We discuss the relationship between the signal intensity detected in the T2-weighted MR images of the retrodiscal tissue of a patient suffering from a TMJ disc perforation.
Material and Methods: Using T2-weighted MR images and double-contrast arthrotomographs with fluoroscopic arthrography, the TMJ's of 93 patients were obtained for diagnostic observations of disc perforations. Observations of each MR image were made at two separate times. Accuracy, sensitivity, specificity and positive and negative predictive values of the disc perforation were determined using high signals detected in the MR images. We also calculated the kappa coefficient of Cohen for examinating the reliability of the observer.
Results: In the first observation, the high signal in the MR image of the retrodiscal tissue was detected in 92% of the perforation group (that is, 35 of 38 patients), and 46% (25 of 55 patients) of the non-perforation group. In addition, a low signal was detected in 8 % of the perforation group (3 of 38 patients), and 54% (30 of 55 patients) of the non-perforation group. In the second observation, a high signal was detected in 87% of the perforation group (33 of 38 patients), and 26% (16 of 55 patients) of the non-perforation group. In addition, a signal was detected in 13% of the perforation group (5 of 38 patients), and 74% (39 of 55 patients) of the non-perforation group. A significant difference (p<0.05) was obtained between the perforation group and the non-perforation group in high signal frequencies detected during both observations. When the high signal was regarded as on indication of a disc perforation, the sensitivity in diagnostic detection was 70-77%. In addition the negative predictive value was 89-91%. The kappa coefficient of Cohen showing the observer's reliability was 0.759, which can be classified into the category of substantial. This value was also considered to be clinically acceptable.
Conclusion: The frequency of high signals was significantly higher in the perforation group of patients. A high signal is considered to be an accurate indicator of a disc perforation on MR images. In addition when a low signal was observed on T2-weighted MR images of the retrodiscal tissue, we were able to discount the diagnosis of a disc perforation. This method using the signal intensity of MR images as a standard is effective one for detecting disc perforations.
