Desmoplastic fibroma

Desmoplastic fibromas are extremely rare bone tumours that do not metastasise but may be locally aggressive. They are considered to be a bony counterpart of soft tissue desmoid tumours and are histologically identical. 

Epidemiology

Desmoplastic fibroma of bone is rare and mostly found in young adults and adolescents. It accounts for less than 0.1% of all bone tumours ¹. There is no sex predilection.

Diagnosis

The diagnosis of desmoplastic fibroma is secured by histology and molecular pathology.

Diagnostic criteria

Diagnostic criteria according to the WHO classification of soft tissue and bone tumours (5^th edition)¹:

• bland spindle cell morphology in bone

• collagenous matrix

The following molecular criteria are desirable ¹:

• absence of GNAS mutations for exclusion of fibrous dysplasia

• absence of MDM2 amplification for exclusion of low-grade central osteosarcoma

Clinical presentation

Usual complaints are pain or deformity. Some patients might also present with a fracture or the tumour might be found incidentally ¹.

Pathology

Desmoplastic fibroma of bone is a tumour made up of spindle cells resembling desmoid-type fibromatosis and features an infiltrative growth pattern ¹.

Aetiology

The aetiology of desmoplastic fibroma of boneis unknown¹.

Location

MostThe most frequent locations of desmoplastic fibroma of boneinclude ^1-4-5:

• mandible

• long bones (femur, radius, tibia)

  • usually located in the metaphysics or diametaphysis

• pelvic bones

Macroscopic appearance

Macroscopically desmoplastic fibroma of bone usually appears as a whorled, creamy-coloured tumour due to high collagen content featuring a firm consistency ¹.

Microscopic appearance

Microscopic features of desmoplastic fibroma of bone include the following ¹:

• low cellularity consistent ofwith bland spindle cells in a collagenous matrix

• scant mitoses

• no necrosis

• main cell types include fibroblasts, myofibroblasts, and undifferentiated mesenchymal cells ⁵

Immunophenotype

Immunohistochemistry stains can be positive for β-catenin ¹.

Radiographic features

General imaging features of desmoplastic fibroma of bone comprise the following ^1-3:

• usually well-defined or partly well-defined

• narrow transition zone

• lobulated form

• expansile growth

• sometimes with cortical bone destruction and extension into the surrounding tissues

Plain radiograph

On plain radiographs desmoplastic fibroma of bone will usually show the following characteristics ^3,4-5:

• osteolytic or mixed osteolytic / mildly sclerotic matrix

• well-defined or partly well-defined margins

• possible endosteal scalloping or cortical breakthrough

• geographic pattern of bone destruction

• often non-sclerotic margins

• internal pseudotrabeculation: >90% 

• no matrix mineralisation

• widening of the host bone from gradual apposition of periosteal new bone formation: ~90%

CT

CT will show a soft tissue density mass and will show cortical erosion in a high percentage possibly associated with infiltration of the surrounding tissues ³.

MRI

In addition to the general imaging features, MRI shines in depicting soft tissue expansion ^1,3,4. In addition to the solid tumour component, there might be cystic changes present.

Signal characteristics are usually as follows:

• T1: low signal intensity (isointense or hypointense to muscle)

• T2: background intermediate to high signal with intrinsic low to intermediate intensity foci within^6,7

• T1 C+ (Gd): heterogeneous enhancement

Nuclear medicine

Bone scintigraphy/FDG PET

Desmoplastic fibroma of bone might show increased uptake ¹.

Radiology report

The radiological report should include a description of the following:

• form and location

• tumour margins and transition zone

• endosteal scalloping

• cortical breakthrough

• infiltration of the surrounding tissues

Treatment and prognosis

Despite being benign it is a still locally aggressive tumour. En bloc resection is the current treatment of choice⁸.  

Due to its rarity, the prognosis is difficult but it is considered a slow-growing progressive tumour, which shows a local aggressive behaviour ¹.

Complications

If left untreated it can lead to the following ^1,2:

• pathologic fracture

• transition to osteosarcoma (extremely rare)

• perineural extension ⁹

History and etymology

InitiallyDesmoplastic fibroma was initially described by H Lthe American bone pathologist Henry Lewis Jaffe (1896-1979) in 1958 ⁶¹⁰.

Differential diagnosis

Conditions which can mimic the presentation and/or the appearance of desmoplastic fibroma of bone include:

• osteosarcoma

• osteoblastoma

• non-ossifying fibroma

• chondromyxoid fibroma

• brown tumour

• giant cell tumour of bone

See also

• desmoid-type fibromatosis