Friday, September 10, 2010

Congenital Pulmonary Airway Malformation

Congenital pulmonary airway malformation (CPAM), formerly congenital cystic adenomatoid malformation (CCAM), is the most commonly diagnosed prenatal lung malformation. There is abnormal branching of the immature bronchioles and abnormal alveolar development. The immature airways usually communicate with the normal tracheobronchial tree, resulting in both cystic and solid areas.

The expanded classification of CPAM includes the original types 1, 2, and 3, and two new types: 0 and 4.
  • Type 0: Represents an abnormality of the trachea and mainstem bronchi. Incompatible with life.
  • Type 1: Represents an abnormality of the bronchial/proximal bronchiolar region. The most common type (60%). Single or multiple large cysts (2–10 cm in diameter) surrounded by smaller cysts and a compressed normal parenchyma. CT shows one or more large, air-filled cysts with or without gas-fluid levels. MR shows T2-hyperintense uni- or multilocular lesions with discrete walls.
  • Type 2: Represents an abnormality of the bronchiolar region. Small cysts (0.5 cm - 2 cm). Second most common type (20%). Frequently associated with other congenital anomalies. CT may show a gas-filled multicystic mass or a focal area of consolidation (our case). The MR appearance depends on the composition of the malformation and is variable.
  • Type 3: Represents an abnormality of the terminal bronchiolar/alveolar duct region. Third most common type (10%). Tiny cysts (< 0.2 cm in diameter). Frequently associated with other congenital anomalies. Associated with maternal polyhydramnios in ~80% of cases. Can involve an entire lobe or the whole lung. The tiny cysts are too small to resolve by CT; therefore, the lesion appears as a solid mass. MR shows a homogeneously T2-hyperintense solid mass with normal adjacent parenchyma.
  • Type 4: Represents an abnormality of the distal acinus or alveolar saccular/alveolus region. May or may not be the same thing as pleuropulmonary blastoma. Presents before 4 years of age. Sudden respiratory distress due to tension pneumothorax is a unique feature of this subtype. Imaging reveals a large lesion, usually localized to one lobe, with large air-filled cysts. Mediastinal shift may be out of proportion to the mild/absent symptoms.
It is important to remember that CPAM and sequestration can coexist and manifest as a mixed lesion, so a search for systemic arterial supply is helpful. Internal gas-fluid levels may be seen in any of the subtypes if there is superimposed infection.

The images shown here are from a neonate with a lung mass identified at prenatal ultrasound. The radiograph shows an oval lesion in the left lung base medially, which was confirmed by CT. Biopsy showed a type 2 CPAM.


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