Stanford School of Medicine
Surgical Pathology Criteria
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Inclusion Body Fibromatosis (Infantile Digital Fibroma)


  • Fibrous and spindle cell lesion primarily of digits of infants, characterized by intracytoplasmic eosinophilic inclusions

Alternate/Historical Names

  • Infantile digital fibromatosis
  • Recurring digital fibroma
  • Reye tumor

Diagnostic Criteria

  • Nearly always under 1 year of age
    • May be congenital
    • Rare lesions reported in adults
  • Vast majority on 3rd, 4th or 5th digits of hands and feet
    • Rare lesions reported in other sites
    • May be multiple
  • May involve dermis and subcutis
  • Poorly circumscribed
    • May entrap and surround skin adnexae
  • Cellular lesion with bundles of spindle cells
    • Vesicular nuclei
    • Fibrotic stroma
  • Perinuclear round eosinophilic inclusions
    • Vary from rare to frequent
    • Approximately size of erythrocytes (3-15 mcrons)
    • Red on trichrome stain
    • Black on iron hematoxylin stain
    • Negative on PAS and Alcian blue stains
    • Similar bodies have been reported in breast phyllodes and fibroepithelial tumors
  • Mitotic figures may be present but not atypical
  • Virtually always under 2 cm
    • Range 0.3-3.5 cm

Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates : 1/11/07, 3/2/08, 1/20/09, 1/29/12

Supplemental studies


  Spindle Cells
Smooth muscle actin 100%
Calponin 100%
CD99 100%
Desmin 100%
CD117 75%
CD34 9%
Keratin Negative to rare (1 case+)
Beta catenin Negative
Inclusion bodies smooth muscle actin positive but may require special fixation or pretreatment

Differential diagnosis

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


Fibrous Hamartoma of Infancy Inclusion Body Fibromatosis
Not reported in digits Vast majority in hands or feet
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells Lacks triphasic pattern
No inclusions Inclusions


Fibroma of Tendon Sheath Inclusion Body Fibromatosis
Most common in adults Vast majority very young
Usually densely collagenized Usually cellular
No inclusions Inclusions usually present


Palmar or Plantar Fibromatosis Inclusion Body Fibromatosis
Usually in palm or sole Usually on digits
Uncommon in children Vast majority very young
No inclusions Inclusions


Infantile Fibrosarcoma Inclusion Body Fibromatosis
Rare in hand Vast majority in hands or feet
Usually >2 cm Rarely >2 cm
No inclusions Inclusions


Nodular Fasciitis Inclusion Body Fibromatosis
Rare in hands and feet Vast majority in hands or feet
Uncommon in children Vast majority very young
No inclusions Inclusions


Myofibroma Inclusion Body Fibromatosis
Rare on digits Usually on digits
Biphasic nodules with central primitive cells Lacks primitive cells and perivascular clustering of cells
No inclusions Inclusions


Neurofibroma Inclusion Body Fibromatosis
S100 positive S100 negative
No inclusions Inclusions


Leiomyoma Inclusion Body Fibromatosis
Abundant fusiform cytoplasm Scant cytoplasm
No inclusions Inclusions


  • Nearly all under 1 year
  • Nearly all under 2 cm
  • Vast majority on 3rd, 4th or 5th digits of hands and feet
  • Rare lesions reported in adults and other sites
  • May be multiple
    • Synchronous or metachronous
  • Recurrences do occur but are not destructive; never metastasizes
    • Frequently spontaneous regression



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
  • Bittesini L, Dei Tos AP, Doglioni C, Della Libera D, Laurino L, Fletcher CD.  Fibroepithelial tumor of the breast with digital fibroma-like inclusions in the stromal component. Case report with immunocytochemical and ultrastructural analysis.  Am J Surg Pathol 1994 Mar;18(3):296-301
  • Mukai M, Torikata C, Iri H, Hata J, Naito M, Shimoda T.  Immunohistochemical identification of aggregated actin filaments in formalin-fixed, paraffin-embedded sections. I. A study of infantile digital fibromatosis by a new pretreatment.  Am J Surg Pathol 1992 Feb;16(2):110-5 
  • Canioni D, Richard S, Rambaud C, Manach Y, Nezelof C.  Lingual localization of an inclusion body fibromatosis (Reye's tumor).  Pathol Res Pract 1991 Sep;187(7):886-9 
  • Choi KC, Hashimoto K, Setoyama M, Kagetsu N, Tronnier M, Sturman S.  Infantile digital fibromatosis. Immunohistochemical and immunoelectron microscopic studies.  J Cutan Pathol 1990 Aug;17(4):225-32 
  • Viale G, Doglioni C, Iuzzolino P, Bontempini L, Colombi R, Coggi G, Dell'Orto P.  Infantile digital fibromatosis-like tumour (inclusion body fibromatosis) of adulthood: report of two cases with ultrastructural and immunocytochemical findings.  Histopathology 1988 Apr;12(4):415-24 
  • Yun K.  Infantile digital fibromatosis. Immunohistochemical and ultrastructural observations of cytoplasmic inclusions.  Cancer 1988 Feb 1;61(3):500-7 
  • Fringes B, Thais H, Bohm N, Altmannsberger M, Osborn M.  Identification of actin microfilaments in the intracytoplasmic inclusions present in recurring infantile digital fibromatosis (Reye tumor).  Pediatr Pathol 1986;6(2-3):311-24
  • Purdy LJ, Colby TV.  Infantile digital fibromatosis occurring outside the digit.  Am J Surg Pathol 1984 Oct;8(10):787-90 
  • Allen PW.  Recurring digital fibrous tumours of childhood.  Pathology 1972 Jul;4(3):215-23
  • Grenier N, Liang C, Capaldi L, Ney A, Lapidus C, Schappell D, Katarincic J, Robinson-Bostom L. A range of histologic findings in infantile digital fibromatosis. Pediatr Dermatol. 2008 Jan-Feb;25(1):72-5.
  • Hiraoka N, Mukai M, Hosoda Y, Hata J. Phyllodes tumor of the breast containing the intracytoplasmic inclusion bodies identical with infantile digital fibromatosis. Am J Surg Pathol. 1994 May;18(5):506-11.
  • Laskin WB, Miettinen M, Fetsch JF. Infantile digital fibroma/fibromatosis: a clinicopathologic and immunohistochemical study of 69 tumors from 57 patients with long-term follow-up. Am J Surg Pathol. 2009 Jan;33(1):1-13
  • 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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