Objective: A central hypoechogenic line, which is perpendicular to the meniscocapsular junction, is a common ultrasonographic finding of the meniscus. The purpose of this study was to determine the histological basis of the central hypoechogenic line of the meniscus.
Methods: A total of 13 menisci were collected from 10 patients who underwent total knee replacement. All menisci appeared grossly normal were selected. Ultrasonographic images of each meniscus were obtained using 17MHz probe on coronal plane of the knee joint. Multiple histological slides were made from the imaged portion of each meniscus. Region-by-region correlation between the ultrasonographic images and histological slides was performed.
Results: Ten out of 13 menisci showed central hypoechogenic lines on ultrasonographic images. Those lines extended from the peripheral to central portion. The number of lines on US image was one (n = 8), two (n = 1) or three (n = 1). The line in the peripheral portion was more clearly demarcated than that in the central portion on US images. On histological slides hypoechogenic lines corresponded central core structure, which was normal dense fibrous tissue. Four menisci showed no line on ultrasonographic images. Histological examination of those menisci showed diffuse mucinous or fibrinous degeneration in both peripheral and central portions of menisci.
Conclusions: Central hypoechogenic line detected on ultrasonographic images of menisci could be a normal dense fibrous structure of the meniscus. The interpretation of central hypoechogenic line as the true meniscal tear should be made with caution.