Inclusion Body Fibromatosis (Infantile Digital Fibroma)
Definition
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
Immunohistology
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
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