Preoperative assessment of hemifacial spasm by the coronal heavily T2-weighted MR cisternography

Microvascular decompression (MVD) has become a well-established surgical procedure for hemifacial spasm (HFS). Before surgery, it is essential to evaluate any possible deformity of the brainstem and establish the precise location of the offending vessels. In the present study of HFS patients we examined coronal sections taken by heavily T2-weighted MR cisternography in addition to routine axial sections, and assessed the usefulness of these images through comparison with intraoperative findings. Eighty patients with HFS underwent preoperative coronal heavily T2-weighted MR cisternography before microvascular decompression surgery. Three neurosurgeons examined the preoperative axial and coronal MR images and evaluated vessel invagination into the brainstem. The usefulness of coronal sections was assessed statistically by the Mann-Whitney U test. Invagination of the offending vessel into the brainstem was observed in 24 cases (30.0%). In 19 patients, it was predicted preoperatively that compression of the flocculus and brainstem would be required in order to approach the offending vessels. Coronal MR cisternography was significantly more useful in cases with vessel invagination into the brainstem than in cases without invagination. Coronal sections obtained by MR cisternography are able to demonstrate the severity of vessel invagination into the brainstem as well as revealing the presence of the offending vessel. This information is helpful for planning a suitable approach to the root exit zone.