Retrospective analysis of accuracy and positive predictive value of preoperative lumbar MRI grading after successful outcome following outpatient endoscopic decompression for lumbar foraminal and lateral recess stenosis.

OBJECTIVES: The aim of this study was to analyze the accuracy and positive predictive value (PPV) of preoperative lumbar MRI grading for successful outcome after outpatient endoscopic decompression for lumbar foraminal and lateral recess stenosis. Lumbar MRI is commonly employed in preoperative decision making to identify symptomatic pain generators amenable to surgical decompression. However, its accuracy and positive predictive value for successful postoperative pain relief after endoscopic transforaminal decompression for sciatica-type back and leg pain has not been reported. PATIENTS AND METHODS: A retrospective study of 1839 consecutive patients with a mean follow-up of 33 months that underwent lumbar endoscopic transforaminal decompression at 2076 lumbar levels was conducted. The sensitivity, specificity, accuracy, and positive predictive value of preoperative MRI grading correctly identifying the symptomatic surgical level were calculated based on the recorded intraoperatively visualized pathology and clinical outcomes assessed by both Macnab criteria and VAS score reduction.
RESULTS: Of the 1839 patients evaluated, 1750 had intraoperatively visualized stenosis in the lateral recess at the surgical level whereas 89 patients did not. Analysis of radiologist grading of exiting nerve root compression in the lumbar MRI reports in patients with visualized compressive pathology: true positive (1196), false negative (554); as compared with patients without visualized compressive pathology showed: false positive (30), and true negative (59); and allowed for calculation of sensitivity (68.34%), specificity (68.29%), accuracy (68.24%) and the positive predictive value (97.38%) in relation to successful clinical outcome of the subsequent endoscopic decompression surgery. Sensitivity (87.2%), specificity (73.03%), and accuracy (86.51%) improved when the treating surgeon graded same MRI scan for traversing nerve root compression. Taking different spinal stenosis classification systems by the radiologist and surgeon into consideration, Kappa statistic assessment of agreement between radiology and surgeon reporting of stenosis showed different degrees of concordance for extruded herniated disc (κ = 0.42; 331 patients), contained disc herniation (κ = -0.01; 648 patients), and stenosis (κ = 0.25; 860 patients). Disagreement (κ = 0.216; 440 patients) predominantly existed in grading the relevance of foraminal stenosis in the entry- (κ = 0.18; 278/440 patients), mid- (κ = -0.036; 121/440 patients), and less so in the exit zone (κ = -0.036; 41/440 patients) associated with contained (κ = -0.10; 178/440 patients), extruded disc herniations (κ = 0.4; 62/440 patients), and stenosis (κ = 0.25; 200/440 patients).
CONCLUSION: The grading of a preoperative MRI scan for lumbar foraminal and lateral recess stenosis may significantly differ between radiologist and surgeon. The endoscopic spine surgeon should read and grade the lumbar MRI scan independently to aid in appropriate patient selection for successful transforaminal endoscopic decompression surgery. More contemporary MRI reporting criteria are needed to describe the surgical anatomy in the neuroforamen and lateral recess relevant during the minimally invasive endoscopic transforaminal decompression.