Enchondroma

Enchondroma typically presents in middle-aged adults as a solitary, well-defined, intramedullary cartilage tumour within the metaphysis of small tubular bones of the hands and feet.

Description

Enchondroma is a benign cartilaginous neoplasm originating from the medullary bone. Characterized by the proliferation of mature hyaline cartilage, it is the most common benign bone tumor in adults. These tumors are typically asymptomatic and are often incidental findings. Enchondromas are a part of the group of benign cartilaginous tumors and are distinguished by their intramedullary location.

Pathogenesis

Enchondromas arise from residual cartilaginous rests that persist in the medullary cavity. These rests proliferate and form a tumor. The exact mechanism is not fully understood, but genetic alterations, particularly in the IDH1 and IDH2 genes, have been implicated in the pathogenesis.

Subtypes

• Solitary Enchondroma: Most common subtype, typically found in small bones of the hands and feet.
• Ollier Disease: Multiple enchondromatosis, predominantly unilateral.
• Maffucci Syndrome: Multiple enchondromas associated with soft tissue hemangiomas.

Epidemiology, Risk Factors & Associations

• Most common in adults aged 20-50 years (60%).
• No significant gender predilection.
• Genetic predisposition: IDH1 and IDH2 mutations (30-50%).
• Associations: Increased risk in Ollier disease and Maffucci syndrome.

Clinical Features

Clinically, enchondromas are often asymptomatic. When symptomatic, they may present with pain or pathologic fractures. There are no pathognomonic signs or symptoms.

Complications

• Risk of malignant transformation to chondrosarcoma (1-5%), higher in Ollier disease and Maffucci syndrome.
• Most common metastatic sites if malignant: lungs and lymph nodes.

Pathological Features

Histopathology

• Macroscopic: Well-circumscribed, lobulated, grey-white lesion.
• Microscopic: Mature hyaline cartilage with endochondral ossification.

Serology

• Non-specific.

Biochemistry

• Alkaline phosphatase may be slightly elevated.

Radiological Features

General Features

• Well-defined, lytic lesion with central calcifications.
• Most common in the small tubular bones of hands and feet.
• Usually metaphyseal or metadiaphyseal in location.
• Calcifications are often stippled or flocculent (seen in 50-70% of cases).

Features worrisome for malignant transformation:

• New lytic destruction at edge of lesion without matrix
• Destruction of established chondroid matrix
• Endosteal scalloping greater than 2/3 the cortical thickness
• Soft tissue mass

Associations:

• Ollier’s Disease: multiple lesions with asymmetric distribution.
• Maffucci Syndrome: associated with soft tissue hemangiomas.

XR

• Shows well-defined, lytic lesion with intralesional calcifications.

CT

• Non-contrast: Well-defined margins with matrix calcifications.
• Contrast: Typically non-enhancing.

MRI

• T1: Mass with nodules of iso- to hypointense signal compared to muscle.
• T2: Nodules appear hyperintense due to high water content of the mucopolysaccharide extracellular matrix
• T1 Gad+: The periphery as well as stroma between the chondroid nodules may enhance. The nodules do not enhance.

US

• B-mode: Hypoechoic lesion.
• Colour: Minimal vascularity.

NM

• PET FDG: Typically shows low uptake unless malignant transformation occurs.

Grading and Staging

Enchondromas are benign and do not have a formal grading system. Staging is not typically done.

Diagnosis

Diagnosis is primarily radiological, often incidental. Confirmation by histopathology in cases where malignancy is suspected or in symptomatic lesions.

Differential Diagnosis

• Osteochondroma: exophytic growth pattern, continuity with marrow space.
• Chondrosarcoma: Onset of pain suggests malignant transformation, size > 6 cm favours chondrosarcoma. Endosteal scalloping involving more than two-thirds of the cortical thickness.
• Bone cysts: lack of chondroid matrix.

Management

Management includes observation for asymptomatic lesions. Referral to orthopedic oncology for symptomatic lesions, lesions with atypical features, or suspected malignant transformation. Surgical excision may be required for symptomatic relief or biopsy for histological confirmation.

Differential Diagnosis

• Low-grade chondrosarcoma – Bone pain related to lesion at night. Depth of endosteal scalloping greater than two-thirds of the cortical thickness or cortical disruption with possible soft tissue extension. Epiphyseal location, though rarely seen in hands and feet. Large lesion size (i.e., over 6 cm) favours chondrosarcomas
• Giant cell tumour – Lytic, expansile lesion. Inhomogeneous/low T2 signal different from lobulated cartilage signal of enchondroma
• Aneurysmal bone cyst – Lytic, expansile lesion. Generally younger patient population. Fluid-fluid levels present on MR
• Simple bone cyst – Lytic, expansile lesion. Generally seen in childhood. Entirely cystic on MR