A comparison of MR images and histological findings in menisci of persons in middle or advanced age

Signal abnormalities in magnetic resonance (MR) images of the meniscus can result from various factors and may lead to a decrease in the diagnostic accuracy for meniscal tears. In particular, change in intrameniscal signal intensity has been frequently noted in persons in middle or advanced age, and is presumed to be related to the degeneration of meniscus. However, the types of histological change that might cause a change in signal intensity have not been determined. The present study compared MR images of menisci in persons of middle or advanced age with corresponding surgical and arthroscopic findings. The mean age of subjects was 62.1 years at the time of the study; 102 knees underwent arthroscopy or surgery after MRI. Regarding the validity of MR imaging, the sensitivity was as high as 83.5%, but specificity and accuracy were low (87.5% and 86.8%, respectively). There were many cases in which a change in intrameniscal signal intensity mimicked meniscal tears in persons in middle or advanced age. In order to demonstrate how a given change in intrameniscal signal intensity corresponded to a particular morbid condition, menisci were histologically examined and compared with the corresponding MR images. A total of 65 knees (21 knees from above-knee amputations and 44 removed during surgery) were studied from subjects with a mean age of 65.9 years; there were 87 medial and lateral menisci in total. The menisci were removed after MRI, and the specimens were prepared after macroscopic observation, after which they were investigated pathohistologically. The MR images were classified into 5 grades, from 0 to 4. In total, the normal signal intensity group (Grade 0) comprised 52% of specimens. Among anterior segments, Grade 0 was 73%, and the normal, low signal intensity group comprised the majority of specimens. Among posterior segments, a change in signal intensity (Grades 1 to 4) was noted in 75%. Analysis of MR grade and macroscopic findings revealed that almost no tears were present in specimens with a signal intensity of Grade 0 or 1. Regarding the correlation of MRI grade and histological findings, a high possibility causing microscopic tears and degeneration was expected in accordance with the progress of the grading, and a correlation of the progress of grading and histological changes was observed. Since changes in intrameniscal signal intensity are often revealed by MRI due to degeneration in persons in middle or advanced age, precise diagnosis may require a combination of careful physical examination and arthroscopy, keeping in mind that there will be cases in which it is difficult to distinguish a meniscal tear from natural degeneration of the meniscus by MRI alone. (author)