Angiomyofibroblastoma

Definition

Circumscribed edematous lesion of the external genitalia and perineal soft tissue

Restricted to external genitalia and perineal soft tissue
- Rare in males
Most under 5 cm
Circumscribed with thin pseudocapsule
Edematous background with prominent vascularity
- Thin walled dilated capillaries and venules
- Scattered bundles of collagen
- Occasionally sclerotic
- No necrosis
Alternating hypercellular and hypocellular areas
- Cells frequently aggregated around vessels
  - Nests and occasional solid compact foci
  - Also scattered individual cells
  - Hypocellular areas can resemble aggressive angiomyxoma except the vessels are not as thick walled
- Spindle to round cells
  - May be epithelioid
  - May have plasmacytoid appearance
  - Eosinophilic cytoplasm, occasionally hyaline
  - Bland to minimally atypical oval nuclei
    - Inconspicuous nucleoli
    - Mitotic figures rare, no atypical mitotic figures
  - Binucleate and multinucleate cells common
Frequently fat in lesion
- Not clear if this is entrapped or lesional fat
- May occasionally be prominent ("lipomatous variant")
- Two reported scrotal lesions were predominantly adipose tissue
Occasional findings
- Prominent spindle cell population
- Stellate cells
- Degenerative nuclear hyperchromasia
- Mast cells may be numerous

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