Other nonneoplastic
Pseudoangiomatous stromal hyperplasia

Topic Completed: 21 April 2020

Minor changes: 21 April 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Pseudoangiomatous stromal hyperplasia [TI] free full text[sb]

Indu Agarwal, M.D.
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Cite this page: Agarwal I, Blanco L. Pseudoangiomatous stromal hyperplasia. website. Accessed April 15th, 2021.
Definition / general
  • Benign myofibroblastic proliferation simulating a vascular lesion
  • First described in 1986 (Hum Pathol 1986;17:185)
Essential features
  • Benign myofibroblastic proliferation simulating a vascular lesion
  • Usually an incidental finding but may produce palpable or mammographic mass
  • Complex interanastomosing spaces in dense collagenous, keloid-like stroma
  • Some of these spaces have spindle shaped myofibroblasts at their margins that simulate endothelial cells
  • Spindle cells are positive for ER, PR and CD34 but negative for other vascular markers, e.g. CD31
  • Also called pseudoangiomatous hyperplasia of mammary stroma
  • PASH is an incidental microscopic finding in up to 23% of breast surgical resections (Int J Surg 2011;9:20)
  • Breast stroma
Clinical features
  • Histologic examination of resected tissue
Radiology description
  • May produce a mammographically detected mass
Radiology images

Contributed by Mark R. Wick, M.D.
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Round mass

Prognostic factors
  • Nonneoplastic but mass forming lesion may rarely recur, especially in younger patients
Case reports
Gross description
Gross images

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Well demarcated lesion

Microscopic (histologic) description
  • Complex interanastomosing spaces in dense collagenous, keloid-like stroma
  • Some of these spaces have spindle shaped myofibroblasts at their margins that simulate endothelial cells
  • Spaces are usually empty but may contain rare erythrocytes
  • 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
  • Fascicular PASH: cellular variant, in which myofibroblasts aggregate into fascicles with reduced or absent clefting, resembles myofibroblastoma
Microscopic (histologic) images

Contributed by Indu Agarwal, M.D.
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Interlobular PASH

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Slit-like spaces

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Spindle cells lining the spaces

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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
Sample pathology report
  • Left breast, at 5 o'clock and 4 cm from the nipple, ultrasound core needle biopsy:
    • Breast tissue with pseudoangiomatous stromal hyperplasia
Differential diagnosis
  • Low grade angiosarcoma:
    • Hemorrhagic, soft, interanastomosing vascular channels containing red blood cells with invasion into breast parenchyma
    • Papillary endothelial growth and hyperchromatic endothelial cells
    • CD31+, factor VIII+ (Arch Pathol Lab Med 2009;133:1335)
  • Myofibroblastoma:
    • Neoplastic clonal tumors with characteristic genetic change (del 13q14) (this can be demonstrated by loss of Rb protein immunohistochemistry in myofibroblastoma)
    • Solid mass of spindle cells which surrounds and involves ducts and lobules
  • Other spindle cell tumors e.g. fibromatosis:
    • Tumor cells arranged in long fascicles without significant clefting, nuclear beta catenin staining and CD34-
Board review style question #1

    The finding shown in the image above was obtained on the core needle biopsy of the breast in a 35 year old woman. What is the most likely mammographic finding?

  1. Architectural distortion
  2. Calcifications
  3. Irregular mass
  4. Mass with smooth borders
  5. No abnormality, incidental finding
Board review style answer #1
E. No abnormality, incidental finding

Pseudoangiomatous hyperplasia is usually an incidental finding but may less commonly produce palpable or mammographic mass.

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Reference: Pseudoangiomatous stromal hyperplasia
Board review style question #2
    Which of the following set of immunohistochemical stains would be most suitable for the diagnosis of pseudoangiomatous hyperplasia (PASH)?

  1. CD34-, CD31-, ER-, nuclear beta-catenin+
  2. CD34-, CD31-, nuclear beta catenin+, AE1 / AE3+
  3. CD34+, CD31-, ER+, factor VIII-
  4. CD34+, CD31+, ER-, factor VIII+
Board review style answer #2
C. CD34+, CD31-, ER+, factor VIII-

The immunoprofile in option D is most consistent with angiosarcoma or other vascular lesions, with positive vascular markers. Option A is the immunoprofile for fibromatosis with positive nuclear beta catenin. It is important to note that fibromatosis is negative for CD34 as it does not arise from myofibroblasts. Option B is the classic staining pattern for a spindle cell carcinoma with positive AE1 / AE3.

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Reference: Pseudoangiomatous stromal hyperplasia
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