Enchondromas can occur anywhere in the skeleton. In very rare cases, a benign enchondroma undergoes malignant transformation into secondary chondrosarcoma (see Plate 6-17). However, aggressive appearing lesions in the hands are still nearly always benign. The uncommon occurrence of multiple lesions is known as enchondromatosis, or Ollier disease, and these patients more commonly have malignant degeneration of their enchondromas so they require surveillance of their lesions (see Plate 6-17).

Diagnostic Studies. Radiographs show a central radiolucent lesion with a well-defined but minimally thickened bony margin. During the active phase in adolescence, the lesion may slowly enlarge. In the inactive, or latent, phase in adulthood, the cartilaginous tissue may calcify in a diffuse punctate or stippled configuration. These calcifications sometimes appear on the radiograph as subtle “smoke ring” or “ring and arc” images. As the lesion matures, it develops a more reactive margin.

Bone scans can demonstrate radioisotope uptake. CT or MRI may be used to assess cortical erosion, intralesional calcification, and exact location. CT is also useful to rule out a soft tissue mass, which is indicative of chondrosarcoma. There are parathyroid hormone receptor-1 (PTHR1) mutations in about 10% of patients with enchondromatosis.

Biopsy is usually not needed to confirm the diagnosis of enchondroma, because its cartilaginous nature is evident radiographically and it is not destructive of the cortex, although these benign lesions can scallop the inside of the cortex. It can be difficult to distinguish between an active benign enchondroma and a low-grade malignant chondrosarcoma on the basis of histologic examination alone. Therefore, if there is radiographic evidence of full-thickness cortical destruction (not just endosteal scalloping from within) or MRI appearance of a soft tissue mass, this may provide evidence that the lesion is a chondrosarcoma.

Treatment/Prognosis. Asymptomatic solitary enchondromas are presumed benign and require only follow-up if pain develops or there is an increase in size. If solitary or multiple enchondromas become symptomatic and begin to enlarge, staging studies with radiographs (and if still indeterminate then MRI) are indicated to rule out malignancy.

The prognosis for benign enchondroma is excellent. The lesion usually becomes latent in adulthood, and less than 1% of asymptomatic solitary enchondromas become malignant. In enchondromatosis, however, the risk of malignant transformation is much greater (approximately 10% of cases).