Lung tumor
Benign tumors
Micronodular pneumocyte hyperplasia

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

Revised: 26 July 2016, last major update July 2016

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Micronodular pneumocyte hyperplasia

Cite this page: Micronodular pneumocyte hyperplasia. website. Accessed October 21st, 2016.
Definition / General
Essential Features
  • Rare pulmonary manifestation of tuberous sclerosis complex that may occur in conjunction with LAM
  • Composed of multiple nodules of enlarged but benign type II pneumocytes that may mimic atypical adenomatous hyperplasia
  • Positive for cytokeratins and TTF1 by immunohistochemical stains, while negative for SMA
  • Also called multifocal micronodular pneumocyte hyperplasia (MMPH)
  • Older terminology: acinar atypical adenomatoid proliferation of epithelium, multiple adenomatoid lesions, micronodular hyperplasia of type II pneumocytes
  • Young and middle aged adults, predominantly women
  • Often associated with tuberous sclerosis complex but may be sporadic
  • Functional loss of TSC 1 or TSC2 and hyperphosphorylation of mTOR related protein may cause this benign neoplastic proliferation of pneumocytes (Mod Pathol 2010;23:1251)
Clinical Features
  • Non-specific; may present with pneumothorax, shortness of breath, cough
  • Histologic examination
Radiology Description
Prognostic Factors
  • Typically indolent with no clinical significance
  • Rare case studies report respiratory failure
Case Reports
Gross Description
  • Small (1 - 10 mm), well-demarcated, randomly distributed parenchymal lung nodules
Gross Images

Images hosted on other servers:

Figure A: Macroscopic examination
showing white tinged lesions

Micro Description
  • Multiple, sharply demarcated or circumscribed nodules
  • Tubulopapillary proliferation of type II pneumocytes lining fibrotic and thickened alveolar septa, moderate lymphocytic infiltration, no nuclear atypia (Int J Surg Pathol 2010;18:522)
  • Enlarged type II pneumocytes with abundant eosinophilic cytoplasm, vesicular nuclei, distinct nucleoli, occasional eosinophilic inclusions
  • Increased alveolar macrophages
Micro Images

Images hosted on PathOut servers:

Courtesy of Roseann Wu, M.D., M.P.H.

Images hosted on other servers:

Various images

Morphology of pulmonary lesions

Multifocal micronodular pneumocyte hyperplasia

Positive Stains
  • Pan-cytokeratin, TTF1, EMA, surfactant apoproteins A and B
Negative Stains
Electron Microscopy Description
  • Osmiophilic lamellar inclusions and surface microvilli of type II pneumocytes
Molecular / Cytogenetics Description
Differential Diagnosis
Additional References