From the Archives of the AFIP: Intralobar Sequestration

Radiologic-Pathologic Correlation

Abstract Introduction Postulated Pathogenesis Clinical Characteristics

Pathologic Features Histologic Features Radiologic Appearance

Therapy And Prognosis Conclusions Source Information References

Postulated Pathogenesis

Many theories in the medical literature describe a shared embryologic origin of all pulmonary sequestrations. Intralobar and extralobar sequestrations have almost uniformly been considered closely related developmental anomalies that occur at different stages of embryonic life. Pryce (3) proposed that an anomalous systemic artery, which produces traction on a segment of the developing embryonic lung, creates a sequestration by inducing interstitial damage and partial detachment of lung tissue. Smith attributed the development of sequestration to focal insufficiency of pulmonary arterial supply, which results in the persistence of the thoracic aortic branches. He also thought that cystic change within a sequestration was caused by the local effects of systemic blood pressure (9). Gerle et al (7) outlined the spectrum of bronchopulmonary foregut malformations and proposed that all sequestrations originated as accessory lung buds from the ventral primitive foregut, which migrate caudally, retain their splanchnic (and therefore systemic) blood supply, and maintain a connection to foregut structures.

Although extralobar sequestration is clearly a congenital anomaly, most cases of intralobar sequestration appear to have an acquired origin, as indicated by substantial evidence (2,10). Intralobar sequestration is virtually absent in infants, and associated anomalies are relatively uncommon (occurring in 6% 12% of cases), compared with their prevalence (26% 85%) with other congenital lesions of the chest (2,10). Two different cases have been reported in which an aspirated foreign body (a juniper twig and a ballpoint tip) was found lodged within an obstructed bronchus proximal to an intralobar sequestration; these cases are fascinating accounts that support an acquired origin of this lesion in childhood (10,11).

Stocker and Malczak (10) postulated a relationship between normally occurring small systemic pulmonary ligament arteries and the development of intralobar sequestration. They found these arteries in 90% of randomly selected pediatric autopsy subjects without congenital pulmonary, cardiac, or vascular disease (10). Small systemic pulmonary ligament arteries arise from the anterior thoracic aorta, contribute to the esophageal arterial plexus, and traverse the pulmonary ligament to ramify in the visceral pleura of the lower lobes of the lung (Figure 2, Figure 3).These vessels are distinct from the pulmonary circulation and from the bronchial, vertebral, and intercostal arteries (10).

Stocker and Malczak (10) proposed that these normally occurring arteries may become parasitized to supply the infected portion of a lower lobe if the normal pulmonary arterial supply is compromised.Stocker and Malczak (10) have proposed that in most cases intralobar sequestration may simply represent a portion of lung that has acquired a systemic blood supply subsequent to chronic postobstructive pneumonia (Figure 4). According to the hypothesis, a lower lobe bronchus becomes obstructed and a postobstructive pneumonia results (Figure 4a) (10). This phase is followed by partial or complete interruption of the normal pulmonary arterial supply to the infected lung tissue and the acquisition of a systemic blood supply through parasitization of the neighboring pulmonary ligament arteries (Figure 4b, Figure 4c) (10). These arteries supply the pleural granulation tissue and hypertrophy as they become incorporated into the underlying lung parenchyma (10). The phrenic vessels that originate from the celiac axis and supply the diaphragmatic surface of the pleura may be similarly recruited to supply the sequestration (10). Multiple episodes of pneumonia may need to occur before a substantial systemic arterial supply is established (10).

On the basis of the previous discussion, we believe that there is significant evidence to support an acquired origin for most cases of intralobar sequestration. However, a number of these lesions are clearly congenital in origin. There are rare reported cases of bilateral intralobar sequestration (2,12,14), coexistent intralobar and extralobar forms (1,15), neonatal congestive heart failure as a manifestation of intralobar sequestration (16,18), the (rare) occurrence of an associated bronchopulmonary malformation (2,7,19,21), and coincident intralobar sequestration and bronchogenic cyst (21,24). In these cases, the systemic arterial supply clearly represents an anomaly of embryonic development.

Abstract Introduction Postulated Pathogenesis Clinical Characteristics

Pathologic Features Histologic Features Radiologic Appearance

Therapy And Prognosis Conclusions Source Information References