Soft tissue
Fibroblastic / myofibroblastic tumors
Fibromatosis - deep (desmoid type)

Topic Completed: 1 July 2012

Revised: 15 February 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Fibromatosis [title] desmoid "loattrfree full text"[sb]
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Cite this page: Arora K. Fibromatosis - deep (desmoid type). website. Accessed February 18th, 2019.
Definition / general
  • Clonal fibroblastic proliferation of deep soft tissue with infiltrative growth
  • "Desmos" (Greek) means tendon-like
  • Locally aggressive (local recurrence, but no metastases)
  • See also: breast, colon, small bowel
Diagrams / tables

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Site distribution

Clinical features
  • Usually ages 15 - 39 years, may be painful
  • Common sites in children are head and neck
  • May be fatal due to local effects, particularly in head and neck
  • Can be "staged" based on size, symptoms and complications (Dis Colon Rectum 2008;51:897)
  • Prognostic factors: age, tumor size, tumor site (J Clin Oncol 2011;29:3553)
  • Abdominal fibromatosis:
    • Arises within abdominal wall of women during or after pregnancy
    • May see with cesarean section scar
  • Extra-abdominal fibromatosis:
    • Arises outside abdomen and abdominal wall, usually in muscles of shoulder, chest wall, back and thigh, equal gender frequencies
  • Intra-abdominal fibromatosis:
    • Mesenteric, pelvic or retroperitoneal locations, associated with Gardner's syndrome (familial adenomatous polyposis, multiple osteomas)
    • Often postsurgical
Radiology images

Contributed by Mark R. Wick, M.D.

CT scan, right chest wall

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Various images

Case reports
Clinical images

Contributed by Mark R. Wick, M.D.


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Paraspinous subcutaneous mass

Various images

Gross description
  • Large, firm, white cut surface, infiltrative borders
  • Often in muscular fascia, cuts with gritty sensation, 5 - 10 cm
Gross images

Contributed by Mark R. Wick, M.D.

Various images

 AFIP images

Extra-abdominal fibromatosis

Intra-abdominal fibromatosis: gray glossy cut surface

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Mass in mesentery of small bowel

Well defined margins, lesion with infiltrative margins

Tumor infiltrates thoracic wall

Operative specimen

Trunk tumor

Thigh tumor

Gray-white tumor of Gardner syndrome

Firm, white lobulated fusiform mass

Intraabdominal fibromatosis: gray glossy cut surface

Microscopic (histologic) description
  • Poorly circumscribed with infiltration of adjacent tissue
  • Uniform cellularity between exuberant fibrous proliferation and low grade fibrosarcoma
  • Cells are bipolar fibroblasts and myofibroblasts (reduced amphophilic cytoplasm that merges with surrounding collagen, open chromatin, well defined nuclear membrane, one distinct nucleolus)
  • Usually more collagenous and less cellular than nodular fasciitis
  • Mucopolysaccharide matrix with thin walled, curvilinear, non-branching or ectatic vessels
  • Stroma varies from collagenous, keloid-like to myxoid
  • Regenerative muscle cells within lesions may resemble giant cells
  • Perivascular lymphocytes at edge of lesion
  • Few mitotic figures, no atypia
  • Postradiation: histologic changes are minimal (Hum Pathol 2012;43:1418)
Microscopic (histologic) images

Contributed by Mark R. Wick, M.D.

Beta cantenin

AFIP images

Extra-abdominal fibromatosis

Low, paucicellular
fibrous proliferation in
long fascicles, numerous
slit-like vessels

Fibroblasts, spindled,
dense, wavy nuclei
and minimal cytoplasm

Margin: infiltration of skeletal muscle


Atrophic and regenerating
muscle fibers, edge of the
lesion, may resemble

Some tumors are myxoid

Myxoid tumors are
uniformly bland, unlike
those in malignant
myxoid tumors

Cellular tumor, scattered mitotic figures, none atypical

Keloid type pattern, observed focally in deep tumors

Intra-abdominal (mesenteric) fibromatosis

Extrinsic to bowel
muscularis propria,
which distinguishes
it from GIST

Paucicellular and
composed of
relatively uniform,
bland spindle cells

Bland, mitotically
active, uniform
cells in myxoid

Less commonly bland spindle cells are within collagen bundles


Trichrome stain highlights
collagen in the fibromatosis,
distinguishes it from overlying
normal muscularis propria

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Extra-abdominal fibromatosis

Paraspinal tumor

Thigh mass

Predominantly cellular with relatively less fibrosis

Predominantly fibrotic with less cellularity

Intra-abdominal fibromatosis

Pelvic tumor

Uniform spindle cells with moderate collagen

Abdominal fibromatosis

Extension into adjacent muscle

Fascicles of fibroblastic spindle cells


Cytology description
Electron microscopy description
  • Fibroblastic and myofibroblastic features, including intrareticular collagen fibers, thin filament bundles, cytoplasmic dense bodies
Molecular / cytogenetics description
Molecular / cytogenetics images

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Trisomy 20 and 8

Differential diagnosis