Meniscial anatomy

1-We have two menisci medial and lateral.

2-The medial meniscus is much longer than lateral one and have wider curve.

3-Medial meniscus is banana shaped, while the lateral one is C shaped.

4-Each meniscus appears as a triangle with hypo intense signal (do not contain water), any intensity seen inside meniscus should be considered abnormal.

5-Each meniscus appears in MRI image formed from anterior horn and posterior one if it is seen in its medial parts while if it is cutted laterally, it will be seen as one unit (body) as seen in the diagram below.

-Remember that in all films of sagital MRI knee, you should find the patella on your left as a viewer, so you can verify always the anterior from posterior horns of menisci.

Normal lateral meniscus. Sagittal FSE PD (TR/TE 2200/15). Image is at the central aspect of the meniscus and demonstrates the triangular configuration of the anterior and posterior horns of the meniscus which are equal in size.

-How to identify lateral from medial menisci:

*By looking to the fibula if it is seen in the field of view.

*From the shape of the upper end of the tibia, where it has a lip where it join the fibula.

*The most important differentiation is that the anterior and posterior horns of the lateral meniscus are equal in size, while in the medial meniscus the posterior horn is always bigger than the anterior horn.

Lateral meniscus

Medial meniscus

Meniscial body

-Take care that just behind the posterior horn of the lateral meniscus there is the tendon of popliteus muscle which could be mistaken as a part of the posterior horn(Remember also that the length of the posterior horn is equal to the anterior horn of the lateral meniscus, so look to the posterior horn, if it is in the same size as the anterior horn, this means that the black area behind it is popliteus tendon and vice versa.

As the popliteus tendon (arrow) courses posterior to the posterior horn of the lateral meniscus, a vertical signal intensity region (arrowhead) is evident on sagittal views. This normal appearance can be confused with a longitudinal meniscal tear.