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ongenital Absence or Hypoplasia of the Carotidrtery: Radioclinical Issues

ustafa Tasar, MD,* Sertac Yetiser, MD,† Aysin Tasar, MD,‡¸ahin Ugurel, MD,* Engin Gonul, MD,§ and Mutlu Saglam, MD*

Purpose: Congenital anomaly of the carotid artery is a rare abnormality. It is usuallydiscovered incidentally by color Doppler carotid sonography, angiography, computedtomography (CT), or magnetic resonance imaging (MRI) of the head and neck taken for someother reason. Most patients are not symptomatic because of sufficient cerebral circulationsupplied to the defective area by the communicating arteries of the circle of Willis,intercavernous anastomosis, communicating arteries from external carotid artery, and bypersistent embryologic arteries to the carotid artery territory. However, sometimes, thisanatomic variation may eventually lead to some clinical signs and symptoms in particularcircumstances in the head and neck of which surgeons are unaware. A retrospective study wasdesigned to emphasize the characteristic radiologic and clinical picture in patients with thecongenital absence (agenesis and aplasia) or hypoplasia of the carotid artery, to delineate theassociated abnormalities and existing collateral vessels, and to find out its incidence.Material and Methods: Five thousand one hundred cerebral MRI and/or catheter angio-grams performed between February 1988 and March 2002 were reviewed for carotid arteryabnormality.Results: Seven patients with congenital absence or hypoplasia (4 of these patients werepresented with hypoplasia of internal carotid artery [ICA], 3 with absence of ICA) of ICA wereidentified (0.13%). The radiologic and clinical study of 5 patients with unilateral (3 of thesepatients were presented with hypoplasia and 2 with absence of ICA) and 2 patients withbilateral (1 was presented with absence of ICA, whereas the other was hypoplasia) congen-ital abnormality with absence or hypoplasia of ICA demonstrate that those patients areusually asymptomatic and they are diagnosed incidentally.Conclusion: It has been concluded that the combined use of magnetic resonance angiog-raphy and CT scanning of the skull base may disclose small but patent ICA. Collateralvessels seem to be usual in such cases, but they may be prominent in cases of acquiredvascular occlusion, or increased hemodynamic pressure in dysplastic changes in collateralarteries are known causes of aneurysms. The main vascular supply for the brain in patientswith congenitally small (hypoplasia) or absent (agenesis or aplasia) ICA is the vertebrobasilarsystem in bilateral cases. However, contralateral carotid vessel is the dominant arterialsupply for unilateral cases, which has to be borne in mind in surgical interventions to theinvolved side.(Am J Otolaryngol 2004;25:339-349. © 2004 Elsevier Inc. All rights reserved.)

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Congenital absence (agenesis, aplasia) orypoplasia of one or both internal carotidrteries (ICAs) is a rare developmental ab-ormality and is discovered incidentally byolor Doppler carotid sonography, angiogra-hy, computed tomography (CT), or mag-

From the Departments of *Radiology; †ENT; ‡Pediat-ics; and §Neurosurgery, Ankara Hospital of Ministry ofealth, Ankara, Turkey.Address correspondence to: Mustafa Tasar, MD, Gul-

ane Medical School, Department of ORL & HNS, 06018tlik, Ankara, Turkey. E-mail: mtasar@gata.edu.tr.© 2004 Elsevier Inc. All rights reserved.0196-0709/$ - see front matter

sdoi:10.1016/j.amjoto.2004.04.008

American Journal of Otolaryngology, Vol 25, No

etic resonance imaging (MRI) of the headnd neck taken for some other reason.1-3 Thencidence of the absence of ICA has beeneported to be around 0.01%.4-7 The term ofhe absence of carotid artery has been sub-tituted for the agenesis, aplasia, or hypo-lasia of the ICA, which may lead to someisunderstanding because the descriptive

lassification of this anomaly is lacking.8 Ithould be kept in mind that the term ofypoplasia here means the underdevelopedarotid with small caliber. These develop-ental anomalies of ICA are strongly sug-

ested when the carotid canal is absent orypoplasic as seen on CT scanning of the

2,6,9

kull base. Absence of blood flow in the

3395 (September-October), 2004: pp 339-349

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340 TASAR ET AL

arotid because of absence of vessel lumenhould be confirmed by angiography.Most patients are not symptomatic because

f sufficient cerebral circulation supplied tohe defective area by the communicating ar-eries of the circle of Willis, intercavernousnastomosis, communicating arteries from ex-ernal carotid artery, and by persistent embry-logic arteries to the carotid artery terri-ory.10-17 They live for years without anyymptom. However, in some patients, symp-oms related with cerebral ischemia becausef less blood flow can occur and enlargementf collateral vessels may lead to associatedntracranial aneurysm with obvious prob-ems.18,19 It is important to realize the clinicalharacteristics, imaging features, and surgicalmplications of this entity because coexistingymptoms may lead the patients to have inva-ive and risky interventions. The aim of thistudy is to emphasize the characteristic radio-ogic and clinical picture in patients with ab-ence or hypoplasia of carotid artery, to delin-ate the associated abnormalities and existingollateral vessels, and to find out its inci-ence.

ATERIALS AND METHODS

Five thousand one hundred cerebral MRI and/oratheter angiograms performed between February988 and March 2002 in our department were re-iewed and 7 patients with congenital absence orypoplasia of ICA (5 unilateral and 2 bilateral)ere identified. Of all 5 patients, 2 were with

bsence and 3 were with hypoplasia of ICA; of 2ilateral cases, one was presented with bilateralbsence and the other was presented with hypopla-ia. All cases were documented clinically and ra-iologically by conventional MRI or by other mag-etic resonance angiography (MRA) techniques.ne bilateral and 4 unilateral absences of ICA werelso examined by digital subtraction angiographyDSA). Two bilateral and 4 unilateral cases werelso examined by color Doppler ultrasonography.ll patients were examined by 1.5 T MR systems

Magnetom SP 63 or Magnetom Vision Plus, Sie-ens, Erlengen, Germany). Axial T1-weighted and2-weighted (spin echo proton density, turbo spincho, and fluid attenuated inversion recovery) se-uences were obtained with head coil in supineosition. Diffusion-weighted images (b0, b500,1000 s/mm2) were obtained from 3 patients toxclude acute ischemic lesions and apparent diffu-ion coefficient maps created (after 1999). The clin-cal and radiologic data of the patients are shown in

able 1. t

Super selective catheterization (Digitron II andultistar Plus, Erlengen, Germany) of both internal

nd external carotid and vertebral arteries wereerformed under local anesthesia via femoral ar-ery. Two different CT scanners were used for brainmaging including the skull base and the temporalone with 2-mm slice thickness (Somotom DRH,iemens, Erlengen, Germany and GE Hi-Speed Ad-antage, General Electric, Milwaukee, WI). CT an-iograms were also obtained with spiral CT scan-er. Skull base and the bony carotid canal weressessed on each CT image. If the bony carotidanal was not visible at the serial cuts of the base ofhe skull, then this abnormality was defined as thebsence of the carotid canal and carotid artery. Ifhe bony canal was present, the diameter of theathological side was compared with that of con-ralateral part. In suspected bilateral cases, diame-er of the canal was compared with that of normalide in patients with unilateral ICA hypoplasia. Ifhe diameter was less than half of the size of nor-al, then it was accepted as abnormal. However,

he patency of the abnormal artery was alwaysontrolled with the angiography. In cases with ab-ent ICA, the presence of collateral vessels andther clinical and radiological abnormalities werenvestigated. Color Doppler sonography was per-ormed with 2 different devices (Acuson XP/10 andoshiba SS270 A, Tokyo, Japan). B-mode andulsed-wave color Doppler images were obtainedhrough both common and ICAs, and then bloodow velocity measurements were made.

ESULTS

Three of 5 patients with unilateral agenesisr hypoplasia and 2 patients with bilateralbsence or hypoplasia were male. The com-on symptom for all patients was headache.T revealed intracerebral and subarachnoidemorrhage in 1 patient with brief and sud-en loss of consciousness and in another oneith a history of pituitary hypogonadism and

hronic headache. Ruptured left middle cere-ral artery (MCA) aneurysm and aortic archbnormality, which was presumably relatedo the patient’s headache in both patients, washown. It was revealed that the left commonarotid artery and brachiocephalic trunk wasunning very close to each other as if a singleessel (case 6) (Fig 1). Unilateral absenceagenesis) of the ICA was considered as therobable cause of the hypogonadism. In 1atient (left hypoplasia) with spontaneous ep-staxis from time to time in addition to theeadache, CT and DSA revealed nasopharyn-eal intense enhancing mass consistent with

he angiofibroma (case 7) (Fig 2).

TABLE 1. Clinical and Radiologic Findings of the Patients

PatientNo. Age/Sex

PresentingComplaints

CDUS andUS CT MR MRA

Diffusion- andPerfusion-weighted

MRI DSAAbnormality

SideType of

AbnormalityMain Collateral

FlowAssociated

Abnormalities

1 53/M Headache NA Hypoplasticbony carotidcanal

� � N � Left Hypoplasia PCOMACOM

�

2 25/M Headache Bilateralsmall CCAandcervicalICA

Bilateralhypoplasticcarotid canal

� � � � Bilateral Hypoplasia PCOMACOM

intercavernousanastomoses

�

3 57/M Headache Bilateralsmall CCA

� � � N � Bilateral Absence(agenesis)

PCOMACOM

�

4 17/F Headache,syncope

� � � � � � Right Absence(agenesis)

ACOMPCOM

�

5 55/F Headache ICA absent Hypoplasticbony carotidcanal

� � N � Left Hypoplasia ACOMPCOM

�

6 17/M Headache,loss ofconciousness

HypoplasticCCA andabsenctICA

HypoplasticCCAintracerebral/subarachnoidhemorrhage

� � � � Left Absence ofICA andhypoplasticCCA

ACOMPCOM

Arcus aortaabnormality,primaryhypogonadism,noduler goitre,leftintracerebralhematoma

7 21/M Headache,episodicnosebleeding

Small CCAandhypoplasticICA

Left hypoplasticbony carotidcanal

� � � � Left ACOMPCOM

hypoplasia Nasopharynxangiofibroma

Abbreviations: N, normal; CCA, common carotid artery; ICA, internal carotid artery; US, ultrasonography; CDUS, color Doppler ultrasonography; M, male; F, female; ACOM,anterior communicant artery; PCOM, posterior communicant artery.

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Color Doppler sonography and angiographyhowed small caliber of CCA in 2 bilateral casescases 2 and 3) (Figs 3 and 4). CCA continued ashe external carotid artery and no ICA wasresent in 3 of 4 patients with unilateral carotidbnormality (2 hypoplasia, 1 absence) (cases 5,, and 7). Skull base and temporal bone CTcans revealed significantly narrow carotid ca-al in 1 patient with bilateral hypoplasia of ICA.arotid canal was also very small in 3 patientsith unilateral hypoplasia. One patient withnilateral agenesis could not be scanned with

Fig 1. Left ICA agenesis in a patient with hypogonodiA) Digital subtruction angiography of the arcus aorta. Bre running very close to each other. Note that left CCAhows marked left ECA and absence of the left ICA. (Contrast enhanced computed tomography of the neck.

T (case 4) and angiography revealed the entity h

Fig 5). Although left intracerebral hematomaith subarachnoid hemorrhage was evident in 1f 6 patients examined by CT (case 6) (Fig 1),rain CT images of other 5 cases were normal.RA images were in well accordance with DSA

mages. Diffusion images in 2 patients with left-ided agenesis were unremarkable (cases 5 and) (Fig 6).

ISCUSSION

ICA is one of the most stable arteries of the

nomaly of the arcus aorta, and the ruptured aneurysm.osephalic trunk, thin left CCA and left subclavian arteryinner than right ICA. (B) Selective left CCA angiographyft CCA is smaller than right CCA as seen on the axial

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343CONGENITAL ABSENCE OR HYPOPLASIA

pment. Tode reported the first case of ICAgenesis in 1787, which was accidentally en-ountered after a cadaveric dissection.11,20

he prevalence of congenital absence of ICAs estimated as 0.01%.18,21 The prevalence ofbsence of ICA is 0.058% and the prevalencef hypoplasia of ICA is 0.079% in our series.nilateral absence or hypoplasia of ICA isore frequent on the left and bilateral absence

r hypoplasia is more exceptional and re-orted to be less than 10% of unilateral in-

Fig 2. Left ICA hypoplasia in a patient with nasophaypoplasic left CCA and hypertrophic left vertebral arasopharyngeal mass and complete absence of left ICAhe neck shows large caliper right CCA and left veoncontrasted computed tomography of the skull base

arrowhead).

olvement. On the other hand, it is one of the c

ajor concerns that the reported incidencesre likely not to be realistic because thereeems to be some confusion in terminology. Its better to classify dysgenesis of the carotidrtery in 3 subgroups as agenesis, aplasia, andypoplasia. ICA with small caliber and patentumen corresponds to hypoplasia. Aplasia in-icates a vascular remnant, which has no vas-ular formation.The etiology of agenesis, aplasia, and hyp-

plasia of ICA is still unknown. There are

eal angiofibroma. (A) Arcus aorta angiography shows(B) Selective left CCA angiography reveals a stainingxial contrast enhanced computed tomography scan of

al artery and left CCA with small caliper. (D) Axialbone windowing reveals hypoplasic left carotid canal

ryngtery.. (C) Artebrwith

onflicting proposals for the maldevelopment

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344 TASAR ET AL

f this artery. One of the theories indicates aecondary regression of the ICA from the be-inning of the intrauterine life. However, thether one claims interruption of the develop-ent of the artery for unknown causes after aeriod of normal growth, which may justifyhe difference between the loss of maturity inome and absence of the artery in others. Las-aunias and Santoyo-Vazquez22 have indi-ated that 7 different embryological segment

Fig 3. Bilateral ICA agenesis in a patient with no othe-dimensional time of flight technique. The anteropostypertrophic vertebrobasilar system and absence of bo

CECT) scan of the posterior fossa shows hypertrofic ahe supratentorial region of the brain shows collateral suommunicant artery and parasellar anostomotic collatcans of the skull base shows both hypoplastic carotid

ranches come together and forms the internal a

arotid artery system. Those are cervical seg-ent from third aortic arch, ascending intra-

etrous segment from second and third aorticrch; horizontal petrous segment from firstnd second aortic arch, ascending segment inoramen lacerum from first aortic arch andrimitive maxillary artery; horizontal segmentf carotid siphon from primitive maxillaryrtery and dorsal ophthalmic artery; clinoidegment from dorsal and ventral ophthalmic

iologic finding and clinical symptom. (A) MRA with theprojection of MRA shows the extremely tortuous andA. (B) Axial contrast enhanced computed tomographyrtuous vertebrobasilar system. (C) Axial CECT scan ofto both cerebral hemisphere via hypertrophic posteriorvessels. (D) Axial noncontrast computed tomographyals.

r raderiorth ICnd topplyeralcan

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345CONGENITAL ABSENCE OR HYPOPLASIA

Fig 4. Bilateral hypoplasia of the ICA. (A) Angiographic view of the arcus aorta shows that both CCA have smalleraliper than the vertebral arteries. Selective (B) right and (C) left CCA angiograms show that both hypoplastic ICAso to the cavernous segment and form the intercavernous, parasellar collateral networks. (D) Axial supratentorialontrast enhanced computed tomography scan of the brain shows hypertrophic parasellar collateral pathways andommunicans with bilateral PCA via posterior communicant artery. (E) Frontal view from the right vertebralrteriography displays collateral flows to both MCA and ACA with parasellar collateral pathways.

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346 TASAR ET AL

rimitive ophthalmic artery and anterior ce-ebral artery. Lack of development of one orore of those branches may eventually lead tooor formation of the carotid system. CCArising from aortic sac may explain the conju-ation of left CCA with brachiocephalic trun-us in case 6. Some authors indicate the com-on embryological origin from the third

ortic arch. However, it is reasonable to as-ume that the external and internal carotidrteries have separate origins because theyave separate stemming from the aortic sac andCA rarely disappears in the absence of ICA.ollateral vessels may appear instead of differ-nt segments of ICA.23-26

There is no clear relation between the sever-ty of cerebral ischemia and ICA absence andypoplasia. However, development of collat-ral vessels, flow direction change in the cir-le of Willis and increased blood flow in ver-ebrobasilar system or contralateral anteriorirculation provides additional supply for thenvolved area. However, it seems in this serieshat blood flow from ECA anastomoses do notontribute significantly for this compensation.articularly in patients with bilateral ICA hy-oplasia, arteriosclerosis and stenosis of com-ensating vessels because of cervical spon-ylolysis in advanced ages may lead to morerominent and severe consequences.18,26 If

here is a possibility of cerebral infarct orcclusion of cerebral vessels MRI, MRA, andT angiography should be included in evalu-

Fig 5. Right carotid angiography shows theranches of the external carotid artery, and there is novidence of the right ICA (agenesis of the right ICA).

tion of those patients. “

Diffusion- and perfusion-weighted se-uences should be added in search of acute,ubacute infarction for a patient with absentr hypoplastic ICA.27-29 Conventional MRI isormal in case 7. Left CCA was evident butCA could not be visualized. Skull-base CThowed small bony carotid canal consistentith ICA hypoplasia. Aortic arch maldevelop-ent reminds other possible vascular abnor-alities in case 6. Hematoma secondary to

upture of aneurysm of MCA was present. Inases with bilateral ICA hypoplasia or absencecases 2 and 3), ICAs were small in diameter athe carotid siphon and vertebral arteries wererominent in the patient with bilaterally hy-oplastic ICA. There was no other develop-ental abnormality.9,22,28,30,31

Concentric stenosis of ICA lumen may de-elop secondary to different acquired pathol-gies like arteriosclerosis, arteritis, fibromus-ular dysplasia, intimal dissection, or Moyaoya disease.29 High-level stenosis of ICA at

he origin of the vessel, accentuated vaso-pasm, acute occlusion of distal ICA, or in-reased intracranial pressure may be called asfunctional stenosis” and show similar imag-ng findings. These acquired causes will bexcluded by demonstrating decreased bonyarotid canal caliber, clinical follow-up,nd/or diffusion-perfusion MR images, whichndicate normal regional cerebral bloodow.27,32 Hypoplastic ICA may be confusedith an enlarged ascending pharyngeal artery

n the presence of occlusion or agenesis ofervical part of ICA. Catheter angiographyelps in differential diagnosis, which is verymportant in treatment planning of acquiredtenosis of ICA. Clinical findings and CT andRI images are also helpful. Patients with

ongenital absence of ICA have no symptomsn terms of cerebral ischemia. However, rup-ure of an aneurysm or acquired extra-intralu-

inal diseases leading to ischemic symptomsay need endarterectomy or anticoagulation

herapies when ipsilateral ICA dysgenesis isresent.18,23,33 The outer diameter of the ves-el is normal, but the wall thickness has beenncreased in acquired luminal stenosis likeakayasu arteritis. However, arterial lumen,iameter of the vessel, and the wall thicknessas been decreased in ICA hypoplasia. Wallhickness of the vessel is normal in case of

functional stenosis,” which results from in-

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347CONGENITAL ABSENCE OR HYPOPLASIA

ufficient volume because of decreased vesselumen. Color Doppler ultrasonography (CDUS)rovides adequate evaluation of the carotid ar-ery stenosis. MR has an advantage to showessel wall disease and dissection better thanDUS because it has better contrast resolution

though worse spatial resolution) than CDUS.

Fig 6. Hypogenesis of the left ICA. (A) Anterioposteright technique show hypertrophic vertebrobasilar systen the proton density scan of the supratenterorial regionase reveals normal right carotid canal (C) and hypopla

dvances of techniques and improvement in t

patial resolution in MRI and CT will be able toelineate arterial diseases in the future.34,35

Ipsilateral decrease in diameter of CCA sup-orts the theory of congenital etiology. CDUSnd US examinations may reveal some abnor-alities like hypoechoic plaques, thrombus,

nd parietal hematoma. CDUS may also show

d oblique views of the MRA with 3-dimensional time ofd right carotid artery system. (B) No abnormality is seene brain. (C) Bone image of the skull base. CT of the skullleft (D) carotid canal.

or anm anof thstic

he level of stenosis and the degree of obstruc-

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348 TASAR ET AL

ion. Well-known disadvantages of CDUS andS are inability to evaluate distal vascular

egions like deep cervical, petrous, and intra-ranial parts. Vascular imaging on MRA de-ends on T1 shortening despite intravascularow of contrast media. It’s easy to displayaximum intensity projection (MIP) images

f vascular structures between aortic arch andillis circle, which is very similar to DSA

mages. Disadvantages of MIP images aremitting arterial stenoses because jugular veinow may overlap because of worse temporalesolution. Sparing of the first part of ICA hadeen described as a sign of dysgenesis byome authors.3,16,22,27,29 There are 2 casesith this type of involvement in our series.SA and MRA may not show parietal sourcesecause they cannot delineate vessel walls.Collateral blood flow to intracranial vesselsay come from contralateral ICA or from ver-

ebrobasilar system through the circle of Wil-is. Persistent trigeminal arteries, persistentympanic or stapedial arteries, hypoglossal ar-ery, intercavernous anastomosis, ophthalmicrteries, branches and anastomoses of ECA,nd rete mirabilis were described as otherollateral pathways.10,12,13,14,18 It has been ob-erved in this study that the vertebrobasilarystem is the main collateral pathway in pa-ients with bilaterally hypoplastic or absentCA. There were no other embryological orcquired collaterals. In previous reports, pres-nce of collaterals may be the sign of a coex-stent vascular occlusion or stenosis in verte-robasilar artery, which diminish the deliveryf blood flow to the agenesis side. Such col-aterals may appear rapidly even in temporarycclusion of ipsilateral carotid arteries by bal-oon catheter.

ICA hypoplasia or absence always accom-anies with a small and/or absent carotid ca-al. Development of ICA is completed at theorth embryonic week, and the bony canal isormed at fifth and sixth embryonic weeks.emonstration of a small carotid canal by CT

s helpful for excluding acquired etiolo-ies.36,37 Skull-base CT showed at least 2imes smaller diameter of the carotid canal in

cases (cases 2, 3, 5, 6, and 7). Upper andower limits of the diameter of the carotidanal in petrous bone were reported to be 4 to.5 mm for the vertical part and 4.5 to 7 mm

38

or the horizontal part by Lenonetti et al. All a

ases in this study had less than 4 mm iniameter. Patients with ICA dysplasia shoulde evaluated for a possible intracranial aneu-ysm of the circle of Willis because the inci-ence of aneurysm was found to be 24% to4% in those patients compared with 2% to% in normal population. Increased hemody-amic pressure in the collateral arteries of theysplastic vessels is known to cause the an-urysms. CT, MRI, and MRA always have toe included in the radiologic agenda of thelinician for imaging of those vessels.In conclusion, hypoplasia or absence of ICA

agenesis or aplasia) is a rare abnormality.ombined use of MRI, MRA, and CT scanningf the skull base and head may disclose smallut patent ICA. Collateral vessels seem to besual in such cases, but they may be promi-ent in case of acquired vascular occlusion orncreased hemodynamic pressure in dysplas-ic changes in collateral arteries are knownauses of aneurysms. The main vascular sup-ly for the brain in patients with congenitallymall or absent ICA is the vertebrobasillarystem in bilateral cases. However, contralat-ral carotid vessel is the dominant arterialupply for unilateral cases, which has to beept in mind in surgical interventions to thenvolved side.

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a1

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349CONGENITAL ABSENCE OR HYPOPLASIA

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