Enchondroma

Clinical Presentation

• Often      asymptomatic, detected incidentally (except in hand lesions).

• Hand      enchondromas: Pain due to bone expansion, cortical thinning, or      microfractures.

• Long      bone enchondromas with pain: Rule out first intra-articular pathologies, atypical      cartilage tumor or chondrosarcoma

Radiographic Features

Enchondromas are typically incidental, well-defined intramedullary lesions smaller than 5 cm. They appear lytic with a narrow transition zone and smooth margins. Characteristic “rings-and-arcs” chondroid calcifications may be present, though lesions in the hands and feet often remain purely lytic. Mild endosteal scalloping or slight expansion can occur, but cortical breakthrough, periosteal reaction, or soft-tissue mass should not be seen. These lesions usually arise in the metaphysis, reflecting their origin from the growth plate; an epiphyseal cartilaginous lesion should raise concern for chondrosarcoma.

Plain Radiograph and CT

Enchondromas usually present as small (<5 cm), intramedullary, lytic lesions with non-aggressive characteristics such as:

· well-defined margins and a narrow transition zone

· possible “rings and arcs” calcification reflecting a chondroid matrix

· in the hands and feet, frequently purely lytic without visible matrix mineralization

· occasional mild expansion and endosteal scalloping

· absence of cortical breakthrough unless secondary to a pathological fracture

MRI Findings

MRI best demonstrates lesion extent and confirms the intramedullary, lobulated nature of enchondromas.

T1-weighted:intermediate to low signal with internal low-signal foci corresponding to calcified cartilage.

T2-weighted:sharply defined high signal due to water-rich cartilage, with “rings-and-arcs” low-signal areas.

Post-contrast (T1 + Gd):peripheral or septal enhancement following the lobulated contours.

No surrounding bone-marrow or soft-tissue edema is expected. However, enhancement patterns may occasionally resemble those of low-grade chondrosarcoma, so correlation with clinical and radiographic features is essential.

Associated Syndromes

• Ollier’s      disease: Multiple enchondromas, unilateral, 20-50% malignant      transformation risk. Lesions are generally unilateral. Short stature, limb      length discrepancy, and angular deformities in bones and joints are      commonly seen.

• Maffucci      syndrome: Enchondromas + soft tissue hemangiomas; higher malignancy      risk than Ollier’s. Due to      phleboliths, hemangiomas are also detected on X-rays.

Common Sites

• Hands      (40-65%): Proximal phalanges > metacarpals > middle phalanges.

• Long      bones: Femur, humerus, tibia (metaphyseal).

• Rare      in carpal/tarsal bones or distal phalanges.

Imaging Features

• X-ray:

  • Hands: Lytic,       sclerotic rim, bone expansion, cortical thinning, calcification is not       usually seen.

  • Long       bones: Metaphyseal, indistinct margins, endosteal scalloping,       matrix calcification.

• CT: Evaluates      calcification and cortical integrity.

• MRI: Assesses      soft tissue extension, peritumoral edema, contrast enhancement (for      differential diagnosis) and fat entrapment.

• PET-CT: Useful      for enchondromatosis/pelvic lesions

Biopsy

• Not      routine; reserved for atypical features (e.g., pain, growth, or imaging      suspicious for chondrosarcoma).

• Target      less calcified, fat entrapment and heterogeneous areas on MRI. Biopsy      tract should align with potential surgical incision.

Treatment

• Asymptomatic,      small (<4 cm), stable lesions: Annual monitoring.(BACTIP Protocole* : Birmingham Atypical Cartilage Tumor Imaging Protocol)

• Surgical      indications:

  • Pain,       growth on follow-up, or pathologic fracture risk.

  • Techniques: Intralesional       curettage + adjuvant + bone-filler (PMMA/graft) ± fixation (fracture risk       in lower extremities).

  • Hand       lesions: Curettage alone/ Curettage and bone filler (PMMA/Graft)

Differential Diagnosis

• Atypical      Cartilage Tumor (ACT):

  • WHO       2020 reclassified grade I chondrosarcomas in extremities as ACT (no metastasis risk but can recur).

  • Suspect       if pain, size >4 cm, generalized endosteal scalloping.

• Chondrosarcoma:

  • Cortical       destruction, soft tissue involvement, axial skeleton location.