Pseudoangiomatous stromal hyperplasia

Last revised by Joshua Yap on 7 Feb 2023

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

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 estrogen-activated tissue, and involved tissue contains estrogen and progesterone receptors. Lesions can be microscopic or nodular (tumourous).

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

PASH can be a relatively common incidental finding at breast biopsy. On histology, it is characterized 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 a low-grade angiosarcoma at histologic analysis 11.

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

Most often it is a circumscribed or partly circumscribed mass. However, they often present as an asymmetry/focal asymmetry 6,13. Lesions typically lack calcification 3,4

Most often it is an oval or round circumscribed mass. Often hypoechoic and may be slightly heterogeneous 4,11. Imaging appearance may be similar to that of fibroadenoma.

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 in 10% of cases 3, they are neither associated with malignancy nor considered to be premalignant lesions 11.

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Cases and figures

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