[Microvascular decompression of pons for idiopathic hemifacial spasm and exploration of its mechanism]

To further explore the cause, mechanism and surgical treatment of idiopathic hemifacial spasm (IHFS).

Routine sagittal and coronal cryoslices of 8 (16 sides) pons were made. The sections were stained with Luxol fast blue and Nissl stains. The location of the facial nucleus and pathway of facial neurofibers in the pons were observed. Twenty-five patients with IHFS whose facial nerve root exit zone(REZ) was not compressed by vessels underwent microvascular decompression of pons.

The distances from the facial nucleus to the ventral surface of pons, the median line, and the ventroexterior surface were 12.0-12.5 mm, 6.0 mm, and 7.5-9.0 mm respectively. The distance from the facial neurofibers in the pons to the surface of the pons was 1.0 to 2.0 mm, with an average of 1.65 mm. The vascular compression was at the surface of pons, within 4 mm anterosuperior to the REZ in 25 IHFS patients. The compressing vessels were the anterior inferior cerebellar arteries and their branches. The results of decompression in 25 patients with IHFS were as follows: spasm immediately disappeared in 8 patients, and within one week in 17 patients. No recurrence was found during a follow-up period from 6 months to 5 years.

The main cause of IHFS was vascular compression, but the position of compression is not necessarily always at the REZ. The "short-circuiting" theory can only explain the cases with vascular compression at the REZ. But in cases who do not have vascular compression at the REZ, there might be dysfunction of the facial nucleus. In the present cases, vascular compression was at the surface of the brain stem anterosuperior to the REZ, pons microvascular decompression is an effective treatment.