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Year : 2022  |  Volume : 20  |  Issue : 3  |  Page : 182-186

Management of symptomatic posterior circulation flow aneurysms associated with agenesis of the internal carotid artery

1 Department of Interventional Radiology, Division of Clinical Radiology, Christian Medical College Hospital, Vellore, Tamil Nadu, India
2 Department of Neurological Sciences, Neurosurgery Unit I, Christian Medical College Hospital, Vellore, Tamil Nadu, India
3 Department of Neurological Sciences, Neurosurgery Unit II, Christian Medical College Hospital, Vellore, Tamil Nadu, India
4 Department of Neurological Sciences, Neurosurgery Unit III, Christian Medical College Hospital, Vellore, Tamil Nadu, India

Date of Submission19-Dec-2021
Date of Decision03-Apr-2022
Date of Acceptance30-Apr-2022
Date of Web Publication01-Aug-2022

Correspondence Address:
Prof. Shyamkumar Nidugala Keshava
Department of Interventional Radiology, Division of Clinical Radiology, Christian Medical College Hospital, Vellore - 632 004, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/cmi.cmi_114_21

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Internal carotid artery agenesis, unilateral or bilateral is a rare congenital anomaly. Cerebral circulation challenged by this lack of anterior supply is compensated by increased flow through the posterior circulation and circle of Willis. This hyperdynamic circulation results in flow-related aneurysms, especially along the branching segments. We present the clinical, imaging and endovascular management of three symptomatic patients with discussion of relevant literature.

Keywords: Carotid agenesis, endovascular coiling, flow aneurysm

How to cite this article:
Padmanabhan A, Moses V, Ahmed M, Prabhu K, Nair BR, Joseph BV, Keshava SN. Management of symptomatic posterior circulation flow aneurysms associated with agenesis of the internal carotid artery. Curr Med Issues 2022;20:182-6

How to cite this URL:
Padmanabhan A, Moses V, Ahmed M, Prabhu K, Nair BR, Joseph BV, Keshava SN. Management of symptomatic posterior circulation flow aneurysms associated with agenesis of the internal carotid artery. Curr Med Issues [serial online] 2022 [cited 2023 Jun 7];20:182-6. Available from: https://www.cmijournal.org/text.asp?2022/20/3/182/352964

  Introduction Top

The brain is supplied by a network of vascular channels broadly classified as anterior and posterior circulation. While both systems have separate embryonic origin,[1] they communicate with one another through circle of Willis forming a mutually balanced supply system. Intracranial aneurysms when present with clinical manifestations due to spontaneous rupture require to be treated to prevent recurrence of bleeding and mortality.

  Case Details Top

Case details of three patients are presented retrospectively after obtaining necessary approval from Institution Review Board-IRB Min.No.I 3768 (Retro) dated: January 27, 2021. Considering the retrospective nature of the study and the patient being provided the best management, the informed consent was waved off.

Case 1

A 52-year-old patient presented with two episodes of loss of consciousness, followed by severe headache and multiple episodes of vomiting. There were no neurological deficits. Recent noncontrast computerized tomography (NCCT) done elsewhere [Figure 1] showed minimal acute subarachnoid hemorrhage (SAH) in the sulcal spaces of the right parietal lobe. Cerebral angiography showed the right internal carotid artery (ICA) agenesis with no visualization from the mid cavernous segment. The carotid canal was small on the right side, measuring 2.5 mm in maximum diameter. The left side carotid canal measured 6 mm. The right anterior circulation was compensated through the posterior communicating segment. Two aneurysms were noted at the origin of the right and left superior cerebellar artery. The aneurysm on the right side was longer, multilobulated, measuring 7 mm in height and 4 mm in the neck. It was also corresponding with the side of the bleed on plain computed tomography (CT). The aneurysm was cannulated with Excelsior microcatheter (Stryker Neurovascular, Fremont, CA, USA) and Transend wire (Stryker Neurovascular, Fremont, CA, USA), and two detachable Guglielmi detachable coils were placed. Postcoiling angiogram showed relative risk Grade II aneurysm occlusion. The second aneurysm was observed on follow-up which did not show interval change after 6 years.
Figure 1: A 52-years-old patient presented with two episodes of loss of consciousness, followed by severe headache and multiple episodes of vomiting. (a) Unenhanced CT showed minimal SAH in the right parietal sulcal space (long arrow). (b) Anteroposterior (left) and lateral (right) angiogram of right common carotid artery injection shows diffusely narrowed caliber (arrow) of the internal carotid artery. (c) Lateral angiogram showing anterior circulation is compensated through PCOA (long arrow). (d) 3D reconstruction angiogram showed flow-related aneurysms in the posterior circulation (arrows) (e) nonsubtracted (left) and subtracted anteroposterior view (right) after unassisted coiling done showing coils (arrow). CT: Computerized tomography, SAH: Subarachnoid hemorrhage, PCOA: Posterior communicating artery, 3D: Three-dimensional.

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Case 2

A 48-year-old patient presented with holocranial headache for 1 year. There was no history of thunderclap headache or loss of consciousness. Magnetic resonance imaging done elsewhere for evaluation revealed basilar top aneurysm. CT through the skull base showed bilateral small carotid canals measuring 1.5 mm each. A diagnostic angiogram showed small caliber of bilateral ICAs, measuring approximately 1.5 mm and ending as ophthalmic arteries [Figure 2]. There was a basilar top aneurysm measuring 12 mm in all dimensions, including height, neck, and width. Considering the wide-necked nature, stent-assisted coiling was planned. The posterior communicating arteries (PCOM) of both sides were arising from near the base of the aneurysm. A Neuroform Atlas Stent (Stryker, Kalamazoo, Michigan) placed in Y configuration was used as a scaffold to achieve neck protection. Nine detachable coils were deployed, and good aneurysm occlusion was achieved. Postcoiling angiogram showed normal filling of all the branch vessels, including PCOM supplying anterior circulation. Follow-up angiogram after 6 months showed occluded aneurysm.
Figure 2: A 48-years-old patient presented with holocranial headache for 1 year. There was no history of thunderclap headache or loss of consciousness. (a) Lateral view angiogram of extracranial (left) and intracranial (right) common carotid artery angiogram shows diffusely narrowed caliber of the internal carotid artery (arrow) suggestive of ICA agenesis (b) Lateral view angiogram shows anterior circulation is compensated through PCOA (arrow) (c) Cone beam CT reconstruction shows large basilar top aneurysm (d) Anteroposterior view (left) and cone beam CT reconstruction (right) after Y- stent-assisted coiling of aneurysm was performed showing densely packed coil mass (arrow) (e) Postcoiling angiogram showing maintained flow to anterior circulation through the PCOA (arrow). ICA: Internal carotid artery, CT: Computerized tomography, PCOA: Posterior communicating artery.

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Case 3

A 22-year-old female presented with a history of sudden onset headache and vomiting. CT angiogram revealed suprasellar cisternal hemorrhage with blood in the fourth ventricle suggestive of SAH. Bilateral carotid canals were small, measuring approximately 2 mm in diameter. Her neurological status was normal, without deficits. A cerebral angiogram revealed bilateral agenesis of paraophthalmic segment of ICA with ICAs ending as ophthalmic arteries [Figure 3]. The distal ICA was reformed from PCOM on the left side. The right distal ICA was filling through the anterior communicating artery as the right PCOM was absent. Angiogram also revealed a very irregular wide-necked aneurysm at the basilar top, which was measuring 10 mm × 6 mm. Stent-assisted coiling was performed with Enterprise stent (Cordis Neurovascular/Johnson and Johnson) and five detachable coils. Postprocedure angiogram showed marginally reduced flow in the left PCOM supplying anterior circulation. Intra-arterial tirofiban was infused – 10 ml was infused as bolus dose and 7 ml/h was infused for the next 24 h. Final check angiogram showed good opacification of the vessel. The patient's recovery was uneventful. She is yet to come for follow-up.
Figure 3: A 22-years-old lady presented with history of sudden onset headache and vomiting. (a) NCCT brain shows blood in the suprasellar cistern (b) Right CCA angiogram (right) and Left CCA angiogram (left) shows diffusely narrowed caliber of the internal carotid artery (arrow) till ophthalmic segment. (c) Anterior circulation is compensated through left PCOA (arrow) (d) 3D reconstruction of the angiogram showed a large fusi-saccular basilar top aneurysm (arrow) (e) Anteroposterior view (left) and lateral view (right) after stent-assisted coiling of the aneurysm showing coil mass (arrow) aneurysm (e) Anteroposterior view (left) and lateral view (right) after stent-assisted coiling of the aneurysm showing coil mass (arrow). NCCT: Noncontrast computerized tomography, CCA: Common carotid artery, PCOA: Posterior communicating artery.

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  Discussion Top

ICA begins from the level of the carotid bifurcation and terminates by splitting to anterior cerebral and middle cerebral arteries. Embryologically, the different segments of ICA are formed from different parts of a mesh network composed of ventral and dorsal aorta along with its branches.[2] This is described extensively by P Lasjaunias in his article in 1984. Nondevelopment of any particular part of this arterial arcade leads to agenesis of the corresponding segment of ICA. This results in alternate pathways compensating to try and maintain cerebral hemodynamic milieu. Detailed embryology is beyond the scope of this case series, however may be found in a great detail in the Lasjaunias textbook.[3]

The angiographic findings in agenesis of ICA can be mistaken for other acquired conditions such as Moyamoya disease; however, the bony carotid canal in the former will be smaller or absent.[4] The bony carotid canal can be best identified on NCCT. This is because carotid artery agenesis occurs very early in embryogenesis and this renders the carotid canal “unnecessary” to traverse the ICA. Considering that other smaller structures such as carotid venous plexus and sympathetic nerve plexus traverse into the skull through the carotid canal, it may not be entirely absent even in complete carotid artery agenesis. The absence of ICA may be segmental beyond the ophthalmic artery, in which case a hypoplastic proximal ICA will be present traversing through the carotid canal. Normally, the size of the carotid canal varies between 5 and 7 mm in adults.[5] In cases of agenesis, the carotid canal is usually around 2–3 mm.[6] In all three cases of ours, the carotid canal was significantly smaller.

Aneurysms form in the collateral circulation in cases with unilateral or bilateral ICA agenesis; the likely hypothesis is below. Since there is no flow through one or both anterior circulations, the posterior circulation turns hyperdynamic to accommodate the total blood volume. This leads to increased flow vector velocities on the arterial walls. In addition, the saccular aneurysms formed are at more at the branching of the vessels in the vertebra-basilar or PCOM. These aneurysms may develop over decades, which may even be detected incidentally.

During endovascular management of these aneurysms, there are additional challenges. Since posterior circulation is the only supply to the entire brain through the circle of Willis, even temporary occlusion offers the risk of catastrophic global cerebral hypoperfusion. It is not possible to quantify the exact risk involved in such situation, and the authors recommend avoiding balloon-assisted coiling. In addition, any minor coil prolapse may cause embolic risk to the entire cerebral circulation. Care must be taken to avoid this risk by minimizing the procedure time. The mean blood pressure should be maintained higher during general anesthesia.

In case 1, we were able to perform unassisted coiling of the aneurysm, thus avoiding flow limitation. There were two aneurysms on imaging. To reduce the time of intervention, the sinister-looking aneurysm which corresponded to the ICH was coiled. The other aneurysm was followed up, which did not show any interval change. In case 2, the basilar top aneurysm was wide necked and potential for the coils to prolapse to the main artery. Thus, stent in Y configuration was deployed to scaffold. A tight packing of the aneurysm was achieved. In case 3 also, the aneurysm was located at the basilar top. The anterior circulation was maintained solely through the left PCOM and it was vital to keep it patent. A single stent was placed to protect it.

Few similar case series have been reported in literature. In 2007, Zink et al. published a series of three cases.[7] In their introduction, they mention a classification for internal carotid agenesis described by Lie in Experta Medica foundation.[8] These described patterns in with the collateral circulation may develop to maintain cerebral circulation in cases with ICA agenesis or hypoplasia. They, in their systematic analysis, have recorded 17.9% of saccular aneurysm, which is more than the incidental occurrence.

Recently developed endosaccular device technology such as Woven EndoBridge (MicroVention, Inc.), Contour device (Cerus Endovascular), Neqstent (Cerus Endovascular)-assisted coiling[9] may be of particular interest. This is because the device can be placed into the aneurysm in a short procedure time, not requiring temporary flow arrest. Once properly sized, the chances of prolapse of these devices are very minimal. They also do not require long-duration antiplatelets like stent-assisted coiling.

In conclusion, ICA agenesis is a rare congenital anomaly marked by the absence of segments of ICA unilaterally or bilaterally. It closely mimics Moyamoya disease but can be differentiated by careful analysis of the carotid canal, which may be smaller but not entirely absent as it carries auxiliary structures. Collateral circulation through other parts of the circle of Willis, owing to hyperdynamic nature, may cause aneurysms. Endovascular management is laden with additional challenges which have to be considered for patient safety. We treated these aneurysms with unassisted- or stent-assisted coiling. Balloon-assisted coiling has the theoretical possibility of global ischemia. Novel endovascular devices may be of particular benefit in this subset of cases.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patients have given their consent for the images and other clinical information to be reported in the journal. The patients understand that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Menshawi K, Mohr JP, Gutierrez J. A functional perspective on the embryology and anatomy of the cerebral blood supply. J Stroke 2015;17:144-58.  Back to cited text no. 1
Lasjaunias P, Santoyo-Vazquez A. Segmental agenesis of the internal carotid artery: Angiographic aspects with embryological discussion. Anat Clin 1984;6:133-41.  Back to cited text no. 2
Lasjaunias P, Berenstein A. Surgical Neuroangiography: 1 Functional Anatomy of Craniofacial Arteries. Berlin, Heidelberg: Springer Berlin Heidelberg; 1987. Available From: http://public.ebookcentral.proquest.com/choice/publicfullrecord.aspx?p=3091678. [Last accessed on 2020 Aug 03].  Back to cited text no. 3
Aoun MA, Nasr AY, Aziz A. Morphometric study of the carotid canal. Life Sci J 2013;10:2922.  Back to cited text no. 4
Chen PY, Liu HY, Lim KE, Lin SK. Internal carotid artery hypoplasia: Role of color-coded carotid duplex sonography. J Ultrasound Med 2015;34:1839-51.  Back to cited text no. 5
Kubis N, Zuber M, Méder JF, Mas JL. CT Scan of the Skull Base in Internal Carotid Artery Hypoplasia. CED. 1996;6(1):40–4.  Back to cited text no. 6
Zink WE, Komotar RJ, Meyers PM. Internal carotid aplasia/hypoplasia and intracranial saccular aneurysms: Series of three new cases and systematic review of the literature. J Neuroimaging 2007;17:141-7.  Back to cited text no. 7
Lie TA, Excerpta Medica Foundation. Congenital Anomalies of the Carotid Arteries. Amsterdam: Excerpta Medica Foundation; 1968.  Back to cited text no. 8
Coil-Assisted Flow Diversion in a Ruptured Basilar Top Aneurysm Using a Neqstent Endosaccular Device: A Novel Treatment. HMP Global Learning Network; 2021. Available from: https://www.hmpgloballearningnetwork.com/site/vdm/case-report/coil-assisted-flow-diversion-ruptured-basilar-top-aneurysm-using-neqstent. [Last accessed on 2021 Oct 31].  Back to cited text no. 9


  [Figure 1], [Figure 2], [Figure 3]


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