An anatomic study of the inferior oblique nerve with high-resolution magnetic resonance imaging

To investigate anatomic features of the inferior oblique nerve (IObN) by high-resolution magnetic resonance (MR) imaging and cadaveric dissection. This study enrolled 100 consecutive outpatients, who underwent 3.0 T MR imaging equipped by the 32-channel head coil. The T2-weighted imaging data of IObN were extracted for analysis and compared with the findings of microsurgical dissection in 14 orbits. 50 male and 50 female subjects allotted to the imaging study were aged from 11 to 78 years. In 94 % sides, the IObN was found to separate from the inferior rectus muscle (IRM) at the level just behind to the posterior pole of the bulb. At the midpoint of the IObN part coursing along the orbital floor and above or adjacent to the infraorbital nerve and artery complex, the mean distance from the lateral margin of the IRM was 1.0 mm on the right and 0.9 mm on the left. The IObN showed upward direction change just below the belly of the inferior oblique muscle and innervated to it at the equator level in 78 sides on the right and 89 on the left. Dissected specimens revealed the consistent morphological findings of the IObN. The IObN seems to be a relatively consistent structure. Anatomic information on the IObN and surrounding structures that are provided by high-resolution MR imaging can be a help for safe surgery.