Giant Cell Tumor of Fibular head - Radiograph and MRI.

Radiograph of the knee in 32 year old male patient showing well defined expansile lytic lesion seen in the  epimetaphyseal region of fibular head with thinning of the cortex and cortical break at few places.

Axial T2 FS image at the level of fibular head showing expansile lytic lesion showing fluid contents with septations, thinning of the cortex and cortical break at few places. No obvious blood fluid levels noted.

Axial T1 weighted image at the level of fibular head showing the lesion with isointense contents and thinning of the cortex.

Coronal T1 weighted images showing the lesion.

Discussion:

• GCT is a common benign but locally aggressive lesion of unknown etiology. 
• It occurs chiefly in men between 20-50 yrs (after epiphyseal closure).
• The tumor is expansile lytic lesion that involves the epiphysis & metaphysis.
• The tumor may enlarge to occupy most of epiphysis & adjacent metaphysis. 
• The tumor may erode & penetrate subchondral bone, articular cartilage, & cruciate ligaments.

Location:

• Epiphysis of distal femur, proximal tibia, & distal radius.
• Other sites: fibula, sacrum, proximal humerus, & distal tibia.
• Can occur in bones of pelvis, particularly ilium near SI joint and sacrum.

Spine:

• Usually located in vertebral body; 
• Radiolucent lesion in vertebral body of a young patient is likely to be GCT; 

Staging:
Stage I:

• Benign latent giant cell tumors.
• No local aggressive activity.

Stage II:

• Benign active GCT. 
• Imaging studies demonstrate alteration of the cortical bone structure.

Stage III:

• Locally aggressive tumors.
• Imaging studies demonstrate a lytic lesion surrounding medullary and cortical bone.
• There may be indication of tumor penetration through the cortex into the soft tissues.

IMAGING:

Radiographic Features: well-defined lytic lesion that involves the metaphysis and epiphysis (typical of a giant cell tumor);

CT Scan: helps to determine the extact amount of cortical destruction and helps determine the optimal location of the cortical window;

Bone Scans: Bone scans may show decreased radioisotope uptake in the center of lesion (doughnut sign). It is also found in ABC.

MRI:

• MRI May show fluid fluid or blood fluid levels.
• Help determine determine extent of tumor destruction and soft tissue involvement.
• May be indicated when the tumor has eroded through the cortex and allows determination of whether concomitant neurovascular structures are involved.
• May help evaluate subchondral penetration.

Differential diagnosis:
1. Aneurysmal bone cyst - ABC.
2. Non Ossifying fibroma.