In 1977, Stocker, et al. [2] described 35 cases of CCAM and divided them into three groups based on clinical and pathological features. Type 1, the most frequently occurring, were lesions that presented in the first hours to days of life and consisted of large cysts composed of walls lined with respiratory epithelium interspersed with tuft-like collections of mucogenic cells. Type 2 were composed of back-to-back bronchiolar-like structures and were associated with other anomalies, which are often severe (e.g. bilateral renal agenesis), in almost 50% of cases. Type 3 were the true adenomatoid lesion of Ch’in and Tang [1] which were often so large as to result in compression and hypoplasia of the other lobes of the lung. Basis for new and expanded classification of congenital pulmonary airway malformation During the period following the publication of the classification of CCAM,w250 cases of cystic and noncystic malformations of the lung were reviewed, and it was determined that there were a significant number of cases within this set that were different enough clinically, radiographically and morphologically (tables 3 and 4) to encompass two other groups of lesion, leading to the proposal of a new classification incorporating five types [3, 4]. In addition, the morphological appearance of the five types suggested differing sites of origin of the lesions within the developing tracheobronchial tree (fig. 1). The expanded classification also included a new term to replace CCAM. Stocker [4] suggested renaming this group of malformations congenital pulmonary airway malformation (CPAM), since only one of the types (type 3) is adenomatoid and only three (types 1, 2 and 4) are cystic. The first lesion in this new classification, called CPAM type 0, is a rarely occurring malformation originally described, by Rutledge and Jensen [5], as acinar dysplasia. The lesion consists of abnormally formed bronchial structures surrounded by loose vascular mesenchyme. There is little development beyond the bronchial stage and the lesion is incompatible with life. CPAM type 4, the other new type, consists of multiple large cysts lined only with type 1 and 2 alveolar cells over a wall composed of loose-to-dense mesenchyme containing multiple large-to-small vessels. Children with CPAM type 4 vary in age at presentation from 1 day to 4 yrs, with y25% presenting in the first week of life, 45% between 1 week and 6 months, and the remaining 30% between 15 months and 4 yrs. Most children display various degrees of respiratory distress, including sudden respiratory distress Table 2. – Pseudocystic or pseudopulmonary lesions CPAM type 0 CPAM type 3 Infantile lobar emphysema Congenital diaphragmatic hernia Long-standing "healed" bronchopulmonary dysplasia Bronchogenic cyst Pneumothorax Pneumomediastinum Pneumopericardium Respiratory syncytial virus pneumonia (with air-trapping) Bronchiectasis, as with cystic fibrosis Lymphangioma/vascular malformation CPAM: congenital pulmonary airway malformation. J.T. STOCKER, A.N. HUSAIN 2