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Radiol Case Rep
Radiol Case Rep
Radiology Case Reports
1930-0433
Elsevier

S1930-0433(24)00668-X
10.1016/j.radcr.2024.07.082
Case Report
Bilateral concurrent type I and type II persistent proatlantal arteries: A case report
Rahman Saif MD saif.rahman@rutgers.edu
⁎
FitzPatrick Maurice MD
Roychowdhury Sudipta MD
Department of Radiology, Robert Wood Johnson University Hospital, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, USA
⁎ Corresponding author. saif.rahman@rutgers.edu
13 8 2024
11 2024
13 8 2024
19 11 48324835
6 5 2024
15 7 2024
© 2024 The Authors. Published by Elsevier Inc. on behalf of University of Washington.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Transient embryonic carotid-vertebrobasilar anastomoses can intermittently persist beyond the embryonic period. These vascular anomalies are often serendipitously identified during evaluation for unrelated disease states and pathologies. The persistent proatlantal intersegmental artery is one such recognized rare fetal anastomotic connection, often arising unilaterally. Bilateral persistence of the proatlantal anastomosis is a rarer occurrence, seldom described in the literature. We report a case of bilateral concurrent type I and type II proatlantal arteries, describe the embryology of persistent carotid-vertebrobasilar anastomoses, and consider pertinent clinical implications.

Keywords

Proatlantal artery
Trigeminal artery
Carotid-vertebrobasilar anastomosis
Vascular embryology
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pmcIntroduction

The persistent primitive proatlantal intersegmental artery represents a rare variant of the fetal carotid-vertebrobasilar anastomoses; and, similar to other persistent fetal anastomotic channels, it represents involutional failure of embryonic vasculature during early development [1,2]. Two variants of proatlantal arteries have been described, arising from either the internal or external carotid vasculature [[3], [4], [5]]. The type I proatlantal artery, described in previous literature as the proatlantal intersegmental artery, arises from the internal carotid artery and ascends to the atlantooccipital region and constitutes the distal ipsilateral vertebral artery which then extends intracranially through the foramen magnum. The type II proatlantal artery, described previously as the first cervical intersegmental artery, arises laterally from the external carotid artery, and passes the C1 or C2 vertebra obliquely to continue as, or perfuse, the distal portion of the vertebral artery, before similarly entering the foramen magnum. Reported cases of a persistent proatlantal artery are infrequent, with unilateral involvement more common [6]. Bilateral persistent proatlantal anastomoses are exceptionally rare and seldom described in the radiologic anatomical literature, and when so, have identical vascular origins from either the internal or external carotid artery on both sides. In the present case, we describe an instance of bilateral concurrent type I and type II persistent fetal proatlantal anastomoses.

Case report

A 27-year-old male was brought by air to the emergency department following a motor vehicle collision. Computed tomography (CT) of the head and neck was performed which demonstrated a frontotemporal calvarial fracture, subdural hemorrhage, cerebral contusions, nondisplaced bilateral first rib fractures and C7 spinous process and laminar fractures. Cervical angiogram imaging was performed to identify arterial vascular injury. No traumatic injury to the cervical vasculature was identified. The distal extradural and intracranial segments of the vertebral arteries were constituted by vessels arising from the internal carotid artery on the right and the external carotid artery on the left. More specifically, the anastomotic vessel on the right originated from the internal carotid artery at the level of the C3 vertebra and it ascended superiorly to the C1 transverse process and coursed horizontally within the suboccipital region (see Fig. 1). An anomalous vessel was also identified arising from the external carotid artery on the left at the C3-C4 interspace while extending superomedially and passing the C1 vertebra transversely to perfuse the distal V3 and V4 segments of the vertebral artery (see Fig. 2). The occipital arteries arose from the anomalous anastomotic vessels on both sides. The proximal segments of the vertebral arteries were developmentally hypoplastic with corresponding hypoplasia of the bilateral transverse foramina in these regions. Findings were consistent with bilateral persistent proatlantal fetal anastomoses, with type I on the right and type II on the left. No additional aberrant vascular connections between the carotid and vertebrobasilar system were present. No other vascular anomalies or aneurysms were identified.Fig. 1 Reconstructed images from a computed tomography angiogram, sagittal (A–C) and coronal (D) projections. The origin of a type I proatlantal artery from the right internal carotid artery at C3 can be seen (arrow). The anomalous vessel courses superiorly and then with distinctive suboccipital horizontal course (B–C) before constituting the ipsilateral vertebral artery (D).

Fig 1

Fig. 2 Computed tomography angiogram, sagittal (A–F) projection. The origin of a type II proatlantal artery from the proximal left external carotid artery at C3-C4 is seen (arrow) in (A–C). The vessel courses superiorly and traverses the C1 vertebra obliquely before constituting the distal left vertebral artery (D–F).

Fig 2

Discussion

During early development when embryonic length is 4 to 5 mm, the primitive vertebrobasilar system receives transient vascular supply from two parallel neural arterial plexuses constituted by the carotid system from trigeminal, hypoglossal, otic, and proatlantal arteries [[5], [6], [7], [8], [9]]. The intracranial and presegmental anastomotic arteries are named according to the cranial nerves with which they course, or with their relationship with the rudimental otic vesicle. The caudal portion of the neural arterial plexus is perfused by eight extracranial anastomosing segments which become intersegmental with development of the cervical vertebral bodies [2,6,8,9]. The first intersegmental artery is named according to its association with the proatlas, a rudimentary vertebral element that arises between the atlas and occipital bone, and supplies a caudal portion of the neural arterial plexus. Seven additional cervical intersegmental arteries, which accompany the corresponding nerve roots, arise from the dorsal aorta and perfuse the caudal end of both neural arteries. The anastomotic channels between the carotid and vertebrobasilar system are generally patent for a period of 7 to 10 days [9]. With maturation and development of the posterior vascular channels, the otic, hypoglossal, and trigeminal anastomoses involute at the 7 to 12 mm embryonic stage in sequential manner, with the proatlantal intersegmental artery persisting until the vertebral arteries develop by the 12 to 14 mm embryonic stage [7,9,10,11]. Six (C1–C6) cervical intersegmental arteries anastomose longitudinally to form the vertebral artery while the distal vertebral suboccipital segment is formed by the distal proatlantal artery [2,5,6]. The seventh cervical segment (C7) is augmented and forms the subclavian artery.

Persistent anastomotic connections between the carotid and vertebrobasilar system are rare, with order of increasing frequency inversely related to presegmental involutional order. Persistent unilateral intersegmental proatlantal anastomosis is exceptionally rare with an estimated incidence of 0.33% [12]. No published data is available to our knowledge regarding the incidence of bilateral proatlantal anastomoses. The proatlantal artery is characterized by a vascular channel arising from either from the cervical internal or external carotid artery which ascends and constitutes the distal transverse suboccipital segment of the vertebral artery near the foramen magnum [2]. It has been suggested that the type I proatlantal artery represents the true persistent proatlantal intersegmental artery while the type II proatlantal artery may represent a persistent primitive first cervical intersegmental artery [8]. No branches typically arise from the proatlantal vessel; however, in some instances, similar to the presented case, the occipital artery originates from the proatlantal artery [5,10]. The vertebral artery segments proximal to the proatlantal anastomosis are generally absent or developmentally hypoplastic [13,14].

Discrimination between the type I proatlantal artery from the more frequently encountered hypoglossal artery necessitates some scrutiny in view of their similar vascular origins from the cervical internal carotid artery. The proatlantal artery originates at a lower cervical level, typically at the C2 or C3 vertebra, while the hypoglossal vessel originates at the C1 vertebra or C1-C2 interspace and has a more anterior course before entering the posterior fossa through the ipsilateral hypoglossal canal [7,15]. The primitive hypoglossal artery also lacks the suboccipital horizontal course which is distinctive of the proatlantal artery.

The present literature suggests that persistence of the trigeminal artery into adult life is more frequent than the hypoglossal or proatlantal anastomoses, with estimated incidence of 0.03% to 2.2% [4,7,9]. The trigeminal artery represents a vascular channel from the proximal cavernous portion of the internal carotid artery to the distal third segment of the basilar artery [7,9]. The persistent otic artery arises from the petrous internal carotid artery, traverses the internal auditory canal, and joins the caudal segment of the basilar artery [11]. There is controversy regarding the otic artery, with some authors recently disputing its persistence into adulthood; nonetheless, the otic artery is felt to have only a minor contribution to the developing rudimentary vertebrobasilar system [4,7,11]. Reported cases of a persistent proatlantal artery are infrequent, with bilateral involvement a rarer occurrence. Previously described bilateral persistent proatlantal anastomoses have identical vascular origins on both sides from either the internal or external carotid artery [6,10,[14], [15], [16], [17]]. To our knowledge, this is the first reported case with concurrent bilateral type I and type II persistent proatlantal arteries. It has been theorized that persistence of these vascular channels may be related to a compensatory effort to maintain adequate perfusion to the posterior circulation during periods of dynamic cerebral development or with developmental failure of the vertebral artery [12,15]. However, the precise etiology and contributing factors to involutional failure are still unclear [9].

While most persistent carotid-vertebrobasilar anastomoses, including the proatlantal artery, are incidentally found, there are procedural and clinical implications related to changes in hemodynamics and cerebral blood flow. The persistence of fetal vascular anastomoses is particularly salient for neurointerventional and endovascular planning and may necessitate procedural modification if present. Similarly, a persistent proatlantal artery heightens risk for iatrogenic injury during carotid endarterectomy, upper cervical fixations, and external carotid ligations [6,11]. Atheromatous disease of the carotid bifurcation or occlusion of the carotid system may induce symptoms of posterior fossa ischemia due to changes in cerebral blood flow. Several cerebrovascular abnormalities associated with a persistent proatlantal artery have been described including vertebral artery aplasia or hypoplasia, additional carotid-vertebrobasilar anastomoses, arteriovenous malformations, and vein of Galen malformations [5,6,10,12]. While the proatlantal artery is also seen in association with aneurysms involving the circle of Willis vasculature, no aneurysms involving the anastomotic proatlantal vessel itself have been described. Moreover, no consensus exists whether this represents a true association or is simply incidental; although, it is postulated that hemodynamic changes associated with persistent fetal anastomoses may partially influence the pathogenesis of intracranial aneurysms [5,11]. A causal relationship has also been demonstrated between the proatlantal artery and pulsatile tinnitus, primarily related to changes in regional blood flow and increased turbulence [3]. Headache, vertigo, visual disturbances, and history of rapidly enlarging head circumference have also been attributed to a persistent proatlantal artery in the literature [5,10,[13], [14], [15]].

Conclusion

Persistent anastomotic remnants of the fetal carotid-vertebrobasilar circulation, such as the proatlantal artery, are infrequently described. Bilateral persistence of the proatlantal vessel is a rarer occurrence and ,when described, have identical vascular origins from either the internal or external carotid vessels bilaterally. The current case describes bilateral concurrent type I and type II proatlantal arteries which were incidentally found. Findings are salient for diagnostic radiologists and interventionalists in view of their clinical and procedural implications.

Patient consent

Consent for publication has been obtained from the patient.

Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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References

1 Hutchinson NA Miller JD. Persistent proatlantal artery J Neurol Neurosurg Psychiatry 33 1970 524 527 5505681
2 Padget DH. Designation of the embryonic intersegmental arteries in reference to the vertebral artery and subclavian stem Anat Rec 119 1954 349 356 13197795
3 Li TH Lan MY Liu JS Tseng YL Wu HS Chang YY. Type II proatlantal intersegmental artery associated with objective pulsatile tinnitus Neurology 71 2008 295 296 18645169
4 Uchino A. Carotid-vertebrobasilar anastomosis: magnetic resonance and computed tomographic angiographic demonstration Jpn J Radiol 37 2019 565 578 31214937
5 Vasovic L Mojsilovic M Andelkovic Z Jovanovic I Arsic S Vlajkovic S Proatlantal intersegmental artery: a review of normal and pathological features Childs Nerv Syst 25 2009 411 421 19212779
6 Pelz D Menon RK Swartz RH Aviv RI Symons SP. Bilateral type II persistent proatlantal intersegmental arteries Can J Neurol Sci 40 2013 873 874 24257233
7 Caldemeyer KS Carrico JB Mathews VP. The radiology and embryology of anomalous arteries of the head and neck AJR Am J Roentgenol 170 1998 197 203 9423632
8 Okahara M Kiyosue H Mori H Tanoue S Sainou M Nagatomi H. Anatomic variations of the cerebral arteries and their embryology: a pictorial review Eur Radiol 12 2002 2548 2561 12271398
9 Vasovic L Jovanovic I Ugrenovic S Vlajkovic S Jovanovic P Stojanovic V Trigeminal artery: a review of normal and pathological features Childs Nerv Syst 28 2012 33 46 22071960
10 Purkayastha S Gupta AK Varma R Kapilamoorthy TR. Proatlantal intersegmental arteries of external carotid artery origin associated with Galen's vein malformation AJNR Am J Neuroradiol 26 2005 2378 2383 16219849
11 Tubbs RS Verma K Riech S Mortazavi MM Shoja MM Loukas M Persistent fetal intracranial arteries: a comprehensive review of anatomical and clinical significance J Neurosurg 114 2011 1127 1134 21235309
12 Ö Özgür G Aytaç Sindel M Sindel T Persistent carotid-vertebrobasilar anastomoses: cases of proatlantal artery type I and type II anat 12 2018 101 104
13 Donmez H Kahriman G Serifov E Mavili E Ozcan N. Incidental finding of a proatlantal intersegmental artery. A case report Neuroradiol J 24 2011 758 761 24059772
14 Woodcock RJ Cloft HJ Dion JE. Bilateral type 1 proatlantal arteries with absence of vertebral arteries AJNR Am J Neuroradiol 22 2001 418 420 11156793
15 Gumus T Onal B Ilgit ET. Bilateral persistence of type 1 proatlantal arteries: report of a case and review of the literature AJNR Am J Neuroradiol 25 2004 1622 1624 15502152
16 Zarghouni M Marichal D Persistent bilateral proatlantal type II artery Proc (Bayl Univ Med Cent) 26 2013 50 51 23382615
17 Fang Y Li S Zhang C. Bilateral type II persistent proatlantal intersegmental artery: a rare variant of persistent carotid-vertebrobasilar anastomoses BJR Case Rep 8 2022 20210154 36177266
