Enchondroma

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)
    • pelvis
    • ribs
    • scapula

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.

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
  • T2
    • 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.

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.

The differential is significantly affected by the modality in question, and most entities below can be excluded with MRI. The exception is chondrosarcoma.

Bone tumours

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.

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Article information

rID: 7620
Synonyms or Alternate Spellings:
  • Chondroma
  • Enchondromas
  • Enchondromata

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Cases and figures

  • Distribution of e...
    Figure 1: distribution of enchondromas
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  • Enchondroma & pat...
    Case 1: with pathological fracture
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  • Figure 2: hand distribution
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  • Enchondroma  T1
    Case 2: T1
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  • Case 3: with pathological fracture
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  • 5 months from pre...
    Case 4
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  • Case 5
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  • Case 6
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  • Case 7
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  • Case 8: rib enchondroma
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  • Case 9: on bone scan
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  • Case 10
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  • Case 11
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  • Case 12: T1
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  • Case 12: T2
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  • Case 13: with pathological fracture
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  • Case 14: in 5th finger
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  • Case 15: involving right 10th rib
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  • Case 16
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  • Case 17
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  • Case 18: bone scan
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  • Case 19
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  • Case 20
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  • Case 21
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