Atypical adenomatous hyperplasia

Topic Completed: 1 December 2016

Minor changes: 1 October 2021

Copyright: 2003-2022, Inc.

PubMed Search: Bronchioloalveolar atypical adenomatous hyperplasia[title]

Roseann Wu, M.D., M.P.H.
Page views in 2021: 9,237
Page views in 2022 to date: 426
Cite this page: Wu R. Atypical adenomatous hyperplasia. website. Accessed January 21st, 2022.
Definition / general
Essential features
  • Along a spectrum with AIS, AAH is considered a precursor to and associated with invasive adenocarcinoma
  • AAH is a ≤ 0.5 cm atypical proliferation of cuboidal cells along alveoli that is distinct from the surrounding lung
  • AAH tends to be multifocal, asymptomatic and incidentally found on resection specimens
  • Also called in past: bronchioloalveolar adenoma, atypical alveolar cuboidal cell hyperplasia, atypical bronchioloalveolar hyperplasia, atypical alveolar epithelial hyperplasia, atypical alveolar cell hyperplasia, alveolar intraepithelial neoplasia, well differentiated bronchioloalveolar carcinoma of club (Clara) cell type / type II pneumocyte type
  • Adenocarcinoma in situ: preinvasive lesion > 0.5 cm
  • Peripheral lung parenchyma
  • Proposed stepwise progression from AAH to AIS to invasive adenocarcinoma
  • Arises from nonciliated bronchiolar (club) cells, type II pneumocytes or progenitor cells
Clinical features
  • Asymptomatic in isolation
  • Incidental finding on specimens resected for other reasons, particularly for lung cancer
Prognostic factors
  • Prognosis driven by any associated invasive carcinoma
Case reports
  • Close followup for development of (additional) lung cancers
Gross description
  • Tend to be multifocal but indistinct on gross examination, tan or white lesions measuring a few millimeters
Microscopic (histologic) description
  • More sharply circumscribed from surrounding lung than inflammatory lesions
  • Spreads along preexisting alveoli, with alveolar lining cells replaced by rounded low cuboidal cells with uniform, variably atypical nuclei, scant cytoplasm, minimal mitotic figures
  • Hyperchromatic nuclei, prominent nucleoli, intranuclear inclusions may be seen
  • Nuclear atypia and crowding less homogenous / severe as compared to adenocarcinomas
Microscopic (histologic) images

Contributed by Roseann Wu, M.D., M.P.H.
Lung AAH Lung AAH

Lung AAH

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Spectrum of AAH to adenocarcinoma

Spectrum of AAH to adenocarcinoma

Cytology images

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FNA shows sheet-like collection
of monotonous pneumocytes with
no overt features of malignancy (Pap)

Molecular / cytogenetics description
Differential diagnosis
Additional references
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