Imaging of spinal metastases: modality performance, complications, and differential diagnosis

Spinal metastases are the most common malignant involvement of the axial skeleton and a major source of cancer-related morbidity. Imaging is central throughout patient management, from initial detection and differential diagnosis of vertebral lesions to staging, treatment planning, and early identification of complications. Magnetic resonance imaging (MRI) is the reference modality owing to its high sensitivity for marrow infiltration and its ability to assess epidural extension and spinal cord compression in a single examination. Computed tomography (CT) remains essential for evaluating cortical destruction and mechanical instability, particularly within the Spinal Instability Neoplastic Score (SINS) framework, although it is less sensitive for early marrow disease. Nuclear medicine and positron emission tomography (PET) techniques provide complementary whole-body assessment, with performance depending on tumour biology. While bone scintigraphy has variable specificity, SPECT improves lesion localisation. ¹⁸F-FDG PET/CT sensitivity varies according to tumour phenotype, whereas ¹⁸F-NaF PET/CT demonstrates high sensitivity for osteoblastic metastases. In prostate cancer, PSMA PET/CT offers excellent staging accuracy. Complications, including pathological vertebral compression fractures and metastatic epidural spinal cord compression, are oncologic emergencies requiring prompt imaging. Current guidelines recommend urgent MRI, ideally within 24 h. Neural compromise is graded using the Bilsky ESCC scale, and instability is assessed with SINS. Emerging MRI-based morphometric parameters remain investigational. Differential diagnosis relies primarily on T1 marrow signal assessment, integrated with CT features and advanced MRI techniques. Optimal imaging strategies require integrating modality performance with tumour biology and clinical context to guide multidisciplinary decision-making.