Axillary Pseudoangiomatous Stromal Hyperplasia (PASH): A case report in an adolescent female

A 17-year-old female presented with progressively enlarging left axillary swelling for several months. No history of trauma and her medical and family histories were unremarkable. On physical examination, there was a painless large left axillary soft pedunculated mass. No fever, pain, or skin changes. Breasts examination was normal.

Initial examination with ultrasound showed a large left axillary mass.  The mass is described as a large circumscribed, transversely oriented hypoechoic, oval mass showing mild vascularity measuring about 9.5 x 2.5 cm. No enlarged axillary lymph nodes. (Figure 1).

A limited left axillary mammogram showed a large well-circumscribed, non-calcified, homogenous, dense mass out bulging through the axilla (Figure 2).

Dynamic contrast-enhanced Magnetic Resonance Imaging (DCE-MRI) showed a large circumscribed left axillary mass exhibits low signal in T1 weighted images, a heterogeneous texture of low and high signal intensity in T2 weighted images with no cystic changes and showed no diffusion restriction in DWI. Dynamic MR with subtraction revealed a moderate heterogenous enhancement in early phase with mild increase enhancement in the delayed images ( type I persistent kinetic features) with slit like spaces that correspond to empty clefts within acellular hyalinized stroma represent pseudoangiomatous clefts; hence its name (Figure 3), both breasts are normal with no abnormal mass or enhancement.

Ultrasound-guided core needle biopsy using a 14 G was performed. The histopathologic examination revealed benign breast tissue with pseudo-angiomatous stromal hyperplasia illustrating stromal expansion and slit-like spaces, negative for atypia, in situ and invasive carcinoma (Figure 4)..

PASH is a benign, not uncommon mesenchymal proliferative breast condition [1]. The pathophysiology remains unclear and most likely related to hormonal stimuli.[2] PASH is usually asymptomatic and discovered incidentally; however, sometimes presented as a painless mass or rapidly enlarged breast. It's common in females of reproductive age and less frequently in males with gynecomastia.[3-9]

PASH can arise along the milk line where accessory breast tissue present [10].

Radiologically, it's challenging to differentiate PASH from other benign breast tissue. In ultrasound it appears as a well-circumscribed oval or round hypoechoic mass and sometimes, as an irregular hypoechoic or heterogeneous mass with cystic changes. On mammogram, it is seen as a partially or well-circumscribed mass or as an area of asymmetry. [2]. The appearance on MRI is nonspecific, PASH can appear as clumped, non-mass enhancement with persistent kinetics [11] or a mass that exhibits low or iso signal on T1 weighted image, high signal on T2 showing homogeneous enhancement with delayed persistent and plateau kinetics [2] and less frequently as foci of enhancement.

Due to the nonspecific appearance of PASH on imaging core needle biopsy is usually done.

however, a definite diagnosis is reached on excisional biopsy.

Histologically, it is composed of complex inter-anastomosing pseudoangiomatous slit-like spaces within the breast surrounded by spindle cells does not contain blood cells within and lacks cellular atypia or mitotic activity. It is essential to differentiate PASH from lesions like low-grade angiosarcoma that contain true vascular space [12] . Differentiation is based on immunochemical staining: PASH shows positivity for CD34, actin, vimentin, desmin, Bcl2, and progesterone receptor and negativity for factor VIII-related antigen, CD31, S100, and cytokeratins.[2] Differentiation from juvenile fibroadenoma and phyllodes based on the presence of slit-like fibrotic spaces; however, PASH has no characteristic appearance,so tissue biopsy is necessary for the final diagnosis[11]. We reviewed the literatures for PASH in adolescents, we found less than 25 cases were diagnosed in adolescence, presented as a breast mass or diffuse enlargement of the breast [13] [14]. Axillary PASH is extremely rare and only 10 cases were described in the literature. [2], all are in adults who are on oral contraceptive or has history of surgery. Our case is the first case reported as axillary PASH in adolescents.

Women with biopsy-proven PASH usually undergo follow-up imaging. Surgical excision may be considered for larger lesions with a good prognosis. The recurrence rate ranges from 7% to 26%.[1] our case is surgically removed due to its size and location and shows no recurrence in 6 months follow-up.

In conclusion, we have reported the first axillary PASH in adolescents. Therefore, PASH should be considered as a differential diagnosis of axillary mass along with lymph nodes and other benign lesions, especially in the presence of accessory breast tissue.

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