Breast nonmalignant
Nonneoplastic changes
Pseudoangiomatous stromal hyperplasia

Topic Completed: 1 April 2010

Revised: 4 September 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Pseudoangiomatous stromal hyperplasia [title] breast

Hind Warzecha, M.D.
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Cite this page: Warzecha H. Pseudoangiomatous stromal hyperplasia . website. Accessed December 11th, 2019.
Definition / general
  • Benign lesion of complex, anastomosing, slit-like spaces, that are either acellular or composed of spindled cells
  • First described in 1986 (Hum Pathol 1986;17:185)
  • Also called pseudoangiomatous hyperplasia of mammary stroma
  • PASH phenomenon: cases in which PASH is an incidental microscopic finding (up to 23% of breast surgicals)
  • Myofibroblastic origin
Clinical features
  • Usually an incidental finding but may produce nodular lesions or have rapid growth
Radiology images

Contributed by Dr. Mark R. Wick


Case reports
Gross description
  • Usually unilateral, well circumscribed, external surface may resemble a capsule; 2 - 15 cm
  • Cut surface is firm, gray white, resembles fibroadenoma
  • No hemorrhage or necrosis
Gross images

Images hosted on other servers:

Nodular lesion

Multiple nodules (fig 2)

Microscopic (histologic) description
  • Proliferation of stromal elements (fibroblastic / myofibroblastic) mixed with breast ducts
  • Dense keloid-like stroma has anastomosing pattern of slit-like clefts (empty spaces) lined by single layer of flat spindle cells simulating vascular spaces
  • Single cells may form delicate bridges between the walls of a space
  • Cellular areas or plump spindle cells may obscure pseudoangiomatous structure
  • Often gynecomastia-like changes (Mod Pathol 2008;21:201)
  • Associated with columnar cell lesion (Int J Clin Exp Pathol 2009;3:87)
  • Rarely multinucleated giant cells (Breast J 2007;13:568)
  • No mitotic figures, no necrosis, no atypia
Microscopic (histologic) images

Contributed by Dr. Mark R. Wick

Various images

 AFIP images

Spindle cells at margins of slit-like spaces

Clefts and anastomosing
spaces in dense
collagenous stroma (small
blood vessel at arrow)

Images hosted on other servers:

Anastomosing pattern of slit-like spaces

Spindle cells at margins of slit-like spaces

With columnar cell lesion

Various images

Clefts (but not endothelium) are CD31 negative

Spindle cells (not ductal cells) are cytokeratin negative

Vimentin+ spindle cells

ER-beta positive


With gynecomastia (A: vimentin, B: CD34)

Cytology description
  • Moderately cellular with cohesive clusters of bland ductal cells (occasionally with staghorn pattern), single naked nuclei, some spindle cells with moderate cytoplasm and fine chromatin
  • Occasional loose hypocellular stromal tissue fragments containing spindle cells and paired elongated nuclei in fibrillary matrix (Acta Cytol 2003;47:373)
  • Findings can confirm benign nature of disease but are nonspecific, resembling fibroadenoma or phyllodes tumor (Indian J Pathol Microbiol 2005;48:260)
  • Finding plump spindled mesenchymal cells is suggestive (Diagn Cytopathol 2005;32:345)
Negative stains
Electron microscopy description
  • Spaces are not true vascular channels but due to disruption and separation of stromal collagen fibers
Differential diagnosis
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