CASE
A 47-year-old female complained of shortness of breath and occasional chest pain. As part of the workup being done by the cardiology service, she was sent to the radiology department for a coronary artery CT. Figure 1 shows an axial CT image through the lower chest. What does this image reveal?
DISCUSSION
Figure 1 shows dilated vascular structures compatible with a pulmonary arteriovenous malformation (AVM) or fistula near the base of the left lung. A coronal view confirms the presence of the structures (see Figure 2, page 62). A pulmonary AVM is an abnormal connection between a pulmonary artery and a vein. Although the connection can develop secondary to trauma, most AVMs are congenital. Approximately 70% of pulmonary AVMs are associated with hereditary hemorrhagic telangiectasia (Rendu-Osler-Weber syndrome), a genetic disorder that leads to vascular malformations.1 Most pulmonary AVMs are seen in patients between the ages of 40 and 60 years, with females affected twice as often as males. Figure 3 is a reconstructed image demonstrating the lengthwise anatomy of our patient's AVM.
Symptoms may vary, depending on the size of the AVM. Some patients are asymptomatic, while others have symptoms ranging from dyspnea, hemoptysis, chest pain, cough, and chronic hypoxemia to cyanosis or heart failure. More importantly, the presence of a pulmonary AVM can lead to paradoxical emboli, allowing an embolus to enter the systemic circulation. This can cause cerebral ischemia or infarction or lead to a brain abscess because the circulating blood does not go through the usual capillary filtering process and blood clots and bacteria are allowed to enter the brain. Patients may also have seizures, migraines, or a hemothorax. In some cases, polycythemia may also be present.
An estimated 53% to 70% of pulmonary AVMs are located in the lower lobes, and approximately 70% are unilateral.2 Pulmonary AVMs are usually characterized as simple or complex. A simple AVM has one feeding artery and one draining vein.3 Although a few pulmonary AVMs are supplied by a systemic vessel, most are fed by a pulmonary artery and drain into the left atrium.
On physical examination, the patient may appear cyanotic and have digital clubbing. A chest bruit is sometimes heard on auscultation. Nasopharyngeal telangiectasias may be present. The patient should be questioned about a family history of hereditary hemorrhagic telangiectasia. Radiography, CT or MRI of the chest, or pulmonary angiography may be indicated. The chest radiograph may demonstrate a round or oval, lobulated mass, usually in a lower lobe. A “feeding vessel” can sometimes be demonstrated radiating from the hilum to the mass. CT may show the feeding artery and draining vein and is more sensitive than a chest radiograph. CT is also helpful in distinguishing an AVM from a neoplasm. A pulmonary AVM may be difficult to visualize on MRI, particularly if the malformation is less than 5 mm in diameter and located peripherally. MRI may be useful in patients who have contraindications to a contrast-enhanced CT.
Arterial blood gases often provide useful information. Most patients with pulmonary AVM have hypoxemia with orthodeoxia (desaturation in the upright position).4 Because of the right-to-left shunt present with a pulmonary AVM, supplemental oxygen does not significantly improve oxygen saturation.
Contrast echocardiography can determine the presence of a cardiac or intrapulmonary shunt. In this study, 5 to 10 mL of indocyanine green or agitated saline is injected into a peripher peripheral vein while the right and left atria are imaged with echocardiography. These liquids contain microbubbles that are visible with ultrasound. In a patient without a right-to-left shunt, a cloud of echoes quickly appears in the right atrium and rapidly dissipates into the pulmonary circulation without entering the left heart. In the presence of an intracardiac shunt, the cloud is seen in the left heart within one cardiac cycle after its appearance in the right atrium. In a patient with a pulmonary AVM, there is a delay of three to eight cardiac cycles while the cloud of echoes courses through the pulmonary circulation before it is seen in the left atrium.
Treatment of pulmonary AVMs is generally dependent on size, number, location, and the patient's overall condition. The goal of treatment is to prevent neurologic and pulmonary complications. Traditionally, the indications for treatment have included progressive enlargement of the AVM, the appearance of paradoxical emboli, and the development of symptomatic hypoxemia. Large AVMs may necessitate pulmonary lobectomy. Most AVMs are treated with percutaneous transcatheter embolization. JAAPA
Julie Vajnar is the department editor for Diagnostic Imaging Review and practices in a radiology group at North Oaks Health System, Hammond, Louisiana. She has indicated no relationships to disclose relating to the content of this article.
REFERENCES
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