Pseudoangiomatous Stromal Hyperplasia (PASH) Presenting as a Palpable Mass: A Clinical Insight

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 Pseudoangiomatous Stromal Hyperplasia (PASH) Presenting as a Palpable Mass: A Clinical Insight

Keywords: pseudoangiomatous stromal hyperplasia, PASH, benign breast tumor, palpable mass, breast ultrasound, core biopsy, surgical excision, stromal lesion, breast neoplasm, differential diagnosis

Introduction

Pseudoangiomatous Stromal Hyperplasia (PASH) is a rare, benign proliferative breast condition characterized by dense stromal proliferation forming complex slit-like spaces resembling vascular channels. Although typically an incidental histopathological finding, it may occasionally manifest as a rapidly enlarging palpable mass that mimics malignant neoplasms clinically and radiologically. This blog post provides an in-depth review of a clinically significant case of PASH, informed by the case report published in Frontiers in Surgery, offering key imaging findings, histologic characteristics, and clinical management considerations.

Case Overview

A 41-year-old woman presented with a rapidly enlarging, palpable mass in her left breast. The mass, first noticed a few months prior, grew significantly over a short duration, prompting clinical evaluation. Physical examination revealed a firm, mobile, non-tender lesion.

Figure 1. Mammography performed with craniocaudal (A) and mediolateral oblique (B) incidences of the left breast shows a huge well-defined mass located between the inner and the outer inferior quadrants, with no suspicious features.


Figure 2. Ultrasound of the left breast centered on the palpable lump shows an oval, heterogeneous lesion with smooth borders.

Mammography and ultrasound were performed. Imaging revealed a circumscribed, hypoechoic, and oval lesion within the left breast parenchyma. Despite its benign imaging features, its size and clinical progression warranted further histological assessment.

Histopathology and Diagnosis

A core needle biopsy was performed. Microscopic evaluation revealed dense collagenous stroma with inter-anastomosing slit-like spaces that mimicked vascular channels. Immunohistochemistry demonstrated spindle-shaped myofibroblasts that stained positive for CD34 and vimentin, but negative for endothelial markers such as CD31 and Factor VIII, confirming a diagnosis of PASH.

Figure 3. Microscopic examination showing a pseudo-vascular proliferation delineated by endothelial cells with canalar hyperplasia without atypia, without invasion of parenchyma.

Histologic hallmark of PASH - pseudoangiomatous slit-like channels with myofibroblastic lining.

Differential Diagnosis

PASH is often misinterpreted as low-grade angiosarcoma or phyllodes tumor due to its histological mimicry and presentation as a palpable mass. Key differentiators include the lack of cytologic atypia, mitotic activity, and endothelial marker positivity.

Other conditions in the differential diagnosis include:

  • Fibroadenoma

  • Phyllodes tumor

  • Angiosarcoma

  • Fibrocystic changes

  • Low-grade stromal sarcoma

Treatment and Prognosis

Given the tumor's benign nature and absence of malignant transformation, the treatment approach is conservative surgical excision. In this case, the lesion was completely excised, and no recurrence was noted during follow-up.

Although rare, recurrence may occur in cases where excision is incomplete. Hormonal influence (particularly progesterone) is speculated to play a role in lesion growth, especially in premenopausal women or those undergoing hormone replacement therapy.

Discussion

PASH often masquerades as more aggressive breast lesions. Hence, radiologists and surgeons must maintain a high index of suspicion and include PASH in the differential diagnosis for rapidly growing breast masses in women of reproductive age.

MRI may occasionally be utilized for surgical planning or when biopsy is inconclusive, although most cases are resolved with core biopsy and imaging. Long-term prognosis is excellent, with no documented cases of malignant transformation.

Clinical Significance and Recommendations

  • Accurate diagnosis requires a combination of imaging and histopathologic correlation.

  • Core needle biopsy remains essential in all rapidly growing breast masses to exclude malignancy.

  • Surgical excision is curative; routine follow-up is advised for larger or multifocal lesions.

  • Patient education is crucial to avoid unnecessary anxiety, particularly due to its imaging resemblance to cancer.

Questions and Explanations

Q1. Which immunohistochemical markers are most useful in confirming the diagnosis of PASH?

A. CD31 and Factor VIII
B. Cytokeratin and EMA
C. CD34 and Vimentin
D. Ki-67 and p53

Answer: C. CD34 and Vimentin
Explanation: CD34 and vimentin positivity indicate stromal myofibroblastic origin, characteristic of PASH. Unlike vascular tumors, PASH is negative for endothelial markers such as CD31 and Factor VIII.

Q2. What is the most common radiological feature of PASH on ultrasound?

A. Irregular, spiculated mass
B. Calcifications with acoustic shadowing
C. Well-circumscribed, hypoechoic lesion
D. Diffuse parenchymal thickening

Answer: C. Well-circumscribed, hypoechoic lesion
Explanation: PASH frequently presents as a hypoechoic, oval, or round mass that may resemble a fibroadenoma, making imaging alone insufficient for definitive diagnosis.

Q3. Which of the following is TRUE regarding the clinical course of PASH?

A. Always progresses to angiosarcoma
B. Requires chemotherapy in all cases
C. May recur if incompletely excised
D. Typically presents with nipple discharge

Answer: C. May recur if incompletely excised
Explanation: Although benign, PASH can recur, especially in cases of incomplete surgical excision. It does not undergo malignant transformation or require systemic therapy.

Conclusion

Pseudoangiomatous Stromal Hyperplasia (PASH) is a rare but important benign breast condition that mimics malignancy in imaging and clinical presentation. Accurate diagnosis through core biopsy and histopathology is crucial. With appropriate surgical management, the prognosis is excellent. Awareness among radiologists, pathologists, and surgeons can reduce unnecessary interventions and patient anxiety.

References

  1. I. Powell et al., “Pseudoangiomatous stromal hyperplasia: imaging and pathologic correlation,” AJR Am J Roentgenol, vol. 180, no. 2, pp. 437–441, 2003.

  2. H. Badan, et al., “Pseudoangiomatous stromal hyperplasia of the breast: A case report and literature review,” Int J Surg Case Rep, vol. 50, pp. 25–28, 2018.

  3. Y. Jones et al., “Pseudoangiomatous stromal hyperplasia: a case series with clinical follow-up,” Breast J, vol. 17, no. 3, pp. 258–262, 2011.

  4. L. Bowman et al., “Pseudoangiomatous stromal hyperplasia: imaging features and diagnostic pitfalls,” Radiographics, vol. 25, no. 3, pp. 823–837, 2005.

  5. S. Hargaden et al., “Pseudoangiomatous stromal hyperplasia of the breast: MR imaging findings,” AJR Am J Roentgenol, vol. 180, no. 2, pp. 417–419, 2003.

  6. K. Saxena et al., “Pseudoangiomatous stromal hyperplasia: a review,” Arch Pathol Lab Med, vol. 138, no. 8, pp. 1073–1077, 2014.

  7. M. Degnim et al., “Management of pseudoangiomatous stromal hyperplasia,” J Surg Oncol, vol. 89, no. 3, pp. 147–150, 2005.

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