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Pseudoangiomatous stromal hyperplasia (PASH) is a benign proliferative lesion of the breast stroma characterized histologically by dense collagenous stroma with slit-like spaces mimicking vascular channels, but not lined by true endothelial cells.
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It most commonly affects premenopausal women, and is often discovered incidentally or as a palpable mass.
Epidemiology:
| Feature | Details |
|---|---|
| Age | Most common in premenopausal women (30–50 years) |
| Association | Often incidental finding; may be related to hormonal changes, oral contraceptives, or HRT |
| Risk | Not premalignant; no increased risk of carcinoma |
Histopathology
| Feature | Description |
|---|---|
| Architecture | Dense collagenous stroma with inter-anastomosing slit-like spaces |
| Lining | Myoid spindle cells (not endothelium) |
| IHC staining | Positive for CD34, vimentin, smooth muscle actin (SMA); negative for CD31 (rules out vascular tumor) |
| Type | Features |
|---|---|
| Focal/Incidental | Asymptomatic, microscopic lesion found on biopsy for other reasons |
| Mass-forming | Slow-growing, painless, palpable mass; mobile and well-circumscribed |
| Diffuse/juvenile variant | Rare, can cause massive breast enlargement in adolescents (PASH mastopathy) |
| Modality | Imaging features |
|---|---|
| Mammography | Often indistinguishable from fibroadenoma |
| • Shape: Oval or round, well-circumscribed mass | |
| • Density: Equal or slightly higher than breast tissue | |
| US | • Echotexture: Hypoechoic, oval, well-defined mass |
| • Orientation: Often parallel to skin (wider-than-tall) | |
| • Internal pattern: May have homogeneous or heterogeneous echotexture; occasional posterior enhancement | |
| • Vascularity: Typically avascular or minimally vascular on Doppler | |
| MR | Used for problem-solving or evaluating extent in diffuse cases |
| • Variable enhancement; sometimes shows persistent enhancement pattern (Type I) |
Pseudoangiomatous stromal hyperplasia. A 41-year-old woman presented with a palpable breast mass. Mediolateral oblique mammogram (a) shows a high-density well-circumscribed mass (arrow). Longitudinal grayscale ultrasound (b) shows a large, oval circumscribed mass. Core needle biopsy showed pseudoangiomatous stromal hyperplasia (PASH). A different patient, a 40-year-old woman, was found to have a new breast mass (arrow) on mammography, craniocaudal spot view (c). Transverse grayscale (d) ultrasound reveals a corresponding oval isoechoic circumscribed mass. Core needle biopsy showed PASH
Guirguis, M.S., Adrada, B., Santiago, L. et al. Mimickers of breast malignancy: imaging findings, pathologic concordance and clinical management. Insights Imaging 12, 53 (2021). https://doi.org/10.1186/s13244-021-00991-x
Incidentally detected nodular pseudoangiomatous stromal hyperplasia in a patient with mastalgia. Craniocaudal and mediolateral oblique images of left breast (A, B) show an oval equal density lesion with circumscribed margins in upper outer quadrant, showing no significant enhancement on recombined postcontrast images (C, D). On ultrasonography, the lesion appears hypoechoic with indistinct margins and cystic spaces (E), shows mild vascularity (F), and is soft on elastography (G). On magnetic resonance imaging, the lesion shows intermediate signal intensity on axial T1-weighted (H) and T2-weighted inversion recovery (I) images with no diffusion restriction on diffusion-weighted image and apparent diffusion coefficient map (arrow in J, K). On early and delayed postcontrast subtracted images, minimal enhancement is observed (arrowhead in L, M). (N) Photomicrograph (40× magnification; hematoxylin and eosin stain) showing collagenized sparsely cellular stroma with slit-like spaces (arrow) rimmed by spindled myofibroblasts (arrowhead).
Parameswaran PR, Rupa Renganathan, Subramaniam P, Thakur V. Radiological Spectrum of Pseudoangiomatous Stromal Hyperplasia of Breast—A Case Series. Indian journal of radiology and imaging - new series/Indian journal of radiology and imaging/Indian Journal of Radiology & Imaging. 2022;32(04):582-590. doi:https://doi.org/10.1055/s-0042-1750174