Tiger-Striped PASH: Recognition of a Unique Morphology Allows for a Zippered-Up Diagnosis of Pseudoangiomatous Stromal Hyperplasia of Breast

Abstract

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is histologically characterized by anastomosing and slit-like spaces invested by collagenous stroma and lined by flattened, spindle cells. These clear spaces that may mimic microscopic vascular channels do not contain red blood cells. Immunohistochemistry (IHC) studies may also help to confirm a diagnosis of PASH, with the spindled cells marking positively with CD34 and PR while demonstrating no reactivity with more specific endothelial antigens such as CD31 and ERG. In the current case, a 39-year-old female was diagnosed with cellular PASH of the right breast with unique histological patterns showing "tiger-striped" and "zippered" histologies. To our knowledge, this is the first report of these unique variant PASH morphologies.

Figure 1

(a) MRI of the right breast with IV gadolinium shows an oval enhancing mass in the upper inner right breast middle depth; (b) T2-weighted images show bright signal, though less bright than cysts seen elsewhere in the breast. Slit-like spaces are not definitely appreciated, possibly due to the small size of the finding. (c) Second-look ultrasound shows an oval, microlobulated, hypoechoic mass in the upper inner right breast, corresponding with that seen on MRI.

Figure 2

Low-power histologic assessment shows scattered nonneoplastic breast epithelial elements including scattered ducts and the edge of a terminal duct lobular unit with stromal expansion between and within these epithelial structures. Eosinophilic expanses of fibrous tissue are noted with linear arrangements of spindle cell nuclei resulting in a tiger-stripe-like pattern ((a) hematoxylin and eosin, 100X). At intermediate magnification, the nuclear arrangements with offset eosinophilic cytoplasmic bands emphasize the striped morphology ((b) hematoxylin and eosin, 200X).

Figure 3

High-power histologic assessment confirming a zippered morphology with interlacing lesional nuclei oriented perpendicular to the cleft space ((a) hematoxylin and eosin, 400X). The lesional spindled cells demonstrate diffuse and strong immunoreactivity with CD34 while the adjacent epithelium is nonreactive ((b) CD34 IHC, 600X). The lesional spindled cells also show immunoreactivity with progesterone receptor ((c) PR IHC, 600X).