Temporal Bone Magnetic Resonance Imaging Study in Hemifacial Spasm

ABSTRACT

BACKGROUND: Hemifacial spasm (HS) has been attributed frequently to vascular compression of facial nerve root exit zone from brainstem. A recent brain CT scan study showed that patients with HS had narrower posterior fossa than normal controls. However, cause relationship between narrowed posterior fossa and vascular tortuosity is unknown. METHODS: In 25 patients with HS and 29 controls, using temporal bone MRI, we measured petrous angle (PA) and pons diameter index (PDI) to define correlation between severity of posterior fossa narrowing and compression to brainstem. We compared severity of narrowing of posterior fossa between patients with and without tortuous arteries in posterior fossa. We also compared degree of narrowing of posterior fossa and clinical severity of HS. RESULTS: The mean (+/-standard deviation) of PA of 24 patients with HS (115.5 +/-6.0 degree) was significantly smaller than that of controls ( 118.6 +/- 4.8 degree). The mean (+/-standard deviation) of PDI of patients with HS (82.5 +/-4.7%) was significantly greater than that of controls (77.3 +/-3.7%). However, there was no correlation between PA and PDI in patients with HS. There was no correlation between degree of narrowing of posterior fossa and clinical severity of HS. CONCLUSIONS: Patients with HS have narrower posterior fossa as compared with controls. However, narrow posterior fossa does not seem to be a single important factor causing deformity of brainstem or tortuous arteries in posterior fossa.