The classical histological change of CCAM is that normal pulmonary alveoli are replaced by cysts composed of adenomatoid hyperplastic bronchioles. Based on the size and number of the cysts, this lesion was initially classified into 3 groups . All types are intrinsically the same lesion, but vary on the radiological presentation. Type I CCAM accounts for 70% of cases, is characterized by single or multiple cysts more than 3 cm in diameter lined by pseudostratified ciliated columnar epithelium, along with mucous cells which are considered to potentially mutant to adenocarcinoma . Type II lesion is consisted of multiple terminal bronchiolar-like uniform cysts smaller than 2 cm in diameter, lined by cuboidal to columnar epithelium. Type III CCAM usually involves an entire lobe of lung and has a spongy-like appearance, constructed by bulk gland-like structures. Another 2 types were proposed in 2002 . The new classification system with added type 0 and IV was not widely applied because type 0 is very difficult to differentiate from bronchogenic cyst, and the similarities between type IV and cystic pluropulmonary blastoma may result in misdiagnosis . Late-onset CCAM in adults may be more complicated on radiographic images due to recurrent infections. In this report, case 1 was classified into Stocker's type II CCAM for its uniform size of the cysts and regular proliferation pattern of the bronchiolar epithelium (Figure 1, b, c). Case 2 met the diagnostic criteria of type I for its distinct pathology change that multicysts, containing at least one large cyst larger than 3 cm in diameter with smaller ones in its periphery, were lined by bronchial epithelium with discontinuous smooth muscle within the cystic walls (Figure 2, a, c).
In our report, aspergillus hyphea confirmed by GMS stain were discovered in case 1 (Figure 1, d), which is extremely rare in CCAM cases. By far, bacterial infection is the most frequently reported CCAM complication which causes acute fever and lung abscess . To our knowledge, an aspergilloma within CCAM have been previously documented only in one case . Presentations of aspergillosis may be varied from that of bacterial infection. It may either produce a fulminant invasive pulmonary infection or quietly coexisting for year in the human host without symptoms. Aspergillosis may display cystic cavities or one solid mass on the CT scan that resemble lung tumor or tuberculoma. In this case, aspergillus caused localized tissue damage and produced massive exudates and necrotic debris that constituted areas of consolidation mixed into the cystic lesion, making a complex CT scan image. However, multicysts with uniform size and adenomatoid hyperplastic bronchial structures revealed by gross and histological examination led to the diagnosis of cystic malformation.
In case 2 we presented with, the lesion involving bilateral lobes of the lung is also uncommonly encountered. In CCAM associated literatures, a few bilateral CCAM cases in adult patients have been reported [11–13]. Bilateral CCAM may appear like interstitial pneumonia because of similar CT scan presentations showing grid-like opacity through the entire lung fields. The extensive involvement of the lesion increased risk and difficulty of the surgery. Therefore, most patients with such lesions are treated with conservative treatment after diagnosis confirmed by lung biopsy. In this report, the patient of case 2 was initially diagnosed as "interstitial pneumonia with bulla formation", due to the ventilating dysfunction associated clinical presentations and the thin-walled multicysitc lesion with fibrosis-like change of the peripheral lung tissue. However, an open lung biopsy revealed proliferative malformation rather than interstitial pneumonia. It is noticeable that the patient's mother had also been previously discovered multicystic lesions in bilateral lower lobes of the lung, indicated that the disease might have some kind of familial relevance. Up till now, the exact mechanisms of CCAM remain unknown, but Roberts et al. suggested that this lesion might be familial and related to chromosome abnormalities . Although the result of karyotype analysis in this case was unremarkable, the possibility that this congenital lesion might be heritable or related to chromosome or genetic malfunction could not be completely ruled out.