Agenesis of the left internal carotid artery: a case report

¹Neurology Department, Nouakchott Military Hospital, Nouakchott, Mauritania, ²Neurovascular Department of the Raymond Poincaré University Hospital Center in Garches, Garches, France

^&Corresponding author
Mohamed Mahmady, Neurology Department, Nouakchott Military Hospital, Nouakchott, Mauritania

Introduction    

Internal carotid artery (ICA) agenesis is a rare malformation, occurring in less than 0.01% of the general population [1]. Tode described the first case of absent ICA in 1787, and since then, approximately 100 cases have been reported [2]. Verbiest first demonstrated this abnormality angiographically in 1954 [1]. Internal carotid artery (ICA) agenesis may be inconsequential; however, the presence of ICA agenesis may be associated with risks of vascular complications such as cerebral aneurysms and cerebral infarction and should therefore be further evaluated when monitoring for this abnormality.

Patient and observation     

Patient information: we present the case of a 79-year-old right-handed female patient living alone with a medical history of hypertension, dyslipidemia, and colon cancer treated with radiotherapy and chemotherapy, currently in remission for 3 years.

Clinical findings: the patient woke up with right hemiparesis with dysarthria and decreased sensitivity for 3.5 hours. She reported a previous episode of vertigo associated with right-sided weakness, which resolved rapidly without any intervention. She was transferred to our medical center for possible recanalization.

Diagnostic assessment: a brain MRI with vascular sequences was performed, objectifying an acute infarction in the territory of the anterior choroidal artery in diffusion with negative flair. However, the left carotid siphon was not visualized on the TOF sequence, which raised suspicion of a possible occlusion or abnormality of the carotid artery (Figure 1, Figure 2). Subsequently, a brain and supra-aortic MRI (magnetic resonance angiography) was requested, which revealed a complete absence of the internal carotid artery with intercavernous anastomosis (Figure 3).

Diagnosis: CT angiography of the head and neck also confirmed the complete absence of the left internal carotid artery. It also showed that the left hemisphere vascularization was maintained by a branch of the cavernous segment of the contralateral internal carotid artery anastomosing with the left middle cerebral artery and the CT scan of the skull base revealed the absence of a left carotid canal (Figure 4, Figure 5, Figure 6)

Therapeutic interventions: due to her low National Stroke Status Scale (NIHSS) score of 4, no thrombolysis was recommended. The patient was started on bivalent antiplatelet therapy and statins. Her blood pressure was managed according to the acute stroke protocol.

Patient perspective: 5 days later, the patient was discharged with complete recovery of her right-sided weakness. The patient was satisfied with the quality of care and therapeutic outcomes.

Informed consent: the patient was informed about the procedure of publishing a research paper and gave consent.

Discussion     

Carotid agenesis is defined as a complete absence of the internal carotid artery and carotid canal, whereas hypoplasia is defined as a narrowing of a segment or the entire length of the internal carotid artery (ICA) with the presence of a carotid canal [1,2]. Its incidence is less than 0.01% of the general population without gender predominance [3]. There are approximately 100 cases of ICA agenesis reported in the literature. The first case of ICA agenesis was described by Tode in 1787. In 1954, Verbiest demonstrated ICA agenesis on angiography [4]. Embryologically, ICA agenesis is thought to be due to abnormal regression of the first and third aortic arches related to mechanical stress or excessive flexion of the cephalic part of the embryo during its development. There are 6 types of different (A-F) carotid agenesis [5] (Figure 7). They are classified according to the laterality of the agenesis, the presence of collateral circulation via the circle of Willis, and an intercavernous anastomosis. Our case fits the description of a type D ICA agenesis (Figure 3, Figure 4) where there is a unilateral left internal carotid agenesis with collateral supply via an intercavernous anastomosis of the cavernous segment of the collateral internal carotid artery, which is extremely rare, see image. Interestingly, the vascularization of the left hemisphere was maintained by a branch of the cavernous part of the right ICA communicating with the left middle cerebral artery (Figure 3).

The absence of a carotid artery siphon on the axial cerebral MRA (Figure 2) was the first clue to ICA agenesis. CT angiography of the head and neck confirmed the diagnosis and showed a complete absence of the left carotid canal (Figure 6). The intercavernous anastomosis observed in our case leads to collateralization of the circle of Willis [1]. The skull base forms at 5-6 weeks and therefore in the case of ICA agenesis, the carotid canal does not form during organogenesis, thus serving as a critical element of the diagnosis. Examination of the carotid canal on a skull base CT scan with a parenchymal window is essential to establish the diagnosis of internal carotid artery agenesis and to help differentiate ICA agenesis from hypoplasia. The carotid canal is present in hypoplasia and absent in agenesis [1,2]. In the very rare type of ICA agenesis (Lie type “D”), the sylvian artery is supplied by an intercavernous anastomosis, with this abnormal vessel being transphenoidal, intrasellar, or supra clinoid [6]. Reports of this conformation with collateralization via an intercavernous anastomosis were reviewed by Oz et al. in 2016, including a total of 36 patients [3]. Patients with such an anomaly are at higher risk of transient ischemic attacks. They also have a high incidence of intracranial aneurysm. It is estimated to be 25-43%, compared to 2-4% of the general population [6-8]. Therefore, it requires screening and monitoring. Tahmasebpour et al. proposed the theory of increased regional blood flow as an important factor in the development of cerebral aneurysm [8]. Others associate this with hemodynamic disturbances [7]. Our case is type D, this type of anastomosis has important surgical implications higher risk of complications with certain procedures such as transsphenoidal surgeries and carotid endarterectomies

Conclusion     

Agenesis of ICA is a rare congenital anomaly with a higher risk of cerebrovascular accident, cerebral aneurysm, and surgery-related complications. Identification and subtyping of this congenital anomaly is very crucial. It may prevent wrong diagnosis such as severe carotid artery stenosis or total ICA occlusion, and unnecessary intervention. It would also help to plan surgical interventions for carotid endarterectomy or cerebral aneurysm if necessary.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Patient management and manuscript review: Sandrine Deltour and Linda Lanouar. All authors have read and accepted the final version of this manuscript.

Acknowledgments     

We would like to thank my supervisors at the Raymon Poincaré Hospital in Garches, in particular the PUPH Sandrine Deltour, who allowed me to write this work during my internship in the neurovascular department in 2023.

Figures     

Figure 1: MRI brain DWI: (A) a small infarct in the territory of left anterior choroidal artery, barely visible in flair (B)

Figure 2: (A,B) the axial section in cerebral MR angiography shows the total absence of the left carotid siphon with visualization of the left sylvian artery.

Figure 3: AP view of 3D rendering of MRI angiography of the neck and brain showing a right CCA (A), a relatively small left CCA (B), the right ICA is widely patent (C), basilar trunk (D), intracranial anastomosis by an issi branch of the cavernous potion of the right ICA (E) in communication with the left sylvian artery (F)

Figure 4: AP view of the 3D rendering of a neck and brain angiography CT showing a right ICA (A), an intracranial anastemosis by an issi branch of the cavernous portion of the right ICA (B) in comminution with the left sylvian arter

Figure 5: axial computed tomography of the skull base demonstrates the presence of the right petrosal carotid canal (arrow) in contrast to the absent left carotid canal (circled)

Figure 6: AP view of the 3D rendering of the axial CT scan of the skull base demonstrates the presence of the right carotid siphon and a cavernous branch anastomoses with the left sylvian artery (arrow)

Figure 7: different (A-F) carotid agenesis according to lee's classification

References