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Review
. 2017 Jun 15;57(6):267-277.
doi: 10.2176/nmc.ra.2017-0050. Epub 2017 May 1.

Carotid-vertebrobasilar Anastomoses with Reference to Their Segmental Property

Katsunari Namba  1
Affiliations
Review

Carotid-vertebrobasilar Anastomoses with Reference to Their Segmental Property

Katsunari Namba. Neurol Med Chir (Tokyo). .

Abstract

The primitive carotid-vertebrobasilar anastomoses are primitive embryonic cerebral vessels that temporarily provide arterial supply from the internal carotid artery to the longitudinal neural artery, the future vertebrobasilar artery in the hindbrain. Four types known are the trigeminal, otic, hypoglossal, and proatlantal intersegmental arteries. The arteries are accompanied by their corresponding nerves and resemble an intersegmental pattern. These vessels exist in the very early period of cerebral arterial development and rapidly involute within a week. Occasionally, persistence of the carotid to vertebrobasilar anastomosis is discovered in the adult period, and is considered as the vestige of the corresponding primitive embryonic vessel. The embryonic development and the segmental property of the primitive carotid-vertebrobasilar anastomoses are discussed. This is followed by a brief description of the persisting anastomoses in adults.

Keywords: carotid-vertebrobasilar anastomoses; hypoglossal artery; otic artery; proatlantal intersegmental artery; trigeminal artery.

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Figures

Fig. 1
Fig. 1
Vessels in an embryo of 4 mm. The primitive trigeminal artery (arrow) is arising from the primitive internal carotid artery (ICA). A few primitive otic arteries arise opposite to the second aortic arch (small arrows). The caudal end of the hindbrain is supplied by the primitive hypoglossal (arrowhead) and proatlantal intersegmental (double arrowheads) arteries. The primitive carotid-vertebrobasilar anastomoses communicate the primitive ICA and dorsal aorta with the longitudinal neural artery, and accompany their corresponding nerves. AA: aortic arch; P: pharyngeal arch.
Fig. 2
Fig. 2
Vessels in an embryo of 7–12 mm. Fusion of the first to sixth cervical segmental arteries (C1–C7) results in the formation of the vertebral artery. Note that the distal portion of the proatlantal intersegmental artery (PIA, C1) remains as the horizontal portion of the vertebral artery (arrow). Persistence of the proximal portion of the PIA results in the persistent PIA seen in adults (arrowhead). The muscular components of each pharyngeal arch are associated with its own cranial nerve. DA: dorsal aorta; ICA: internal carotid artery; P: pharyngeal arch; SA: subclavian artery; VA: vertebral artery.
Fig. 3
Fig. 3
Rhombomeres and their relationship to the pharyngeal arches. The hindbrain has eight distinct segments called the rhombomeres (R1–R8). The rhombomeres give rise to motor nuclei to cranial nerves IV, V, VI, VII, IX, X, XI, and XII, as well as neural crest cells to the pharyngeal arches. Migration of the neural crest cells occur in three streams (arrows) to their designated pharyngeal arches. The neural crest cells provide guidance cues for the sensory cranial nerve fibers in the ganglia to establish connection with the corresponding rhombomeres. P: pharyngeal arch.
Fig. 4
Fig. 4
Persistent primitive trigeminal artery, lateral type. An incidentally discovered persistent primitive trigeminal artery (PTA) originating from the left internal carotid artery (ICA) in a patient who underwent clipping surgery for a ruptured anterior communicating artery aneurysm. Left ICA angiogram in AP (A) and lateral (B) views demonstrates a prominent PTA first coursing posterolaterally, then posteromedially to communicate with the upper basilar artery. CT-like axial image reconstruction of the three-dimensional rotational angiogram (3DRA) shows the PTA coursing near the apex of the petrous bone, reaffirming the lateral type PTA. Note that a small branch to the pons is originating from the PTA near the petrous apex in a magnified thin slice reconstructed axial 3DRA (arrow).
Fig. 5
Fig. 5
Persistent primitive trigeminal artery variant. Left internal carotid artery angiogram (A) and three-dimensional rotational angiogram (B) in lateral views show an incidental small PTA variant originating from the cavernous internal carotid artery supplying the left posterior inferior cerebellar artery territory.
Fig. 6
Fig. 6
Origin of the persistent primitive otic artery. The persistent primitive otic artery (POA) should arise in the lateral portion of the petrous canal, close to the medial turn. The expected origin of the POA is indicated in an internal carotid artery angiogram in AP (A) and lateral (B) views. Compare with the origin of the persistent primitive trigeminal artery in Fig. 4.
Fig. 7
Fig. 7
Persistent primitive hypoglossal artery. An incidental persistent primitive hypoglossal artery (PHA) was discovered during an angiographic workup for a left cavernous internal carotid artery aneurysm. Right common carotid artery angiogram in AP (A) and lateral (B) views demonstrates a large PHA originating from the ICA at the C2 level (arrow). The ipsilateral vertebral artery was absent (not shown) and the contralateral was hypoplastic (small arrows). CT-like axial image reconstruction of the three-dimensional rotational angiogram shows the PHA passing through the right hypoglossal canal (C, arrow).
Fig. 8
Fig. 8
Persistent primitive hypoglossal artery variant. Right external carotid angiogram (A) and three-dimensional rotational angiogram (3DRA) (B) in lateral views show the hypoglossal branch of the ascending pharyngeal artery (arrows) partially supplying the right posterior inferior cerebellar artery territory (arrowheads). This vessel was considered a persistent primitive hypoglossal artery (PHA) variant. The patient underwent angiographic workup for a left cerebellar hemorrhage that was judged unrelated to the PHA variant. Note the PHA variant traversing the right hypoglossal canal in the axially reconstructed 3DRA image (C, arrow).
Fig. 9
Fig. 9
Course of the persistent primitive proatlantal intersegmental artery. Three-dimensional rotational angiogram of a right common carotid artery in lateral view in a patient with a persistent primitive hypoglossal artery (PHA). Added is a schematic drawing of the course of the persistent primitive proatlantal intersegmental artery (PIA) in the suboccipital region. Note the dorsal course of the PIA compared to the PHA.
Fig. 10
Fig. 10
Cervical segmental arteries. Left subclavian artery angiogram in lateral view in a patient with severe left common carotid and left vertebral artery stenosis. The left occipital and vertebral arteries are reconstituted via the C1, C2, C3, and C5 segmental arteries. Anastomosis between the occipital and vertebral arteries is prominent at the C1 level, which may represent an embryonic link between the two vessels via the primitive proatlantal intersegmental artery. Note the C1 and C2 segmental artery reconstituting the occipital artery.
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