Magnetic resonance imaging of the ocular motor nerves in normal volunteers

Abstract

To display the detail functional anatomy of ocular motor nerves in the orbits, cavernous sinus and brainstem by high-resolution MRI. Twenty normal subjects between 24 and 38 years of age, mean age was 28.25 +/- 4.07 (SD). Imaging of the ocular motor nerves at the brainstem was performed in 0.8 mm thickness image planes using 3D-FIESTA sequence; nerves in the cavernous sinus was imaged with a head coil, the FSE/T(1)WI was obtained in coronal planes; nerves to extraocular muscles (EOMs) in the orbits were imaged with FSE/T(1)WI oblique-coronal planes using surface coils, and within 2.0 mm thick planes. A human orbit was celloidin embedding and serially sectioned at 0.1 mm of thickness for HE stain, which would be used to distinguish motor nerves to the EOMs. Oculomotor nerves (CN3) and abducens (CN6) of the cisternal segment were well demonstrable in all normal subjects. Trochlear nerves (CN4) were depicted 95%. CN3 could be demonstrated consistently in the cavernous sinus, because of their small diameter, CN4 and CN6 not always detectable. The larger inferior division of CN3 and branches to the target EOMs and CN6 were demonstrated well in all species. The superior division of CN3 was demonstrated 60%, CN4 was showed 40%. 3D-FIESTA Sequence combined with MPR (Multiplanar Reformation) could precisely show the ocular motor nerves, as well as the relationships with adjacent structures in the cistern. The inferior division of CN3 and the CN6 could be well depicted in the orbits. But of the small sizes and complicated neighboring structures in the orbit, the superior division of the CN3 and the CN4 could not be demonstrated consistently. The capabilities of MRI can be fully used only with thorough knowledge of the complicated topographic relationships in the corresponding region.