Retroperitoneal and Pelvic Fibromatosis
Definition
- Cytologically bland, at most moderately cellular, deep infiltrative fibroproliferative process primarily involving retroperitoneum or pelvis
Alternate / Historical Names
-
Intra-abdominal fibromatosis
Diagnostic Criteria
- Over age 5 years by definition
- Essentially the same as abdominal desmoid fibromatosis except for location and lack of association with pregnancy or polyposis
- Primarily based in retroperitoneum or pelvis by definition
- Extremely rare outside the pelvic retroperitoneum
- If retroperitoneum involved by extension from mesentery, lesion should be considered mesenteric fibromatosis
- Low to moderate cellularity
- Bland spindle cells in fascicles or haphazard
- Nuclei small, dark to slightly enlarged and vesicular
- Cytoplasm scant
- Stroma may be densely collagenous or myxoid
- May have keloid like fibers
- Rare metaplastic cartilage and bone
- Mitotic figures infrequent
- Rarely >5 per HPF
- Never atypical
- Inflammation not prominent
- May be seen focally, usually peripherally
- Gross circumscription may be deceptive
- Nearly always over 3 cm
- Usually 3-7 cm
- Focal hemorrhage may be seen
- Hemosiderin rare
Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting: October 15, 2007
Updates: January 26, 2008; February 2, 2009; February 8, 2009
