Figure 4b. Right superior oblique myokymia in a 39-year-old man. (a) On the transverse 3D CISS MR image (12.25/5.90), the trochlear nerve can be identified on both sides (arrowheads). On the right, a medial SCA branch (arrow) is located at the REZ of the trochlear nerve. The nerve itself can be identified as a separate structure in its distal portion. The proximal portion of the trochlear nerve cannot be distinguished from the artery, however. This finding is consistent with a vascular compression of the nerve. (b) Transverse source image from a nonenhanced 3D TOF MR angiogram (31/7) confirms that the structure that is in close contact with the trochlear nerve at the REZ is an artery (arrow), which is indistinguishable from the trochlear nerve.