Residency Program - Case of the Month
February 2013 - Presented by Adam Stelling, M.D.
Congenital Pulmonary Airway Malformation, Type II
Congenital Pulmonary Airway Malformation (CPAM), also known as Congenital Cystic Adenomatoid malformation, is a developmental lung abnormality with a highly variable clinical presentation based on size, location, and subtype. Embryologically, CPAM is thought to be due to an overproliferation of primitive bronchioles with a suppression of apoptosis in the early pseudoglandular phase of development . Some investigators consider this to be caused by an arrest in maturation. In a study of nine infants with CPAM, the lesional tissue was stained with CD34 and MIB-1 to assess vascular development and cellular proliferation. Compared to controls, CPAM had asynchronous development showing hypovascularity and a high proliferative index . Typically, there are connections with the main bronchial tree and vascular supply is via the pulmonary circulation. The proximal-distal source of the lesion is thought to give rise to one of three classic subtypes. Type 1 malformations are the most common and have the best prognosis. They are defined by cysts >2 cm in diameter that are lined by pseudostratified ciliated columnar epithelia. In type 2 lesions, the cysts are <2 cm in diameter and are lined by ciliated simple cuboidal to columnar epithelia. The prognosis is worse due to a strong association with other foregut developmental anomalies such as esophageal atresia. Type 3 CPAMs are generally large, non-cystic, and havethe worst prognosis. Histologically, there are alveolar sized structures lined by non-cilliated cuboidal cells . Diagnosis may occur prenatally on ultrasound, in the neonate with respiratory distress, or in an adult who presents with pulmonary infection.
The primary differential diagnosis is Bronchopulmonary Sequestration. They may resemble CPAM when they appear cystic on imaging. However, unlike CPAM, sequestrations do not have connections to the tracheobronchial tree and blood supply comes from an anomalous systemic artery . Other developmental anomalies include bronchogenic cysts which usually present as single cysts within the mediastinum and always have associated hyaline cartilage.
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