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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Inclusion body fibromatosis


Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 21 July 2012, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Dermal fibroblastic and myofibroblastic lesion with cytoplasmic eosinophilic inclusions, usually in digits of infants
● Also called infantile digital fibromatosis, infantile digital fibroma (J Hand Surg Am 1995;20:1014)
● Distinct lesion from classic fibromatosis (Am J Surg Pathol 2009;33:1)

Clinical description
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● Rare; lesions usually present at birth or in first 2 years
● Similar lesions in adults
● Often are multiple

Sites
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● Usually exterior surface of distal phalanges of fingers and toes, but not thumb or great toe, also oral cavity and breast
● 50% recur, do not metastasize
● Similar inclusions reported in breast fibroadenoma (Arch Pathol Lab Med 2007;131:1126), breast phyllodes tumor (Am J Surg Pathol 1994;18:506, Breast J 2008;14:198), cervical polyp (Pathology 1998;30:215), GI leiomyomas (Cesk Patol 2006;42:139)

Case reports
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● 6 month old girl (Indian J Pathol Microbiol 2010;53:827)
● 1 year old boy with spontaneous regression (J Dermatol 1998;25:523)
● 2 year old with post-surgical involvement of all 4 extremities (Ann Plast Surg 2008;61:472)

Treatment
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● Conservative excision (preserve function because recurrences are not destructive and tumors do not metastasize) or watchful waiting (Am J Surg Pathol 2009;33:1, Pediatr Dermatol 2008;25:72)

Clinical images
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Various images

Gross description
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● Nodules with stretched overlying skin, lesions are ill defined, white-tan, usually 2 cm or less
● No hemorrhage or necrosis

Micro description
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● Nonencapsulated, dermal proliferation of hypocellular sheets or fascicles of fibroblasts and myofibroblasts with variable collagen
● Some spindle cells have peculiar eosinophilic (hyaline) cytoplasmic inclusions the size of a lymphocyte nucleus
● Usually mitotic figures
● May infiltrate into adjacent tissue
● No atypia

Micro images
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Proliferation extends from epidermis to deep dermis or subcutis


Fibroblastic cells swirl around and engulf an eccrine duct


Cells are bland and monomorphic


Inclusions resemble red blood cells


Various images

Cytology
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Acta Cytol 2011;55:481

Positive stains
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Inclusions - trichrome (stain red), PTAH, variable staining for actins
Spindle cells - vimentin, muscle actins (tram track pattern), calponin, desmin, CD99; often CD117

Negative stains
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Inclusions - PAS
Spindle cells - keratin, ER, PR, beta-catenin

Electron microscopic description
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● Spindle cells are myofibroblasts with rough endoplasmic reticulum and free lying inclusions composed of compact masses of actin granules and filaments without a limiting membrane (Am J Pathol 1979;94:19)

Differential diagnosis
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● Infantile fibrosarcoma: not digits, usually > 2 cm, more cellular, chromatin is denser and more irregular, more mitotic figures, no inclusions
● Infantile desmoid fibromatosis: rare on hand, usually > 2 cm, more cellular, no inclusions

Additional references
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Stanford University

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic tumors > Inclusion body fibromatosis


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