ACCURACY OF MRI AND MRA IN THE DIAGNOSIS OF SUPERIOR LABRUM ANTERIOR AND POSTERIOR (SLAP) LESIONS

Abstract

Introduction: Superior labrum anterior posterior (SLAP) lesions of the glenoid labrum are now well described. Symptoms of SLAP lesions are non-specific and definitive diagnosis has relied heavily on arthroscopic findings. While magnetic resonance imaging (MRI) has been well established as a very useful diagnostic tool for glenohumeral pathology, there are conflicting reports in the literature regarding the value of MRI in identifying SLAP lesions. Whether MR arthrography (MRA) is superior to conventional MRI for evaluating the superior glenoid labrum also remains controversial. The objective of this study was to evaluate and compare the accuracy of MRI and MRA in detecting SLAP lesions in a cohort of patients who underwent shoulder arthroscopy. Methods: Between 1991 and 1999, 252 patients underwent a primary shoulder arthroscopy as well as pre-operative MRI or MRA at our institution. The operative reports and imaging reports were evaluated for each patient. There were 155 males and 97 females. The average age at the time of surgery was 43 (17–77) years. SLAP lesion were classified as type I, II, III and IV according to the system described by Synder et al., Imaging reports were positive for a SLAP lesion only if a superior labral tear or SLAP lesion was specifically sighted in the text of the report. The presence or absence of a SLAP lesion was determined by the operative report. Statistical analysis was performed. Results: One hundred and twenty-two SLAP lesions were identified at arthroscopy. There were 87 Type I, 20 Type II, 9 Type III, and 7 Type IV. Eighty-seven patients with a SLAP lesion underwent pre-operative MRI and 35 patients underwent pre-operative MRA, 4 underwent both. MRI was found to have an overall sensitivity of 35% and specificity of 92%. When classified by type, the sensitivity was 32% for a type I lesion, 31% for type II, 71% for type III, and 33% for type IV. MRA was found to have an overall sensitivity and specificity of 29% and 100%, respectively. According to type of lesion, the sensitivity was 25% for type I, 25% for type II, 50% for type III, and 50% for type IV. Conclusions: These results demonstrate that both MRI and MRA are highly specific for detecting SLAP lesions, but are less sensitive. As expected, there was a trend toward increased sensitivity with increased complexity or grade of the SLAP lesion. Overall, there does not seem to be any appreciable difference between MRI and MRA with respect to SLAP lesions. Therefore, both imaging studies are useful tools in the pre-operative diagnosis of SLAP lesions.