Strengthened thalamoparietal functional connectivity in patients with hemifacial spasm: a cross-sectional resting-state fMRI study.

OBJECTIVE: In spite of the well-known importance of thalamus in hemifacial spasm (HFS), the thalamic resting-state networks in HFS is still rarely mentioned. This study aimed to investigate resting-state functional connectivity (FC) of the thalamus in HFS patients and examine its association with clinical measures. METHODS: 25 HFS patients and 28 matched healthy controls underwent functional MRI at rest. Using the left and right thalamus as seed regions respectively, we compared the thalamic resting-state networks between patient and control groups using two independent sample t-test. RESULTS: Compared with controls, HFS patients exhibited strengthened bilateral thalamus-seeded FC with the parietal cortex. Enhanced FC between right thalamus and left somatosensory association cortex was linked to worse motor disturbance, and the increased right thalamus-right supramarginal gyrus connection were correlated with improvement of affective symptoms. CONCLUSION: Our findings indicate that the right thalamus-left somatosensory association cortex hyperconnectivity may represent the underlying neuroplasticity related to sensorimotor dysfunction. In addition, the upregulated FC between the right thalamus and right supramarginal gyrus in HFS, is part of the thalamo-default mode network pathway involved in emotional adaptation. ADVANCES IN KNOWLEDGE: This study provides new insights on the integrative role of thalamo-parietal connectivity, which participates in differential neural circuitry as a mechanism underlying motor and emotional functions in HFS patients.

Appropriate time to establish baseline responses for brain stem auditory evoked potentials during microvascular decompression for hemifacial spasm.

PURPOSE: To evaluate the appropriate time to establish baseline responses for brain stem auditory evoked potentials (BAEPs) during microvascular decompression for hemifacial spasm and its implications on the alarm criteria and outcomes. METHODS: Overall, 61 patients who had intraoperative monitoring with BAEP during microvascular decompression were retrospectively identified. The latencies and amplitudes of wave V before skin incision and at dura opening (before major manipulation) were compared with the latency and amplitude of wave V at change start (first alarm reported to the surgeon). Also, the results with respect to postoperative outcomes were evaluated. RESULTS: More alarms would have been communicated to the surgeon when baseline values were set at the beginning of the procedure, when compared with baseline values reset at dura opening (before major manipulation). CONCLUSIONS: Significant variations in BAEP latency exist before any major manipulations during microvascular decompression. Despite a false-negative case, baselines can be set before any major manipulations (e.g., just before dura opening), with an understanding of the etiology of changes to BAEPs during microvascular decompression. SIGNIFICANCE: This is the first study to establish that during intraoperative BAEP monitoring, baselines that are reset before any significant manipulations are performed, rather than at the beginning of the procedure, have a higher level of sensitivity with regards to hearing outcomes.

Neurophysiological mechanisms of conduction impairment of the auditory nerve during cerebellopontine angle surgery.

OBJECTIVE: Intraoperative auditory brainstem response (ABR)-monitoring is useful for hearing preservation in patients undergoing cerebellopontine angle surgery. Prolongation of the latency of wave V, for example, is observed under surgical stress such as cerebellar retraction. We analyzed intraoperative ABR findings to study the neurophysiological mechanism(s) underlying latency prolongation. METHODS: The ABR recorded during microvascular decompression surgery was studied in 18 patients with hemifacial spasm. We measured each trace of the ABR records, both the latency of each wave and some interpeak latencies. We also analyzed their waveforms especially in the early component, to assess changes during surgery. RESULTS: The latency of wave V varied with cerebellar retraction. The delayed latency of wave V was correlated with the prolonged interpeak latency of waves I-III. An additional wave (designated wave I') between waves I and II was appeared; it was accompanied by a prolongation in the latency of wave V. Wave I' contributed to prolongation of the interpeak latency of waves I-III, resulting in a delay in the latency of wave V. Chronological analysis revealed that the minimum latency of wave I' was the same as wave IN, suggesting that wave I' arose near the porus acusticus internus (PAI). CONCLUSION: Our study showed that cerebellar retraction may result in conduction impairment of the auditory nerve near the PAI, suggesting that the Obersteiner-Redlich zone is an electrophysiologically vulnerable site and wave I' is derived from the change in the vector of wave IN. SIGNIFICANCE: Our findings may provide neurophysiological evidence to support the theoretical model of ABR generators by Scherg and von Cramon.

Successful treatment of hemifacial spasm with selective facial nerve block using doxorubicin (adriamycin) under local anesthesia.

OBJECTIVE: To describe our experience with selective chemical rhizotomy of facial nerves using adriamycin (ADM) in a patient with hemifacial spasm (HFS). This unique technique is less invasive than intracranial neurosurgery and enables one to perform a permanent nerve block under local anesthesia. PATIENT: The patient, a 73-year-old female, had difficulty opening her left eye. Following unsuccessful treatment with anti-epileptic medicine, she received selective intraneural injections of ADM under local anesthesia. One week after the surgery the spasms had disappeared completely. No major complications were caused by this procedure and there had been no recurrence of spasms 3 years after the surgery. RESULTS: It is thought that recurrence of HFS should be observed after simple neurotomy due to regrowth of nerve fibers. However, this did not occur after chemical rhizotomy with ADM. This method clearly differs from previously used varieties of simple neurotomy because the latter technique does not cause severe destructive changes in the facial motor nucleus. CONCLUSION: Selective facial nerve chemical rhizotomy with ADM under local anesthesia may be effective in treating a subgroup of patients with HFS, especially elderly patients and those in the high-risk group for general anesthesia and intracranial neurosurgery.