Residency Program - Case of the Month

Answer:

Congenital Pulmonary Airway Malformation, Type II

Discussion:

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 [1]. 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 [2]. 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 [3]. Diagnosis may occur prenatally on ultrasound, in the neonate with respiratory distress, or in an adult who presents with pulmonary infection.

Differential Diagnosis:

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 [4].  Other developmental anomalies include bronchogenic cysts which usually present as single cysts within the mediastinum and always have associated hyaline cartilage.

References:

1. Zylak CJ, Eyler WR, Spizarny DL, Stone CH. Developmental lung anomalies in the adult: radiologic-pathologic correlation. Radiographics 2002; 22 Spec No:S25.

2. Cangiarella J, Greco MA, Askin F, et al. Congenital cystic adenomatoid malformation of the lung: insights into the pathogenesis utilizing quantitative analysis of vascular marker CD34 (QBEND-10) and cell proliferation marker MIB-1. Mod Pathol 1995; 8:913.

3. Stocker JT, Madewell JE, Drake RM. Congenital cystic adenomatoid malformation of the lung. Classification and morphologic spectrum. Hum Pathol 1977; 8:155.

4. Nuchtern JG, Harberg FJ. Congenital lung cysts. Semin Pediatr Surg 1994; 3:233.