What is pulmonary sequestration in a fetus?

What is Pulmonary Sequestration in a Fetus?

Pulmonary sequestration is a congenital lung malformation where abnormal, non-functioning lung tissue receives its blood supply from an anomalous systemic artery (typically from the thoracic or abdominal aorta) rather than the pulmonary artery, and this tissue does not communicate with the normal bronchial tree. 1, 2

Key Anatomic Features

Arterial Supply:

• Approximately 80% receive blood from a direct branch of the thoracic or abdominal aorta 3
• 15% are supplied by another systemic artery 3
• Only 5% receive blood from the pulmonary artery 3

Venous Drainage:

• Most drain into systemic circulation (azygos vein, hemiazygos vein, or inferior vena cava) 3
• Approximately 25% drain through pulmonary veins 3, 2
• Rare cases may drain into the portal vein 3

Types:

• Intralobar sequestration: Abnormal tissue within the normal lung pleura 2
• Extralobar sequestration (ELS): Separate tissue with its own pleural covering, occurring in approximately 90% of cases in the left hemithorax 3

Prenatal Diagnosis and Natural History

Ultrasound Findings:

• Appears as an echogenic lung mass on prenatal ultrasound 1
• Diagnosis typically made around 23 weeks' gestation (range 19-31 weeks) 1
• The key diagnostic feature is identifying the systemic arterial blood supply rather than pulmonary arterial supply 1

Favorable Prognosis:

• Many pulmonary sequestrations regress completely before birth 1
• In one series, large lesions in 4 of 14 fetuses regressed completely prior to delivery 1
• Mean gestational age at delivery is typically 37 weeks (range 32-40 weeks) 1

Complications and Management

Hydrops Fetalis:

• Pulmonary sequestrations cause hydrops only when complicated by tension hydrothorax 1
• Large bronchopulmonary sequestrations can be treated with neodymium:yttrium-aluminium-garnet laser ablation of the feeding vessel 4
• If tension hydrothorax develops, thoracoamniotic shunt placement may be required prenatally 1
• Only 2 of 14 fetuses in one series required prenatal intervention for ipsilateral tension hydrothorax 1

Associated Anomalies:

• Approximately 21% (3 of 14 cases) may have mixed lesions combining features of congenital cystic adenomatoid malformation (CPAM) and pulmonary sequestration 1
• Other congenital anomalies may be present and are responsible for most mortality associated with sequestrations 2

Postnatal Outcomes

Surgical Management:

• Persistent lesions are safely resected postnatally without significant morbidity or mortality 1
• Elective resection is typically performed after birth for lesions that do not regress 1
• The condition is considered the second most common congenital lung anomaly 2

Critical Distinction from CPAM:

• While CPAM is the most frequent pulmonary lesion associated with nonimmune hydrops fetalis 4, pulmonary sequestration has a more favorable natural history with frequent spontaneous regression 1
• Unlike microcystic CPAM (which may respond to maternal corticosteroids), sequestrations are managed expectantly unless complicated by hydrothorax 4, 5