Extralobar Pulmonary Sequestration

Lt. Extralobar Sequestration
Aortic supply to Sequestration
Bilateral Sequestrations

Findings:

The sonogram demonstrates a wedge-shaped echogenic mass in the lower left hemithorax just above the diaphragm. No cysts are seen within the mass and there was no evidence of intrathoracic mass effect or hydrops fetalis. Vascular supply to the mass was noted to be from the infradiaphragmatic aorta. The amniotic fluid volume was normal and no other morphologic abnormalities were seen.

Discussion:

Pulmonary sequestration is a rare pulmonary congenital malformation seen in approximately 1.1-1.8% of all pulmonary resections. It is a malformation that affects between 0.15-1.7% of all individuals.This abnormality manifests as either an intralobar and extralobar form, differentiated by the pleural covering and blood supply. The intralobar form of pulmonary sequestration consists of lung that is within the pleural covering but lacks communication to the tracheobronchial tree. Usually seen in the lower lobes. The blood supply is usually from an aortic branch within the inferior pulmonary ligament, the venous drainage is through the pulmonary veins, thus creating a left to right shunt. Intralobar sequestration is the most common form of this entity accounting for 75-85% of all sequestrations. It is thought to be an acquired lesion and although most are asymptomatic it is often associated with recurrent pulmonary infections in the neonate. It may also be associated with hydrothorax, mediastinal shift and vascular compromise. Associated malformations are uncommon.

Extralobar sequestration is seen in 15-25% of all sequestrations and approximately 0.5-6% of all congenital malformations of the lung. It is sequestered lung that arises after formation of the pleura and thus has its own pleural covering. Eighty percent occur on the left side, posteriorly. While most cases occur within the thorax, cases have been described within the mediastinum, pericardium or below the hemidiaphragm. The blood supply is from the aorta and venous drainage is through systemic veins in over 80% of cases. Extralobar sequestration occurs more frequently in males with a ratio of 4:1. Approximately 50-60% of patients have associated malformations, the most common being congenital diaphragmatic hernia. Other associated malformations include communications with the esophagus or stomach (T-E fistula), bronchogenic cyst, pericardial defect, congenital heart disease, vertebral abnormalities, megacolon and cystic adenomatoid malformation of the lung. Type II cystic adenomatoid malformation of the lung has been reported in 15-25% of patients with extralobar sequestration.

Sonographically, sequestrations appear as an echogenic solid mass in the left lower thorax. If the lesions are large they may cause mediastinal shift and may cause either polyhydramnios or hydrops or both, likely due to compression of either the esophagus or venous or lymphatic structures. As was mentioned above, the hallmark of this disease is identification of aortic supply and sytemic venous drainage. This can be demonstrated nicely with color Doppler flow imaging. In the past several years there have been numerous reports of resolution of hydrops in patients with sequestration, as well as decreased size of the sequestration, itself. Therefore, while it is appropriate to consider the prognosis poor when hydrops develops in patients with this condition, the parents should be advised that it is not uniformly fatal.

Differential Diagnosis:

The major differential diagnosis to consider when a probable sequestration is seen is cystic adenomatoid malformation of the lung (CCAM), The cysts in a CCAM and the systemic blood supply in a sequestration are often helpful features. Unfortunately, CCAM or cysts may coexist with sequestration, making specific diagnosis difficult. It is for this reason that mass effect, rather than the specific diagnosis is more important in management decisions. Other diagnostic considerations include: mediastinal teratoma, neuroblastoma and diaphragmatic hernia.

References:

Rosado-de-Christenson ML, Frazier AA, Stocker JT and Templeton PA. Extralobar Sequestration: Radiologic-Pathologic correlation. Radiographics 13:425-441, 1993

Piccone W, Burt ME. Pulmonary sequestration in the neonate. Chest 97:244-246, 1990

Jones DA, Vill MD and Izquierdo LA. Lung, extralobar intrathoracic sequestration. Fetus 2:6:5-7, 1992

Abuhamad AZ, Bass T, Katz ME and Heyl PS. Familial recurrence of pulmonary sequestration. Obstet Gynecol 87:843-845,1996

daSilva OP, Ramanan R, Romano W, Bocking A and Evans M. Nonimmune hydrops fetalis, pulmonary sequestration, and favorable neonatal outcome. Obstet Gynecol 88:681-683, 1996

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