Table of Contents
Definition / general | Epidemiology | Sites | Case reports | Treatment | Clinical images | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Positive stains | Negative stains | Electron microscopy description | Molecular / cytogenetics description | Differential diagnosis | Additional referencesCite this page: Arora K. Fibrous hamartoma of infancy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuefibroushamart.html. Accessed January 23rd, 2021.
Definition / general
- 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
- Rare; usually age 2 years or less (25% discovered at birth), does not occur after puberty, 2/3 male
- Usually boys
Sites
- 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
- 6 month old girl with fibrous hamartoma of infancy manifesting as multiple nodules with hypertrichosis (J Dermatol 2006;33:427)
- 6 month old boy with recurrent and synchronous fibrous hamartoma of infancy (Pediatr Surg Int 2005;21:119)
- 11 month old boy with fibrous hamartoma of infancy (The Internet Journal of Dermatology 2001;1(2))
- 4 year old boy with fibrous hamartoma of infancy in an unusual location (Gulf J Oncolog 2010;(8):52)
- 10 year old boy with fibrous hamartoma of infancy (Acta Derm Venereol 2005;85:276)
- Giant fibrous hamartoma of infancy (J Am Acad Dermatol 2011;64:579)
Treatment
- 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
Gross description
- Poorly circumscribed, gray-white with yellow fat, usually 5 cm or less
Microscopic (histologic) description
- Poorly circumscribed, organoid with 3 components:
- Trabecular or stellate immature mesenchymal cells with scant cytoplasm and bland straight or wavy nuclei in myxoid matrix
- Fibrocollagenous tissue composed of bland fibroblasts or myofibroblasts
- 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
Microscopic (histologic) images
Cytology description
- 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
Negative stains
Electron microscopy description
- Fibrous trabeculae are composed of fibroblasts and myofibroblasts, primitive mesenchymal cells have slender cytoplasmic processes with few organelles
Molecular / cytogenetics description
- EGFR exon 20 insertion / duplication mutations are characteristic (Am J Surg Pathol 2016;40:1713)
- 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
- 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