Surg Radiol Anat (2012) 34:475–477

DOI 10.1007/s00276-011-0901-z

ANATOMIC VARIATIONS

Unilateral agenesis of the internal carotid artery presented as transient ischaemic attack: a case report

Olga Kiritsi · George Noussios · Konstantinos Tsitas · Dimitrios Lappas

Received: 12 April 2011 / Accepted: 7 November 2011 / Published online: 22 November 2011© Springer-Verlag 2011

Abstract Dysgenesis of the internal carotid artery (ICA)is a rare vascular disorder with a variety of diVerent grades(agenesis, aplasia, and hypoplasia). The left internal carotidartery is reported to be aVected by dysgenesis three timesmore often than the right one. Most of the patients withdysgenesis of the internal carotid artery are asymptomatic.We report a case of a patient with right internal carotidartery agenesis presented to our hospital as transient ischae-mic attack. CT scans at skull base level with bone settingsshowed absence of the right carotid canal, consistent withcongenital agenesis of the internal carotid artery. MR imag-ing of the brain revealed signal void of the intracranial por-tion of right internal carotid artery. Maximum intensityprojection reconstruction conWrmed the agenesis of theright ICA, with the right middle cerebral artery fed througha dilated posterior communicating artery and the right ante-rior cerebral artery supplied by the anterior communicatingartery (fetal type of collateral Xow). In patients with agene-sis of the internal carotid artery non-invasive imaging tech-niques are currently the mainstay of diagnosis.

Keywords ICA · Agenesis · Fetal type · Collateral Xow

Introduction

Dysgenesis of the internal carotid artery (ICA) is a rare vas-cular disorder [1]. Agenesis denotes a complete develop-mental arrest of ICA associated with concomitant absenceof the ipsilateral carotid canal. The left ICA is reported tobe aVected by dysgenesis three times more often than theright one [9].

Lie [6] described six pathways of collateral circulation inassociation with the absence of the ICA. The fetal type isthe most commonly encountered. While most of thepatients with dysgenesis of the ICA are asymptomatic, wereport a case of a patient with right ICA agenesis and fetaltype collateral circulation presented as transient ischaemicattack.

Case report

A 54-year-old Caucasian Greek male presented to ouremergency department with transient left sided weaknessand numbness of the upper and lower extremity. Historytaking revealed that he felt of such symptoms four times inthe past. However, it was the Wrst time to seek for medicalcare. Sonographic evaluation of the carotid system (notshown) revealed absence of the right internal carotid artery.The patient subsequently underwent CT and MR imagingof the brain and MR angiography of the carotid system andthe brain vessels. CT scans at skull base level with bonesettings (not shown) showed absence of the right carotidcanal, with the left one normal. MR imaging of the brainrevealed signal void of the intracranial portion of the right

O. Kiritsi“Hippokratis”, Diagnostic Center, Kozani, Greece

G. Noussios (&)Laboratory of Sports Medicine, Department of Physical Education and Sports Sciences at Serres, “Aristotle” University of Thessaloniki, Thessaloniki, Greecee-mail: geornous@hotmail.com

K. TsitasGeneral Hospital Katerini, Katerini, Greece

D. LappasLaboratory of Anatomy of Medical School of National and Kapodistrian, University of Athens, Athens, Greece

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ICA (Fig. 1a). Source image of a 3D-TOF MRA of thecerebral arteries (Fig. 1b) showed Xow within the left ICAand the basilar artery; the right ICA is not discernible. Amaximum intensity projection reconstruction (Fig. 1c) con-Wrmed the agenesis of the right ICA, with the right middlecerebral artery (MCA) fed through a dilated posterior com-municating artery (PCoA) and the right anterior cerebralartery (ACA) supplied by the anterior communicatingartery (ACoA) (fetal type of collateral Xow). A thin vesselcommunicated between the right anterior and middle cere-bral artery, which by nature is a start of right anterior cere-bral artery. A maximum intensity projection reconstructionof the extracranial portion of the carotid system conWrmedthe agenesis of the right ICA with the right carotid bifurca-tion not identiWed. The vertebral arteries were dilated(Fig. 1d). A drawn plan shows the way of right cerebralvascularisation in our case (Fig. 2). The patient’s symptomsresolved spontaneously and were attributed to transientischemic attack, due to hypotension. He was dischargedfrom the hospital without any medication prescribed.

Discussion

In 1954, the Wrst case of ICA agenesis which revealed atcerebral angiography was reported by Verbiest [1].

At the 4–5 mm embryonic stage, the primitive ICA iscomposed of seven segments separated by embryonic ves-sels. Segment one is derived from the third aortic arch,whereas all the other segments (2–7) come from the dorsalaorta. The distal ICA then bifurcates into the rostral andcaudal division of the ICA. ICA is completely formed byabout 6 weeks after fertilization [5]. Agenesis or aplasia ofthe internal carotid artery probably occurs at this stage.

Dysgenesis of the ICA is a rare vascular disorder [1]with a variety of diVerent grades (agenesis, aplasia, andhypoplasia). Lie [6] deWned agenesis as complete failure ofan organ to develop with concomitant absence of thecarotid canal, aplasia as lack of development (but its pre-cursor did exist at one time and as a consequence of thecarotid canal is present), and hypoplasia as incompletedevelopment of the organ [8], combined with a reduced cal-ibre carotid canal. The prevalence of dysgenesis of the ICAis not known; it is probably <0.01% of the population [3].The left ICA is reported to be aVected by dysgenesis threetimes more often than the right one [4] and bilateralabsence or hypoplasia of ICA is more exceptional [9].Anomalies of the ICA in the neck also exist, including vas-cular neoplasms especially in pediatric population orectopic position.

Three major patterns of collateral circulation weredescribed in patients with unilateral agenesis/aplasia ofthe ICA [3]. In the fetal type which is the most commonlyencountered, the ACA of the aVected side is supplied bythe contralateral ICA through the ACoA, and the ipsilat-eral MCA arises from the basilar artery through an

Fig. 1 a MR imaging of the brain revealed signal void of the intracra-nial portion of the right ICA. b Source image of a 3D-TOF MRA of thecerebral arteries showed Xow within the left ICA and the basilar artery.c A maximum intensity projection reconstruction conWrmed the agen-esis of the right ICA, with the right middle cerebral artery (MCA) fedthrough a dilated posterior communicating artery (PCoA) and the rightanterior cerebral artery (ACA) supplied by the anterior communicatingartery (ACoA) (fetal type of collateral Xow). d The extracranial portionof the carotid system conWrmed the agenesis of the right ICA with theright carotid bifurcation not identiWed. The vertebral arteries weredilated

Fig. 2 Drawn plan of the way of right cerebral vascularisation in ourcase. ACA anterior cerebral artery, ACoA anterior communicating ar-tery, BA basilar artery, ICA internal carotid artery, MCA middle cere-bral artery, PCA posterior cerebral artery, RT right, LT left

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enlarged PCoA; the two-halves of the circle of Willis maybe completely separated. The second type is called adult(because it is similar to the collateral pattern that occursafter thrombosis of the ICA), in which the ACA and theMCA of the aVected side are supplied via the ACoA. Inthe third type, which is the least common the collateralsupply of the aVected hemisphere is made through anoma-lous anastomoses with the contralateral cavernous ICA(or with the external carotid system) or through the persis-tence of primitive vessels in the extrauterine life. Lie [6]described six pathways of collateral circulation in associ-ation with absence of the ICA. In types A, B, and C, uni-lateral (types A and B) or bilateral (type C) absence of theICA is associated with hypertrophied AcomA and PcomA(type A), patent AcomA (type B), or carotid–vertebrobas-ilar anastomoses (type C). Type D represents intercavern-ous communication to the ipsilateral carotid siphon fromthe contralateral cavernous ICA in the setting of unilateralagenesis of the cervical segment of the ICA. In type E theACAs are supplied by hypoplastic ICAs, whereas in typeF transcranial anastomoses from the internal maxillarybranches of the external carotid artery (ECA) system formsupply to the distal ICA, the so-called rete mirabile. Ourpatient had a fetal type of collateral supply. Otherresearchers simpliWed Lie’s original six collateral path-ways into three main types: collateral Xow through thecircle of Willis (most frequent), collateral Xow via persis-tent fetal circulation, and reconstitution of the ICAthrough skull base collaterals from the ECA [4].

Most of the patients with dysgenesis of the ICA areasymptomatic owing to the development of collateral arte-rial Xow suYcient to maintain cerebral function. The anom-aly is often detected as an incidental Wnding. However,when symptoms are present they include recurrent head-ache, blurring vision, hearing loss, hemiparesis with orwithout cranial nerve palsy, Horner syndrome, and intracra-nial haemorrhage due to ruptured aneurysms [2]. Absenceof the ICA is associated with 25–34% of aneurysm forma-tion on the circle of Willis [2, 10]. Xie et al. presented acase of a 45-year-old male patient with left hemifacialspasm for 6 years, absence of left internal carotid arteryICA and vertebral artery, presence of a 6 mm aneurysm inthe bifurcation of the right internal carotid artery and aright-sided aortic arch with subclavian steal phenomenon.The other rare reported pathologic abnormalities associatedwith ICA agenesis are corpus callosum agenesis, neuroW-bromatosis, meningocele, coarctation of aorta, and cardiacanomalies [2, 10].

CT is the ideal imaging modality to study the carotidcanal in cases of dysgenesis of the ICA, showing that it isabsent (agenesis) or of small size (aplasia and hypoplasia)in the aVected side [7]. Furthermore, in cases of internalcarotid artery thrombosis the carotid canal is of normal cal-ibre. MRA has been the most extensively used tool toinvestigate patients with dysgenesis of the ICA. If enlargedanastomotic vessels can be detected on MRI or MRA, thediagnosis of ICA dysgenesis is almost deWnitive. However,with MRI and MRA it may be diYcult to distinguishbetween hypoplasia and agenesis. In such cases, CT of theskull could be performed.

In conclusion, in patients with agenesis of the ICA non-invasive imaging techniques are currently the mainstay ofdiagnosis. In addition the existence of this dysgenesis issomething that surgeons need to know before employinginvasive techniques which may be otherwise be cata-strophic, for example in case of a coexistent aneurysm andsurgery in and around the sella turcica [6]. In addition, incases of occlusion of the contralateral ICA, bypass surgerycould be beneWcial only after careful selection of patients.

References

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