CASE 12578 Published on 10.04.2015

Agenesis of the Internal Carotid Artery with Intracavernous Anastomosis

Section

Neuroradiology

Case Type

Clinical Cases

Authors

Ilias Bagetakos, Max Scheffler

From the Department of Radiology
Geneva University Hospital
Rue Gabrielle-Perret-Gentil 4
1205 Geneva, Switzerland
Patient

57 years, male

Categories
Area of Interest Neuroradiology brain ; Imaging Technique CT-Angiography, MR-Angiography
Clinical History
A 57-year-old man presented to the emergency department with right lower limb paresis since 20 hours. No associated sensory deficit was noted. The patient had a past medical history of non treated hypertension and tobacco use.
Imaging Findings
A computed tomography angiography (CTA) of the head and neck was performed, demonstrating agenesis of the left internal carotid artery with an intercavernous anastomosis supplying blood to the left middle cerebral artery (MCA). The left A1 segment of the anterior cerebral artery (ACA) was hypoplastic or absent. A thrombus was seen in the A2 segment of the left anterior cerebral artery. The non enhanced series of the scan (non contrast computed tomography [NCCT]) demonstrated a zone of cortical hypodensity in the left superior frontal gyrus (F1), suspicious of early ischemia. No spontaneous hyperdensity was noted on the NCCT that could have evoqued haemorrhage (Fig 1).
A brain magnetic resonance (MR) examination performed the following day showed multiple acute ischemic lesions in the left ACA and ACA-MCA border territories on the diffusion weighted sequence (DWI) without any sign of haemorrhagic transformation on the T2* sequence. No significant mass effect was noted (Fig 2).
Discussion
Unilateral agenesis of the internal carotid artery (ICA) is a rare developmental anomaly occuring in less than 0.01% of the population [1]. It has a left-sided predominance of 3:1 [2]. During embryogenesis, induction anomalies of the 3rd aortic arch may lead to hypoplasia or complete agenesis of the ICA. Intrauterine mechanical or hemodynamic stress has a causative role, through rotation of the embryo around constrictive amniotic bands, or exaggerated unilateral folding [2, 3, 4].
Arterial insufficiency is usually prevented by collateralization through the contralateral ICA and the vertebrobasilar system. Three different anatomic configurations are recognized, combining subtypes illustrated by Lie in 1968 [5]. The first and most commonly encountered type is the fetal type, with the anterior cerebral artery (ACA) of the affected side supplied by the contralateral ICA via the anterior communicating (Acom) artery, and the ipsilateral middle cerebral artery (MCA) arising from the basilar artery through an enlarged posterior communicating artery. In type 2 or adult type ICA agenesis, both the ACA and the MCA on the affected side are supplied via the Acom artery, a situation resembling persistant MCA perfusion in thrombotic ICA occlusion. The third and least common type, presented by our patient, shows absence of the cervical to petrous segments of the affected ICA, with an intercavernous collateral vessel arising from the contralateral ICA and reconstituting most of the cavernous to terminal segments of the ICA, thus supplying the MCA of the affected hemisphere [2, 6]. In 13 out of 16 cases of type 3 ICA agenesis, the ipsilateral A1 segment of the ACA was hypoplastic or aplastic [2]. It has been proposed that the cavernous anastomotic vessel results from fusioned trigeminal arteries, plexiform channels around Rathke's pouch, or inferior hypophyseal arteries [2, 7].
ICA agenesis is mostly fortuitously discovered by CTA or MRA. If most cases of ICA agenesis are asymptomatic, patients may have complaints related to mass effect (hypopituitarism, Horner syndrome, trigeminal neuralgia) or altered hemodynamics with transient ischemic attacks, stroke, and associated cerebral aneurysms at a rate of 25-34% vs. 2-4% in the general population [2, 6, 8, 9]. The finding requires scrupulous documentation as it can have implications during carotid endarterectomy, transsphenoidal hypophyseal surgery, and in thromboembolic disease, notably if an intravascular treatment is envisaged [7].
In conclusion, unilateral agenesis of the ICA constitutes a rarely encountered anatomic variant affecting future surgical or interventional procedures. It is associated with intracranial aneurysms and ischemic events.
Differential Diagnosis List
Ischemic left ACA stroke in type 3 left ICA agenesis
Internal carotid artery thrombosis
High grade carotid stenosis
Internal carotid artery dissection
Pituitary adenoma
Final Diagnosis
Ischemic left ACA stroke in type 3 left ICA agenesis
Case information
URL: https://www.eurorad.org/case/12578
DOI: 10.1594/EURORAD/CASE.12578
ISSN: 1563-4086