Pulmonary Arteriovenous Malformations

Progressive dyspnea prompted a 24-year-old woman to seek medical attention. Initially, her symptoms occurred only with exertion, but they later occurred at rest as well. She had no fever, chills, hemoptysis, or chest pain. Physical examination findings were unremarkable with no expiratory wheezing, symmetric chest wall excursion, and good air movement in both lung fields.

Her arterial blood gas values on 60% oxygen delivered by face mask were consistent with hypoxemic respiratory failure: pH was 7.4; PCO₂, 34.3 mm Hg; and PO₂, 61 mm Hg. The only significant laboratory finding was polycythemia with a hemoglobin level of 16.7 g/dL and a hematocrit of 49.4%, which suggested chronic hypoxia.

A CT angiogram from another hospital displayed multiple possible pulmonary arteriovenous malformations; the diagnosis was confirmed by non-contrast CT that revealed an additional large arteriovenous malformation in the left lower lobe measuring 5.3 3 3.3 cm (arrow). Further workup included a pulmonary shunt fraction study that showed a shunt fraction of 32%.

Embolization of these lesions improved the patient’s symptoms and resolved the hypoxia. A second angiogram showed that blood flow through the lesions had ceased.

Pulmonary arteriovenous malformations were first described in 1897 and have been named pulmonary arteriovenous fistulae, pulmonary atriovenous aneurysms, and pulmonary telangiectesias. The presence of these lesions should be suspected in patients with stigmata of right-to-left shunting, pulmonary nodules, mucocutaneous telangiectasias, or hemoptysis. Relatives of patients with hereditary hemorrhagic telangiectasia should also be evaluated because pulmonary arteriovenous malformations are a diagnostic criterion for this disease.

CT is more sensitive than angiography in detecting pulmonary arteriovenous malformations (98% versus 60%). All affected patients have some elevation in the fraction of cardiac output that bypasses the pulmonary capillaries. This shunt fraction can be assessed by the 100% oxygen method, which involves measurement of PaO₂ and SaO₂ after the patient breathes 100% oxygen through a mouthpiece or an airtight mask for 15 to 20 minutes. Shunt fractions greater than 5% warrant further diagnostic workup. Contrast echocardiography is also a sensitive tool; it can diagnose small right-to-left shunts that are not detected by the 100% oxygen method.

Untreated pulmonary arteriovenous malformations carry high mortality and morbidity. Approximately 25% are thought to enlarge,¹ and 15% of cases end in death related to stroke, cerebral abscess, hemothorax, or hemoptysis.² Permanent neurologic complications increase with age and number of arteriovenous malformations.

Indications for treatment include paradoxical emboli, symptomatic hypoxemia, and progressive enlargement of lesions (diameter of greater than 2 cm). Treatment options include surgery and arterial embolization. Embolization of proximal arteries that feed the arteriovenous malformations is the preferred method because it minimizes lung parenchymal loss, avoids major surgery, and allows intervention on multiple lesions during a single procedure. Surgery for excision and 
lobectomy is now reserved for patients with contrast material allergies and certain large lesions.

Surgery is occasionally associated with right heart failure, worsened pulmonary hypertension, enlargement of previously unrecognized arteriovenous malformations, stroke, and recurrence. Embolization is associated with a low risk of deep venous thrombosis caused by the angiography catheter.