Pseudoangiomatous Stromal Hyperplasia

Definition

Microscopic or clinically apparent breast lesion of variable cellularity featuring dense collegenous stroma punctuated by slit like spaces

May be a circumscribed mass or microscopic incidental finding
- Masses reported ranging from 0.8 - 11 cm
- May be solitary or multifocal
Dense hyalinized collagen bundles
- May expand intralobular stroma
- Surrounds ducts and lobules
- Usually circumscribed but merges with surrounding stroma
Anastomosing pseudovascular slit like spaces dissect through collagen bundles
- No true vascular lining or structure
- No erythrocytes in spaces
Spaces often lined by spindle cells with range of cellularity
- Classically almost inconspicuous, discontinuous flat bland cells
  - One male case described with multinucleated cells
  - Classical areas also present in all cellular cases described
- Spectrum of increased cellularity
  - Cells associated with spaces more numerous and larger
    - Nuclei may be larger and vesicular
  - Increased cellularity may obscure or obliterate pseuovascular spaces
  - May show marked cellularity with bundles and fascicles of cells
    - May predominate over collagenous stroma
- CD34 positive but CD31 and Factor VIII negative
Rare cases described in ectopic breast tissue
- Axillary and inguinal

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting/updates: 5/1/06, 3/16/08, 3/6/12