Other tumors

Micronodular pneumocyte hyperplasia

Topic Completed: 1 July 2016

Minor changes: 10 September 2021

Copyright: 2002-2021,, Inc.

PubMed Search: Micronodular pneumocyte hyperplasia

Roseann Wu, M.D., M.P.H.
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Cite this page: Wu R. Micronodular pneumocyte hyperplasia. website. Accessed October 25th, 2021.
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<br>showing white tinged lesions

Figure A: Macroscopic examination
showing white tinged lesions

Microscopic (histologic) 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
Microscopic (histologic) images

Contributed by Roseann Wu, M.D., M.P.H.
Micronodular pneumocyte hyperplasia

Micronodular pneumocyte hyperplasia

TTF1 stain

TTF1 stain

Images hosted on other servers:
Morphology of pulmonary lesions

Morphology of pulmonary lesions

Multifocal micronodular pneumocyte hyperplasia

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
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