Various etiologies have been proposed, including trauma, hemorrhage, chronic infection, and mucoid degeneration.
Magnetic resonance imaging is the modality of choice for diagnosis of meniscal cysts.
In their most subtle form, meniscal cysts present as focal areas of high signal intensity within a swollen meniscus.
It is not uncommon for radiologists to miss this type of meniscal cyst because the signal intensity is not quite as great as fluid on T2 weighted sequences.2 When this fluid is extruded into the adjacent soft tissues, the swollen meniscus subsequently assumes a more normal shape, and the extruded fluid demonstrates a higher T2 signal typical of parameniscal cysts.
Sagittal T2 images of a medial meniscus horizontal tear extending into a meniscal cyst.