Introduction

During the embryonic period, the formation of the vertebral artery (VA) occurs through the fusion of the posterior intersegmental arteries in the extracranial segments and the fusion of the primitive carotid-vertebrobasilar anastomoses in the intracranial segment [7]. Failure in this fusion process can result in vascular anomalies such as duplication or fenestration [10]. Although the terms “fenestration” and “duplication” are sometimes used interchangeably in the literature, fenestration refers to a VA with a single origin splitting into two separate channels that subsequently rejoin distally, whereas duplication refers to a VA with two origins, a variable course, and fusion level [3]. Fenestrated vertebral artery (FVA) usually occurs in the extracranial segment (70%), albeit rarely below the C2 level, and less frequently in the intracranial segment (30%) [7, 9]. As with other VA variations and anomalies, FVA often occurs on the left side and is detected incidentally [7].

While FVA is generally considered asymptomatic, it has been reported to be associated with aneurysms, cerebral infarction, or arteriovenous malformations [2, 8, 9, 11].

The superior cerebellar artery (SCA) arises from the distal portion of the basilar artery and passes by the oculomotor, trochlear, and trigeminal nerves [4]. It has been reported that the SCA can trigger neurovascular compression due to its close proximity to the cranial nerves [4]. Although duplication of the SCA is a common variation, the reported incidence of bilateral duplication ranges between 0.9% and 5% [4].

Here, we report a rare case of a large FVA involving the V3 and V4 segments of the main trunk of the VA, as well as bilateral duplicated SCAs.

Case presentation

A 63-year-old female patient presented to the neurology outpatient clinic with complaints of dizziness and balance disorder. Diffusion-weighted MRI (DW-MRI) was performed, revealing restricted diffusion consistent with an acute stroke affecting the thalamus bilaterally and the right lower corner of the pons, which was also visible on FLAIR imaging (Fig. 1). Apparent diffusion coefficient values supported the diagnosis. Upon detection of 50% stenosis at the V4 level of the right VA on brain CTA, which was considered symptomatic, the patient underwent DSA (Fig. 1). During the procedure, significant stenosis, as mentioned on the CTA report, was not observed. However, CTA and DSA revealed that the VA divided into two branches, one passing below the C1 vertebra and the other above, which then fused before entering the foramen magnum. This conformation indicates VA fenestration involving the V3 and proximal V4 segments (Fig. 2). The right anterior inferior cerebellar artery (AICA) arising from the proximal basilar artery was identified, while the posterior inferior cerebellar artery (PICA) could not be visualized on DSA. Additionally, bilateral duplication of the SCA was observed (Fig. 2).

Fig. 1
figure 1

The arrow indicates (a) the infarct in the cerebellopontine angle; (b) the infarct in the left thalamus; (c) the infarct in the right thalamus (DW-MRI images). CTA image showing the VA stenosis in the axial plane (d), coronal plane (e), and sagittal plane (f)

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Fig. 2
figure 2

(a) DSA image of the right VA showing the origin of the V3 segment (red line), the origin of the V4 segment (blue line), the branches forming the FVA (white arrows), the AICA (yellow arrow); (b) CTA image on sagittal plane, showing the branches forming the FVA (yellow arrows); (c) DSA image showing the left duplicated SCA (red arrows); (d) DSA image showing the right duplicated SCA (red arrows)

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After completion of the DSA procedure without any complications, the patient was admitted to the ward and monitored for 24 h. Treatment with acetylsalicylic acid and clopidogrel was prescribed, and physical therapy was recommended. The patient is currently alive and well.

Discussion

On the 32nd day of embryonic development, seven cervical intersegmental arteries arise from the dorsal aortae. By the 40th day, the first two intersegmental arteries regress, and the proximal part of the subclavian artery and the VA begin to develop from the 3rd to 7th intersegmental arteries [6]. The proximal VA and the subclavian artery develop from the 7th intersegmental artery, while the remaining intersegmental arteries form the rest of the VA [6].

The intracranial segment of the VA is formed by the fusion of the primitive lateral basilovertebral artery with the primitive vertebrobasilar axis [9]. If a failure occurs during this fusion process and some intersegmental artery anastomoses persist, it results in a vascular anomaly known as fenestration [9].

FVA is classified into two types: extracranial and intracranial. In the largest study on FVA conducted by D’Sa et al. (2020), MRI and CTA scans from 44,759 patients were reviewed. The prevalence of FVA was reported as 0.01%, with the majority involving the V4 segment, i.e., the intracranial segment [1]. In the same study, fenestrations in multiple segments were not observed [1]. Apart from the cases reported by Hasegawa et al. and Uchino et al., we are unaware of a report of a large fenestration involving both segments [2, 9]. Hasegawa reported that the second branch responsible for the fenestration was PICA, whereas in Uchino’s case, a thin anastomotic branch between PICA and VA led to fenestration [2, 9]. Contrastingly, in our case reported here, fenestration involved the main trunk of the VA, and it was located on the right side. Specifically, in our patient, we observed that the VA running in its normal course bifurcated into two branches at the V3 segment (between C1 and C2), with one branch travelling in its usual course above C1, while the other descended below C1, ascending after piercing the dura mater and re-fusing proximally at the V4 segment. Since neither branch of the fenestration gave rise to further branches towards the cerebellum, we were certain it did not involve PICA. When examining the course of VA on DSA, we could not visualize PICA but identified that AICA originated from the proximal basilar artery. To our knowledge, this type of fenestration is reported here for the first time.

Although FVA is usually considered clinically insignificant, there are studies suggesting that it may be associated with a higher risk of cerebral infarction, aneurysm, or arteriovenous malformation [2, 8, 9, 11]. In our case, the stenosis causing thalamic infarction originated from the posterior circulation system. We think that fenestration of the VA can disrupt normal blood flow and lead to hemodynamic changes, potentially resulting in thalamic infarction.

On the other hand, although these anomalies may not have pathological significance, recognition of these anomalies beforehand by surgeons performing surgical intervention on the craniocervical junction and by interventional neurologists and radiologists performing endovascular treatment to the posterior circulation is important to avoid any untoward injuries [3].

On approximately the 28th day of embryonic development (4 mm), two parallel neural channels begin to supply the hindbrain. At this stage, the SCA, a branch of the future basilar artery, forms as the single vessel supplying the primitive cerebellum [5]. The SCA exhibits considerable variability with regard to its point of origin from the basilar artery, type, and number [4]. However, bilateral duplication of the SCA has been reported as a rare variation, with an incidence of 0.9 − 5% [4]. Its close proximity to the cranial nerves can potentially trigger neurovascular compression syndromes such as trigeminal neuralgia. Awareness of these variations is crucial before performing surgical interventions and endovascular procedures in this region, which can aid in making an accurate diagnosis, choosing appropriate therapeutic methods, eventually improving surgical outcomes [4].

Limitations

Not all vessels and their courses could be presented in this case report due to unavailability of 3D images.