Stanford School of Medicine
Surgical Pathology Criteria
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Extra-abdominal Desmoid Fibromatosis


  • 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

Supplemental studies


Beta-catenin positive
Actin positive
Desmin usually negative, occasionally focal
CD34 negative
S100 negative
Keratin negative
Estrogen receptor 0-10%
Progesterone receptor 0-25%
Cathepsin-D positive
Response to hormone therapy is not related to receptor status


Trisomies 8 and 20, common in extra-abdominal desmoids are rare in abdominal desmoids

Differential diagnosis

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Scar
Uniform Multiple stages of organization
Hemosiderin rare Hemosiderin common
Rare under 3 cm Rare over 3 cm
Inflammation not prominent Inflammation may be prominent
Usually infiltrates muscle Infiltration of muscle uncommon


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Nodular Fasciitis
Usually dense collagenous stroma Collagenous stroma focal or rare
Linear fascicles of cells Undulating bundles of cells
Infrequent mitotic figures Frequent mitotic figures
Usually >3 cm Usually <4 cm
Beta-catenin 80-90% Beta-catenin negative


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Proliferative Myositis
Muscle fibers damaged or obliterated Muscle fibers not damaged
Muscle fibers at edge of lesion Muscle fibers throughout
No ganglion-like cells Ganglion-like cells present
Predominantly collagenous Predominantly myxoid
Usually >3 cm Usually <4 cm
Both involve muscle


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Desmoplastic Fibroblastoma
Mild to moderate cellularity Paucicellular
Moderate vascularity Hypovascular
Extensive infiltration of muscle Only focal muscle infiltration
Spindle cells usually in fascicular pattern Spindle and stellate cells randomly aranged


Fibromatosis, Extra-abdominal Desmoid Nuchal Fibroma
Involves deep tissues Involves superficial tissues
Cellular areas Paucicellular throughout


Extra-abdominal Desmoid Fibromatosis Palmar and Plantar Fibromatosis
Rare on hands and feet Occurs on hands and feet
Primarily one large mass Multiple small nodules
Infiltrates muscle No muscle infiltration


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Intramuscular Myxoma
Mild to moderate cellularity Markedly hypocellular
Areas with collagen No collagen
Prominent vessels Sparse vessels


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Plexiform Fibrohistiocytic Tumor
Deep to subcutis, in muscle Superficial
Generally solid mass Plexiform architecture
Rare under 3 cm Rare over 3 cm
Giant cells and histiocytes rare Nodules of giant cells and histiocytes


Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Inflammatory Myofibroblastic Tumor
Rare <12 years of age Age usually <14, rare >30
Inflammation not prominent Prominent inflammation, particularly plasma cells
Alk1 negative Alk1 frequently positive
Beta catenin 80-90% Beta catenin negative


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Adult Fibrosarcoma
Mild to moderate cellularity Usually more cellular
Fine chromatin Usually clumped chromatin
Rarely >5 mitotic figures / hpf Usually >5 mitotic figures / hpf
Rarely necrotic Frequent necrosis
Distinction between grade I fibrosarcoma and fibromatosis may not always be clear


Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Myxofibrosarcoma
No pleomorphism Cytologic pleomorphism present
Usually dense stroma but focally may be myxoid No dense stroma
Vessels lack arching pattern Arching vessels


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Desmoplastic Melanoma
Based below subcutis, involves muscle Usually based in dermis
S100 negative S100 positive


Fibromatosis, Abdominal Desmoid and Extra-abdominal Desmoid Calcifying Fibrous Pseudotumor
Nearly always has cellular areas Uniformly paucicellular
Infiltrative pattern prominent Microscopically infiltrative at most
No calcification Calcification present
Inflammation uncommon Chronic inflammation present


  • Over age 5 years by definition
    • Nearly always over 12 years
    • Most age 15-40
  • Not associated with pregnancy
  • Not associated with familial polyposis/Gardner syndrome
  • Excludes lesions of abdominal wall and abdominal cavity, by definition
    • Most common on trunk and proximal extremities
    • Rare in feet or hands
  • May be multicentric
    • Not considered to be metastases
  • Frequent recurrence
    • 20-75%
    • Recurrences may be locally aggressive and destructive
    • No metastases
  • Deep fibromatoses differ primarily in their clinical association
      Abdominal Extra-abdominal Mesenteric Pelvic / Retroperitoneal Infantile
    Pregnancy + - - - -
    Familial polyposis rare - 10-15% - -




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