Importance of wide canal sign in the MR diagnosis of lumbar isthmic spondylolisthesis / 实用放射学杂志

ABSTRACT

Objective To evaluate the importance of wide canal sign (increased anteroposterior diameter of the spinal canal at L5) in the MR diagnosis of lumbar isthmic spondylolisthesis.Methods One hundred cases of bilateral isthmic spondylolisthesis at L5 confirmed with conventional radiography and/or CT were randomly collected.Another age and sex matched 100 cases without spon-dylolisthesis were collected as control group.The sagittal canal diameters at the L1 and L5 levels were measured and analyzed for all 100 cases of bilateral isthmic spondylolisthesis and 100 control subjects.For each group,the sagittal canal ratio(defined as the maxi-mum anteroposterior diameter of the canal at L5 level divided by the diameter of the canal at L1 )was calculated and compared be-tween the two groups ,and anylyzed with ROC curve.Results The mean midline sagittal anteroposterior diameter was (22.3 ± 1.34)mm at L5 in patients with lumbar isthmic spondylolisthesis,and (18.8±1.57)mm in the control subjects.The sagittal canal ratio was 1.32 in the isthmic spondylolisthesis group and 1.12 in the control subjects,which was different significantly.ROC curve illustrated that the sagittal canal ratio 1.25 was a most meanful point with 88% sensitivity and 90% specificity.Conclusion The sag-ittal canal ratio at L5 is bigger than 1.25 meaning abnormally increased sagittal canal diameter (wide canal sign),which specifically indicates the presence of bilateral pars interarticularis defects.Using this sign can help to make correct MR diagnosis and differential diagnosis of isthmic spondylolisthesis .