Pathology of Fibromatosis

Dr Sampurna Roy MD                 

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.    

2. Microscopically,  there is proliferation of palely eosinophilic fibroblasts and myofibroblasts.

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:  β-catenin is extremely useful in distinguishing desmoid fibromatosis from other spindle cell neoplasms. Vimentin - Positive ; Variably positivity for SMA, CD117 and 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.

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)

B. Plantar fibromatosis (Ledderhose's disease)

C. Penile fibromatosis (Peyronie's disease)

D. Knucle pads

II  Deep (musculoaponeurotic) fibromatoses: Also known as "deep fibromatosis" or "aggressive fibromatosis".

" The incidence of desmoid-type fibromatoses is 2–5/million/year.

They represent about 0.03% of all tumors and only 3% of all soft tissue tumors.

12–18% of the desmoid-type fibromatoses are intra-abdominal; 80% of them are located in the mesentery of the small bowel, but some may originate from the ileocolic mesentery.

Only rarely desmoid-type fibromatosis can occur in the pancreas, gastroesophageal junction, diaphragm, or the appendix."

Desmoid-type fibromatosis of the mesentery: report of a sporadic case with emphasis on differential diagnostic problems.

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. Fibromatosis of abdominal wall (abdominal desmoid)

C. Intraabdominal fibromatosis (intraabdominal desmoid)-  This usually occurs in the mesentery, in the retroperitoneum or in the omentum, is the most biologically aggressive type due to its capability of infiltration of both pelvic and abdominal organs.

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.

Gross: Firm, white, whorled cut surface which may be poorly circumscribed.

Microscopic features:

The lesion  shows proliferation of bland appearing spindle-shaped fibroblasts in a collagenous stroma with infiltrative borders.

Mitoses are rare and no atypia is seen.

Keloid-like collagen or extensive hyalinization may be present.

Those arising in the mesentery and pelvis, may show extensive myxoid change or may have fasciitis-like morphology.

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.

Immunohistochemistry:

Stain positive for vimentin and variably positive for smooth muscle actin or other muscle-specific markers by immunohistochemistry.

Rare cells may also be positive for S100 protein.

Nuclear staining for β-catenin by immunohistochemistry is positive in at least 80% of cases with some studies showig 98% nuclear staining. 

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.

GIST differs from desmoid-type fibromatosis in that it is stained for CD34 and CD117 stains, not usually expressed in desmoid-type fibromatosis.

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.

Differential diagnosis of mesenteric desmoid-type fibromatosis:  Desmoid-type fibromatosis of the mesentery: report of a sporadic case with emphasis on differential diagnostic problems.

- GIST : stained for CD34 and CD117 stains, not usually expressed in desmoid-type fibromatosis.

- Leiomyoma, Leiomyosarcoma: Express smooth muscle cell markers, including desmin, α-smooth muscle actin, and h-caldesmon, but they are negative for beta-catenin.

While all three markers are diffusely coexpressed in leiomyoma, their staining can vary in leiomyosarcomas, with cases which are stained only with α-smooth muscle actin.

Although desmoid-type fibromatosis is variably stained with α-smooth muscle actin, unlike leiomyosarcoma, it lacks cytological atypia, hypercellularity, high mitotic rate, atypical mitoses, and/or necrosis.

- Solitary fibrous tumour: May arise at any site in the body, including the mesentery.

It is characterized by a proliferation of haphazardly arranged  spindled cells.

This results in a hemangiopericytomatous growth pattern.

It is CD34 like desmoid-type fibromatosis.

However, it is negative for beta-catenin.

- Neurofibroma and low grade malignant nerve sheath tumour   Unlike desmoid-type fibromatosis, these tumors are S-100 protein positive and they do not express myogenic markers (α-smooth muscle actin or desmin).