Anatomical features of the cisternal segment of the oculomotor nerve: neurovascular relationships and abnormal compression on magnetic resonance imaging.

OBJECT

The object of this study was to assess the detailed anatomical features and vascular relationships of the cisternal segment of the oculomotor nerve, and to assess the utility of MR imaging in oculomotor nerve palsy caused by abnormal compression related to arteries and tumors.

METHODS

The anatomy of the oculomotor nerve was depicted using 3D Fourier transformation constructive interference in steady-state (CISS) MR imaging in 196 volunteers (392 total nerves), in 9 patients with paralysis of the oculomotor nerve, and in 1 preoperative patient with cholesteatoma in the pontine cistern. The vessels adjacent to the oculomotor nerve were detected and compared using 3D time-of-flight MR imaging. The 3D CISS multiplanar reconstruction (MPR) images of the oculomotor nerve in cadavers and in specimens from the cadavers were used to verify the oculomotor nerve shown in the 196 patients. The images were assessed with respect to the demonstration of the oculomotor nerve, the optimal display angles on MPR images, the visualized length of the nerve, neurovascular relationships, and abnormal compression caused by arteries and tumors.

RESULTS

Three-dimensional CISS MR imaging depicted the cisternal segment of the oculomotor nerve with certainty in 100% of the patients in the transverse, sagittal, and coronal planes. Three-dimensional CISS imaging of the oculomotor nerve in 196 volunteers revealed similar results corresponding to 3D CISS MPR images of cadavers and cadaver specimens. The maximum visualized length of the oculomotor nerve was 14.61 +/- 2.33 mm. The angle between the oculomotor nerve and the median sagittal plane was 24.48 +/- 4.57 degrees on the left and 24.48 +/- 5.07 degrees on the right. The posterior cerebral artery was observed to contact the oculomotor nerve in 216 (55.1%) of 392 nerves, and the superior cerebellar artery was observed to contact the oculomotor nerve in 231 (58.9%) of 392 nerves. The abnormal nerve compression in 9 patients with paralysis of the oculomotor nerve was displayed well in all patients. The adjacent relationship of the oculomotor nerve in 1 preoperative patient with cholesteatoma in the pontine cistern was also demonstrated clearly.

CONCLUSIONS

Use of 3D CISS sequences and 3D time-of-flight sequences enables accurate identification of the cisternal segment of the oculomotor nerve, neurovascular relationships, and abnormal compression caused by arteries and tumors.