2023 Volume 10 Pages 253-257
W report the first case of hemifacial spasm (HFS) caused by vascular compression of the anterior inferior cerebellar artery (AICA) -posterior inferior cerebellar artery (PICA) common trunk anomaly at the cisternal portion of cranial nerve VII (CN VII). A 71-year-old female with a typical right HFS was admitted to our hospital. As per her magnetic resonance (MR) imaging results, no offending arteries were noted around the CN VII root exit zone (REZ). Computed tomography angiography revealed an AICA-PICA common trunk anomaly with a dominant PICA, with the rostral branch of the AICA-PICA common trunk anomaly compressing the CN VII at the cisternal portion. The patient underwent microvascular decompression (MVD), and the HFS disappeared after surgery. The amplitude of the abnormal muscle responses (AMR) disappeared immediately after complete transposition of the offending artery. However, the patient experienced mild transient facial palsy 3 days after MVD which was eventually resolved with the administration of vitamin B12. No HFS recurrence was observed during the 1-year follow-up period. The AICA-PICA common trunk anomaly has been found to cause HFS as it compressed the CN VII at the cisternal portion, and not at the REZ. AMR monitoring might be helpful for cases where the unusual vessel particularly compresses the CN VII.
Hemifacial spasm (HFS) has been commonly attributed to blood vessels compressing the cranial nerve VII (CN VII) at the root exit zone (REZ).1) However, HFS caused by vascular compression in the distal, cisternal portions of the CN VII has also been reported in a few cases.2-13) Microvascular decompression (MVD) has been noted to be a promising treatment for neurovascular compression syndromes including HFS and trigeminal neuralgia.5-7,11-20) Common offending vessels in HFS are the anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA), and vertebral artery. Only two cases of HFS associated with an AICA-PICA common trunk anomaly with a dominant PICA have been reported to date, and the vessels compressed the REZ in both cases.21,22). Here, we report the first case of HFS caused by vascular compression of the AICA-PICA common trunk anomaly with a dominant PICA at the cisternal portion of CN VII. Ethics approval was obtained from the Institutional Review Board of the Kyushu University Hospital (no. 23003-00). Written informed consent was obtained from the patient for the publication of this case report and any accompanying images.
A 71-year-old female with an 8-year history of right HFS was admitted to our hospital. The spasm was initially confined to her right superior orbicularis oculi muscle and gradually affected the entire right side. The platysma was not involved. Medical treatment with carbamazepine was deemed ineffective. She was also treated with repeated botulinum toxin injections before admission; however, the effect was only temporary. Her physical and neurological examinations, including hearing tests, were normal. No tinnitus or discernible noise was observed in the right ear. Typical clonic hemifacial spasms were evident.
Preoperative magnetic resonance (MR) imaging revealed no offending artery around the REZ of CN VII (Fig. 1A). CN VII arose >5 mm from the REZ of cranial nerve VIII (CN VIII) in the brainstem. Both nerves traveled apart toward the internal acoustic meatus in the cerebellopontine cistern. Computed tomography angiography then revealed an AICA-PICA common trunk anomaly with a dominant PICA (Fig. 1B). The rostral branch of the AICA-PICA common trunk anomaly compressed the CN VII at the cisternal portion (Fig. 1A, C). This artery passes between CV VII and VIII and was suspected to be the offending artery.
Preoperative Images.
A) Preoperative magnetic resonance imaging with 3D heavily T2-weighted image (3D-hT2WI) reveals that there is no offending artery around the cranial nerve VII (CN VII) (yellow arrowheads) at the root exit zone (REZ). The cisternal segment of CN VII is bent by the offending artery (red arrow). CN VII arises >5 mm away from the cranial nerve VIII (CN VIII) (blue arrowhead) in the brainstem.
B) Computed tomography angiography shows the anterior inferior cerebellar artery (AICA) -the posterior inferior cerebellar artery (PICA) common trunk with a dominant PICA, and this artery is suspected to be the offending artery.
C) The preoperative schema of vascular compression of the rostral branch of AICA-PICA common trunk anomaly with a dominant PICA at cisternal portion of CN VII (asterisk).
The patient then underwent MVD for the right CN VII via the lateral suboccipital approach under general anesthesia. Auditory brainstem evoked responses were monitored throughout the surgery. The abnormal muscle response (AMR), which can be evoked by stimulating one facial nerve branch in the muscles innervated by other branches of the facial nerve and is specific to patients with HFS, was also monitored. The entire courses of CN VII, CN VIII, and the arteries running near the nerves were exposed (Fig. 2A, F). CN VII arose >5 mm from the REZ of CN VIII in the brainstem. As expected, there was no offending vessel around the REZ of CN VII (Fig. 2B, C, D, F). The AICA-PICA common trunk anomaly ran through CN VII and CN VIII, and the rostral branch of the AICA-PICA common trunk anomaly compressed CN VII at the cisternal portion; as a result, CNVII was bent (Fig. 2B, C, D, F). The perforators from the AICA-PICA common trunk anomaly were running to the brainstem, not to the CN VII. The offending artery was then carefully detached from the CN VII and transposed by fixing the petrous bone dura mater with Teflon felt and fibrin glue (Fig. 2E, F). The transposition of the offending artery was difficult due to a perforator. When the compression of the offending artery on CN VII was partially released, the AMR amplitude decreased (Fig. 3A). Finally, the AMR disappeared after complete transposition of the offending artery from the CN VII (Fig. 3B).
Intraoperative photograph of microvascular decompression (MVD).
A) The rostral branch of AICA-PICA common trunk anomaly runs near CN VII and CN VIII.
B) C) D) The rostral branch of AICA-PICA common trunk compresses CN VII at the cisternal portion (asterisk). There is no offending vessel in the CN VII at the REZ. The cisternal segment of CN VII is bent by the offending artery (black dotted lines).
E) The offending artery is carefully detached from CN VII (dotted lines) and then transposed and fixed to the nearby dura of the petrous bone with Teflon felt and fibrin glue.
F) The intraoperative schema of vascular compression of the rostral branch of AICA-PICA common trunk anomaly with a dominant PICA at the cisternal portion of CN VII (asterisk) (left) and vascular decompression (right).
Abnormal muscle responses (AMRs).
A) When the AICA is partly transposed from CN VII, the amplitude of the AMRs was decreased.
B) The AMRs disappear completely after complete transposition of the offending artery.
The HFS was completely resolved immediately after surgery. However, the patient developed mild House-Brackmann grade 2 facial nerve palsy 3 days after MVD, and was administered vitamin B12. Her facial nerve palsy completely resolved 6 weeks later. No HFS recurrence was observed during the 1-year follow-up period.
CN VII consists of a short central nervous system (CNS) segment with a central oligodendrocyte-derived myelination length at the proximal end and long peripheral nervous system (PNS) segment with peripheral Schwann cell-derived myelination at the distal end.7,23-25) Depending on the type of myelin sheath, tolerance to external forces may differ, with the CNS segment myelin sheath being considered more vulnerable than the PNS.26) The CNS segment is replaced by the PNS segment at the REZ, which is located within from 0.8 to 2.5 mm of the site where CN VII emerges from the brainstem.24,25,27) Due to the structural difference between the CNS and PNS segments, numerous researchers have supported the hypothesis that the cause of HFS is vascular compression, not at the PNS segment but at the CNS segment of CN VII.26,28,29) However, HFS caused by vascular compression at the cisternal portions of the CN VII has also been reported in a few cases.2-13) Some researchers have reported in their case series that the rate of HFS caused by vascular compression at the cisternal portions of the CN VII is 0.7-2.1%.5,7,30) The underlying mechanism remains to be unclear; however, as with proximal compression, structural changes, such as partial demyelination and axonal degeneration of the PNS segment of CN VII, and physiological changes may be involved in the pathogenesis of this entity.5,7,31) In contrast, Nomura et al.32) reported that the length of the CNS segment of CN VII was greater than that previously reported in pathological studies.24,25,27) These reports suggest that vascular compression of the CNS segment at the cisternal portion of the CN VII may also cause HFS. In this case, the distance from the brainstem to the vascular compression point was 5 mm.
Previous reports have demonstrated that the clinical outcomes of patients with HFS and distal compression may be worse than those of patients with proximal compression.7,13) Chang et al.7) reported that excellent surgical results (complete resolution of spasm) were achieved in 87.7% (1773/2022) of patients in the proximal compression group, 86.1% (87/101) in the mixed compression group, and 71.4% (10/14) in the cisternal compression group from a total of 2127 cases. In our case, although the compression point was at the cisternal portion of CN VII, the facial spasms disappeared immediately after surgery.
In cases where the compression site was at the cisternal portion of CN VII, the offending artery was the AICA in 84.3% and the PICA in 10.9% of patients.13) In this present case, the offending vessel was determined to be the rostral branch of the AICA-PICA common trunk anomaly with a dominant PICA. The AICA-PICA common trunk anomaly has been identified as one of the most common vessel variants in the posterior circulation;33,34) however, this anomaly rarely causes HFS.21,22,34) In a study examining 159 HFS cases, the AICA-PICA common trunk anomaly with a dominant AICA or a dominant PICA compressed the REZ of the CN VII in 14 and 2 cases, respectively.22) No case has been previously reported in which the AICA-PICA common trunk anomaly with a dominant PICA caused HFS by compressing the cisternal portion of the CN VII.
The disappearance of AMR during MVD apparently guarantees a high probability of relief from HFS; however, its role in HFS caused by vascular compression at the cisternal portion of CN VII has rarely been demonstrated.6,10,35,36) In the present case, when the offending artery was partially transposed from CN VII, the amplitude of the AMR decreased and disappeared completely after complete transposition of the artery. We demonstrated that AMR was helpful in treating HFS caused by vascular compression, even at the cisternal portion of CN VII.
In our case, the patient experienced transient facial nerve palsy 3 days after MVD. Postoperative transient facial nerve palsy is commonly reported in 2.8-8.3% of patients after MVD;34) however, there are no reports of postoperative delayed transient facial nerve palsy associated with vascular compression at the cisternal portion of the CN VII. While many factors may have contributed to postoperative facial nerve palsy, direct manipulation of the nerves and impairment of blood supply should be taken into consideration.34)
We report the first case of HFS caused by vascular compression of the AICA-PICA common trunk anomaly with a dominant PICA at the cisternal portion of CN VII. AMR monitoring may be helpful for HFS caused by vascular compression at the cisternal portions of CN VII. Postoperative delayed transient facial nerve palsy can occur even in patients with HFS caused by vascular compression at the cisternal portion of the CN VII.
We would like to thank Editage (www.editage.com) for the English language editing.
This study was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS) (JP21K17456 to T. S.).
The authors declare no conflict of interest.
