Pseudoangiomatous stromal hyperplasia

Pseudoangiomatous stromal hyperplasia (PASH) is a benign, relatively uncommon form of stromal (mesenchymal) overgrowth within breast tissue that derives from a possible hormonal aetiology. 

Typically affects women of reproductive age. It rarely affects males.

The tumoral form of PASH commonly manifests as a single, circumscribed, palpable mass in a premenopausal female. The mass can be large (5-6 cm in diameter), with reported diameters ranging from 1-12 cm.

It represents a clinicopathologic spectrum ranging from focal, incidental microscopic findings to clinically and mammographically evident breast masses. The development of PASH is presumed to be related to the interaction of progesterone in oestrogen-activated tissue, and involved tissue contains oestrogen and progesterone receptors. Lesions can be microscopic or nodular (tumourous).

Macroscopic appearance

On a gross pathological cut slice, tumourous PASH is typically a well-circumscribed, firm, rubbery mass with solid, homogenous, gray-white cut surface. 

Microscopic appearance

PASH can be a relatively common incidental finding at breast biopsy. On histology, it is characterised by the presence of open slit-like spaces in dense collagenous stroma which is lined by a discontinuous layer of flat, spindle-shaped myofibroblasts with bland nuclei. It can also contain complex anastomosing spaces that may be confused with an angiosarcoma at histologic analysis 11.

Imaging features are not sufficiently specific to allow for a prospective diagnosis. Histological confirmation, preferably with core biopsy, should always be considered 5.

Mammography

Often it is seen as a circumscribed or partly circumscribed mass. Lesions typically lack calcification 3-4

Ultrasound

May be seen as a circumscribed mass. Often hypoechoic and may be slightly heterogeneous 4,11. Imaging appearance may be similar to that of fibroadenoma.

MRI

Features are often non-specific. Lesions may present as clumped non-mass-like regions of persistent enhancement on contrast-enhanced imaging 1.

Although mass lesions in PASH often grow over time and may recur after excisional biopsy, they are neither associated with malignancy nor considered to be premalignant lesions 11.


Breast imaging and pathology
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Article Information

rID: 12658
System: Breast
Section: Pathology
Tag: cases
Synonyms or Alternate Spellings:
  • Pseudoangiomatous stromal hyperplasia (PASH)
  • PASH

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