurysm”)
• Elastin stains highlight abnormal vascular elastic structure
• Evidence of prior episodes of hemorrhage, in the form of hemosiderin and siderophages, may be seen
Immunopathology/special stains
• Not contributory
Main differential diagnoses
• Pseudo-AVM: refers to the artifactual approximation of vessels after atelectasis
• True aneurysms of pulmonary arteries: thinning and aneurysmal dilatation of arterial walls without communication with venous channels
• Capillary hemangiomatosis: an excess of capillary loops within the alveolar walls/interstitium and interlobular septae
Fig 1 Arteriovenous malformation of the lung. Gross photograph of lobectomy specimen. Pleural surface shows conglomerate of large, tortuous vessels (A) and cut surface shows vascular channels of multiple sizes localized to the subpleural area (B). Remaining lung is normal.
Fig 2 Arteriovenous malformation of the lung. Multiple vascular channels are present in these low- (A), medium- (B), and high-power (C) images. D, There is transition from arterial to venous wall, as seen here.