A Novel Method for the Quantitative Evaluation of Lumbar Spinal Stenosis

Abstract

Study design A retrospective study of computed tomography (CT) myelographic images in patients with degenerative lumbar spinal stenosis (LSS). Objectives To introduce a new technique for the quantitative evaluation of LSS. Background Advances in hardware and software technology now permit inexpensive digitalization of radiological images, and enable methodologies for quantifying space available for neural elements in spinal canal. However, a valid method with quantitative evaluation of spinal stenosis in living patients has not been developed yet. Methods and materials Preoperative CT myelographic scans of 50 patients with degenerative LSS were collected for retrospective investigation. The patients subsequently underwent lumbar decompressive surgery. They included scans from thoracic vertebra 12 (T12) to sacrum (S1), in which each segment was scanned through both the vertebral body and disk. All CT scan films were digitized using a high-resolution digital camera. ImageTool™ software was used to measure three parameters: cross-sectional area of dural sac at disk level (A), cross-sectional area of spinal canal at midpedicular level (B), and cross-sectional area of vertebral body (C). The dural sac canal ratio (DSCR) was calculated as A/ B×100%. Low DSCR implied severe dural sac compression with a high degree of stenosis. The spinal canal vertebral ratio (CVR) was also calculated as B/ C×100%. Low CVR implied a low baseline of canal capacity for neural elements. They were calculated from T12 to S1. Results The study consisted of 26 male and 24 female patients, with an average age of 68.4 (35–97) years. A total of 295 segments were evaluated, of which 118 (40%) were surgically decompressed. There were wide ranges of canal cross-sectional areas (140–475 mm2) and dural sac cross-sectional area (54–435 mm2). Male patients had a slightly larger canal cross-sectional area than female patients at each level. The mean CVR was found decreased from T12 (26.1%) to L4 (18.3%). This was higher in female than in male patients, especially from T12 to L2 ( P < 0.01). There were significant correlations between spinal canal and dural sac cross-sectional area ( r = 0.55, P < 0.001), and also between CVR and DSCR ( r = 0.31, P < 0.001). Of the levels decompressed, 82% was performed from the level L2 to L5, in which there was no significant difference in canal cross-sectional area and CVR between decompression and nondecompression ( P > 0.05). There was a good correspondence between decreasing mean DSCR and increasing percentile of levels decompressed. Conclusion DSCR represents a useful method for the quantitative diagnosis of lumbar spinal canal stenosis. ImageTool™ software is a useful tool in measuring spinal morphometry.