PATHOLOGY OF CYSTIC ADENOMATOID

MALFORMATION (CAML)

CAML has been classified into three subgroups based upon clinical, gross and histologic features (1,2).

Histologic features to all types of CAML include:

1. Adenomatoid increase in structures resembling terminal bronchioles.
2. Polypoid configuration of columnar (type I), mixed (type II), or cuboidal (type III) epithelial lining of cystic structures.
3. Proliferation of smooth muscle and elastic tissue in the cyst walls.
4. Absence of cartilage.
5. Absence of inflammation.

• Type I lesions contain relatively well differentiated bronchial components but no bronchial cartilage. The absence of bronchial cartilage signifies that the insult occurred prior to the 10th week of gestation.
• Type II lesions probably occur prior to 31 days of gestation based on the high frequency of associated structural anomalies involving other organ systems developing at this time.
• Type III lesions have minimal differentiation of epithelial and mesenchymal structures, suggesting that the embryologic insult occurred after the appearance of the two lung buds (between 26 and 28 days).

Microscopic criteria of CCAM

Proliferation of polypoid glandular epithelium

Proliferation of smooth muscle and elastic tissue in cyst walls

Absence of cartilage

Absence of inflammation

Normal arterial and venous connections.

REFERENCES

1. Miller RK, Sieber WK, Yunis EJ. Congenital cystic adenomatoid malformation of the lung: A report of 17 cases and review of the literature. Pathol Annu 1989;I:387-407.
2. Stocker JT, Madewell JE, Drake RM. Congenital cystic adenomatoid malformation of the lung. Hum Pathol 1977;8:155-171.