Pseudoangiomatous Stromal Hyperplasia
Key Facts
Terminology
Pseudoangiomatous stromal hyperplasia (PASH)
Proliferation of stromal myofibroblasts forming clefts that resemble vascular spaces
Etiology/Pathogenesis
Majority of affected persons are women of childbearing age
Postmenopausal women taking hormonal therapy may also be affected
Similar stromal changes are seen in gynecomastia and juvenile hyperplasia
Clinical Issues
May be incidental finding in approximately 23% of biopsies
PASH can also form palpable masses or radiographic densities
Masses are circumscribed or ill defined
Frequently grow in size
Microscopic Pathology
Prominent slit-like stromal clefts are present
Immunoperoxidase studies will confirm that cells are myofibroblasts
Top Differential Diagnoses
Angiosarcoma
Myofibroblastoma
Fibrous tumors
Diagnostic Checklist
Most important lesion in differential diagnosis is angiosarcoma
 Some cases of PASH form firm rubbery circumscribed masses. This lesion has been bisected to show the white whorled surface of the tumor  within an area of yellow adipose tissue  . |
 The stromal myofibroblasts forming PASH surround normal ducts and lobules and are associated with characteristic clefts. In this case, there is a discrete mass with a circumscribed border  . |
TERMINOLOGY
Abbreviations
Pseudoangiomatous stromal hyperplasia (PASH)
Synonyms
Pseudoangiomatous hyperplasia of mammary stroma
Nodular myofibroblastic stromal hyperplasia
Nodular or tumorous PASH
Definitions
Proliferation of myofibroblasts associated with stromal clefts that resemble vascular spaces
ETIOLOGY/PATHOGENESIS
Possible Relation to Hormonal Milieu
Occurs most frequently in women of childbearing age
Postmenopausal women receiving hormonal therapy may also be affected
Similar stromal changes are often present in gynecomastia and juvenile hyperplasia
Thus, stromal proliferation of myofibroblasts is likely due to hormonal stimulation or hormonal imbalance
It has been suggested that the clefts are prelymphatic channels that drain into true lymphatics
Some carcinomas invade with pattern suggesting that they involve clefts seen in PASH
CLINICAL ISSUES
Presentation
May be incidental finding in approximately 23% of biopsies
Also forms palpable masses or radiographic densities (nodular or tumorous PASH)
Masses are circumscribed or ill defined
PASH frequently grows in size
Rapid growth can occur during pregnancy and may be associated with peau d’orange and skin necrosis
Treatment
Mass-forming PASH should be biopsied to exclude malignancy
After malignancy is excluded, no other treatment is necessary
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