A case of PASH presenting as unilateral breast enlargement

A 33-year-old woman consulted her gynaecologist because of unilateral right-sided mastodynia and redness of the breast.  There was no clinically visible asymmetry between both breasts. An ultrasound performed by the gynaecologist did not show any abnormalities and a tentative diagnosis of unilateral mastitis was made. Because the patient’s complaints persisted after a trial of antibiotic treatment, further investigations were carried out. Blood results were normal. A mammography was performed.

Mammography (images not available) showed dense glandular tissue, more pronounced on the right side, with a slightly larger right breast. Repeated ultrasound examination (Figure 1) showed asymmetrically enlarged dense heterogenous fibroglandular tissue on the right side, without signs of inflammation and without visualisation of suspicious lesions. There were no enlarged ducts nor axillary lymph nodes.

An additional MRI was performed. Axial T1-weighted image (Figure 2) showed a larger right breast. Axial T2-weighted MR image with fat suppression (Figure 3) demonstrated diffusely dispersed heterogeneous hyperintense signal alterations in all quadrants of the right breast. Dynamic T1-weighted gadolinium-enhanced image (Figure 4) revealed diffuse asymmetrical non-mass enhancement in the right breast with a type II enhancement curve (Figure 5) , mimicking possible malignancy.

MRI-guided vacuum-assisted biopsies were performed within the areas of asymmetrical enhancement revealing fibrous mammary parenchyma with local areas of PASH (pseudoangiomatous stromal hyperplasia) without evidence of carcinoma.

Background

Pseudoangiomatous stromal hyperplasia (PASH) is a benign overgrowth of stromal tissue within the breast of unknown aetiology, though it is believed that hormonal factors might play a role in its origin. [1] It is named after the slit-like pseudovascular spaces lined by spindle cells that can be appreciated on histological examination. [2] It is commonly found incidentally on microscopic studies or may present as asymmetry of the breasts. The tumoral form, which can present as clinically and radiologically evident masses, is more rare. [3]

Clinical Perspective

PASH mostly affects premenopausal women. [4,5] Since it is believed to be an excessive response of myofibroblasts to hormonal stimuli, it is associated with the use of oral contraceptives, hormonal replacement therapy (HRT) and the use of hormones associated with in vitro fertilization (IVF). [2]
It is commonly incidentally found on biopsies performed for other reasons, but when symptomatic, patients may present with gynaecomastia, asymmetrical breast enlargement or a palpable breast mass in case of the tumoral form of PASH. [3,5]

Imaging Perspective

The imaging characteristics of PASH are known to be non-specific and can vary widely. [2]
PASH may be seen on mammography as an asymmetric increase in density of the fibroglandular mammary tissue or it may present as a well-circumscribed mass. [2,4] Some cases are not detectable on mammography alone. [5]
On ultrasound, the tumoral form mostly presents as a well-circumscribed hypoechoic mass, possibly mimicking a benign lesion, such as a fibroadenoma. [6] However, other presentations such as ill-defined, hyperechoic or partially cystic lesions are also possible. [2]
MRI findings may range from a contrast-enhancing mass to non-mass-like enhancement, with persistent kinetics. [6] Lesions are mostly isointense on T1-weighted images and hyperintense on T2-weighted images, with a linear reticular ‘lace-like’ pattern. [2]
Imaging findings are not sufficiently specific and ultrasound- or MRI-guided biopsy is often necessary to confirm the diagnosis. [1]

Outcome

PASH is not a premalignant lesion [6] and routine surgical excision is not recommended. [8] However, literature reports of accompanying carcinoma exist, and it is important to exclude malignancy, especially ductal carcinoma in situ (DCIS). [2]
Recurrence after surgical excision is possible, probably due to incomplete excision.
In this case, the patient stopped the use of oral contraceptives, after which her symptoms diminished.

Take-Home Message / Teaching Points

PASH is a benign disorder that may present with asymmetry of the breasts or in rare cases as clinically and radiologically evident masses, possibly mimicking other benign lesions or malignancy. Imaging findings are not sufficiently specific and biopsy is often needed to confirm the diagnosis.

Written informed consent was obtained.