Radiological Signs in Bone Tumours

The single most important radiographic feature is the MARGIN of the lesion, classified by Lodwick: Type IA — geographic destruction with a well-defined sclerotic rim. This is the classic appearance of benign lesions (non-ossifying fibroma, enchondroma, simple bone cyst). The sclerotic rim indicates the host bone is keeping pace with the lesion's growth. Type IB — geographic destruction with a well-defined margin but NO sclerotic rim. This suggests a low-grade malignancy or aggressive benign lesion (GCT, chondrosarcoma). Type IC — geographic with an ill-defined margin. Intermediate aggressiveness. Type II — moth-eaten pattern (multiple small lytic areas without defined margins). Moderately aggressive malignancy. Type III — permeative pattern (cortical destruction without any defined lesion margin). Highly aggressive — Ewing sarcoma, osteosarcoma, lymphoma, metastases.

When a bone tumour is suspected: (1) Plain radiograph: ALWAYS the first investigation. Provides the most diagnostic information for pattern recognition. (2) MRI of the ENTIRE involved bone (including the joint above and below): shows intramedullary extent, soft tissue mass size, skip lesions, and neurovascular relationship. Essential for surgical planning. (3) CT chest: MUST be performed for pulmonary metastasis staging (the lungs are the most common site of metastasis for primary bone tumours). (4) Bone scan or PET-CT: for skeletal staging (detecting other skeletal lesions). (5) CT-guided biopsy: for histological diagnosis. CRITICAL: the biopsy tract must be planned with the surgeon who will perform the definitive surgery — a poorly placed biopsy contaminates tissue planes and may compromise limb salvage surgery.

The single most contentious area in bone tumour imaging. There is no fully reliable radiological or even histological boundary between an enchondroma and a low-grade cartilage tumour. Deep endosteal scalloping (over two-thirds of cortical thickness), lesion length, lesion-related pain, cortical destruction and a soft-tissue mass favour an atypical cartilaginous tumour / grade 1 chondrosarcoma, but each sign is less sensitive for low-grade than high-grade disease (Douis 2017). Dynamic contrast-enhanced MRI has NOT proven discriminatory. Many incidental small asymptomatic chondroid lesions in long bones are now followed rather than biopsied.

Peritumoural high T2 signal may represent oedema rather than infiltrating tumour, so MRI can overestimate intramedullary extent (a recognised limitation of the Bloem staging data). This matters for planning resection margins; surgeons correlate MRI with the histology of the resected specimen and increasingly use the marrow signal interface rather than the oedema edge to define the margin.

Technetium-99m bone scintigraphy remains widely used for skeletal staging, but FDG PET-CT offers better characterisation of metabolic activity, response assessment and detection of soft-tissue and nodal disease. Access, cost and local protocol drive the choice, and guidelines differ on whether PET-CT is routine or selective. Myeloma is a key caveat — it is frequently photopenic ("cold") on bone scan, so skeletal survey, whole-body MRI or PET-CT is preferred.

Open biopsy was historically the reference standard, but CT- or ultrasound-guided core needle biopsy at a specialist centre now achieves comparable diagnostic yield with lower morbidity for most lesions. The non-negotiable principle from the Mankin data is unchanged: whoever performs the biopsy must place the tract so it can be excised en bloc with the definitive resection, ideally planned by the operating surgeon.