Enchondromas, also known as chondromas 7, are relatively common intramedullary cartilage neoplasms with benign imaging features. They share histologic features with low-grade chondrosarcoma, and are sometimes classified under the umbrella term low grade chondral series tumors.
Enchondromas account for the E in the popular mnemonic for lytic bone lesions FEGNOMASHIC.
- most frequently diagnosed in childhood to early adulthood with a peak incidence of 10-30 years
- most common primary benign bone tumor of hand/wrist
- account for ~5% (range 3-10%) of all bone tumors, and ~17.5% (range 12-24%) of benign bone tumors 1
Enchondromas are most commonly an incidental finding, most significant in that they shouldn't be confused with more aggressive lesions.
As a rule, enchondromas should be asymptomatic; however, lesions of the hands/feet may present with pain from pathological fracture or impending fracture 8.
Malignant transformation into a low-grade chondrosarcoma is rare, and may present with pain.
Enchondromas comprise lobules of mature hyaline cartilage which are partially or completely encased by surrounding normal bone 9. The cartilaginous lobules may undergo endochondral ossification, often resulting in the characteristic 'rings and arcs' pattern of mineralization.
They arise from rests of growth plate cartilage/chondrocytes which become isolated within mature bone. Hence, they may be seen in any bone formed from cartilage.
By definition, they show no histologic evidence of local invasion (which would suggest low-grade chondrosarcoma). However, it is important to be aware that enchondroma cannot be reliably distinguished from chondrosarcoma by histology, and diagnosis depends on correlation of clinical, imaging, and pathology findings 9.
Grossly, lesions are usually <3 cm, translucent, nodular, and are grossly grey-blue.
Two syndromes are associated with multiple enchondromas:
Enchondromas are typically located in a central or eccentric position within the medullary cavity of tubular bones:
- small tubular bones of the hands and feet (~50%) 4
- proximal phalanx most common 8
- large tubular bones
- e.g. femur, tibia, humerus
- rare: (consider chondrosarcoma)
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.
Enchondromas have a somewhat variable appearance by imaging, although characterization by excluding suspicious features is key. Since most are asymptomatic incidental findings, lesions in a characteristic location and appearance are not usually further investigated.
Imaging is generally less helpful in corroborating benignity of lesions in the hands/feet, as well as in enchondromatosis or skeletally immature patients 9.
Radiograph and CT
Enchondromas have a variable appearance, although typicall they are small <5 cm lytic lesions with non-aggressive features:
- narrow zone of transition
- sharply defined margins
- +/- chondroid calcification (rings and arcs calcification)
- often no matrix mineralization (purely lytic) in the hands/feet
- +/- expansile
- more commonly in hands/feet
- may have mild endosteal scalloping
- should not "grow" through cortex (unless pathologic fracture)
- pertinent negatives 9:
- no gross bone destruction
- 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 edema
Differentiation of an enchondroma from a low-grade chondrosarcoma is problematic, as they can have 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.
Treatment and prognosis
The majority of enchondromas remain asymptomatic and require no treatment.
Pathologic fractures are commonly treated by curettage and bone grafting, with follow-up x-rays to monitor for healing and recurrence. An incisional biopsy is obtained intraoperatively. Recurrence is reported in 2-15%, and suggests malignancy 8.
If malignant transformation is suspected, which occurs in less than 5% of cases, then treatment is more aggressive 4.
- pathological fracture
- malignant transformation into chondrosarcoma
The differential is significantly affected by the modality in question, and most entities below can be excluded with MRI. The exception is chondrosarcoma.
- 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
- 8. Lifchez SD, Kelamis J. Surgery of the Hand and Wrist. In: Brunicardi F, Hunter JG, Billiar T, Andersen D, Matthews J, Dunn D, Pollock RE. Schwartz's Principles of Surgery, 10th edition. (2014). ISBN: 9780071796750
- 9. Reith JD. Chapter 40 - Bone and Joints. In: Goldblum JR, Lamps LW, McKenney J, Myers JL. Rosai and Ackerman's Surgical Pathology (2017). 1740-1809. ISBN: 9780323263399
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The differential diagnosis for bone tumors is dependent on the age of the patient, with a very different set of differentials for the pediatric patient.
- bone-forming tumors
- cartilage-forming tumors
- chondromyxoid fibroma
- juxtacortical chondroma
- fibrous bone lesions
- bone marrow tumors
- other bone tumors or tumor-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumor of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal hemangiopericytoma
- primary intraosseous hemangioma
- post-traumatic cystic bone lesion
- simple bone cyst
- impending fracture risk