This 22-year-old has medial pain from a fall. You are shown three sagittal images (images 1-3): a T1, a simple 2D gradient-echo, and a proton density with fat suppression frequency selective. You are also shown a coronal proton density fat suppression image (image 4). Your first step is to establish if this is a meniscus tear. Spoiler alert: it’s not. What are your next steps?
Now that you’ve established this isn’t a meniscal tear, your next job is to decide what it is and if it’s a surgical meniscus. That answer is ‘no’ as well, and I’ll outline the reasons below.
- On the T1-weighted image (image 1), there is a vague, ill-defined signal in the meniscus that is not associated with signs of an axial load or translational insult such as bone contusion or subchondral fracture.
- Even though the gradient-echo image (image 2), shows prominent signal in the outer and middle thirds of the meniscus (and the patient has medial pain), such signal is:
- a. Always more prominent on gradient-echo imaging such as GRASS, FLASH, FISP and field echo
- b. The signal is window-framed by lower signal
- c. The signal does not extend into the inner third of the meniscus
- d. The signal is more intense in the outer third of the meniscus and fades as one moves inward
- e. The signal is not as bright as hyaline cartilage
- f. The signal is window-framed on every border except the posterior border where such signal is allowed to communicate with the capsule
- g. No verticality or proximal to distal orientation of the signal is noted
- h. The signal slopes gently downward from posterior to anterior
- i. The signal is not globular or cystic
Now, let’s think about the various causes or names of intrameniscal signal:
- Intrameniscal tear — I’ll use this term when there are other signs of trauma such as bone contusion, cartilage contusion, and an unequivocal abnormality that preferentially involves the inner third of the meniscus. I will also use this term when there is verticality associated with the signal.
- Meniscal contusion — Ill-defined signal with amorphous shape centrally associated with overlying bone, cartilage, or soft tissue contusion and a history of trauma.
- Meniscal ossicle — It has to have the signal of bone.
- Meniscal degeneration or mucoid degeneration — The patient should be older (preferably older than 40) and there should be other signs of degeneration such as alteration in meniscal size, chondromalacia, or alteration in femoral condylar shape, conformity or tibial shift.
- Intrameniscal cyst — The signal should be round or globular and bright on a T2 spin-echo.
- Meniscal vascularity — Young (up to age 25 but usually pre-teen), no trauma to the region, preferential to the outer third
Now, take a look at image 3. The proton density fat suppression is lauded as a meniscal sensitive sequence. Yet, the signal appears to fade and almost dissipate on this image. This would not support the diagnosis of a meniscal tear.
Finally, the proton density image (image 4) in the coronal projection shows a “dead center” symmetric horizontal area of signal change that in no way goes toward the femoral surface or the tibial surface. This is typical of noncommunicating “benign” meniscal signal. In a 22-year-old, vascularity is a common cause of this pattern. For more case review, check out MRI Online.