An Optimized CT Protocol for Detecting Suspected Cauda Equina Syndrome: A Comparative Analysis with MRI

Abstract

Background and purpose: Lumbar disc herniation, potentially leading to nerve root compression and cauda equina syndrome, is typically evaluated using MR imaging. However, the limited availability of MR imaging outside regular hours in certain health care systems poses considerable challenges. This purpose of this study was to prospectively evaluate the diagnostic accuracy of an optimized CT lumbar spine protocol as a potential alternative to MR imaging in assessing suspected neural compression.

Materials and methods: Patients presenting to the emergency department with suspected cauda equina syndrome or acute radicular symptoms secondary to lumbar disc herniation referred for MR imaging were prospectively enrolled for an additional CT optimized to assess spinal stenosis. An expert radiologist, blinded to clinical data, graded canal stenosis at each lumbar level on CT. The same grading process was applied to MR imaging after a 4-week interval to maintain blinding.

Results: Fifty-nine individuals were included in the final analysis. In 22 (39%) cases, no significant stenosis was identified. In a further 22 (37%) cases, disc pathology was identified that was managed conservatively. Thirteen (22%) individuals proceeded to urgent surgical decompression. In 1 (2%) instance, an alternative diagnosis was identified. Compared with MR imaging, the sensitivity, specificity, and positive and negative predictive values for CT in detecting disc pathology in patients presenting with symptoms suggestive of acute neural compression were 97% (95% CI, 82%-99%), 97% (95% CI, 83%-99%), 97% (95% CI, 92%-99%), and 97% (95% CI, 83%-99%), respectively. CT accurately identified all cases requiring urgent decompression.

Conclusions: CT accurately predicted MR imaging findings in patients with suspected cauda equina and nerve root compression, demonstrating its utility as an adjunct tool for patient triage in emergency settings with limited MR imaging access. This protocol could enhance the allocation of emergency resources by appropriately selecting patients for emergent MR imaging.

FIG 1.

An example of a high-quality spinal stenosis CT protocol for suspected CES in a 26-year-old man. A, Midline sagittal CT demonstrates relatively mild bulging discs, most notably at L4-L5 where there is a right central protrusion, but no high-grade spinal stenosis. B, Axial CT through the L4-L5 disc level in the same patient demonstrates the degree of spinal stenosis. C, Axial T2-weighted image through same L4-L5 level.

FIG 2.

An example of a spinal stenosis CT protocol demonstrating to good effect a large disc extrusion in a 41-year-old woman with suspected CES. A, Midline sagittal CT demonstrates a large disc extrusion at L4-L5, which is causing a relatively high-grade spinal stenosis. B, Axial CT through the L4-L5 level demonstrates the same disc, which is central to the right subarticular zone extrusion. The degree of thecal sac stenosis can be confidently assessed, and there is severe right subarticular stenosis. C, Sagittal T2-weighted MR imaging demonstrates the L4-L5 disc herniation to a similar effect as in sagittal CT. D, Axial T2-weighted MR imaging through the L4-L5 disc level closely matches the axial CT representation of the disc herniation.

FIG 3.

Images demonstrate the appearance of a positive case of CES using the spinal stenosis CT protocol in a 44-year-old man. A, Axial CT through the nonstenotic L3-L4 disc level. B, Axial CT through the highly stenotic L4-L5 level, which is due to a large central disc extrusion effacing the thecal sac. C, Axial CT through the L5-S1 level with normal thecal sac dimensions.

FIG 4.

A 42-year-old female patient with suspected CES. A, Midline sagittal CT using a spinal stenosis protocol demonstrating a relatively large central disc extrusion with caudal migration at L4-L5, which is causing a high-grade spinal stenosis. B, Axial CT through the disc herniation at L4-L5. Sometimes the margins of the disc herniation are ill-defined; however, when scrolling through the axial CT, it is very evident that the thecal sac has been effaced at this level. C, Midline sagittal T2-weighted MR imaging of the same patient on the same day demonstrates the large disc extrusion with caudal migration from the L4 to L5 disc. D, Axial T2-weighted MR imaging of the L4-L5 disc level with complete effacement of thecal sac.