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Surgical Pathology Criteria
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Fibrous Hamartoma of Infancy

Definition

  • Triphasic soft tissue mass (fibrous, adipose, primitive mesenchymal) presenting in infants

Diagnostic Criteria

  • Most cases under age 4
    • Congenital to 19 years
  • Superficial soft tissue lesion
    • Rarely attached to muscle or fascia
  • Poorly circumscribed
  • Triphasic lesion
    • Spindle cell fibrous trabeculae
      • Variably cellular
    • Disorganized mature fat
    • Islands of immature mesenchymal cells
      • Small round to spindled cells
      • Cytologically bland
      • Scant cytoplasm, small blue cell pattern
      • May be myxoid
      • Trabeculae of immature mesenchymal cells may occasionally infiltrate fat
  • Mitotic figures rare in all components
  • Scattered lymphocytes may be present
  • Overlying skin may show eccrine changes
    • Hyperplasia
    • Duct dilation
    • Intralumenal papillae
    • Squamous metaplasia of ducts

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

Original posting : November 20, 2007
Last Update: March 26, 2014

Supplemental studies

Immunohistology

  • Spindled fibrous component
    Vimentin, CD34 positive
    Actin, smooth muscle and muscle specific positive
    Desmin variable
    S100 negative
  • Immature mesenchyme
    Vimentin positive
    CD34 variable
    Actin, smooth muscle and muscle specific negative
    Desmin negative
    S100 negative
  • Mature fat is S100 positive

Differential diagnosis

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

 

Fibrous Hamartoma of Infancy Fibrolipoma
Poorly circumscribed Encapsulated
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells No immature component

 

Fibrous Hamartoma of Infancy Calcifying Aponeurotic Fibroma
Nodules of immature mesenchyme No immature mesenchyme
No palisaded pattern Palisaded cells around nodules
No cartilage or calcification Cartilage and calcification
Never on hands or feet Frequent on hands and feet

 

Fibrous Hamartoma of Infancy Myofibroma
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells Biphasic lesion with outer spindled cells and inner immature cells
Lacks hemangiopericytomatous vessels Hemangiopericytoma-like vessels frequent

 

Fibrous Hamartoma of Infancy Rhabdomyosarcoma
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells Not triphasic
Cytologically bland Cytologically atypical

 

Fibrous Hamartoma of Infancy Infantile Fibrosarcoma
Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells Not triphasic
Mitotic figures restricted to immature foci Frequent mitotic figures

 

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

 

Gardner Associated Fibroma Fibrous Hamartoma of Infancy
Lacks triphasic pattern, no immature component Triphasic lesion with spindle cell fibrous areas, adipose tissue and clusters of immature mesenchymal cells
Age range 2 mo to 36 years All but rare cases congenital to 4 years

Clinical

  • Congenital to 19 years
    • All but rare cases under 4 years, most under 2
  • 0.5-20 cm, most under 5 cm
  • Rapid growth
  • Most near axilla/shoulder or inguinal/external genitalia
    • Not reported in hands
  • Rare recurrence, not aggressive
    • May be years later

Lists

Predominantly Pediatric Fibrous Lesions

Bibliography

  • 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
  • Popek EJ, Montgomery EA, Fourcroy JL.  Fibrous hamartoma of infancy in the genital region: findings in 15 cases.  J Urol 1994 Sep;152(3):990-3
  • Sotelo-Avila C, Bale PM.  Subdermal fibrous hamartoma of infancy: pathology of 40 cases and differential diagnosis.  Pediatr Pathol 1994 Jan-Feb;14(1):39-52 
  • Michal M, Mukensnabl P, Chlumska A, Kodet R.  Fibrous hamartoma of infancy. A study of eight cases with immunohistochemical and electron microscopical findings.  Pathol Res Pract 1992 Dec;188(8):1049-53
  • Groisman G, Lichtig C.  Fibrous hamartoma of infancy: an immunohistochemical and ultrastructural study. Hum Pathol 1991 Sep;22(9):914-8
  • Paller AS, Gonzalez-Crussi F, Sherman JO.  Fibrous hamartoma of infancy. Eight additional cases and a review of the literature.  Arch Dermatol 1989 Jan;125(1):88-91
  • Fletcher CD, Powell G, van Noorden S, McKee PH.  Fibrous hamartoma of infancy: a histochemical and immunohistochemical study.  Histopathology 1988 Jan;12(1):65-74
  • Enzinger F.  Fibrous hamartoma of infancy.  Cancer 1965; 18:241-8.
  • Grynspan D, Meir K, Senger C, Ball NJ. Cutaneous changes in fibrous hamartoma of infancy. J Cutan Pathol. 2007 Jan;34(1):39-43.
  • Saab ST, McClain CM, Coffin CM. Fibrous hamartoma of infancy: a clinicopathologic analysis of 60 cases. Am J Surg Pathol. 2014 Mar;38(3):394-401. PubMed PMID: 24525510.

 
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