Hemifacial spasm etiology
Although classical hemifacial spasm (HFS) has been attributed to an atraumatic pulsatile vascular compression around the root exit zone (REZ) of the facial nerve, rare tumor-related HFS associated with meningiomas, epidermoid tumors, lipomas, and schwannomas in the cerebellopontine angle have been reported. The exact mechanism and the necessity of microvascular decompression for tumor-induced HFS is not clear, especially for vestibular schwannomas.
In clinical pediatric neurosurgery practice, fourth ventricle tumor and cerebellar tumors are not rare. However, reports of secondary refractory hemifacial spasm are very rare. No report is currently available on the treatment of hemifacial spasm secondary to fourth ventricle and cerebellar tumors in China. Zamponi et al. [Childs Nerv Syst 2011 Jun;27(6):1001-5] reported that these lesions can occur in neonates and infants, and surgical resection is effective 1).
Imaging data of 341 patients with a HFS who underwent microvascular decompression were reviewed retrospectively and compared with 360 controls. The hemodynamics of typical anatomical variations of the vertebral artery (VA) were analyzed using computational fluid dynamics (CFD) software.
Asymmetry of the left and right VAs was prevalent, and the left VA was the most dominant VA. A dominant VA was more prevalent in the HFS group than in the control group (p=0.026). A Left HFS had a significantly higher proportion of a left dominant VA, and a right HFS had a significantly higher proportion of right dominant VA (p<0.001). CFD models showed that angulation and tortuosity of vessels caused remarkable pressure difference between vascular walls of opposite sides. Dynamic clinical observations showed the mode of vessel transposition coincided with biomechanical characteristics.
Anatomical variations and hemodynamics of the vertebrobasilar arterial system are likely to contribute to vascular compression formation in a HFS2).
Liu et al. retrospectively analyzed 10 patients with vestibular schwannomas out of 5218 cases of hemifacial spasm between 2004 and 2014.
Hemifacial spasm occurred ipsilateral to the vestibular schwannoma in 9 patients and contralateral to the lesion in 1 patient. The mean follow-up period was 86 months (range, 22-140 months). All patients underwent surgery for resection of the vestibular schwannoma. Following the principle of neurovascular compression, offending vessels were found in 7 patients, no offending vessels in 2 patients, and a tumor with the displacement of brain stem contributing to contralateral facial nerve compression in 1 patient. HFS was relieved immediately postoperatively in 9 patients, whereas it improved gradually and then resolved after one month in one patient with a contralateral vestibular schwannoma.
For HFS induced by vestibular schwannomas in this study, the majority of cases are caused by a combination of tumor and vascular co-compression at the REZ. Surgical intervention resulted in resolution of symptoms. For HFS with ipsilateral vestibular schwannoma, exploration of the facial nerve root for vascular compression should be performed routinely after tumor resection. It is critical to check that no vessel is contact with the entire nerve root 3).
During the period from October 1984 to October 2008, Han et al. treated 6,910 HFS patients using a microsurgical procedure. Of these HFS patients, 55 cases were associated with cerebellopontine angle tumors. A small craniectomy was performed in order to excise the tumor. All tumors were found to compress the root exit zone (REZ) of the facial nerve to different extents, but concomitant vascular compression of the facial nerve was observed in a majority of cases, and microvascular decompression of the facial nerve at REZ was conducted in 43 of 55 patients (78.2%) by displacing the co-compressing vasculature away from the REZ and retaining it using a Teflon pad. Intraoperative findings and postoperative pathological examinations suggested that the tumors were epidermoid cysts, meningiomas, and Schwannomas. Follow-up in 48 of 55 patients for 4-230 months after surgery showed that the clinical symptoms of HFS disappeared in 43 cases, improved in two cases, and recurred in three cases. Ten patients had sequelae associated with the operation. They concluded from this study that the majority of cases of tumor-related HFS are caused by combined tumor and vascular co-compression at the REZ, and tumor removal and microvascular decompression are required in order to relieve the symptoms 4).
Kindling-like hyperactivity of the facial motor nucleus induced by constant stimulation of compressing artery is considered as the predominant mechanism underlying the pathogenesis of Hemifacial spasm (HFS).
In nearly all cases, primary hemifacial spasm is related to arterial compression of the facial nerve at root exit zone (REZ). The offending arterial loops originate from the posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA), or vertebrobasilar artery (VB). In as many as 40% of the patients, neurovascular conflicts are multiple. The cross-compression is almost always seen on magnetic resonance imagingcombined with magnetic resonance angiography.
Hemifacial spasm (HFS) associated with type 1 Chiari malformation is particularly uncommon and is limited to isolated case report.
Li et al retrospectively evaluated 13 patients who had simultaneously HFS and type 1 Chiari malformation among 675 HFS patients. Clinical features and radiological findings were collected from each patient and analyzed. All these 13 patients were surgically treated with MVD through retro-mastoid microsurgical approach, and postoperative outcomes were evaluated. A review of literature about this association was also provided. In this study, the frequency of type 1 Chiari malformation in HFS patients was 1.9 %. The clinical profile of this series of patients did not differ from typical form of primary HFS. MVD achieved satisfactory results in 11 patients (85 %) in short- and long-term follow-up. There was no mortality or severe complication occurred postoperatively. Although rare, clinician should be aware of the association of HFS and type 1 Chiari malformation and consider MVD as an effective surgical management 5).