Enchondromas (or chondromas 7) are a relatively common benign medullary cartilaginous neoplasm with benign imaging features. They account for the E in the popular mnemonic for bubbly bone lesions FEGNOMASHIC. They are sometimes classified under the umbrella term low grade chondral series tumours.
Enchondromas are most frequently diagnosed in childhood to early adulthood with a peak incidence of 10-30 years. They account for ~5% (range 3-10%) of all bone tumours and ~17.5% (range 12-24%) of benign bone tumours 1.
Mostly, they are an incidental finding. They are usually asymptomatic, but may be complicated by a pathological fracture or malignant transformation into a low-grade chondrosarcoma. The latter is rare.
It is important to note that if an enchondroma is painful in the absence of a fracture, it should be considered malignant.
Enchondromas arise from rests of growth plate cartilage/chondrocytes that subsequently proliferate and slowly enlarge and are composed of mature hyaline cartilage. Hence, they are seen in any bone formed from cartilage. Lesions are usually <3 cm, translucent, nodular, and are grossly grey-blue.
Two syndromes are associated with multiple enchondromas:
Almost all enchondromas are located centrally within the medullary cavity of tubular bones. The typical distribution is:
- small tubular bones of the hands and feet: 50% 4
- large tubular bones, e.g. femur, tibia, humerus
Rarely an enchondroma may extend through the cortex and demonstrate an exophytic growth pattern. This is known as an enchondroma protuberans, and may either be seen sporadically or as part of Ollier disease 2.
Radiograph and CT
When located in the phalanges, enchondromas are expansile and are usually purely lytic. In other locations, enchondromas are expansile, with characteristic “rings and arcs” calcifications. Typically, enchondromas are small 1-2 cm lytic lesions with non-aggressive features:
- narrow zone of transition
- sharply defined scalloped margins: may have mild endosteal scalloping
- expansion of the overlying cortex may be present, but there should not be cortical breakthrough unless fractured
- chondroid calcifications may be present: rings and arcs calcification
- no periosteal reaction
- no soft tissue mass
The majority of enchondromas more frequently arise in the metaphyseal region, owing presumably to their origin from the growth plate 1, although they are frequently seen in the diaphysis. They only rarely are seen in the epiphysis, and a cartilaginous lesion in an epiphysis is more likely to be a chondrosarcoma 3.
MRI is useful in evaluating for soft tissue extension and for confirming the diagnosis. Enchondromas appear as well circumscribed somewhat lobulated masses replacing marrow 1.
- T1: intermediate to low-signal
T1 C+ (Gd)
- enhancement is variable, and may be seen both peripherally or of translesional septae
- similar pattern of enhancement may be seen in chondrosarcomas 3,6
- typically of background intense high signal
- they can be focal regions of signal drop out where calcification present
- no bone marrow or soft tissue oedema
Differentiation of an enchondroma from a low-grade chondrosarcoma is problematic, as they can have very similar appearances. See enchondroma vs. low-grade chondrosarcoma.
Increased uptake on the bone scan can be seen with enchondromas. Intense uptake occurs with underlying pathological fracture or cortical expansion in small bones 5.
- pathological fractures
- malignant transformation into: chondrosarcomas
Treatment and prognosis
The majority of enchondromas remain asymptomatic and require no treatment. In the setting of a fracture, the bone may be allowed to heal. If necessary, a curettage and bone grafting can be performed at a later time.
If malignant transformation is suspected, which occurs in less than 5% of cases, then treatment is more aggressive 4. See also: chondrosarcoma.
The differential is significantly affected by the modality in question, and most entities below can be excluded with MRI. The exception is chondrosarcoma.
- bone infarct
- difficult to distinguish
- see: enchondroma vs low grade chondrosarcoma
- intraosseous ganglion
- other benign lytic bone lesions
- lytic metastasis to bone
- granulomatous disease
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- cartilage-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumour of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal haemangiopericytoma
- primary intraosseous haemangioma
- simple bone cyst
- impending fracture risk
- 1. Walden MJ, Murphey MD, Vidal JA. Incidental enchondromas of the knee. AJR Am J Roentgenol. 2008;190 (6): 1611-5. doi:10.2214/AJR.07.2796 - Pubmed citation
- 2. An YY, Kim JY, Ahn MI et-al. Enchondroma protuberans of the hand. AJR Am J Roentgenol. 2008;190 (1): 40-4. doi:10.2214/AJR.07.2529 - Pubmed citation
- 3. Murphey MD, Flemming DJ, Boyea SR et-al. Enchondroma versus chondrosarcoma in the appendicular skeleton: differentiating features. Radiographics. 18 (5): 1213-37. Radiographics (abstract) - Pubmed citation
- 4. Skinner HB. Current diagnosis & treatment in orthopedics. McGraw-Hill Medical. (2003) ISBN:0071387587. Read it at Google Books - Find it at Amazon
- 5. Ferrer-Santacreu EM, Ortiz-Cruz EJ, González-López JM et-al. Enchondroma versus Low-Grade Chondrosarcoma in Appendicular Skeleton: Clinical and Radiological Criteria. J Oncol. 2012;2012: 437958. doi:10.1155/2012/437958 - Free text at pubmed - Pubmed citation
- 6. Aoki J, Sone S, Fujioka F et-al. MR of enchondroma and chondrosarcoma: rings and arcs of Gd-DTPA enhancement. J Comput Assist Tomogr. 1991;15 (6): 1011-6. Pubmed citation
- 7. Douis H, Saifuddin A. The imaging of cartilaginous bone tumours. I. Benign lesions. Skeletal Radiol. 2012;41 (10): 1195-212. doi:10.1007/s00256-012-1427-0 - Pubmed citation