Pseudosequestration of the Left Lung

Abstract

Bronchovascular malformations of the lung constitute a broad spectrum of developmental disorders in which a part of the lung is perfused exclusively from the systemic arterial tree with or without tracheobronchial communication. We report the case of an infant with severe pulmonary artery hypertension whose entire left lung was supplied by collateral vessels from the celiac trunk and the left subclavian artery. The left tracheobronchial tree was normal. Coil embolization of the collateral vessels was performed to reduce the pulmonary blood flow.

Anomalous systemic blood supply to a lung in the presence of a normal tracheobronchial communication and rudimentary pulmonary artery (PA) arborization is a rare congenital anomaly. In consideration of the normal bronchial connection, this anomaly might or might not belong within the sequestration spectrum. We report a case of an infant who had systemic arterialization of the entire left lung, which was managed with coil embolization of the aberrant systemic arteries.

Case Report

In June 2006, a 5-month-old boy weighing 4.5 kg was referred to our institution because of respiratory distress, which had been present since his early days of life and had now progressed to the point of ventilatory support. The primary diagnosis was pulmonary hypertension with lower respiratory tract infection and associated tracheobronchomalacia. He maintained stable hemodynamic levels while on mechanical ventilation, but he had markedly reduced air entry on the left side, with fine crepitant rales and wheezing bilaterally. In addition, he had facial dysmorphisms (including antimongoloid slant) and glandular hypospadias. Chest radiography revealed bilateral haziness in the lung fields without cardiomegaly. Echocardiography showed a small left PA. There was no intracardiac shunt or outflow tract obstruction. The condition was managed with antibiotics, anticongestive therapies, and sildenafil. A 64-slice computed tomographic (CT) scan of the chest showed a normal tracheobronchial tree (Fig. 1). The lung parenchyma on the right lower lobe showed mild emphysematous changes. On cardiac catheterization, marked hypoplasia of the left PA was found, together with very poor peripheral arborization (Fig. 2). The right PA was about 4 mm in diameter. The left PA measured about 1 mm at the bifurcation and immediately terminated into a few small branches. A large, tortuous collateral vessel traveled upward from the celiac trunk transdiaphragmatically and supplied most of the left lower lobe (Fig. 3). The upper half of the left lung was supplied by a large collateral vessel that arose from the left subclavian artery (Fig. 4). There were a few small collateral vessels from the descending thoracic aorta to the periphery of the left lung. Levophase angiography revealed that venous drainage from the lung was entering the left atrium via the pulmonary veins. The main PA pressure was 46/17 mmHg (mean, 27 mmHg). In view of the poor general condition of the patient, a staged approach was adopted. The child successfully underwent coil embolization of the major collateral vessels to the lung (Fig. 5). However, the pulmonary pressures never regressed, and the child could not be weaned from the mechanical ventilator. The child succumbed to a lower respiratory tract infection.

Fig. 1 A 64-slice computed tomographic image shows a normal tracheobronchial tree on the left side.

Fig. 2 A pulmonary angiogram shows a good-sized right pulmonary artery and a diminutive left pulmonary artery.

Fig. 3 A descending aortogram displays the collateral vessel that supplies the left lower lobe of the lung.

Fig. 4 A left subclavian angiogram shows the collateral vessel that supplies the left upper lobe of the lung.

Fig. 5 Multiple coils were deployed to embolize the huge collateral vessel that extended from the abdominal aorta to the left lower lobe.

Discussion

Pulmonary sequestration is defined as a mass of abnormal pulmonary tissue that does not communicate with the tracheobronchial tree through a normally located bronchus and that is supplied by an anomalous systemic artery.¹ Systemic arterialization of the normal lung is a rare congenital anomaly. Although classified previously as Pryce's type I sequestration, such a lung is never actually “sequestered” from the normal tracheobronchial tree. Sade and associates² introduced the concept of “sequestration spectrum” for the classification of these complex bronchovascular anomalies, as did Clements and Warner³ with their concept of “pulmonary malinosculation spectrum.” Our patient had predominant involvement of the lower lobe; origin of the aberrant vessels in the pulmonary ligament from the descending thoracic aorta, distinct from the bronchial arteries; and aberrant vessels with an elastic wall histologically similar to the wall of the PA. These factors render difficult a decision to categorize this anomaly as anything other than a variant form of sequestration. Normal mucosal and submucosal continuity (without inflammatory changes) has been demonstrated between the sequestered lung and the normal tracheobronchial tree.⁴ Therefore, it appears that bronchial isolation is not mandatory in sequestration. Indeed, Takahashi and associates⁵ have suggested the terms “arterial sequestration” for isolated systemic arterialization of a normal lung and “bronchoarterial sequestration” for application to classic sequestered lung.

Yamanaka and colleagues⁶ have discussed 12 cases of systemic arterialization of the lung segments (8 previously described in the English literature, and 4 of their own). The age of these 12 patients ranged from 0 to 68 years (mean, 21.2 yr), less than 6 years of age in 6 patients, and over 20 years in 6 patients. The predominant features were male sex, left-sided involvement, and descending thoracic aorta as the origin of the aberrant artery. In all cases, a single aberrant artery perfused the basal segments of the lower lobe of the lung. The pulmonary veins from these segments drained normally, into the left atrium. In all of the cases reviewed by Yamanaka and colleagues,⁶ 2 distinct patterns of aberrant arterial supply became evident—the left lower lobe was supplied by a vessel arising from the descending thoracic aorta, while the right lower lobe was supplied by a vessel arising from the abdominal aorta or the celiac axis. The artery was narrow at its origin and dilated as it entered the lobe, especially in the left-sided cases. The surface of the affected segments was telangiectatic, and the tissue could easily be distinguished from normal. Our patient was also a male infant with a left-sided anomaly, but the entire left lung was involved and was supplied by 2 aberrant vessels. In contrast with previous reports, the left lower lobe was supplied by a vessel from the celiac trunk, and the left upper lobe was supplied by a vessel from the left subclavian artery. These vessels were the sole blood supply to the lung, as evidenced by the pulmonary an-giogram, which showed a diminutive left PA.

Most patients who present with pseudosequestration of the lung are asymptomatic, having been referred because of an abnormal radiologic finding or a continuous or systolic murmur. Symptomatic patients usually present with hemoptysis, exertional dyspnea, and congestive cardiac failure due to left-sided volume overload secondary to left-to-left shunt. In our patient, the clinical presentation was severe respiratory distress with pulmonary hypertension that required ventilatory support.

The CT scan provides diagnostic information pertaining to the origin and supply of the aberrant vessel and the native hypoplastic PA; it is the best noninvasive method for the diagnosis of this malformation.⁷ Aortic and pulmonary angiograms help to delineate the anatomy of the aberrant collateral vessels and the planning of definitive therapy. Before any intervention, it is essential to know the native PA supply and the venous drainage of the involved lung. Surgery is indicated for all patients with this anomaly, because the condition is associated with such risks as hemopytsis due to pulmonary hypertension and heart failure due to left-to-left shunt. Surgical procedures include lobectomy, basal segmentectomy or anastomosis of the aberrant artery to the PA, or ligation of the anomalous artery.⁶ Successful ligation of the anomalous systemic artery in a case of dual blood supply (from the systemic and pulmonary arteries) has been reported.⁸ Coil embolization of the systemic vessel has also been performed in adult patients who presented with hemoptysis and chest pain.^9,10 We successfully used this technique in an infant as part of a staged procedure, in consideration of our patient's morbid condition, which precluded surgical intervention at that time.

Conclusion

We have discussed a rare presentation in an infant of pseudosequestration of the left lung with a diminutive native pulmonary artery, which to our knowledge has not been previously documented. The clinical presentation of this patient with pulmonary hypertension expands the symptomatic spectrum for these complex bronchovascular malformations.