Stanford School of Medicine
Surgical Pathology Criteria
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Infantile Fibromatosis


  • Bland fibroproliferative process that invades skeletal muscle, occurring age 8 and under, with two types:
    • One type identical to adult desmoid fibromatosis
    • Diffuse mesenchymal type, often containing fat

Alternate/Historical Names

  • Aggressive infantile fibromatosis
  • Cellular fibromatosis
  • Congenital fibromatosis
  • Diffuse mesenchymal fibromatosis
  • Fibrosarcoma-like fibromatosis
  • Infantile desmoid-type fibromatosis
  • Lipofibromatosis

Diagnostic Criteria

  • Limited to patients 8 years of age or under
    • Some studies use a limit of 10 years
  • Infiltration of skeletal muscle
    • Involvement may be superficial
  • Usually involves head, neck or thigh
  • Two patterns
    • Immature or diffuse pattern
      • Uniform bland cells in myxoid stroma
        • Nuclei round or oval to spindled
        • Scant cytoplasm
      • Infiltrates between muscle fibers
        • Many muscle fibers remain intact
        • Peripheral inflammation may be present
        • May surround nerves
        • May invade bone, especially in head and neck
      • Fat is often present
    • Adult type is identical to adult extra-abdominal desmoid fibromatosis
      • Bland spindle cells in collagenous stroma
      • Variable cellularity
      • Destruction of muscle with invasion
      • Beta-catenin positive

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

      Original posting/updates: 10/15/07, 1/26/08, 1/29/12

Supplemental studies


  • Smooth muscle actin variable
  • Desmin variable

Differential diagnosis

Applies to immature / diffuse / mesenchymal type
(for differential diagnosis of adult type see extra-abdominal desmoid fibromatosis)

Infantile Fibromatosis Infantile Fibrosarcoma
Mild to moderate cellularity Usually more cellular
Fine chromatin Usually clumped chromatin
Rarely > 5 mitotic figures per HPF Usually > 5 mitotic figures per HPF
Atypical mitotic figures rare Atypical mitotic figures common
Variably collagenous stroma Little collagen in stroma
No herringbone pattern Frequent herringbone pattern
Hemorrhage and necrosis rare Frequent hemorrhage and necrosis
Muscle fibers preserved Muscle fibers destroyed
Lacks t(12;15) t(12;15) in most cases
Distinction between grade I fibrosarcoma and desmoid fibromatosis may not always be clear


Fibrous Hamartoma of Infancy Infantile Fibromatosis
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells Not triphasic
Primarily superficial Usually centered on muscle


Inflammatory Myofibroblastic Tumor Infantile Fibromatosis
Frequent in abdomen Rare in abdomen
Usually age 0-14 years Age <5 years
Prominent inflammation Variable, peripheral inflammation
Variable locations Centered in muscle


Lipoblastomatosis Infantile Fibromatosis
At least focal plexiform capillaries No plexiform capillaries
Contains lipoblasts Mature fat cells only
Lobular pattern Infiltrative pattern


Myxoid Liposarcoma Infantile Fibromatosis
Chicken-wire vascular pattern No chicken-wire pattern
Contains lipoblasts Mature fat cells only
Essentially does not occur <5 years of age <5 years of age


Embryonal Rhabdomyosarcoma Infantile Fibromatosis
Rarely involves skeletal muscle Usually centered on skeletal muscle
Cytologically atypical Cytologically bland
No fat component Fat frequently part of lesion
MyoD1 positive MyoD1 negative
Desmin positive Desmin variable


Infantile Fibromatosis Inclusion Body Fibromatosis
Rare in hand Vast majority in hands or feet
Usually >2 cm Rarely >2 cm
Involves skeletal muscle Muscle not involved
No inclusions Inclusions usually present


  • Upper limit of age varies in different series for distinguishing infantile and adult desmoid fibromatoses
    • Limits from 5 to 10 have been proposed
    • Some find very few tumors between age 5 and 10
  • Locations include
    • Head and neck, including oral
    • Extremities
    • Trunk
    • Rare in abdomen
  • Local recurrence very common and may be destructive
    • Never metastasizes


Predominantly Pediatric Fibrous Lesions



  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 4th edition, 2001
  • Coffin CM, Dehner LP. Fibroblastic-myofibroblastic tumors in children and adolescents: a clinicopathologic study of 108 examples in 103 patients. Pediatr Pathol. 1991 Jul-Aug;11(4):569-88.
  • Ayala AG, Ro JY, Goepfert H, Cangir A, Khorsand J, Flake G.  Desmoid fibromatosis: a clinicopathologic study of 25 children.  Semin Diagn Pathol 1986 May;3(2):138-50
  • Chung EB.  Pitfalls in diagnosing benign soft tissue tumors in infancy and childhood.  Pathol Annu. 1985;20 Pt 2:323-86.
  • Rosenberg HS, Stenback WA, Spjut HJ.  The fibromatoses of infancy and childhood.  Perspect Pediatr Pathol 1978;4:269-348
  • Schmidt D, Klinge P, Leuschner I, Harms D.  Infantile desmoid-type fibromatosis. Morphological features correlate with biological behaviour.  J Pathol 1991 Aug;164(4):315-9
  • Thway K, Gibson S, Ramsay A, Sebire NJ. Beta-catenin expression in pediatric fibroblastic and myofibroblastic lesions: a study of 100 cases. Pediatr Dev Pathol. 2009 Jul-Aug;12(4):292-6.
  • Thway K, Fisher C, Sebire NJ. Pediatric fibroblastic and myofibroblastic lesions. Adv Anat Pathol. 2012 Jan;19(1):54-65.
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