Enchondroma

Enchondroma is a benign intramedullary tumour of hyaline cartilage and the most common tumour of hand bones, making up 50% of them. Most are silent, turning up on a radiograph taken for something else or announcing themselves as a low-energy fracture through a thinned cortex. The clinical work lies with the minority that are not benign, or not benign any longer.

Who. Peak incidence is 20-40 years, with a range of 10 to 60 and equal numbers of men and women.

Where. 90% arise in the tubular bones of the hands and feet. The proximal phalanx is the commonest site, then the metacarpal, then the middle phalanx.

How many. 90% of patients have a single sporadic lesion. The rest have multiple enchondromas, which is a different disease with a different risk and is classified separately.

Origin. Enchondromas arise from persistent rests of growth plate cartilage that fail to undergo normal enchondral ossification. The islands stay in the medullary cavity and may slowly enlarge. The exact molecular mechanism is unclear, but mutations in isocitrate dehydrogenase (IDH1 and IDH2) have been identified in enchondromas and in secondary chondrosarcomas alike, so the mutation marks the lineage rather than the behaviour: other genetic changes drive malignant transformation.

Macroscopically the lesion is lobulated, translucent blue-grey, firm hyaline cartilage in the central medullary cavity, with punctate white calcifications throughout. In hand bones it is typically 1-5cm.

Down the microscope it is hypocellular hyaline cartilage. Small, uniform chondrocytes sit in lacunae with small, regular, single nuclei in abundant matrix, and dystrophic calcification is common. Low cellularity is the reassuring feature.

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Telling it from low-grade chondrosarcoma on histology is difficult. The features that favour malignancy are increased cellularity, nuclear atypia with enlarged hyperchromatic nuclei, binucleate cells, myxoid degeneration and permeation into surrounding bone. None of them settles the question alone, and clinical and radiological correlation is essential: pain, axial location and a soft-tissue mass are more reliable indicators of malignancy than subtle histological change.

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Where it sits. Enchondroma is classified under benign chondrogenic tumours in the WHO Classification of Tumours of Soft Tissue and Bone. The rest of the cartilage family is worth holding in mind, and so is where each member sits: in the medulla, on the surface or in the epiphysis.

One lesion or many. Ollier disease is multiple enchondromas with a unilateral predominance. Maffucci syndrome is multiple enchondromas plus spindle cell haemangiomas. Neither is inherited: both follow somatic mosaic IDH1/IDH2 mutation. Metachondromatosis is rare and pairs enchondromas with osteochondromas.

How much risk, and driven by what. A solitary lesion carries a 1-2% lifetime risk of malignant transformation. In enchondromatosis the observed figure is 40% overall in Verdegaal's 161-patient series, and site decides it: 15% where disease is confined to the hands and feet, against 43-46% once long bones or the pelvis are involved, with a pelvic odds ratio of 3.8. The older 25-30% figure predates that series. Maffucci syndrome is conventionally held to carry a higher risk still, but the "approaching 100%" figure is not derived in any primary study - Verdegaal's series contained only 17 Maffucci patients and reported no separate rate - so it should not be quoted.

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How it presents. Half of enchondromas are incidental, found on a film taken for another reason. The commonest symptomatic presentation in the hand is a pathological fracture; otherwise a slow-growing, painless firm swelling of the affected bone. In Ollier disease the presentation may instead be angular deformity or limb length discrepancy.

What you find. The bone is diffusely expanded and the overlying skin is normal, with no erythema or warmth. The mass is firm, fixed to bone and not tender unless the bone has fractured, and movement is limited only by a fracture or a large lesion, with no mechanical block on passive motion.

The red flags. New pain in the absence of trauma is the single most important clinical discriminator between a benign enchondroma and malignant transformation, and it earns an urgent MRI with biopsy considered. The others are progressive enlargement on serial imaging, a palpable soft-tissue extension, an axial or proximal location, age over 40 years at new diagnosis, and the rare systemic symptoms of weight loss and fatigue.

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The company it keeps. Age, site, the presence or absence of pain and the pattern of calcification separate the intramedullary cartilage lesions from each other and from their mimics.

Enchondroma against bone infarct is the pairing that catches candidates, because both are central and both calcify. Enchondroma calcifies in the organised lobular rings-and-arcs pattern, expands the bone and may scallop the cortex. An infarct calcifies serpiginously, following the vascular distribution, is ringed by dense peripheral sclerosis, is often one of several, and neither expands nor scallops the bone. The answer to give is that both show central calcification, but the pattern and the behaviour at the cortex are different.

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Fibrous dysplasia is the commonest mimic. It gives a ground-glass, sclerotic-rimmed lesion that lacks the discrete punctate and ring-and-arc calcification of cartilage, and it stays low signal on T2 rather than lobular and bright.

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Enchondroma against low-grade chondrosarcoma is the decision the rest of the page turns on, and Murphey's criteria are how it is made. Read them together rather than hunting for one discriminator, and read them in the right bone: they were derived proximal to the metacarpals and metatarsals. In the hand, scalloping and expansion are expected and chondrosarcoma is rare, so applying the criteria there overcalls malignancy.

The fork. A solitary hand lesion with classic benign features is a problem of reassurance and, if it has fractured, of timing. Anything axial or proximal, painful, over 5cm, breaching cortex or arising over the age of 40 is a problem of diagnosis, and it belongs in the imaging-biopsy-pathology pathway before anyone operates. Multiple enchondromatosis is a third path: lifelong surveillance rather than a single decision.

Algorithm

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Curettage and bone grafting for hand enchondroma. The operation turns on four things: get to every recess of the cavity, take out all the cartilage, fill the defect so that a recurrence can be seen on a follow-up film, and send everything you remove to the pathologist.

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What goes wrong after curettage. Recurrence comes from cartilage left behind, and everything else follows from the window, the graft and the time spent immobilised.

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Pathological fracture is a complication of the disease, not of the surgery. Cortical thinning weakens the bone, and 38% of hand enchondromas present with a fracture through it, the proximal phalanx accounting for 40%. There is no way to prevent it; immobilise, let the fracture heal and curette afterwards, and tell the patient at diagnosis that this is what the lesion may do.

The hand is mobilised early, with finger exercises from day 1 and full activity by 3 months.

Read the early films with patience. Cancellous bone reconstitutes within about two months, but restoration of normal bone morphology takes up to a year, so a follow-up film that still looks mottled does not mean the operation has failed.

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Hand lesions do well. Curettage of a hand enchondroma has a low recurrence rate, minimal functional cost and return to full function by 3 months, and a curetted phalangeal lesion can still look durable at six years. Axial and proximal lesions recur more often, because complete removal through a difficult approach is harder to achieve.

Solitary lesions stay benign. The lifetime malignant transformation risk is 1-2%, the hand behaves best of all, and cure is the expectation after curettage. Axial lesions carry the higher risk and need surveillance. Where wide excision is performed for a grade 1 chondrosarcoma, 5-year survival is 90%.

Multiple enchondromatosis is a lifelong condition rather than an episode. Surveillance is lifelong and imaging repeated, and quality of life is impaired by the deformities and the operations they require.

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Global Epidemiology

Enchondroma is among the commonest bone tumours worldwide, but its true frequency is far higher than symptomatic series suggest. Population imaging studies repeatedly find incidental cartilage lesions in roughly 3% of adults, and modern terminology now separates benign enchondroma from atypical cartilaginous tumour (ACT) / grade 1 chondrosarcoma in long bones.

Side-by-Side Guidance: Diagnosis and Surveillance of Long-Bone Cartilage Tumours

There is no single randomised-trial-based guideline; international practice rests on bone-tumour society consensus and large referral-centre series. The major bodies converge on active surveillance for asymptomatic, imaging-benign lesions and referral of any red-flag lesion to a sarcoma unit.

Registries and Practice Variation

There is no dedicated international enchondroma registry. Outcome data derive from sarcoma-unit cohorts and national bone-tumour referral databanks (e.g. the European Musculoskeletal Oncology Society network underpinning Verdegaal 2011). Practice still varies:

• Bone-void management after hand curettage (autograft vs allograft vs cement vs nothing) shows no proven difference in recurrence or complications (Bachoura 2015, PMID 26330779) - choice is surgeon-dependent.
• Long-bone ACT/grade 1: increasing international move from wide resection toward active surveillance or intralesional curettage, but thresholds differ between centres.
• IDH1/IDH2 mutation testing is available in tertiary molecular pathology laboratories and supports diagnosis in difficult cases but is not yet a routine global standard.