Interpreting acute postoperative MRI after lumbar spinal fusion: a practical framework for clinical decision-making.

INTRODUCTION: Magnetic resonance imaging (MRI) is frequently performed in the acute postoperative period following lumbar spinal fusion in patients with neurological deterioration or unexpected pain. However, interpretation is often challenging due to expected postoperative changes and metal artifact, which may obscure or mimic clinically significant pathology. In the absence of a structured interpretive approach, this can lead to diagnostic uncertainty and potentially unnecessary reoperation. METHODS: A narrative review of the literature was performed focusing on acute postoperative MRI findings following lumbar spinal fusion, mechanisms of metal artifact, and contemporary artifact reduction techniques. Evidence was synthesised across four thematic domains to develop a practical, clinically applicable framework for MRI interpretation. RESULTS: Expected postoperative MRI findings include soft tissue enhancement, vertebral body or endplate enhancement, instrumentation-related artifact, and epidural fluid collections, which are frequently observed and often clinically benign. In contrast, pathological findings include significant reduction in dural sac cross-sectional area, loss of surrounding cerebrospinal fluid signal, and rim-enhancing epidural or paraspinal collections suggestive of infection. A diagnostic grey zone persists in the acute setting, where supine imaging may exaggerate apparent compression and the natural history of dural sac re-expansion and epidural collections remains poorly defined. Metal artifact further limits interpretation, although techniques such as SEMAC, MAVRIC, and VAT can significantly improve image quality. CONCLUSION: Interpretation of acute postoperative MRI following lumbar spinal fusion requires a structured, clinically integrated approach. This review proposes a practical framework to distinguish expected findings from pathological features while recognizing areas of uncertainty. Appropriate use of artifact-reduction techniques and close collaboration between surgical and radiological teams are essential to improve diagnostic accuracy and guide decision-making.