Enchondroma

Enchondroma is a benign tumour of hyaline cartilage that develops within the medullary cavity of bone. It is usually solitary and found incidentally, and it is one of the commonest benign bone tumours, making up about 10 to 25% of them.

The hands (phalanges and metacarpals, 40 to 50%) are the commonest site, then the femur, humerus, tibia, ribs and feet. It occurs at any age but mostly between 10 and 50 years, with no sex preference. Multiple enchondromas occur in enchondromatosis (Ollier disease and Maffucci syndrome), which carry a much higher risk of malignant change.

Most lesions are asymptomatic and are found on imaging for other reasons. The usual presentation is a pathological fracture through a hand lesion. Complications are fracture, rarely deformity, and malignant transformation to a chondrosarcoma, which is under 1% for solitary lesions in the hands and about 1 to 2% in the long bones, with higher rates in the pelvis, proximal femur, humerus, and shoulder girdle.

Pathophysiology.

Rests of growth plate cartilage that fail to ossify during growth are displaced into the metaphysis and diaphysis. Mutations in IDH1 or IDH2 (in about 50% of enchondromas) lead to production of 2-hydroxyglutarate and altered methylation. The same mutations occur in chondrosarcomas, which explains the continuum from enchondroma to atypical cartilaginous tumour (low grade chondrosarcoma) and the difficulty in separating them.

Most patients have no symptoms. In the hand, there may be painless swelling, a bony enlargement of a finger, or sudden pain after a minor injury (fracture). In long bones, pain is unusual; deep, persistent or night pain without a fracture suggests malignant change.

Examine the site for tenderness and swelling, range and deformity. Check other bones for multiple lesions, and the skin and soft tissue for haemangiomas (Maffucci syndrome).

• Radiographs: a well defined lucent lesion in the medulla with stippled, punctate or ring-and-arc calcification (chondroid matrix), mild endosteal scalloping and a thin sclerotic margin. In the hand, expansion and cortical thinning are common and the matrix is often lucent.
• MRI: a lobulated lesion with high signal on fluid sensitive sequences and low signal in the calcified areas; used when the diagnosis is uncertain.
• Features suggesting atypical cartilaginous tumour or chondrosarcoma: pain that is not due to a fracture, endosteal scalloping over two thirds of the cortical thickness, cortical destruction, soft tissue mass, periosteal reaction, size over 5 to 6 cm, growth on follow up, and a lesion in a long bone with oedema.
• Bone scan: mild to moderate uptake; marked uptake is more often in chondrosarcoma.
• Biopsy is difficult and is not reliable for separating grades; interpret with imaging, in a bone tumour centre.

Differential diagnosis.

• Atypical cartilaginous tumour and chondrosarcoma (grades 1 to 3).
• Bone infarct and fibrous dysplasia.
• Chondromyxoid fibroma and unicameral bone cyst.
• Metastasis, giant cell tumour and chondroblastoma.

Observation. Asymptomatic lesions with typical imaging need no surgery. Follow with imaging (radiograph or MRI) at 6 months and 12 months, then every year or two for several years, and report new pain. Lesions in the hand rarely need surveillance beyond the first year.

Surgery.

• Hand enchondroma with pathological fracture: allow the fracture to heal (immobilisation for 3 to 6 weeks), then curettage with bone graft or substitute if the lesion is symptomatic or at risk of refracture; some are treated at the same time as fracture fixation.
• Symptomatic or enlarging long bone lesion without malignancy features: intralesional curettage with burring and, where needed, graft or cement, with possible internal fixation for lesions with fracture risk.
• Suspected atypical cartilaginous tumour: extended curettage with adjuvants (phenol, cryotherapy or argon beam) or wide excision, chosen by site and tumour team; grade 2 or 3 chondrosarcoma needs wide resection.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over; 30 mg/kg to a maximum of 2 g in children) within 60 minutes before incision as a single dose; with severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Analgesia.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2; avoid exceeding 60 mg in 24 hours without senior review); monitor sedation and respiration and prescribe a laxative.

Monitoring. After surgery, radiographs at 6 weeks, 3 months, 6 months and 12 months to check graft incorporation and recurrence. Observed lesions are followed at 6 months and 12 months, then every year or two. Any new pain, growth or change in imaging needs prompt review and MRI.

Referral and escalation. Refer any enchondroma in a long bone, pelvis or axial skeleton, any lesion with pain or atypical features, and any patient with multiple lesions to a bone tumour service. Urgent referral for a rapidly growing lesion, a soft tissue mass or cortical destruction.

Special groups.

• Enchondromatosis (Ollier disease, Maffucci syndrome): high risk of malignant change (a large share of patients by middle age), with lifelong surveillance.
• Children: lesions near the physis may cause growth disturbance and need review.
• Pregnancy: avoid NSAIDs in the third trimester; defer non-urgent surgery.
• Kidney impairment: avoid NSAIDs and reduce morphine doses.