The term 'Fibromatosis' was introduced  for the first time by Arthur Purdy Stout.
Fibromatosis includes a broad group of related fibrous lesions .

Salient Features:

1. Macroscopically, cut surface is usually pale, whorled and fibrous with irregular margin. Image1  ;   Image2
2. Microscopically,  there is proliferation of palely eosinophilic fibroblasts and myofibroblasts. Image1  ;   Image2   
3. Infiltrative pattern
4. Presence of abundant collagen between the tumour cells.
5. Absence of cytological features of malignancy.
6. Cellularity and mitotic activity are extremely variable.
7. Other light microscopic features include:
    i.   thick-walled blood vessels sharply outlined from surrounding tissue.
    ii.  perivascular lymphocytic infiltrate at the advancing edge of the tumour.
    iii. rarely metaplastic ossification or cartilage formation.
8. Immunohistochemistry: Vimentin - Positive ; Variably positivity for SMA, CD117 & desmin ; CD34 - Negative.  Staining correlates with the cellularity.
9. Aggressive clinical behaviour characterized  by repeated local recurrences. There is no evidence of metastasis.
10. Ultrastructural study confirms fibroblastic and myofibroblastic features. Presence of intracytoplasmic collagen formation has been described.

Fibromatosis is subdivided into two major groups:  Superficial fibromatoses are genetically distinct from deep fibromatoses.Mod Pathol. 2001 Jul;14(7):695-701.

I  Superficial (fascial) fibromatoses: 

Features: 1. Slow growing tumour ; 2. Small size ;  3. Arise from fascia or aponeurosis ;   4. Less aggressive.

A. Palmar fibromatosis (Dupuytren's contracture) Image
B. Plantar fibromatosis (Ledderhose's disease) Image
C. Penile fibromatosis (Peyronie's diseasee)
D. Knucle pads

II  Deep (musculoaponeurotic) fibromatoses:

Features: 1. Rapidly growing tumour ;  2. Usually attain large size ;  3. Involve deeper structures (musculature of trunk and the extremities).

A. Extraabdominal fibromatosis (extraabdominal desmoid)
B. Abdominal fibromatosis (abdominal desmoid)
C. Intraabdominal fibromatosis (intraabdominal desmoid)
            1. Pelvic fibromatosis
            2. Mesenteric fibromatosis
            3. Gardner's syndrome (Familial adenomatous polyposis)

Desmoid tumor can be defined as a pseudoencapsulated infiltrative growth of well-differentiated collagenous fibroblasts and fibrocytes arising either in fascia or musculoaponeurotic structures.

The etiology of desmoid tumors is poorly defined. The most commonly implicated etiologic factors are trauma, hormonal disturbances, and genetic or hereditary factors.

Desmoid tumours of the anterior abdominal wall are much less common than extra-abdominal desmoids.

They may occur at any age but are most common in the third and fourth decades.

Although both sexes may be affected, abdominal desmoids predominate in females, particularly in females of childbearing age.

Extra-abdominal desmoids, which most commonly occur on the back, chest wall, head and neck, or lower extremity, have a male predominance.

Most patients complain of a painless mass of several months or years' duration.

The microscopic picture is variable and generally corresponds to the patient's age. The pattern usually found in the older child exhibits moderate cellular fibrous tissue with an intertwining fascicular pattern. Less cellular examples of the tumour are associated with larger amounts of collagen and are encountered in older subjects.

The primary consideration in surgical treatment of desmoid tumours should be the prevention of local recurrence.

In most instances, this can be achieved by wide local excision or muscle group resection.

Recurrence after surgery is well recognized and tumour recurrence as late as 5 and 10 years after initial surgery has been documented.

Desmoplastic fibroma of bone is considered the osseous counterpart of the soft tissue desmoid tumour.

Other related lesions: Infantile Myofibromatosis ; Juvenile hyaline fibromatosis ; Inclusion Body Fibromatosis ; Fibromatosis colli ; Calcifying aponeurotic fibroma.

Differential Diagnosis:

-Gastrointestinal Stromal Tumour:  

Gross features of GIST:  Soft and lobulated with hemorrhage, necrosis, or cystification. 

Intra-abdominal fibromatosis : Firm, tan, and homogeneous.

Microscopic features of GIST: Presence of spindle or epithelioid cells with variable architecture, nuclear atypia, and myxoid or hyalinized stroma. Necrosis and hemorrhage present in some cases.

Intra-abdominal fibromatosis:  Composed of broad, sweeping fascicles of monotonous spindle cells. Bland nuclear features, and finely collagenous stroma. Necrosis, hemorrhage, and myxoid degeneration are not seen.

Gastrointestinal Stromal Tumor Versus Intra-abdominal Fibromatosis of the Bowel Wall A Clinically Important Differential Diagnosis . Am J Surg Pathol 2000;24:947-957

Mesenteric Fibromatosis With Involvement of the Gastrointestinal Tract A GIST Simulator: A Study of 25 Cases. Am J Clin Pathol 2004;121:93-98

Reactive nodular fibrous pseudotumor of the gastrointestinal tract and mesentery: a clinicopathologic study of five cases. Am J Surg Pathol 2003;27(4):532-40

Beta-catenin immunohistochemistry separates mesenteric fibromatosis from gastrointestinal stromal tumor and sclerosing mesenteritis.Am J Surg Pathol. 2002 ;26(10):1296-301.

-Neurofibroma and low grade malignant nerve sheath tumour characterized by wavy elongated  nuclei and S100 positivity.

-Nodular fasciitis : Loose myxoid stroma and hemorrhage in NF. In fibromatosis greater degree of cellularity and more interstitial collagen.

-Fibrosarcoma:  Uniform mature appearance of cells and only few or no  mitotic figures in fibromatosis. Presence of atypical mitotic figures and one or more mitotic figures per high power field should raise the suspicion of malignancy.

Fibrosarcoma versus fibromatoses and cellular nodular fasciitis. A comparative study of their proliferative activity using proliferating cell nuclear antigen, DNA flow cytometry, and p53.Am J Surg Pathol. 1994 Jul;18(7):712-9.

-Low grade myofibroblastic sarcoma:  Diffusely hypercellular, shows atleast focal  mild focal nuclear atypia and is diffusely infiltrative within skeletal muscle.

-Exuberant fibroblastic proliferation after injury:    Eg. Trauma.  Focal areas of hemorrhage is present, in older case there is deposition of hemosiderin in macrophages.