atypical adenomatous hyperplasia of the lung

Atypical adenomatous hyperplasia (AAH) of the lung is a putative precursor lesion of adenocarcinoma of the lung. This entity replaces part of a spectrum of the former bronchoalveolar carcinoma (BAC).


AAHs are represented by localized small cell proliferation, usually measuring ≤0.5 cm, of mildly to moderately atypical type II pneumocytes and/or Clara cells that line along the alveolar walls, alveolar septae, or respiratory bronchiole . Subgrading of those lesions according to the spectrum of cellularity and atypia is not recommended .

Radiographic features 

Their radiographic appearances can be somewhat variable but have been commonly described as ground-glass nodules measuring less than 5 mm , opposed to adenocarcinomas in situ, which are also pre-invasive lesions, that tend to be larger.

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