Meniscal Ossicles: What Are They, Where to Look and How to Report:
Area of ossification within the meniscus.
This is a nice article from AJR on Meniscal Ossicles which indicates that they are post traumatic in origin. (Meniscal Ossicle: Post-traumatic Origin and Association with Posterior Meniscal Root Tears. Mohankumar et al AJR 2014; 203:1040-1046).
Two possible causes:
1. Post traumatic metaplasia and heterotopic ossification of a meniscal tear (either posterior horn or root).
2. Avulsion of bone related to a meniscal root tear (less common).
Ossicles are iso-intense to bone marrow on all sequences.
Image above: well corticated meniscal ossicle (yellow arrow) following bone marrow signal. (Image Radiology Education Asia)
Be Careful of this:
Look at both the PD and PDFS/ T2FS sequences together as you may miss it if you look only at the PDFS/ T2FS sequence. This is because it contains marrow fat which will loose signal on PDFS and make the ossicle look like normal meniscus.