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

Author: Komal Arora, M.D.

Revised: 9 July 2018, last major update July 2012

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Fibromatosis [title] desmoid

Cite this page: Arora, K. Fibromatosis - deep (desmoid type). website. Accessed August 15th, 2018.
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
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 post-surgical
Case reports
Clinical images

Images hosted on PathOut server:

Calf (left) and CT scan, right chest wall (right), courtesy of Mark R. Wick, M.D.

Images hosted on other servers:

Site distribution

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

Images hosted on PathOut server:

Courtesy of Mark R. Wick, M.D.

Extra-abdominal fibromatosis

Intra-abdominal fibromatosis: gray glossy cut surface

Images hosted on other servers:

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
  • Post radiation: histologic changes are minimal (Hum Pathol 2012;43:1418)
Microscopic (histologic) images

Scroll to see all images:

Images hosted on PathOut server:

Beta cantenin, courtesy of Mark R. Wick, M.D.

Extra-abdominal fibromatosis - AFIP:

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 rhabdomyoblasts

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 - AFIP:

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 stroma

Less commonly bland spindle cells are within collagen bundles

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

Images hosted on other servers:

Extra-abdominal fibromatosis - other sources:

Paraspinal tumor

Thigh mass

Predominantly cellular with relatively less fibrosis

Predominantly fibrotic with less cellularity

Intra-abdominal (mesenteric) fibromatosis - AFIP:

Pelvic tumor

Intra-abdominal fibromatosis - other sources:

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

Images hosted on other servers:

Trisomy 20 and 8

Differential diagnosis