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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Fibrous hamartoma of infancy


ReviewerS: Komal Arora, M.D., Vijay Shankar, M.D. (see Reviewers page)
Revised: 15 March 2013, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Tumor-like condition in newborns to 2 year olds
● Poorly circumscribed proliferation of immature spindle cells in organoid pattern with fat and dense fibrocollagenous tissue

Epidemiology
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● Rare; usually age 2 years or less (25% discovered at birth), does not occur after puberty, 2/3 male
● Usually boys

Sites
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● Axilla, shoulder and inguinal region (J Urol 1994;152:990)
● Not hands and feet
● Solitary, rapidly growing, freely movable mass of subcutis or dermis

Case reports
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● 6 month old girl with arm mass (Univ Oklahoma)
● 6 month old girl with multiple nodules with overlying hypertrichosis (J Dermatol 2006;33:427)
● 6 month old boy with recurrent tumor (Pediatr Surg Int 2005;21:119)
● 11 month old boy with thigh mass (Internet J of Dermatol 2001;1(2)
● 4 year old boy with gluteal tumor (Gulf J Oncolog 2010;1:52)
● 10 year old boy with progressively enlarging tumor on face (Acta Derm Venereol 2005;85:276)
● Giant tumors (J Am Acad Dermatol 2011;64:579)

Treatment
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● Benign, although may recur locally
● Excision, need not be aggressive as recurrence is uncommon (J Am Acad Dermatol 2006;54:800, J Korean Surg Soc 2011;81:61)

Clinical images
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Axillary tumor in 6 month old Nigerian boy


Scapular tumor in 7 year old Nigerian girl


Scapular tumor in 7 year old Nigerian girl, at surgery showing well developed capsule

Gross description
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● Poorly circumscribed, gray-white with yellow fat, usually 5 cm or less

Micro description
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● Poorly circumscribed, organoid with 3 components:
(1) trabecular or stellate immature mesenchymal cells with scant cytoplasm and bland straight or wavy nuclei in myxoid matrix
(2) fibrocollagenous tissue composed of bland fibroblasts or myofibroblasts
(3) mature fat; overlying epidermis usually has eccrine changes, including hyperplasia, duct dilation, intraluminal papillary formations and squamous syringometaplasia (J Cutan Pathol 2007;34:39)
● No/scant mitotic figures

Micro images
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Triphasic pattern of fibrous spindle cells delimiting islands of mature fat and primitive spindle cells


Primitive spindle cells may infiltrate fat


Primitive spindle cells and fibrous spindle cells are bland and uniform with no/rare mitotic figures

   
Three cell types

           

           
Various images

Cytology
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● Moderate cellularity, adipose tissue fragments, clusters of fibroblastic cells, myxoid and collagenous matrix
● No mitotic figures, no atypia (Diagn Cytopathol 2003;28:272, Acta Cytol 2008;52:201)

Positive stains
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● Vimentin (fibrous and mesenchyme areas)
● Spindle cells in fibrous trabeculae may be actin+, desmin+

Negative stains
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● Beta-catenin (Pediatr Dev Pathol 2009;12:292)

Electron microscopy description
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● Fibrous trabeculae are composed of fibroblasts and myofibroblasts, primitive mesenchymal cells have slender cytoplasmic processes with few organelles

Cytogenetics
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● Rarely complex translocations (Cancer Genet Cytogenet 2006;171:115, Cancer Genet Cytogenet 2010;201:66)
● Rarely t(2;3) (Arch Pathol Lab Med 2005;129:520)

Differential diagnosis
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Calcifying aponeurotic fibroma: almost always hands or feet, prominent calcification, no primitive cells within myxoid stroma
● Myofibroma: prominent hemangiopericytoma-like pattern, usually no fat

Additional references
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Stanford University

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic tumors > Fibrous hamartoma of infancy


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