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.
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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 (5th 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 bone is unknown 1.
Location
The most frequent locations of desmoplastic fibroma of bone include 1-5:
-
long bones (femur, radius, tibia)
usually located in the metaphysis 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 with 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 3-5:
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
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 choice 8.
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:
transition to osteosarcoma (extremely rare)
perineural extension 9
History and etymology
Desmoplastic fibroma was initially described by the American bone pathologist Henry Lewis Jaffe (1896-1979) in 1958 10.
Differential diagnosis
Conditions which can mimic the presentation and/or the appearance of desmoplastic fibroma of bone include:
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