Lung tumor
Dysplasia / carcinoma in situ
Bronchioloalveolar atypical adenomatous hyperplasia (AAH)

Author: Roseann Wu, M.D. (see Authors page)

Revised: 7 December 2016, last major update December 2016

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Bronchioloalveolar atypical adenomatous hyperplasia[title]

Cite this page: Bronchioalveolar atypical adenomatous hyperplasia. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/lungtumorbronchAAH.html. Accessed December 8th, 2016.
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
Terminology
  • 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 Clara cell type / type II pneumocyte type
  • Adenocarcinoma in situ: preinvasive lesion > 0.5 cm
Epidemiology
Sites
  • Peripheral lung parenchyma
Pathophysiology
  • Proposed stepwise progression from AAH to AIS to invasive adenocarcinoma
Etiology
  • Arises from nonciliated bronchiolar (Clara) cells, type II pneumocytes or progenitor cells
Clinical Features
  • Asymptomatic in isolation
Diagnosis
  • Incidental finding on specimens resected for other reasons, particularly for lung cancer
Prognostic Factors
  • Prognosis driven by any associated invasive carcinoma
Case Reports
Treatment
  • 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
Micro 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
Micro Images
Images hosted on PathOut server, courtesy of Roseann I. Wu, MD, MPH:

Lung AAH



Image hosted on other servers:

Spectrum of AAH to adenocarcinoma

Cytology Images
Image hosted on other servers:

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

Molecular / Cytogenetics Description
Differential Diagnosis
Additional References