Enchondroma

Enchondromas are relatively common benign medullary cartilaginous neoplasm, usually found in children or young adults which can lead to pathological fractures or undergo malignant degeneration. They account of the E in the popular mnemonic for bubbly bone lesions FEGNOMASHIC. 

Epidemiology

Enchondromas are most frequently diagnosed in childhood to early adulthood with a peak incidence of 10-30 years. They account for 3-10 % of all bone tumours and 12-24 % of benign bone tumours ¹.

Clinical presentation

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. 

Pathology

Enchondromas arise from chondrocytes and are composed of mature hyaline cartilage.

Associations

Two syndromes are associated with multiple enchondromas:

• Ollier disease
• Maffucci syndrome

Location

Almost all enchondromas are located in 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 a exophytic growth pattern. This is known as an enchondroma protuberans, and may either be seen sporadically or as part of Ollier disease ².

Radiographic features

Plain film and CT

Typically enchondromas are small 1 - 2cm 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

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.
• 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 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.

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 chondrosarcoma. 

Differential diagnosis

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
• chondrosarcoma
  • difficult to distinguish
  • see: enchondroma vs low grade chondrosarcoma
• intraosseous ganglion
• other benign lytic bone lesions
• metastases
• granulomatous disease : sarcoidosis, tuberculosis