24th May 2025

Pseudoangiomatous Stromal Hyperplasia (PASH)

Pseuodangiomatous Stromal Hyperplasia (PASH) is a relatively uncommon benign breast condition, that usually affects women of reproductive age. PASH is characterised by a benign proliferation of stromal tissue that mimics a vascular lesion. Typically, it is asymptomatic and therefore, is usually an incidental finding during clinical examination and/or imaging. Whilst hormonal changes are thought to be responsible, the exact aetiology is unknown.

Clinical examination typically reveals a single, painless, well circumscribed mass of varying size, ranging from anywhere between 1cm and 12cm anecdotally. Imaging (both mammography and ultrasound) demonstrates a round, well circumscribed, non-calcified mass, features which are largely non-specific and therefore, histological confirmation is often warranted.

Histology reveals a pattern of slit-like spaces, set within a dense collagenous stroma and lined by spindle shaped myofibroblasts with bland nuclei. The slit-like spaces may resemble vascular channels and as such, PASH may be confused with low grade angiosarcoma.

PASH does not carry an increased risk of breast cancer and for the majority of patients, no treatment or follow-up is indicated. Further assessment is usually reserved for any patients that notice a change in size or character of the lump.