Lung
Preinvasive
Atypical adenomatous hyperplasia
Author: Roseann Wu, M.D., M.P.H.
Topic Completed: 1 December 2016
Minor changes: 1 October 2021
Copyright: 2003-2021 PathologyOutlines.com, Inc.
PubMed Search: Bronchioloalveolar atypical adenomatous hyperplasia[title]
Table of Contents
Definition / general | Essential features | Terminology | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Prognostic factors | Case reports | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Cytology images | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Wu R. Atypical adenomatous hyperplasia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungtumorbronchAAH.html. Accessed October 15th, 2021.
Definition / general
- WHO: preinvasive adenomatous lesion ≤ 0.5 cm (J Thorac Oncol 2015 Sep;10:1243)
- Small atypical glandular proliferation in lung parenchyma associated with coexisting invasive adenocarcinoma
- May be precursor of nonmucinous adenocarcinoma in situ (AIS, formerly known as bronchioloalveolar carcinoma / BAC) and invasive adenocarcinoma (Hum Pathol 2002;33:697, Exp Ther Med 2012;4:1032, Am J Surg Pathol 1996;20:553)
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 club (Clara) cell type / type II pneumocyte type
- Adenocarcinoma in situ: preinvasive lesion > 0.5 cm
Epidemiology
- Incidence higher in patients with primary lung cancer (Thorax 2001;56:302, Br J Cancer 2000;83:632)
Sites
- Peripheral lung parenchyma
Pathophysiology
- Proposed stepwise progression from AAH to AIS to invasive adenocarcinoma
Etiology
- Arises from nonciliated bronchiolar (club) 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
- 12 year old girl with incidental AAH upon surgery for bullae (Korean J Thorac Cardiovasc Surg 2016;49:141)
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
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
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
- May show some genetic alterations similar to adenocarcinomas (Am J Clin Pathol 1999;111:610, Mod Pathol 2007;20:967)
Differential diagnosis
- Reactive / regenerative lesions i.e. lambertosis, chemotherapy, diffuse alveolar damage: interstitial inflammation
- Micronodular pneumocyte hyperplasia: lacks nuclear atypia
- Adenocarcinoma in situ: uniformly atypical nuclei, > 5 mm size, complex growth, budding / tufting of tumor cells in alveoli
Additional references
- AAH in autopsy cases (Lung Cancer 2001;33:155)
- Case series of patients with five or more AAHs (J Thorac Oncol 2010;5:466)
