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Pulmonary Sequestration vs. Congenital Pulmonary Airway Malformation (CPAM) on Fetal Ultrasonography

Abstract

Pulmonary sequestration (PS) and congenital pulmonary airway malformation (CPAM) are two of the most common congenital lung lesions identified during routine prenatal ultrasonography. While both may present as echogenic thoracic masses, they differ in pathophysiology, vascular supply, and imaging characteristics. Accurate prenatal differentiation using ultrasound, particularly with Doppler, is essential for prognostication and perinatal management. This article reviews and compares the imaging features and clinical implications of PS and CPAM in the fetal period.

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1. Introduction

Advances in prenatal imaging have led to the increased detection of congenital lung malformations, with an estimated incidence of 1 in 10,000 to 1 in 35,000 live births¹. Pulmonary sequestration and CPAM (formerly congenital cystic adenomatoid malformation) are among the most frequently diagnosed fetal thoracic lesions. Despite overlapping sonographic appearances, distinct features—especially on Doppler imaging—aid in their differentiation.

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2. Pulmonary Sequestration (PS)

2.1 Definition and Pathophysiology

Pulmonary sequestration is characterized by non-functional lung tissue that lacks communication with the tracheobronchial tree and receives systemic arterial blood supply, most commonly from the thoracic or abdominal aorta².

2.2 Types

• Intralobar sequestration (ILS): Lies within the normal lobe and shares pleura.

• Extralobar sequestration (ELS): Encased in its own pleura and often found below the diaphragm.

2.3 Sonographic Features

• Appears as a homogeneous, echogenic mass—typically in the posterior basal lung, often on the left side.

• Color Doppler confirms diagnosis by demonstrating a systemic arterial supply from the aorta³.

• May cause mediastinal shift or fetal hydrops if large.

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3. Congenital Pulmonary Airway Malformation (CPAM)

3.1 Definition and Pathogenesis

CPAM results from abnormal branching of the terminal bronchioles, producing cystic or adenomatous overgrowths of pulmonary tissue that may or may not communicate with the airway. Blood supply is via the pulmonary artery⁴.

3.2 Classification (Stocker System)

• Type I (macrocystic): Dominated by one or more cysts >2 cm.

• Type II (microcystic): Smaller cysts <2 cm.

• Type III (solid/adenomatoid): Appears solid and echogenic on USG.

3.3 Sonographic Features

• May appear cystic, solid, or mixed.

• Often presents as a hyperechoic intrathoracic mass, especially in microcystic or solid types.

• Color Doppler shows pulmonary arterial supply, not systemic⁵.

• Large lesions may lead to polyhydramnios, mediastinal shift, or hydrops.

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4. Key Differentiating Features on Fetal Ultrasonography

Feature	Pulmonary Sequestration (PS)	Congenital Pulmonary Airway Malformation (CPAM)
Echotexture	Homogeneous, echogenic mass	Cystic, mixed, or solid mass
Blood supply	Systemic (aortic) – visible on Doppler	Pulmonary arterial supply
Airway connection	None	May connect with airway
Common location	Posterior/inferior lobe, often left side	Variable, often unilateral
Pleural covering	ELS has separate pleura; ILS does not	Normal pleura
Associated anomalies	Rare; hydrops if large	More commonly associated with hydrops, polyhydramnios
Management approach	Monitor; surgical removal postnatally if symptomatic	May require prenatal or postnatal intervention

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5. Diagnostic and Prognostic Tools

• Color Doppler ultrasonography is essential to distinguish vascular supply.

• CPAM Volume Ratio (CVR) is used to monitor lesion growth and predict risk of hydrops (CVR > 1.6 suggests higher risk)⁶.

• MRI may be used postnatally or in complex cases for better lesion delineation.

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6. Management and Outcomes

6.1 Prenatal

• Serial ultrasound monitoring.

• Maternal corticosteroids (e.g., betamethasone) may be considered for large lesions causing hydrops.

• Fetal interventions like thoracoamniotic shunting may be indicated for macrocystic CPAM with mediastinal compression.

6.2 Postnatal

• Elective surgical resection is the standard for symptomatic lesions or those at risk of infection or malignancy.

• Asymptomatic cases may also undergo resection due to potential complications.

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7. Conclusion

Differentiating pulmonary sequestration from CPAM on fetal ultrasound is vital for optimal prenatal counseling and postnatal management. Doppler imaging, lesion location, echotexture, and vascular pattern provide key diagnostic clues. With proper surveillance and intervention, outcomes for most affected fetuses are favorable.

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References

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Footnotes

1. Lee EY, Boiselle PM, Cleveland RH. Multidetector CT evaluation of congenital lung anomalies. Radiology. 2008;247(3):632-648. ↩

2. Corbett HJ, Humphrey GM. Pulmonary sequestration. Paediatr Respir Rev. 2004;5(1):59–68. ↩

3. Adzick NS. Management of fetal lung lesions. Clin Perinatol. 2009;36(2):363–376. ↩

4. Stocker JT. Congenital pulmonary airway malformation: A new name and an expanded classification of congenital cystic lung lesions. Histopathology. 2002;41 Suppl 2:424–431. ↩

5. Hubbard AM, Crombleholme TM, Adzick NS. Prenatal MRI evaluation of congenital lung lesions. Semin Pediatr Surg. 2003;12(1):29–33. ↩

6. Crombleholme TM, Coleman B, Hedrick H, et al. Cystic adenomatoid malformation volume ratio predicts outcome in prenatally diagnosed cystic lung lesions. J Pediatr Surg. 2002;37(3):331–338. ↩