95: Pulmonary Arteriovenous Malformation

The term pulmonary arteriovenous malformation (AVM) refers to lesions that have abnormal communications between the pulmonary arteries and pulmonary veins. Numerous other names have been used in the past to describe these lesions, such as pulmonary telangiectasias, aneurysms, fistulas, hemangiomas, and cavernous angiomas. These lesions can be congenital, usually as part of the hereditary hemorrhagic telangiectasia, also known as Rendu–Osler–Weber syndrome, or acquired from bronchiectasis, infections, hepatic cirrhosis, mitral stenosis, malignancies, or trauma. AVMs have been described based on number (single vs. multiple), location (unilateral vs. bilateral; parenchymal vs. pleural), and size or type of drainage (simple vs. complex).^1,2

Clinical suspicion for the presence of pulmonary AVM should arise when there is the presence of nonspiculated pulmonary nodule suggestive of AVM; a family history of hereditary hemorrhagic telangiectasia; sequelae of right-to-left shunting such as hypoxemia, dyspnea, clubbing, cyanosis, and polycythemia; and systemic embolism such as cerebral stroke or cerebral abscess. Epistaxis can be reported in up to 85% of patients with hereditary hemorrhagic telangiectasia.¹ A continuous bruit can be auscultated over the lesion. The triad of cyanosis, clubbing, and polycythemia is seen in 20% of patients. Approximately 90% of AVMs are unilateral, and 50% to 67% of patients have a single AVM.^1,2 Rarely, patients may present with massive hemothorax under tension from acute hemorrhage secondary to rupture of the AVM.

Workup should include a chest computed tomography (CT) scan, which is the most sensitive test, evaluation of the shunt fraction, and pulmonary angiography to assess the feasibility of embolization. Approximately 25% of AVMs tend to enlarge up to a rate of 2 mm per year, and patients who are not treated have a stroke rate of 13% and a brain abscess rate of 11%. Complications are more common in patients who have AVMs greater than 2 cm or afferent vessels greater than 3 mm.^1,2 At minimum, treatment should be offered to these patients, if not to all patients with angiographically accessible lesions.¹

Embolization of pulmonary AVMs was first described in 1977.^1,2 Pulmonary angiography is performed, and numerous techniques have been described, including coils, balloons, sclerosing agents, and Amplatzer occluding devices.³ Multiple AVMs may be embolized at a single session or a few weeks apart. Embolization is feasible in most patients with angiographically accessible lesions, although treating patients with multiple feeding vessels can be challenging. Complications after balloon occlusion include balloon migration with distal embolization, balloon deflation, and pulmonary infarction. Long-term follow-up after embolization procedures is sparse. Recurrence after embolization has been reported.

Surgery is reserved for patients who cannot be embolized or who have failed embolization. Surgical techniques used include thoracotomy and video-assisted thoracic surgery, and the extent of resection can range from fistulectomy and segmental resection to lobectomy and even pneumonectomy.⁴ While pneumonectomy has been used in the past, most lesions today can be treated with lung-sparing techniques. Preoperative pulmonary function testing is done as indicated based on the anticipated degree of pulmonary resection.

When anatomic resections such as segmentectomy or lobectomy are deemed necessary to resect the AVM, as can be the case for deep fistulas (Fig. 95-1), they are carried out in the standard manner. However, when fistulectomy is performed for hilar or subpleural fistulas, then attention must be paid to ensure meticulous dissection, ligation, and division of all feeding vessels and prevention of complications such as thrombosis, air embolism, and bleeding (Fig. 95-2).

A standard thoracotomy is used for exposure. The pulmonary artery and vein proximal and distal to the fistula are dissected and controlled with tourniquets.⁴ After systemic heparinization, the tourniquets are cinched. The fistula is then dissected, and all tributaries are identified, ligated, and divided. The main trunk of the fistula can be clipped and divided or resected with the artery, followed by vein repair by means of standard vascular techniques.⁵ The pulmonary artery tourniquet and then the pulmonary vein tourniquet are loosened with gentle lung reinflation, as is done with lung transplantation, to flush clot or air before tying the sutures to avoid embolism. If there is concern about proximity of the arterial and venous suture lines, tissue can be positioned between them. However, this is not practical if multiple fistulas are resected. Instead, standard anatomic resection of lung parenchyma, that is, lobectomy or segmentectomy, is carried out either with open technique or thoracoscopically. Arterial blood gas analysis should reveal resolution of the A-a gradient if all fistulas have been resected.

The duration of postoperative hospitalization is determined by the size of the incision and the extent of the pulmonary resection. Chest tubes are removed as usual. Routine anticoagulation with systemic heparinization is not advocated. Recurrence after surgical resection is rare.

Pulmonary or systemic embolism from air or clot and thrombosis at the arterioplasty or venoplasty are the procedure-specific complications. Thrombosis, however, can be insidious and extensive, resulting in pulmonary infarction. Persistent hypoxemia should prompt investigation, especially if all the AVMs were addressed during the surgery. Prevention with systemic heparinization intraoperatively is the best policy. Cerebral embolism is the most serious complication and should be apparent in the immediate postoperative period.

Pulmonary AVMs remain rare lesions that should be treated to avoid the sequelae of systemic embolization, cerebral abscess, and hypoxemia. Interventional radiology procedures can be used to address most of these lesions, and when surgical intervention is needed, lung-sparing procedures should be used with attention to embolic and thrombotic complications.

A 31-year-old man presented with hemoptysis, hypoxia, and a nodule on chest x-ray (Fig. 95-3). A chest CT scan was done that revealed a pulmonary AVM (Fig. 95-4). Angiography and embolization were performed without complications (Figs. 95-5 and 95-6).

Although many AVMs can be successfully treated via embolization, for those lesions that are not angiographically accessible or have failed embolization, understanding the surgical management of these lesions is critically important so as to avoid potentially serious complications such as thrombosis with resultant pulmonary infarct or embolic stroke.