Extra-abdominal Desmoid Fibromatosis
Definition
- Cytologically bland, at most moderately cellular, deep infiltrative fibroproliferative process involving sites other than abdominal wall or abdominal cavity
Alternate / Historical Names
- Extra-abdominal fibromatosis
- Musculoaponeurotic fibromatosis
- Aggressive fibromatosis
Diagnostic Criteria
- Over age 5 years by definition
- Excludes lesions of abdominal wall and abdominal cavity by definition
- Peripheral infiltration of skeletal muscle is seen in nearly all cases
- Very important diagnostic feature
- Muscle fibers show degenerative changes
- Muscle rare in center of lesion
- Lesion centered below level of subcutis
- Subcutis may be involved by large lesions
- May surround nerves
- Low to moderate cellularity
- Bland spindle cells in fascicles or haphazardly arranged, separated by abundant collagen
- Nuclei uniform small, dark to slightly enlarged and vesicular
- Cytoplasm scant
- Stroma may be densely collagenous or myxoid
- If myxoid, usually focal
- 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
- Thin walled compressed “slit like” vessels frequent
- 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
Last Update: March 16, 2008
