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Micronodular pneumocyte hyperplasia

Author: Roseann I. Wu, M.D., M.P.H.

Last author update: 1 July 2016

Last staff update: 18 September 2023

Copyright: 2002-2024, PathologyOutlines.com, Inc.

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Cite this page: Wu R. Micronodular pneumocyte hyperplasia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungtumormicronodpneumohyper.html. Accessed November 30th, 2024.

Definition / general

First recognized in 1991 by HH Popper (Histopathology 1991;18:347)
Benign, hamartomatous, multinodular proliferation of type II pneumocytes
Often associated with tuberous sclerosis complex
May coexist with lymphangioleiomyomatosis (LAM)

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

Terminology

Also called multifocal micronodular pneumocyte hyperplasia (MMPH)
Older terminology: acinar atypical adenomatoid proliferation of epithelium, multiple adenomatoid lesions, micronodular hyperplasia of type II pneumocytes

Epidemiology

Young and middle aged adults, predominantly women
Often associated with tuberous sclerosis complex but may be sporadic

Pathophysiology

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

Diagnosis

Histologic examination

Radiology description

Xray: multiple pulmonary nodules
CT: multiple diffuse, small, solid and ground glass pulmonary nodules that remain stable in short term follow-up (J Comput Assist Tomogr 2012;36:518)
Imaging may mimic miliary tuberculosis (Int J Clin Exp Pathol 2015;8:2165)

Prognostic factors

Typically indolent with no clinical significance
Rare case studies report respiratory failure

Case reports

13 year old girl with tuberous sclerosis, renal cell carcinoma, angiomyolipomas and multifocal micronodular pneumocyte hyperplasia (Chem Pharm Bull (Tokyo) 1990;38:498)
16 year old girl with respiratory failure (Histopathology 2002;41:263)
51 year old woman with tuberous sclerosis complex but no classical clinical findings (J Med Case Rep 2012 Oct 16;6:352)

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.