Chondromyxoid fibroma

Tumor biology and incidence

Rare benign, aggressive cartilage tumor characterized by lobulated areas of spindle shaped and myxoid (stellate) cells, with abundant chondroid or myxoid matrix and interspersed giant cells
Not known to metastasize.
Least common cartilage tumor, 1% of all primary bone tumors
- Accounts for 2% of benign bone tumors

Age

Most common from 10-30 years of age; mainly adolescents and young adults

Gender

Male:Female = 2:1

Presentation

Pain near a joint without a history of trauma
Occasionally tender wwelling
Pathologic fracture (rare)
May present with a soft tissue mass and restriction of motion
Constitutional symptoms usually absent

Physical findings

Swelling
Tenderness to palpation of the affected area
Decreased range of motion

Plain films

Eccentric, radiolucent lesions with well-defined margins
Sclerotic border and "soap bubble" appearance common
Usually a purely lytic lesion, but can have mineralization and calcification
No periosteal reaction

Site

Metaphysis of long, tubular bones
More often found in the lower extremity: proximal tibia, distal femur
Usually central in location if in the small bones of the hand

Size

Between 1 and 10 cm, with 3-4 cm the average

Tumor effect on bone

Radioluscent
Can cause fusiform expansion in small bones

Bone response to tumor

Sharply circumscribed, geographic, with a sclerotic, scalloped margin
- Metaphyseal reactive sclerosis frequently observed, producing the geographic margin
Eccentric lobulated bony expansion/periosteal neo-corticalization may occur
Pseudocapsule appearance

Matrix

Calcifications not often seen on plain radiographs

Cortex

Often eroded or ballooned out

Soft tissue mass

None

Bone scan

Increased uptake of chondromyxoid fibromas seen on bone scan, but contributes little to diagnosis
Multiple lesions highly uncharacteristic of chondromyxoid fibroma

CT scan

Helps define architecture and cortical integrity
Can show mineralization of tumor

MRI

Typical cartilaginous lesions: Demonstrate low signal intensity on T1-weighted images and high signal intensity on T2-weighted images

Differential diagnosis

Giant cell tumor (generally older patients, do not have calcifications; borders generally less well defined)
Chondrosarcoma
Fibrous dysplasia and non-ossifying fibroma
Chondroblastoma (epiphyseal; rarely metaphyseal)
Unicameral bone cyst (rare after teens; lesion is central)
Aneurysmal bone cyst (also eccentric, but has greater cortical expansion)
Infection
Osteoblastoma
Osteosarcoma (either telangiectatic or chondroblastic)
Brown tumor

Natural history

No metastatic cases reported
Can be locally aggressive
Can cause bone destruction
Propensity to recur once treated
If untreated, tends to grow and infiltrate surrounding tissues

Pathology

Gross: firm tan tissue
Microscopic: Lobular pattern
- Lobule is less cellular centrally
- Composed of stellate cells in a myxoid or chondroid type matrix
- At periphery, more cellular, with spindle shaped cells
- Multinucleated cells also present

Diagnosis and treatment

Open biopsy usually necessary for this rare tumor
Curettage and bone grafting or marginal excision
Consider en bloc resection with a marginal margin if location permits removal without significant associated morbidity
Recurrence rates lower than 20%

Complications

Local recurrence rates reported between 15-25%, depending on age of the patient and type of resection (higher with intralesional excision)
Pathologic fracture through the lesion occurs 5% of the time
Complications related to surgical treatment
- Infection
- Failure of allograft
- Fracture
Malignant transformation rare; reported in association with radiation treatment
- XRT contraindicated