Surgical Threshold Measurements for Cervical Spinal Stenosis: Post-Myelogram Computed Tomography Versus MRI

MRI and CT myelography (CTM) are common diagnostic tests used for preoperative assessment of patients with cervical spondylotic myelopathy. The purpose of this study is to determine if MRI and CTM result in the same quantification regarding the severity of canal stenosis and cord compression.

Fifty patients with cervical spondylotic myelopathy underwent MRI and CT myelogram within a 6-month time frame preoperatively. Each spine segment (C3-C7) was measured for AP diameter of the canal and spinal cord on MRI axial, CTM axial, MRI sagittal, and CTM sagittal images. Thresholds for surgically relevant stenosis (<7 mm AP canal diameter and >0.8 AP cord:canal ratio) were developed by group consensus and used to stratify the per level data.

The mean age of the cohort was 59.6 years with 30 men and 20 women. Using the <7 mm threshold for surgery, there was 87% agreement for MRI and CTM on sagittal images and 95% agreement on axial images. More levels met criteria for surgery on MRI compared with CTM with 15% on sagittal MRI, 6% on axial MRI, 5% on sagittal CTM, and 3% on axial CTM. Using the >0.8 threshold, there was 83% agreement for MRI and CTM on sagittal images and 86% agreement on the axial images. More levels met criteria for surgery on MRI compared with CTM with 17% on sagittal MRI, 16% on axial MRI, 3% on sagittal CTM, and 3% on axial CTM.

The results of this study show that although MRI and CTM have relatively good agreement (83% to 95%) with regard to quantitative measurements of cervical spinal stenosis and cord compression, MRI may overestimate stenosis severity in approximately 12% of levels. Axial MRI images had the highest level of agreement (95%) when compared with CTM.