The purpose of this study was to review cases of congenital cystic adenomatoid malformations (CCAMs) arising in children and adults, in order to assess the recently expanded classification system for these lesions and their association with malignant transformation. Of 28 CCAMs, there were 16 type 1, 4 type 2, and 8 type 4 lesions, 12 of which presented in adults. Five of 16 type 1 CCAMs were accompanied by microscopic foci of bronchioloalveolar carcinoma; two others showed focal mucous cell hyperplasia. In two further cases, foci of nonmucinous atypical adenomatous hyperplasia were identified in the adjacent lung parenchyma. The bronchioloalveolar carcinomas showed less cytologic atypia, proliferative activity (Ki-67), and p53 expression than a comparative group of bronchioloalveolar carcinomas arising de novo, but this was not statistically significant (p = 0.15). Neither bronchioloalveolar carcinomas nor hyperplasia was identified in type 2 or type 4 CCAMs. Four of the eight type 4 CCAMs showed focal stromal hypercellularity, and one case subsequently developed a pleuropulmonary blastoma. We conclude that classification according to the current system is of clinical value. Bronchioloalveolar carcinomas arise in association with type 1 CCAMs, but recurrence following resection is exceptional. Type 4 CCAMs show histologic overlap with grade 1 pleuropulmonary blastomas, and distinction between these entities may not be possible on histology alone. However, stromal cellularity in a type 4 CCAM should raise the possibility of blastomatous transformation.

Congenital cystic adenomatoid malformation (CCAM) of the lung is a congenital lesion that is sometimes complicated by bronchioloalveolar adenocarcinoma (BAC). In some cases foci of atypical goblet cell hyperplasia (AGCH) can be found within the cysts. It has been proposed that CCAM and AGCH predispose to the development of BAC. The present study used comparative genomic hybridization (CGH) to screen 22 cases of CCAM (epithelium, surrounding normal lung tissue, and both preneoplastic and neoplastic lesions) for chromosomal imbalances. Of these 22 cases, 10 were CCAM type 1, 10 were type 2, and 2 were type 3. Of the 10 cases of CCAM type 1, 2 were associated with AGCH, 1 was associated with atypical adenomatous hyperplasia (AAH) and associated tubular adenocarcinoma (AC), and 2 were associated with BAC (1 mucinous and 1 predominantly nonmucinous). The present study also involved immunohistochemistry for interleukin (IL)-13, IL-4 receptor-alpha (IL-4r alpha), cytokines involved in the differentiation of goblet cells, and mucin 2 protein (Muc2). Chromosomal aberrations were not detected in the epithelium or the surrounding normal lung tissue, whereas varying aberrations were found in the neoplastic lesions. The most frequent genomic imbalances observed in both AGCH and the carcinomas were gains in chromosomes 2 and 4. Interestingly, a predominance of gains was also reported in AC of nonsmokers. Chromosomal aberrations in AGCHs arising in CCAMs support their preneoplastic status. Nuclear expression of IL-13, IL-4r alpha, and Muc2 was detected in AGCH, whereas a cytoplasmic and nuclear reaction was seen in normal epithelium. This likely reflects an association with goblet cell differentiation, but it also drives proliferation in AGCH.

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Patients presented over a period of 7 years. There were five men and four women with mean age 68.2 years and age range 51-78 years. Tumours arose in the femur (6 cases), humerus (2 cases) and tibia (1 case). Three MRI patterns were identified: (1) type 1, a lesion with two distinct signal characteristics-hyperintense chondral and reduced SI dedifferentiated tumour (n=6); type 2, mainly reduced SI lesion-dedifferentiated tumour, with areas of signal void corresponding to matrix calcification (n=2); type 3, a heterogeneous lesion with no radiological evidence of underlying chondral tumour (n=1). T2-weighted or STIR MR sequences can identify areas of dedifferentiation, which should be the preferential site of pre-operative biopsy.

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