Differential Diagnosis:
Geographic 1B long bone lesion (well-defined, no sclerosis):
-Enchondroma
-Chondroblastoma
-Chondromyxoid fibroma
-Fibrous dysplasia
-Bone cyst
-Giant cell tumor
-Myeloma/Metastasis

Geographic 1C long bone lesion (Ill-defined):
-Chondrosarcoma
-Enchondroma (active)
-Malignant fibrous histiocytoma (MFH)
-Fibrosarcoma
-Giant cell tumor
-Osteosarcoma (lytic presentation is less than 10%)
-Metastasis

Discussion:
A chondroma is a benign neoplasm of hyaline cartilage. When it arises within the medullary cavity of bone, it is called an enchondroma. Multiple echondromas, or enchondromatosis, is known as Ollier disease. If the enchondromatosis is associated with soft tissue hemangiomas, this is known as Maffucci syndrome.

These lesions typically present between 20 and 50 years of age and are equally frequent in men and women. Enchondromas usually occur as a solitary lesion with approximately 40-65% occurring in the hands, or less frequently, the feet. Solitary enchondromas also occur in the long tubular bones in approximately 25% of cases, more frequently in the upper extremities than in the lower extremities. Rare areas of involvement include the skull, facial bones, patella, clavicle, sternum, scapula, ulna, and vertebrae. A general rule chondroid lesions of the axial skeleton are chondrosarcomas.

Solitary lesions are generally asymptomatic or associated with painless swelling. Often these tumors go unnoticed and are found incidentally on x-ray, occasionally associated with a pathologic fracture.

Radiographic features of solitary enchondromas in the hand or foot are characteristic. A well-defined, medullary lesion with lobulated contour and endosteal erosion. Cortical expansion or thickening, foci of calcification(but lesions of the hand and foot are frequently not mineralized), and pathologic fracture are also possible characteristics. Magnetic resonance imaging typically show a well-circumscribed, lobulated lesion of low signal intensity (less than or equal to skeletal muscle) on T1-weighted spin echo, and high signal intensity (similar to water) on T2-weighted spin echo.

Solitary lesions rarely undergo malignant transformation into chondrosarcomas, however lesions associated with enchondromatosis are more likely to undergo sarcomatous change than monostotic lesions. In addition to sarcomatous transformation, those with Maffucci syndrome are also at risk of developing other malignancies to include ovarian carcinomas and brain gliomas. Lesions larger than 5 cm in diameter are much more likely to be chondrosarcomas and patients are frequently older than those with enchondroma. Other finding in long bone cartilage lesions to suggest chondrosarcoma include greater than 2/3 endosteal scalloping, cortical thickening/remodeling, or soft tissue extension.

Treatment:
Observation if the lesion is asymptomatic. If a pathologic fracture is present, the fracture is first allowed to heal. Otherwise once healed, or if the tumor becomes symptomatic, it is resected with subsequent histological tests to rule out malignancy, and the extirpation cavity can be filled with autogenous spongy bone.