Is this patient’s ACL torn? Why does the injury invoke a Brad Pitt movie?

This 39-year-old presents with chronic knee pain. Is his ACL torn? How do the findings in this case relate to the movie “A River Runs Through It”, starring Brad Pitt? You are shown a sagittal PD SPIR (image 1), sagittal T1 (image 2), and a coronal PD SPIR (image 3).

Answer: Be sure to take note of the arrow in each image. If you look carefully, you can see fibers of the ACL (that are straight, arrows in image 1 and 2) running through a morass of inflammatory tissue, thus the analogy to “A River Runs Through It”. This is perhaps best appreciated on the coronal image (image 3, arrow).

Still, a pseudomass is created. In case you were wondering what causes this swelling, there are several different etiologies. It can occur as a result of a prior single trauma. It can occur due to repetitive microinstability. Finally, it can occur as a manifestation of trochlear notch dysplasia where the notch is too narrow from side to side or too short from top to bottom, as is the case here.

You will hear a number of descriptors and signs for this phenomenon including notch synovitis, ACL swelling, mucoid degeneration and ganglion pseudocyst formation. This reader only uses the term mucoid degeneration or ganglion pseudocyst formation when there is a well-defined area of smooth T2 hyperintensity with mass effect. Check out this similar case in a 35-year-old female. For more knee case review, check out MRI Online.

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