Microvascular decompression for hemifacial spasm associated with large fenestration of the vertebral artery: illustrative case

Abstract

BACKGROUND

Hemifacial spasm (HFS) associated with a large fenestration of the vertebral artery (VA) is extremely rare. Here, the authors report a case of HFS caused by this vascular anomaly and discuss its embryological background and clinical implications.

OBSERVATIONS

A man in his 30s presented with a 7-year history of right-sided HFS. MRI demonstrated vascular compression at the root exit zone of the facial nerve. MR angiography revealed an aberrant artery running parallel to the right VA, forming a large fenestration. Three-dimensional CT angiography demonstrated a common trunk giving rise to the anterior inferior cerebellar artery and posterior inferior cerebellar artery. The offending artery was identified as the common trunk.. Microvascular decompression with real-time abnormal muscle response monitoring achieved sufficient arterial transposition, with careful preservation of the brainstem perforators. The patient experienced complete resolution of spasms postoperatively, without complications.

LESSONS

A large VA fenestration may represent a persistent primitive lateral basilovertebral anastomosis. Successful surgical treatment requires a precise preoperative understanding of the complex vascular architecture and consideration of the limitations imposed by perforating branches during arterial transposition.

https://thejns.org/doi/10.3171/CASE25777

Hemifacial spasm (HFS) is characterized by unilateral, involuntary, intermittent, and paroxysmal contractions of the facial muscles. The primary cause is vascular compression of the facial nerve at the root exit zone (REZ).¹ Microvascular decompression (MVD) remains the only curative treatment.² Although preoperative imaging is essential for delineating vascular anatomy, rare vascular anomalies may complicate the mobilization of the offending artery. We report a case of HFS caused by a large vertebral artery (VA) fenestration associated with a persistent primitive lateral basilovertebral anastomosis (PLBA). In this patient, the anterior inferior cerebellar artery (AICA) and posterior inferior cerebellar artery (PICA) arose from a common trunk, coexisting with remnants of the PLBA. To the best of our knowledge, this represents the first reported case of HFS involving the coexistence of an AICA-PICA common trunk and VA fenestration.

Illustrative Case

A man in his 30s presented with a 7-year history of right-sided HFS that was refractory to oral medication and botulinum toxin injections; spasms persisted despite these treatments. MRI revealed vascular compression of the right REZ (Fig. 1A and B). MR angiography revealed an aberrant artery running parallel to the right VA (Fig. 1C). Three-dimensional CT angiography showed an aberrant artery from the right VA, forming a large fenestration with the offending vessel originating from the common trunk of the right AICA-PICA (Fig. 2A– C). The common trunk of the AICA-PICA compresses the REZ of the facial nerve (Fig. 2C). Given the patient’s young age and poor response to conservative therapy, MVD was performed under general anesthesia with real-time abnormal muscle response (AMR) monitoring at 3-second intervals.³ After dissecting the cerebellar flocculus and surrounding arteries (Fig. 3A), the offending artery was mobilized to the petrosal surface, immediately abolishing the AMR (Fig. 3B and C, Supplementary Figure 1). The arterial loop was separated from cranial nerves VII and VIII (Fig. 3D) and transposed to the petrosal surface using a Teflon sling and fibrin glue (Fig. 3E). However, mobilization was limited by multiple perforating branches (Fig. 3F). A Teflon ball was then inserted between the artery and the medial and lateral aspects of the REZ to achieve sufficient decompression (Fig. 3G and H, Video 1). The patient’s spasms resolved completely after surgery, and he was discharged without neurological deficits. At the 1-year follow-up, the patient remained symptom free.

FIG. 1.

A and B: MR images showing the offending artery attached to the REZ of the right facial nerve (arrows). C: MR angiogram demonstrating an aberrant artery running parallel to the right VA (arrow).

FIG. 2.

A and B: Reconstructed 3D CT angiograms showing persistence of the PLBA (arrow), connecting the common trunk of the AICA-PICA with the right VA. Green indicates the PICA, and purple indicates the AICA. The PLBA, common trunk of the AICA-PICA, and VA form a ring formation of VA. Free-fusion stereoscopic viewing merges two side-by-side images into a single 3D percept. C: Ventrolateral aspect of 3D CT angiogram fused with FIESTA MR image demonstrating the relationship between the common trunk as an offending artery and the cranial nerve VII-VIII complex (yellow). The arrow indicates the supraolivary fossette. The common trunk of the AICA-PICA compresses the REZ of the facial nerve.

FIG. 3.

Intraoperative photographs. A: Cerebellopontine cistern and arteries running between the lower cranial nerves and the flocculus. B: REZ of the right facial nerve following dissection of the offending artery. C: Simultaneous capture of intraoperative AMR and operative video. The AMR disappeared following dissection between the REZ and offending artery. D: Loop of the common trunk of the AICA-PICA distal to the aberrant artery. E: The loop of the common trunk was transposed and fixed to the petrosal surface using a Teflon sling. F: The offending artery (common trunk) crosses the REZ and several perforators to the medulla oblongata, with limited transposition. G: A Teflon ball was inserted between the artery and brainstem medial to the REZ. H: A Teflon ball was inserted between the artery and flocculus to create space at the REZ. Video 1 is the corresponding surgical video.

VIDEO 1. Video illustrating the preoperative imaging findings and key intraoperative steps of MVD for HFS caused by an AICA-PICA common trunk. Three-dimensional CT angiography fused with MRI demonstrates the relationship between the offending artery and the facial nerve REZ, followed by intraoperative footage showing arterial mobilization and decompression using a Teflon sling and interposition. Click here to view.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

This case highlights a rare vascular anomaly in which a large fenestration was formed by an aberrant artery, the VA, and the basilar artery. Large VA fenestrations may represent persistent PLBA and can be associated with complex offending vessels, including an AICA-PICA common trunk. Preoperative 3D angiographic reconstruction proved invaluable for delineating these anatomical variations. Although MVD was successful, mobilization was limited by multiple perforators arising from the offending artery.

Prevalence of Fenestration of the VA

VA fenestration has been reported in association with coexisting vascular diseases, such as aneurysms at the proximal bifurcation of the fenestration,^4–6 and a fusiform aneurysm.⁷ Large VA fenestrations extending to the basilar artery have also been described in autopsy cases.⁸ The reported incidence of basilar artery fenestration ranges from 1.0% to 2.1%, with the most frequent location at the proximal basilar artery, based on large-scale retrospective studies using MR angiography.^9–11 In one MR angiographic study that included the intracranial VA, the overall prevalence of fenestration was 2.77%.⁹ A combined MR and CT angiography study, which also included the extracranial VA, demonstrated a prevalence of 0.1%; however, the most frequent fenestration site within the VA was the intracranial portion (V4 segment).¹² Triantafyllou et al. retrospectively evaluated the presence of vertebral fenestration in 505 patients undergoing 3D CT angiography, identifying 2 cases (0.4%) with fenestration at the vertebrobasilar junction, formed by a variant vessel arising from the VA and reconnecting with the basilar artery shortly after its origin.¹³ A recent meta-analysis of VA fenestrations in the V3 and V4 segments reported a prevalence of 0.3%.¹⁴ Overall, VA fenestration is rare, but reported prevalence varies across studies due to differences in imaging techniques and the anatomical regions examined.

Embryological Consideration

Posterior circulatory fenestration is closely associated with embryonic development. The longitudinal neural artery (LNA) and PLBA play central roles in the vertebrobasilar system.¹⁵ The development of the PLBA has been investigated previously, based on Padget’s study¹⁵ and Moffat’s subsequent clarifications.¹⁶ Basilar artery fenestration may persist when fusion is incomplete during embryonic development.¹⁷ However, large fenestrations cannot be explained solely by the incomplete fusion of the LNA. Instead, persistent primitive vascular structures, including the PLBA, appear to underlie this anomaly. Gregg and Gailloud attempted to explain variations in posterior arterial circulation through persistent primitive arteries, and classified vertebrobasilar anomalies into four types:⁵ atypical persistent trigeminal artery variants; common trunks of origin for one, two, or three cerebellar arteries; aberrant origins of the cerebellar arteries; and vertebrobasilar duplications.

In the schema of the dorsal views of the cranial arterial system at Padget stage 2 (embryos of 5–7 mm) (Fig. 4A), the PLBA is a branch of the proatlantal artery coursing cranially lateral to the LNA, connected by several transverse anastomoses. Some of these anastomoses later develop into the proximal segments of the cerebellar arteries and other branches of the basilar artery (Fig. 4B). In the present case, persistence of the PLBA, combined with agenesis of the proximal PICA, likely resulted in a large fenestration and an anomalous common trunk (Fig. 4C).

FIG. 4.

The role of the PLBA (green) of Padget in variations of the vertebrobasilar system. Pink indicates the origin from the proatlantal artery (ProA). Red indicates the origin from the LNAs. A: Dorsal views of the cranial arterial system at Padget stage 2 (embryos of 5–7 mm). The PLBA is a branch of the proatlantal artery coursing cranially lateral to the LNA, to which it is connected by several transverse connections (orange). B: Dorsal views of the cranial arterial system at Padget stage 3 (embryos of 11–14 mm). LNAs run medially and are fused into the basilar artery (BA). Other PLBA segments regress during embryonic development. Proximal segments of the cerebellar arteries and other branches of the basilar artery arise from the transverse connections. C: In the present case, the PLBA may persist throughout life, and regression or agenesis of the PICA likely leads to the unique vascular structure, including the common trunk of the AICA-PICA (Com Tr). SCA = superior cerebellar artery.

Prevalence of Vertebrobasilar Fenestration in MVD for HFS

We found only one case report describing the relationship between VA fenestration and HFS. Nomura et al. reported direct compression by a VA fenestration in HFS and emphasized the need for careful surgical manipulation, particularly considering the hypoglossal nerve passing through the fenestration.¹⁸ In their report, the fenestration size was small, confined to the VA, and notably smaller than that observed in our case. A detailed comparison between the present case and the previously reported case¹⁸ by Nomura et al. is provided in Supplementary Table 1.

In the present case, the posterior circulation anomaly may represent a variation of the common trunk of the AICA-PICA, likely related to a remnant of the PLBA.^4,5 The common trunk anomaly of the AICA-PICA is a recognized anatomical variation in the posterior circulation^19,20 relevant during MVD surgery for HFS. Goto and Inoue reported on 68 cases (21.5%) of a common trunk in the AICA-PICA among 316 patients with a follow-up period longer than 1 year.²¹ Although common trunk involvement in HFS is frequent, decompression requires extensive dissection of the common trunk and its branches.²¹ Shimano et al. reported that 11.1% of patients undergoing MVD surgery had compression involving a common trunk or its branches and emphasized that the tortuosity of the common trunk and perforators arising from the offending vessel complicates standard artery repositioning.²⁰ In the present case, several short perforators from the offending artery into the brainstem limited arterial transposition. MVD for HFS associated with a large VA fenestration requires surgical precautions similar to those used for AICA-PICA common trunk anomalies.

Preoperative Planning and Surgical Strategy

In the present case, a short AICA-PICA common trunk originated from the VA, along with an aberrant artery arising from the PLBA. Transposition of the distal common trunk was limited because it was anchored by the proximal common trunk and the aberrant artery. Therefore, this anatomical complexity should be thoroughly understood before surgery. Fusion images combining 3D CT angiography and FIESTA MRI clearly demonstrated the relationship between the offending artery and the facial nerve REZ. This preoperative assessment facilitated a better understanding of the complex vascular anatomy and was essential for patient counseling, particularly with regard to the potential risks associated with limited vascular mobility and perforator-rich segments. However, neuroimaging modalities such as CT angiography and MRI have limited spatial resolution, and perforating arteries arising from the common trunk, AICA, and PICA could not be clearly visualized. Accordingly, meticulous surgical manipulation is required to avoid injury to the labyrinthine artery and perforators originating from the AICA-PICA common trunk during decompression.

Observations

A man in his 30s presented with a 7-year history of right-sided HFS refractory to medical therapy and botulinum toxin injections. Preoperative imaging demonstrated vascular compression of the facial nerve REZ by an AICA-PICA common trunk originating from a large VA fenestration. MVD was performed with intraoperative AMR monitoring. Although transposition of the offending artery was limited by multiple perforating branches, adequate decompression was achieved using a combination of vessel mobilization and Teflon placement between the artery and both the medial and lateral aspects of the REZ. The patient experienced complete resolution of symptoms without neurological deficits, which was maintained at the 1-year follow-up.

Lessons

Large VA fenestrations may represent persistent PLBA. Successful surgical treatment requires detailed preoperative evaluation of the vascular anatomy and awareness of the limitations imposed by perforating arteries, similar to those encountered with AICA-PICA common trunk anomalies. Specifically, high-resolution vascular imaging such as 3D angiography or fusion MRI/MR angiography should be used to delineate the course of the PLBA-related aberrant artery and to clarify its anatomical relationship with the REZ. Awareness of anatomical complexity and potential perforator-rich segments is essential for safe and effective MVD in patients with HFS, even in the presence of rare vertebrobasilar anomalies.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Higuchi, Matsumiya, Yokoyama. Acquisition of data: Higuchi, Matsumiya, Origuchi, Yokoyama. Analysis and interpretation of data: Higuchi, Matsumiya. Drafting the article: Higuchi, Matsumiya. Critically revising the article: Higuchi, Matsumiya, Yamakami. Reviewed submitted version of manuscript: Higuchi, Matsumiya, Yokoyama, Yamakami. Approved the final version of the manuscript on behalf of all authors: Higuchi. Statistical analysis: Matsumiya. Administrative/technical/material support: Matsumiya, Nakano. Study supervision: Higuchi, Matsumiya, Horiguchi, Yamakami.

Supplemental Information

Videos

Video 1. https://vimeo.com/1158436012.

Previous Presentations

A portion of this work was presented at the 25th Annual Meeting of Japan Microvascular Decompression Surgery, Yamaguchi, Japan, January 26, 2023.

Online-Only Content

  Supplementary Figure and Table. https://thejns.org/doi/suppl/10.3171/CASE25777.

Correspondence

Yoshinori Higuchi: Chiba University Graduate School of Medicine, Chiba, Japan. yhiguchi@faculty.chiba-u.jp.