Chronic Dissection of the Left Subclavian Artery with Pseudocoarctation

Abstract

Surgical management of a dissection of the subclavian artery is sparsely reported in the literature because of its rare occurrence. Recently, we treated a patient who had presented with a huge left subclavian artery dissection, a small right subclavian artery aneurysm with pseudocoarctation of the aorta, and a small perimembranous ventricular septal defect. Surgical management of the left subclavian artery dissection and correction of the pseudocoarctation of the aorta were achieved effectively. That unusual combination of pathologic conditions prompted us to report this case. (Tex Heart Inst J 2003;30:221–4)

Among peripheral artery aneurysms, a dissection of the intrathoracic subclavian artery is a rare occurrence. We describe the presentation and management of a patient who had a dissection of the left subclavian artery extending into the arch and into the descending thoracic aorta in close proximity to pseudocoarctation, in combination with a small fusiform aneurysm of the right subclavian artery and a small perimembranous ventricular septal defect (VSD).

Case Report

A 41-year-old male athlete presented with persistent cough and dyspnea of recent origin and with extreme fatigue of 1 year's duration. A small perimembranous VSD had been diagnosed when he was a child and later, at 28 years of age, from a pre-employment chest radiograph. On that same occasion (at age 28), a computed tomographic scan of the chest had shown pseudocoarctation of the aorta, just below the origin of the left subclavian artery. Aortography had shown dilatation of the left subclavian artery, along with pseudocoarctation of the aorta beyond it and a small fusiform aneurysm of the right subclavian artery at the origin of the internal mammary artery and the vertebral artery, but no dissection. No further action had been taken, as the patient was asymptomatic.

In the past, the patient had fallen twice: the 1st time during a rugby game at the age of 31 years, when he had broken 2 upper ribs (the side was unspecified and documentation was unavailable); and the 2nd time at the age of 38 years, when he had fallen down some stairs and had broken lumbar vertebrae without neurologic sequelae. Since reaching the age of 40, the patient had tired very easily but had continued his athletic activities until his presenting symptoms arose.

On examination at our center, the systemic blood pressure in both arms was 145/100 mmHg and there was no marked difference in the systemic blood pressure of the lower limbs. We had the patient's history from his file but did not see the aortogram. The cardiologist sent him for radiologic evaluation. A pre-existing precordial murmur and echocardiographic diagnosis of perimembranous VSD were evaluated but were considered too trivial to warrant surgical intervention. However, additional radiologic screening confirmed dilatation of the distal aortic arch and dissection of the root of the left subclavian artery (Figs. 1 and 2). The dissection extended on either side of the arch up to the ligamentum arteriosum distally, but it spared the left common carotid artery proximally. The thoracic aorta below the level of the left subclavian artery had a U-shaped configuration as it passed from anterior to posterior over the left pulmonary artery (Fig. 3). A small fusiform aneurysm of the right subclavian artery at the origins of the vertebral and internal mammary arteries was confirmed. No aortic regurgitation was observed, and the coronary arteries were normal, with left dominance.

Fig. 1 Chest radiograph shows smooth-edged fusiform dilatation on the arch of the aorta extending to the root of the neck.

Fig. 2 Computed tomographic scan shows the subclavian artery dissection.

Fig. 3 Angiogram shows the pseudocoarctation and aneurysmal dilatation of the left subclavian artery.

The patient was taken to surgery for correction of the left subclavian dissection. A left posterolateral thoracotomy was performed through the 4th intercostal space. We divided the 5th rib posteriorly and upon entering the chest found a huge dissection involving the left subclavian artery and the adjacent distal arch of the aorta; immediately beyond the level of the ligamentum arteriosum, we found kinking of the aorta suggestive of pseudocoarctation. Without much difficulty, we taped the aorta distal to the left subclavian artery, but the arch beyond the left common carotid artery was difficult to tape, because the dissection extended throughout the area and posteriorly toward the mediastinal structures and was grossly adherent. Distally, the dissection projected through the thoracic outlet into the neck; maneuvering around the subclavian artery was difficult, but possible. Because of adhesions, the patient was placed on left heart bypass, after heparinization, by cannulating the inferior pulmonary vein intrapericardially and by cannulating the descending thoracic aorta. The adhesions near the subclavian artery distal to the aneurysm and those near the left common carotid artery and left subclavian artery were dissected after left heart bypass was achieved. The arch of the aorta distal to the left common carotid artery was clamped, and the left subclavian artery distal to the aneurysm was clamped within the chest after we pulled the aneurysm down. The descending thoracic aorta distal to the pseudocoarctation was clamped at the level of the thoracic 6th vertebra, and the aneurysm was opened along the length of the aorta. The segment of subclavian artery with evidence of dissection was 8 cm in diameter, with dissection extending along either side of its origin from the arch. Between the dissected flap and the adventitia was a large amount of thrombus, which was evacuated. The whole diseased segment of the aortic arch was excluded and replaced by a 22-mm Hemashield® graft (Meadox Medicals Inc.; Oakland, NJ), with end-to-end anastomoses performed on either side of the aorta. The aortic cross-clamp time was 17 minutes. The diseased part of the left subclavian artery was replaced by an 8-mm GoreTex® interposition graft (W.L. Gore & Associates, Inc.; Flagstaff, Ariz). End-to-end anastomoses were performed between the GoreTex graft and the distal, cut end of the subclavian artery and, at the other end, between the GoreTex graft and the Hemashield graft, with the aid of a side-biting clamp on the Hemashield graft. Left-heart bypass was gradually terminated, heparin reversed, and hemostasis secured. The patient was hemodynamically stable. The postoperative period was uneventful, and he was discharged home on the 7th postoperative day. At his 6-month follow-up, he was doing extremely well and had resumed his athletic activities.

Histopathologic examination confirmed that the dissection was of long-standing duration and had occurred in the outermost part of the media, with no apparent leakage through the adventitia. The dissected segment of the left subclavian artery contained a large amount of mural thrombus, and the adjacent aorta showed chronic dissection with atherosclerosis and much less mural thrombus.

Discussion

Acute dissection of the subclavian artery, although very rare, is a potential late complication of coarctation of the aorta. ¹ This case is a rare surgical presentation with dissecting aneurysm of the left subclavian artery in association with pseudocoarctation. Among peripheral artery aneurysms, an intrathoracic subclavian artery aneurysm is itself uncommon. ^2–4 Intrathoracic segmental involvement is usually secondary to atherosclerosis, medial degeneration, trauma, and infection. ² In this patient, thoracic injury during a rugby game at the age of 31 years and also during a fall at the age of 38 might have precipitated dissection and secondary dilatation in an already vulnerable aorta with pseudocoarctation. ⁵ In isolated kinking of the aorta, dissection can occur some years later, ⁶ and it is necessary to monitor patients with chest films at regular intervals. Gay and Young ⁷ and Turner and coworkers ⁸ reported cases in which aortic aneurysm was associated with pseudocoarctation above or below the malformation, ⁶ but they believed that the relationship was more likely a complication than an association. Pseudocoarctation is often associated with such anomalies as bicuspid aortic valve, ventricular septal defect, patent ductus arteriosus, atrial septal defect, aneurysm of the sinus of Valsalva, and transposition of the great arteries. The treatment of pseudocoarctation in an asymptomatic patient, with or without associated anomalies or complications, has been conservative. Our patient had been diagnosed with pseudocoarctation and a small perimembranous VSD, and he was asymptomatic. No treatment was offered until he exhibited opacity of the upper left side of the chest. As more and more data accumulate on the natural history of pseudocoarctation, the recommendation may tilt in favor of early surgical management.

In 1998, there was a report of a case of bilateral subclavian artery aneurysms in association with pseudocoarctation of aorta, which its authors claimed was the first of its kind in the literature. ⁹ Our patient probably had dissection caused by trauma in association with pseudocoarctation, which motivated us to document the case in the literature. Management of this patient's lesion also warrants discussion, considering the large size and extent of the dissection.

The surgical approach to intrathoracic subclavian artery dissection depends primarily on which side has been affected. ² A left subclavian artery lesion is best approached through a left thoracotomy, which provides exposure of the aorta for proximal control as well as for repair of descending aortic extension. ² We could approach even the neck through the same incision. The procedure could have been done without left-heart bypass, but the huge size of the dissection and its adherence to important structures led us to choose left-heart bypass for safety and proper outcome. It is imperative that the patient be monitored postoperatively at frequent intervals. ¹⁰

We shall repair the right subclavian artery aneurysm in the near future. The natural history of subclavi-an artery aneurysms is unknown. However, a high incidence of death from rupture and exsanguination, regardless of the size of the aneurysm, has been reported. ^9,11 Another grave complication is that of thromboembolism to a limb, causing ischemia. Therefore, an aggressive approach must be taken when dealing with a subclavian artery aneurysm, and a thorough search should be undertaken for aneurysms elsewhere, because of a 25% to 35% incidence of associated aneurysm. ⁹ Overall, we believe that this patient's rare presentation and its proper management with a good result warrant reporting.