Bilateral duplicated hypoplastic superior cerebellar arteries one of which originates from a full-type fetal posterior cerebral artery

The association of bilateral duplication of the superior cerebellar artery with an origin from the posterior cerebral artery is rare but of great interest to anatomists, radiologists, and surgeons. This article reports bilateral duplicated hypoplastic superior cerebellar arteries, one of which arises from a full-type fetal cerebral artery. A 59-year-old woman admitted to the neurosurgery department for a subarachnoid hemorrhage underwent a brain CTA with 3D reconstruction using «3D slicer 4.11» software. Brain CTA and the 3D model were used to analyze the configuration of the posterior circulation. CTA images and the 3D model showed an unusual configuration of the posterior circulation. The basilar artery prolonged the left vertebral artery, while the right vertebral artery ended in the right posterior inferior cerebellar artery. On both sides, a full-type fetal posterior cerebral artery and duplicated hypoplastic superior cerebellar artery were observed. Three cerebellar arteries arose from the basilar artery, while the fourth one emerged from the right fetal posterior cerebral artery. Knowledge of such a configuration of the posterior circulation and others is necessary before radiological and surgical procedures. It helps to understand hemodynamic events, and neurovascular conflicts, improve revascularization procedures, and avoid surgical arterial and nervous injuries.


Introduction
Brain surgery requires perfect knowledge of the pertinent vascular anatomy [3].Thus, the evaluation of cerebellar arteries is of great interest [8].The SCA is the most consistent infratentorial vessel.However, several of its variations have been described [1,3].These include duplication, triplication, and extraordinary origin [1].These variants are of utmost clinical value [3,5].First, the extraordinary origin and duplication of the SCA may provoke neurovascular conflicts by compressing III, IV, and V cranial nerves [2,5].Second, the SCA variant increases the risk of aneurysm and may be the site of thrombosis, which leads to cerebellar infarction [2].In addition, duplication is used in revascularization and arterial bypass [3,7] and prevents ischemic events by providing alternative circulation [2].Thus, surgeons and radiologists must know of such variants before surgical or interventional procedures to get more precision and avoid pitfalls [4,7].Since the association of different and bilateral SCA variants is still less observed, similar cases deserve to be reported.This article illustrates bilateral duplicated and hypoplastic SCAs, one of which arises from a full-type FPCA.

Case report
A 59-year-old woman complained of a general condition deterioration following severe headaches for four days.Her GCS was 15, her blood pressure was 140/80 mmHg, and she was dysarthric.An urgent brain CT showed a frontoparietal and pre-chiasmatic SAH, overflowing the right lateral ventricle.The brain CTA identified a sacciform aneurysm involving the communicating segment of the right ICA.After stabilization, the patient was referred to the neurosurgery department for further assessment.Thus, a 3D modeling of the CTA images performed using "3D slicer 4.11" software confirmed the result of the CTA and showed that the aneurysm involved the origin of the right PCOA.The patient was discharged after successful surgery.Otherwise, the CTA and the 3d model have highlighted multiple variations.First, the BA extended the LVA, whereas the RVA ended in a PICA (Fig. 1a-c); the BA diameter was about 1.4 mm.On both sides, duplicated SCA was associated with a full-type FPCA.Indeed, both PCA prolonged ipsilateral PCOA; P1 segments were absent (Fig. 1d, e).Then, the BA gave from its upper part two SCA, then ended in a third one, while the fourth SCA originated from the right FPCA (Fig. 2a, b).Upper SCAs irrigated the vermis and paravermian area, while the lower ones irrigated the hemispheres (Fig. 1c, d, f, g).The four SCAs were hypoplastic with a mean diameter of 0.73 mm.

Discussion
The posterior circulation is known for its complexity [1].However, the vertebrobasilar tripod giving rise to cerebellar and posterior cerebral arteries is not frequent [8].Several of its variations have been reported [3] and deserve to be explained by a brief embryological review [1].In the embryo, the primitive ICA bifurcates into two divisions, the caudal branches off into the PCHA and the future P1 segment.Posteriorly, LNAs supply the hindbrain and draw blood from the ICA via carotid-basilar anastomoses [6].Later, the LNAs, connected to the caudal division via PCOA [1,6], fuse in front of the hindbrain to form the BA [1,4].Carotid-basilar anastomoses disappear [1,6].With the posterior hindbrain growth, the PCA develops as an expansion of the PCOA [1], incorporating the PCHA [6].Next, the P1 segment enlarges while the PCOA regress: this is the adult configuration of the PCA [1].If the PCOA is still dominant, whereas the P1 segment involves, the PCA is called fulltype FPCA [6].SCA variations seem to be related to a lack of fusion at the caudal end of the BA [1,4,7].A fusion between the PCA and the BA at a lower point explains why the SCA originates from the PCA [1,4].SCA duplication results when one of its branches arises directly from the BA [4].A combination of these mechanisms and a bilateral fetal evolution of PCAs may explain the variation presented in the current case.
In normal vascular anatomy, the SCA originates as a single vessel on both sides, from the distal part of the BA just above the PCAs [1,[3][4][5].Near III, IV, and V cranial nerves, it runs around the midbrain, then bifurcates next to the ipsilateral cerebral peduncle into rostral and caudal trunks [4,7].The SCA supplies the superior part of the cerebellar hemispheres and vermis [7], the pineal gland, the anterior medullary velum, and the tela choroidea [5].Even if consistent [1,3,5,7], SCA has several variations, including duplication, extraordinary origin, and hypoplasia [3].First, duplicated SCA is frequent, ranging from 5 to 28% of cases [1,9]; it is often reported as emerging from the BA [4,5].Second, SCA arising from PCA has been reported in 1.83% [3], 1.9% [4], 4% [7], 4.7% [8], and 9% [5] of cases; in all of them, PCA was adult-type [3-5, 7, 8].However, it is rare to encounter these variations bilaterally [1].Indeed, bilateral duplication was found in 0.5% [5], 0.9% [3], 2% [7], and 2.9% [8] of cases, and a bilateral origin from PCA in less than 2% [1].Next, hypoplastic SCA (outer diameter < 1 mm) is extremely rare at a rate of 0.7% and reported unilaterally [5,9].In addition, it is more unusual to get an association between these variations.In their CTA study on 341 patients, Pekcevik et al. reported that the association of duplicated SCA and origin from PCA occurred in only 0.3% [8].Ogeng'o et al. speculate that the same condition occurred in 2% of the 173 brains they dissected; the association was unilateral and same-sided [7].The particularity of the current case is related to the following points.First, it illustrates an unusual bilateral duplicated and hypoplastic SCA, one of which arises from the ipsilateral PCA.As reported above, most duplicated SCA emerged from the BA, and an association of duplication and origin from PCA is rare; an association with bilateral hypoplasia has never been reported.Second, the PCA that gave rise to the SCA was full-type FPCA.Based on what is reported in the literature (Table 1), this case highlights a new configuration that has not been reported.
Because of its several risks, posterior fossa surgery requires a complete review of the regional vascular and nervous anatomy [1].It includes perfect knowledge of SCA variations because of their utmost radiological and surgical value [5].Uchino et al. assert that SCA variations should be identified before any surgical or interventional procedure on the distal BA [7,9] to get more accuracy [3,5].The close relationship between SCA and III, IV, and V nerves explains why SCA variations may generate neurovascular conflicts [2, 1 3 4, 5].The SCA provokes 66.5-88% of conflictual V neuralgia [5].Indeed, if a trunk that forms an SCA duplication runs caudally, it may compress the V nerve resulting in neuralgia [4].In addition, the IV nerve may be compressed by the SCA or its branches, which leads to its palsy [3].When the SCA originates from the PCA, they form together an arterial clamp, entrapping the III nerve [4].Vascular disturbances such as SCA syndromes are better understood if SCA variations are known; Otherwise, these pathologies may be mismanaged [7,9].Some variations, such as hypoplasia, engender blood disturbance, increasing the risk of hemodynamic events.It includes aneurysms, atherosclerosis, and posterior stroke [2,9].SCA arising from PCA explains unusual posterior stroke with cerebellar infarction [9].However, when thrombosis affects a branch of duplicated SCA, the other maintains the blood supply [2].Several surgical procedures are related to SCA variations.If SCA is duplicated, the surgeon can use the rostral or caudal trunks in a revascularization or arterial bypass procedure.So, the surgeon must focus on two risks.First, the IV nerve close to the rostral branch may be injured.Second, perforator infarction may occur if perforators are sacrificed [3,7,9].In addition, preoperative identification of the SCA variation helps to choose the branch to use and the anastomosis location [3].If the SCA arises from PCA, it may be closed accidentally during aneurysm clipping [4,5].Section or ligation of the SCA, such as in tumor excision, posterior lobectomy, or epilepsy surgery, depends on its variations [9].During V surgery, the surgeon may injure a duplicated SCA close to the nerve [4].Finally, SCA variants are interesting in pinhole surgery.It helps surgeons to get an accurate neurovascular repair, deploy smaller incisions, and avoid abusive brain retraction [4].

Conclusion
SCA is the most consistent infratentorial artery.However, it is not devoid of variation.These especially involve its number and origin, including duplication and origin from PCA. Anatomists, radiologists, and neurosurgeons continue to be interested in these variants since they have several radiological and surgical applications.The association of bilateral SCA duplication and hypoplasia with bilateral full-type FPCA configuration is unusual.In addition, an SCA originating from an FPCA has never been encountered.This case highlights new anatomical knowledge that impacts clinical and surgical practice.It also encourages researchers to perform further studies to provide more knowledge on this topic.
Author contributions MAA: Project development, Data collection, Management and analysis, Manuscript editing and writing.
Funding No funding has been received by the author for preparing this work.

Declarations
Conflict of interest The author has no competing interests to declare that are relevant to the content of this article.
Ethical approval This case report has been performed in accordance with the ethical standards as laid down in the Declaration of Helsinki Consent to publish The data used was totally anonymized radiological images, so consent was waived.

Fig. 1 aFig. 2 a
Fig.1 a-cAxial CTA images in MIP mode (centered on the posterior fossa) and 3d modeling show that the LVA is prolonged by the BA, while the RVA ends in the RPICA.d, e Axial CTA images in MIP mode and 3d modeling showed that both PCA prolonged ipsi-

Table 1
[5,7,8]rations of SCA in literature according to its number and origin (considering only single and duplicated SCA with or without extraordinary origin)[5,7,8]NB: In all types, SCAs were of normal diameter except in our variant where SCAs were hypoplastic.None = absence of the SCA, SCA-PCA = SCA and PCA arising as common trunk from the BA standards of the ethical and deontological committee of the University of Oran 1 Ahmed Ben Bella.
Consent to participate Not applicable.