Case 5. Incidental finding on knee MR for trauma

Case first posted Fri, Nov 22, 2002; by John Hunter

from Chris Beaulieu, Stanford:

29 year old, otherwise healthy man with knee pain after skiing. MRI performed 1 week after injury, for complaint of lateral joint line pain. Other images showed a lateral meniscal tear, but no other internal derangement. What to do about the bone marrow lesion seen? We did CT 1 week after the MRI. We do have a final diagnosis but I would be interested in the group’s differential thoughts and what they would recommend doing next for such a case.

Cor T1W Cor T2W fat sat

Coronal T1W and T2W fat sat MR images

Sag T2W fat satAx PD fat sat

Sagittal T2W fat sat and axial PD fat sat MR images

Ax CT 1 mm thickCor CT reformat

Axial 1mm thick CT image and coronally reformatted CT image

Comments (4)

Jim Choi, M.D. Mar 14, 2007 11:11 PM

What about lymphoma? It would explain the MR marrow abnormality and the vague sclerosis on the CT. Lesion doesn’t fit well for GCT, hemangioma or other benign cartilage tumor.

Kirk Davis, M.D. Mar 14, 2007 11:12 PM

I’ll take a stab, literally: my main response, after showing this case to my colleagues, would be that this lesion deserves biopsy. That is what the clinicians need to know.

Why? It does not look like trauma (good place for contusion after patella disloc in this pt with mild subluxation on MR, but the configuration is all wrong, and there is no edema under the cortex, etc etc). Does not look like infection. CT rules out an unusual appearance of more common lucent lesions such as GCT, ABC, FD. Metabolic?–no. Vascular?–no vessels. Developmental?–no.

Not good for mets based on age and appearance.

My best guess is this is something which is pathophysiologically sneaky, and the sneakiest of them all is lymphoma, with other marrow malignancies lower on the list. It’s not great for that, either. Thus, a weirdo infection would have to make the list as well.

Tom Martin, M.D. Mar 14, 2007 11:14 PM

I’d have to agree with the other respondents – lymphoma would be my #1 choice (or some other funky small round blue cell). I have a similar case done in a 30-something woman with an ACL tear, only she had several lesions. I also had another similar case in an older woman (around 60) who hurt her knee doing track and field. Both were totally incidental findings. The bone scan in the first woman was normal. I’ve actually seen normal bone scans in several lymphoma/leukemia/Ewing’s cases, so I would not let a normal bone scan deter biopsy. Ultimately, I believe that is the next step in the work-up should be. So when do we find out?

Chris Beaulieu, M.D. Mar 14, 2007 11:16 PM

Excellent responses! We went down much the same lines of reasoning, and did an MR-guided biopsy to find lymphoma, which staged out as the only lesion and was treated with XRT, with good response on 6 month followup. I like this case because it nicely illustrates that marrow infiltrative lesions can be virtually invisible on CT.