Enchondroma
Overview
- Benign intramedullary cartilage tumor
- Overwhelmingly occur in the appendicular skeleton, especially small tubular bones (hands/feet)., but can also occur in long bones (e.g. femur, humerus)
- Typically found incidentally in adults, or after pathologic fracture
Epidemiology
- Most common benign bone tumor of the hand
- Age: 10–40 years
- No sex predilection
Pathophysiology
- Arises from residual cartilage rests in the medullary cavity
- Composed of hyaline cartilage
- May show calcification and endosteal scalloping over time
Clinical Features
- Usually asymptomatic
- May present with pain if associated with fracture or malignant transformation
Imaging Features
X-ray
- Well-defined, lytic lesion with chondroid matrix calcification ("rings and arcs")
- May cause endosteal scalloping, especially if >50% of cortical thickness
- No periosteal reaction or soft tissue mass
CT
- Better delineates matrix calcification
- Confirms absence of cortical breakthrough or soft tissue extension
MRI
- T1: Low to intermediate signal
- T2: High signal (due to cartilage)
- May see internal septations, lobulation
- Evaluate for features suggesting malignancy
Differential Diagnosis
| Diagnosis | Key Features |
|---|---|
| Low-grade Chondrosarcoma | Pain without fracture, cortical destruction, soft tissue mass, periosteal reaction |
| Fibrous dysplasia | "Ground-glass" matrix, expansion with cortical thinning, often monostotic |
| Chondromyxoid fibroma | Eccentric location, scalloped margins, metaphyseal, lobulated, rare and locally aggressive |
Management
- Observation if asymptomatic and stable
- Curettage ± bone grafting if symptomatic, growing, or concerning for malignancy
- Refer to ortho-oncology if suspicious for chondrosarcoma
Red Flags for Malignant Transformation
- Pain without fracture
- Cortical breach or soft tissue extension
- Large size (>5 cm in long bone)
- Endosteal scalloping >2/3 cortical thickness
- Interval growth on serial imaging
Pearls
- In hands/feet: almost always benign → pain usually from fracture, not malignancy
- In long bones: more caution needed
- Lesions in axial skeleton (pelvis, ribs): low-grade chondrosarcoma until proven otherwise
