Diagnostic Accuracy of Contrast and Noncontrast Magnetic Resonance Imaging

46 Background: Superior labral anterior posterior (SLAP) lesions are infrequent injuries, 47 and diagnosis by magnetic resonance imaging (MRI) is difficult and controversial. 48 Hypothesis: Based on our clinical experience, the accuracy of the MRI to diagnose a 49 SLAP lesion is less than previously reported. 50 Study Design: Diagnostic Retrospective Study 51 Methods: Between January 2006 and December 2008, 444 patients who had both 52 shoulder arthroscopy and an MRI (non-contrast or MR arthrography) at our institution 53 prior to surgery were identified and were included in the study. The radiologic diagnosis 54 and surgical evaluation were compared to determine the accuracy of diagnosing a SLAP 55 lesion by MRI. Using arthroscopy as the standard; sensitivity, specificity, accuracy, 56 positive predictive value (PPV), and negative predictive value (NPV) were calculated for 57 all MRIs, the non-intra-articular contrast MRI group, and the MR arthrography group. 58 Results: Of the 444 patients, 121 had a SLAP diagnosis by MRI and 44 had a SLAP 59 diagnosis by arthroscopy. Overall, MRI had an accuracy of 76%, a PPV of 24%, and a 60 NPV of 95%. Sensitivity was 66%, and specificity was 77%. MR arthrography had an 61 accuracy of 69%, sensitivity of 80%, and a PPV of 29%. Noncontrast MRI had an 62 accuracy of 85%, sensitivity of 36%, and a PPV of 13%. 63 Conclusions: In our retrospective study of 444 patients, sensitivity, specificity, and 64 accuracy were all lower than previously reported in the literature for diagnosing SLAP 65 lesions. Our data suggests that while MRI could exclude a SLAP lesion (NPV=95%), 66 MRI alone was not an accurate clinical tool. MR arthrography had a large number of 67 false positive readings in this study. We conclude that even with intra-articular contrast, 68 MRI has limitations in the ability to diagnose surgically proven SLAP lesions. 69