Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm
- Department of Neurosurgery, Mitsui Memorial Hospital, Tokyo, Japan
- Department of Otolaryngology, Mitsui Memorial Hospital, Tokyo, Japan
Department of Neurosurgery, Mitsui Memorial Hospital, Tokyo, Japan
DOI:10.4103/sni.sni_8_17Copyright: © 2017 Surgical Neurology International This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Kenichi Amagasaki, Nobuhiko Kurita, Saiko Watanabe, Naoyuki Shono, Atsushi Hosono, Kazuaki Naemura, Hiroshi Nakaguchi. Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm. 26-Apr-2017;8:67
How to cite this URL: Kenichi Amagasaki, Nobuhiko Kurita, Saiko Watanabe, Naoyuki Shono, Atsushi Hosono, Kazuaki Naemura, Hiroshi Nakaguchi. Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm. 26-Apr-2017;8:67. Available from: http://surgicalneurologyint.com/surgicalint-articles/lower-cranial-nerve-palsy-after-the-infrafloccular-approach-in-microvascular-decompression-for-hemifacial-spasm/
Background:The infrafloccular approach was introduced as a variation in microvascular decompression (MVD) for hemifacial spasm. However, the rate of postoperative lower cranial nerve (CN) palsy can be high. This study investigated the surgical factors in relation to the occurrence of postoperative lower CN palsy.
Methods:The case records of 103 patients who underwent MVD were reviewed. Dissection around the lower CNs to approach the root exit zone of CN VII was divided into two steps – incision of the rhomboid lip at the root of the lower CNs and separation of CN IX and flocculus/choroid plexus. The correlations of these steps and other characteristics to the occurrence of lower CN palsy were analyzed.
Results:Ten of the 103 patients suffered from postoperative transient lower CN palsy. The rhomboid lip was incised in 30 cases (29.1%), separation of CN IX and flocculus or choroid plexus was necessary in 24 cases (23.3%), and both steps were required in 7 cases (6.8%). The steps showed no correlation with postoperative lower CN palsy. Posterior inferior cerebellar artery (PICA) as the offending vessel was significantly correlated with postoperative lower CN palsy (P
Conclusions:Our study showed that the offending PICA was the only significant factor for postoperative lower CN palsy. Therefore, correct dissection around the lower CNs, particularly for complicated PICA, is necessary to reduce the risk of postoperative lower CN palsy.
Keywords: Infrafloccular approach, lower cranial nerve palsy, microvascular decompression, PICA
Microvascular decompression (MVD) is an established neurosurgical procedure for the treatment of hemifacial spasm (HFS). In our facility, MVD is performed with the transposition method through the recommended lateral suboccipital infrafloccular approach[
The lateral suboccipital infrafloccular approach was introduced as a variation approach in MVD for HFS. The approach requires strict caudolateral direction of the surgical access;[
Illustrations showing surgical exposure of the root exit zone (REZ) of the CN VII. Left: REZ of the CN VII (asterisk) approached through the angle formed with CN VIII and CN IX. Right: Dissection (purple arrow) along the rootlets of the lower CN. Dissection (red arrow) along the rostral margin of CN IX. Labels VII, VIII, IX, X, and XI show CN VII (facial nerve), VIII (vestibulocochlear nerve), IX (glossopharyngeal nerve), X (vagus nerve), and XI (accessory nerve), respectively. F = Flocculus; CP = Choroid plexus; Rho-L = Rhomboid lip
The offending arteries are another important factor affecting the lower CNs in this surgery. In most cases, the anterior inferior cerebellar artery (AICA), the posterior cerebellar artery (PICA), and the vertebral artery (VA) are observed in the surgical field, and single or multiple arteries can be adequately mobilized. In the surgical view, the VA is situated inside the lower CNs, so manipulation through the lower CNs is often necessary for correct mobilization.[
This study evaluated the lateral suboccipital infrafloccular approach for MVD, and investigated the correlation of the offending vessels to the occurrence of postoperative lower CN palsy.
The clinical records of 107 consecutive patients with HFS who underwent MVD at Mitsui Memorial Hospital between January 2014 and September 2015 were retrospectively reviewed. Two patients with recurrent HFS who underwent reoperation and 2 patients without available operative videos were excluded. Consequently, this study included 103 patients.
Microvascular decompression and dissection process around lower cranial nerves
MVD was performed with the transposition method through the infrafloccular approach under routine monitoring of brainstem auditory evoked potentials. Detailed surgical procedures were described previously.[
Evaluation of hemifacial spasm and complications
HFS was evaluated in March 2016 and the outcome was divided into 3 categories – no spasm, remarkable reduction in spasm, and no change in spasm. Postoperative hearing function was evaluated by the otolaryngologist as described previously.[
Fisher's exact probability test was used to assess the correlations between the presence of postoperative lower CN palsy and the following parameters independently; sex, side, dissection steps (1) and (2) above, and type of offending vessels. The t-test was used to assess the correlation between the presence of postoperative lower CN palsy and age. IBM SPSS Statistics version 23.0 for Microsoft Windows was used for the analysis, and P values of less than 0.05 were interpreted as significant.
Dissection around the lower cranial nerves
The rhomboid lip was incised in 30 cases (29.1%), separation of CN IX and flocculus or choroid plexus was necessary in 24 cases (23.3%), and both steps were required in 7 cases (6.8%). Therefore, dissection around the lower CNs was necessary in a total of 47 cases (45.6%). However, no significant relationship to postoperative lower CN palsy was found.
Outcome of hemifacial spasm and complications
The follow-up period was 6 to 26 months. HFS had completely disappeared in 91 patients, was remarkably reduced in 8 patients, and not changed in 4 patients. Two patients suffered from permanent hearing disturbance, complete loss in one, and mild hearing disturbance in one. Manipulation of the distal segments of CNs VII and VIII was necessary during the decompression process in both patients. Seven patients suffered from transient mild facial palsy which recovered shortly. Ten patients had transient lower CN palsy.
Ten patients with transient lower cranial nerve palsy
Lower CN palsy after MVD for HFS is often transient and can be affected by other factors such as intubation during anesthesia, so the frequency may have been underestimated. In this study, for the evaluation of the postoperative lower CN palsy, two dissection steps were focused on [
HFS associated with offending VA was reported to occur with higher incidence,[
Efficacy and adverse effects in the transposition method through the infrafloccular approach should be monitored continuously in the future. The transposition method should continue to be superior to the interposition method as long as the ultimate purpose of MVD is termination of vascular pulsation to CN VII, especially transposition of the VA to prevent recurrence.[
In conclusion, a relatively high rate of lower CN palsy, although transient, was observed after the infrafloccular approach. Careful dissection around the lower CNs, particularly for complicated PICA, is essential to avoid such complications.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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