Types of Congenital Pulmonary Airway Malformation (CPAM)
CPAM is classified into five distinct types (Type 0, I, II, III, and IV) based on the anatomical origin within the lung, cyst size, and histological appearance of the cystic structures. 1, 2, 3
Classification System
Type 0 CPAM
- Originates from the trachea or bronchus with involvement of all lung lobes 3
- Represents the most proximal airway origin and is incompatible with life 3
Type I CPAM
- Most common type, characterized by large, dilated cysts (typically 2-10 cm in diameter) 1, 4
- Cysts are lined by ciliated columnar epithelium (pseudostratified ciliated columnar epithelium) 4
- Rapidly expands due to aeration immediately after birth, often necessitating urgent surgical intervention 4
- In atypical solid-type presentations, fetal T2-weighted MRI reveals a low-intensity solid lung mass containing multiple irregular T2 high-intensity areas 4
- Histologically may contain a solid component composed of proliferative mucous cells and smaller cysts (0.1-0.6 mm inner diameter) resembling Type 2 cysts 4
Type II CPAM
- Contains multiple smaller cysts (0.5-2 cm in diameter) 1, 2
- Cysts are lined by ciliated low-columnar or cuboidal epithelium 4
- Characterized by multiple emphysematous air bubbles and pseudocysts 2
- Associated with other congenital anomalies in approximately 60% of cases, including renal agenesis, cardiac defects, and skeletal abnormalities 1, 3
Type III CPAM
- Presents as a large, bulky, firm mass with microscopic cysts (less than 0.5 cm) 1, 3
- Appears solid on gross examination due to the small size of the cysts 1
- Characterized by adenomatoid appearance with glandular overgrowth 5
Type IV CPAM
- Rare type with large peripheral cysts (up to 7 cm) 3
- Cysts are lined by flattened alveolar epithelium 3
- May be difficult to distinguish from pleuropulmonary blastoma 3
Clinical Implications by Type
The CPAM type directly influences clinical presentation and urgency of intervention:
- Type I with large CPAM volume ratios (CVR ≥1.6) typically requires emergency surgery on day 1-2 of life due to respiratory failure 4
- Type II commonly presents with respiratory distress in neonates and has the highest association with other congenital anomalies 1, 2
- Type III presents as space-occupying lesions causing early postnatal respiratory distress requiring immediate surgical intervention 6, 1
- All types carry a small but documented risk (0.7%) of malignant transformation, making early surgical resection important 5
Diagnostic Differentiation
Prenatal ultrasound and fetal MRI are essential for identifying CPAM type prenatally, with T2-weighted MRI particularly useful for distinguishing solid versus cystic components 6, 4. Echocardiography should be performed to evaluate for associated cardiac anomalies and hemodynamic effects, particularly in Type II cases 6.