arterial supply from bronchial or nonbronchial systemic arteries into the PAVM sac and during pregnancy.90 Other less common presentations or complications of PAVMs include pleuritic chest pain in 10% of patients with PAVMs, CHF secondary to high output from large extrapulmonary AVMs (primarily intrahepatic) and polycythemia secondary to hypoxemia.91 Chronic hypoxemia stimulates secondary erythrocytosis (polycythemia) to maintain arterial oxygen content After embolization of PAVM, the erythrocytosis response abates with a fall in hemoglobin level within months.92 In addition, PAVM patients have impaired CO2 clearance resulting in abnormally high ventilatory drive and increased minute ventilation on exercise PAVMs patients have high cardiac output at rest and with exercise During exercise, these patients use increased stroke volume, improved oxygen delivery secondary to increased hemoglobin and red cell mass, modified iron handling, and exuberant postural tachycardia as plausible mechanisms for adaptive exercise tolerance.93 Investigations The evaluation of PAVM is often sought for the investigation of respiratory symptoms such as dyspnea or hemoptysis, suspected right-to-left shunting in patients with cyanosis or HHT, or cerebral abscess and/or unexplained embolic stroke A round or oval-shaped mass or nodule may occasionally be seen on chest radiograph; however, the PAVM needs to be fairly large to be detected in this manner, and many (10% to 40%) are not detected, making routine screening by chest radiograph insensitive.47 Several noninvasive methods to assess and quantify right-to-left shunting across the PAVMs include measuring arterial PaO2 on 100% oxygen and perfusion scans using technetium-labeled albumin macroaggregates Transthoracic CE is recommended by the international HHT guidelines as initial screening tool for PAVMs, with a sensitivity of 100% and the specificity of 67% to 91%.65 CE with agitated saline detects intrapulmonary shunting with the use of noninvasive ultrasound to visualize delayed appearance of microbubbles in the left side of the heart after three to four cardiac cycles In contrast, the microbubbles are visualized within one to two cardiac cycles in patients with intracardiac shunt such as patent foramen ovale or an atrial septal defect Chest CT scan, although not part of the PAVMs screening process, is widely considered the gold standard diagnostic tool for further evaluation of patients with a high suspicion of PAVMs to demonstrate size, location, and extent of PAVM prior to therapy The higher resolution of CT is preferred to MRI Pulmonary angiography is no longer considered necessary for diagnostic purposes alone and is solely reserved for therapeutic purposes after diagnosis is established.47 Management Percutaneous TCE is the gold standard for the treatment of PAVMs due to its effectiveness in reducing paradoxical embolism and its associated complications Several series have demonstrated reduction in right-to-left shunting, improvement in oxygenation, reduction in strokes, migraines, reduced erythrocytosis, improved exercise tolerance, and prevention of lung hemorrhage.47,82,94,95 Therefore, regardless of symptoms, any PAVMs with feeding artery greater than 3 mm in diameter as detected by CT are generally recommended for TCE During the procedure, if additional smaller PAVMs are found, the goal is to occlude as many feeding arteries as technically feasible, even those that do not conform to the “3 mm rule.”82,96 After obtaining femoral venous access, antibiotic prophylaxis is administered prior to PAVM embolization The catheter is advanced to both pulmonary arteries, and baseline angiograms provide an overview of the number and distribution of PAVMs Embolization of PAVMs is performed by targeting the supplying artery just proximal to the aneurysmal sac (see Fig 50.8) A coaxial catheter system involving an outer guide catheter for stabilization and an inner catheter for deployment of the device is commonly used (see Figs 50.8 and 50.10) Postdeployment angiograms are necessary to ensure all possible source arteries to the aneurysmal sac are occluded (see Figs 50.10 and 50.11).95 Technical advances with the use of microcatheters, coils, and microvascular plugs have allowed occlusion of even small feeder arteries successfully (see Fig 50.11) FIG 50.10 A 55-year-old man had a history of liver cirrhosis and severe hypoxemia Right and left pulmonary artery angiograms and CT scan (A– D) demonstrate intrapulmonary vascular dilation (arrows) consistent with hepatopulmonary syndrome