Pseudoangiomatous stromal hyperplasia (PASH) is a benign mesenchymal proliferative lesion of the breast. PASH is postulated to be hormonally induced and predominantly occurs in premenopausal women and postmenopausal women on menopausal hormone therapy. Clinical presentation varies from screen-detected lesions to palpable masses. Imaging findings of PASH are nonspecific. The most common mammographic findings are an oval or round circumscribed non-calcified mass or developing asymmetry. On US, PASH is often seen as an oval hypoechoic mass that may be circumscribed and can have an echogenic rim, or, when manifest as mammographic asymmetry, US may show a corresponding non-mass focal area of echogenic tissue. Limited studies have investigated the MRI appearance, with PASH most often manifesting as non-mass enhancement, or, less often, as an oval or irregular mass with persistent kinetics. Histopathologically, PASH can be mistaken for a fibroadenoma or phyllodes tumor and has features overlapping low-grade angiosarcoma. Assessment of radiologic-pathologic concordance is particularly important as PASH is often an incidental finding, adjacent to the targeted lesion at histopathology. Surgical excision or repeat core-needle biopsy is necessary for discordant suspicious cases. After a benign, concordant diagnosis of PASH, the patient may resume routine screening.
Keywords: PASH; pseudoangiomatous hyperplasia; radiologic-pathologic correlation.
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