Diagnosis: Atypical Adenomatous Hyperplasia

Radiologic Findings

Focal area of ground glass attenuation on LUL, which shows no remarkable interval size or configuration changes on 2 months follow-up CT scan.

Brief Review

Atypical Adenomatous Hyperplasia (AAH) of the human lung has been recently implicated as a possible precursor lesion of bronchioloalveolar carcinoma (BAC). The atypical adenomatous hyperplasia-adenocarcinoma sequence has been likened to the adenoma-carcinoma sequence in the large intestine. AAH is proliferative lesion of atypical epithelial cell along the alveolar septa & is commonly multifocal, and may explain multicentricity that is observed with some adenocarcinomas. AAH is the earliest lesion in stepwise development of BAC. AAH has been shown to have immunohistochemical, morphometric, flow cytometric and genetic abnormalities overlapping with adenocarcinoma. Certain population of AAH cells exhibits active proliferation, aneuploidy, 3p & 9p deletions & disruption of cell cycle control but p53 gene aberration or telomerase activation is absent or rare, if any.
AAH is usually discovered incidentally at microscopic exam of surgically resected specimen.
On CT scan, AAH shows small pulmonary nodule with ground-glass attenuation (GGA) which may be due to partial reduction of alveolar air-space owing to increase in cellular component within the lesion.

References

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