Objectives <p>Lumbar spinal stenosis (LSS) is a common condition characterized by the narrowing of the spinal canal, often leading to neural compression. Accurate imaging is crucial for diagnosis and surgical planning, with MRI and CT being the primary modalities. While MRI excels in soft tissue visualization, CT is superior for assessing bony structures. This study compares lumbar spinal canal cross-sectional area measurements on MRI and CT in patients undergoing surgery for LSS.</p> Methods <p>Twenty patients with LSS who underwent lumbar decompression surgery after failed conservative treatment were included. Axial MRI and CT images from L1 to S1 levels were obtained and analyzed using Radiant DICOM Viewer. The spinal canal area was measured and compared between modalities. Statistical analyses assessed the measurement discrepancies, including paired t-tests and Pearson correlations.</p> Results <p>The mean difference in cross-sectional area between MRI and CT across all levels was 26.5 mm², with MRI consistently underestimating the canal area by 15.3%. The correlation between MRI and CT measurements was high (0.775–0.950), yet significant differences were found (<i>p</i> &lt; 0.001). MRI underestimation was more pronounced in smaller spinal canals, though this trend was not statistically significant. Agreement between MRI-only evaluations and surgical findings was moderate (Cohen's Kappa = 44%, <i>p</i> = 0.035).</p> Conclusions <p>MRI's underestimation of spinal canal size compared to CT has implications for surgical planning, particularly in severe stenosis. A multimodal MRI and CT approach may improve diagnostic accuracy and surgical outcomes. Future research should involve larger cohorts to elucidate these findings further.</p>