Insects often uses camouflage to hide from predators. Can you find the butterfly in this picture?
In this case, a patient with chronic shoulder pain was sent for an MR arthrogram. Here is a T1-weighted image with fat saturation:
Here is the corresponding T2-weighted image with fat saturation:
Do you see anything important?
Here are the two images next to each other:
(A) T1-weighted image with fat saturation and (B) T2-weighted image with fat saturation reveal a lobulated paralabral cyst (red arrows) adjacent to the anterosuperior labrum. Note how the hyperintense fluid within the joint on makes this lesion more difficult to perceive on the T2-weighted image. As expected, the paralabral cyst is hypointense on the T1-weighted image.
I have seen several cases where paralabral cysts are missed, because they blend in with the hyperintense joint fluid on T2-weighted images. This is unfortunate, as the presence of a paralabral cyst in the shoulder is highly predictive of a labral tear.
Axial image from the same patient identifies the paralabral cyst (red arrow) and the adjacent tear of the anterosuperior labrum (yellow arrow):
Thus, on MR arthrograms, be careful not to miss paralabral cysts on T2-weighted images, due to the presence of adjacent bright joint fluid.
Did you manage to find the butterfly? Here it is (yellow arrows):