MRI Findings in Patients with a History of Failed Prior Microvascular Decompression for Hemifacial Spasm: How to Image and Where to Look

BACKGROUND AND PURPOSE:A minority of patients who undergo microvascular decompression for hemifacial spasm do not improve after the first operation. We sought to determine the most common locations of unaddressed neurovascular contact in patients with persistent or recurrent hemifacial spasm despite prior microvascular decompression.MATERIALS AND METHODS:Eighteen patients with a history of a microvascular decompression presented with persistent hemifacial spasm. All patients underwent thin-section steady-state free precession MR imaging. Fourteen patients underwent repeat microvascular decompression at our institution. Images were evaluated for the following: the presence of persistent vascular compression of the facial nerve, type of culprit vessel (artery or vein), name of the culprit artery, segment of the nerve in contact with the vessel, and location of the point of contact relative to the existing surgical pledget. The imaging findings were compared with the operative findings.RESULTS:In 12 of the 18 patients (67%), persistent vascular compression was identified by imaging. In 11 of these 12 patients, the culprit vessel was an artery. Compression of the attached segment (along the ventral surface of the pons) was identified in most patients (58%, 7/12). The point of contact was proximal to the surgical pledget in most patients (83%, 10/12). The imaging interpretation was concordant with the surgical results regarding artery versus vein in 86% of cases and regarding the segment of the nerve contacted in 92%.CONCLUSIONS:In patients with persistent hemifacial spasm despite microvascular decompression, the unaddressed vascular compression is typically proximal to the previously placed pledget, usually along the attached segment of the nerve. Re-imaging with high-resolution T2-weighted MR imaging will usually identify the culprit vessel.

Hemifacial spasm (HFS) is characterized by unilateral spasms of the facial musculature.¹ While not life-threatening, the disease can profoundly reduce quality of life. It has an annual incidence of approximately 1 in 100,000 people per year.² HFS is most commonly the result of vascular compression of the facial nerve.³ Microvascular decompression (MVD) of the facial nerve is a well-established treatment for HFS with success rates exceeding 90% for the initial operation.⁴ Patients who have persistent HFS despite undergoing MVD pose a challenge for both neuroradiologists and neurosurgeons. However, many patients with unabated HFS despite prior MVD can and do benefit from repeat operations.^5,6 Failure to identify persistent vascular compression of the facial nerve can discourage reoperation and potential cure. The purpose of this article was to determine whether MR imaging could identify unaddressed neurovascular contact in patients with ongoing HFS despite prior MVD and to report the frequency and most common locations of this residual neurovascular contact.