Congenital Pulmonary Airway Malformation

Melissa L. Rosado-de-Christenson, MD, FACR

Key Facts

Terminology

Abnormal mass of lung tissue with varying degrees of cystic change

Imaging Findings

Unilateral multilocular thin-walled cysts
- Air-filled, fluid-filled, or air-fluid levels
- Dominant cyst surrounded by smaller cysts
Rarely solid mass
Mass effect on adjacent structures
Associated congenital anomalies
Antenatal diagnosis with ultrasound or MR

Top Differential Diagnoses

Congenital Lobar Overinflation
Pulmonary Sequestration
Bronchogenic Cyst
Neuroblastoma

Pathology

Classification based on lesion components reflecting morphology of portions of tracheobronchial tree
Type 1 lesions most frequently diagnosed

Clinical Issues

Neonate with progressive respiratory distress
Antenatal diagnosis with ultrasound
Difficult confident histologic diagnosis in older children and adults due to superimposed acute and chronic inflammation
Treatment with surgical excision
Good prognosis for type 1 lesions

Diagnostic Checklist

Unilateral cystic or solid pulmonary mass in infancy
Characterization with prenatal ultrasound or MR
Postnatal evaluation with chest CT in selected cases

Frontal radiograph coned-down to the left lung shows a focal left lower lobe air-filled multicystic type 1 congenital pulmonary airway malformation. A dominant air-filled cyst

is surrounded by smaller air-filled cysts.

Axial CECT shows a right lower lobe multicystic type 1 CPAM. Larger air-filled cysts

are surrounded by smaller cysts

. The cyst walls are relatively thin without nodular components.

TERMINOLOGY

Definitions

Congenital pulmonary airway malformation (CPAM)
- Currently accepted terminology
- Spectrum of lesions affecting various portions of tracheobronchial tree and distal airways
Congenital cystic adenomatoid malformation (CCAM)
- Outdated terminology
  - Some lesions are not cystic
  - Most lesions are not adenomatoid
CPAM: Abnormal mass of pulmonary tissue with varying degrees of cystic change
Adenomatoid: Term describes intralesional appearance of gland-like back-to-back airways
- Intralesional bronchioles, alveolar ducts, and alveoli
- Airways lined by cuboidal epithelium
Cystic: Term describes intralesional appearance of air-or fluid-filled bronchial-like or bronchiolar-like spaces
CPAM: Communicates with tracheobronchial tree; typically normal blood supply and venous drainage

IMAGING FINDINGS

General Features

Best diagnostic clue
- Multilocular cystic pulmonary lesion in fetus, neonate, or infant
  - Rarely diagnosed beyond infancy as chronic inflammation may preclude confident histologic diagnosis
Patient position/location
- Usually affects single lung lobe
- May be associated with other congenital lesions
Size
- Variable
  - Large lesions may result in pulmonary hypoplasia, fetal hydrops, and fetal demise
Morphology
- Cystic CPAM is most common; multilocular cysts with thick or thin walls
  - Radiologic classification: Large cyst type, dominant cyst > 2.5 cm; small cyst type, dominant cyst ≤ 2.5 cm
- Solid CPAM is rare; large soft tissue mass

Imaging Recommendations

Best imaging tool
- Ultrasound for antenatal diagnosis
  - Unilateral multilocular cystic lung lesion; may exhibit dominant cyst
  - Rarely, solid lung lesion
- Postnatal CT for further lesion characterization in selected patients

CT Findings

Multilocular cystic lesion within pulmonary lobe
- Cysts separated by thin- or thick-walled septa
- Variable cyst size
  - Dominant cyst surrounded by small cysts
  - Uniform cyst size in type 2 lesions
- Interspersed normal lung parenchyma
Cysts contain air, fluid, or air-fluid levels
- May be initially fluid-filled; retained fetal fluid
Solid lesion within pulmonary lobe
- May replace lobe or lung and produce mass effect