Case Report

Agenesis of the Internal Carotid Artery:Color Doppler, CT, and MRAngiography Findings

Ulrich Sliwka, MD,1 Peter Schmidt, MD,2 Jurgen Reul, MD,2 Johannes Noth, MD3

1 Department of Neurology, Friedrich-Schiller University, Philosophenweg 3, D-07740 Jena, Germany2 Department of Neuroradiology, Technical University of Aachen, Pauwelsstrasse 30, D-52057 Aachen, Germany3 Department of Neurology, Technical University of Aachen, Pauwelsstrasse 30, D-52057 Aachen, Germany

Received 19 June 1997; accepted 24 September 1997

ABSTRACT: Agenesis of the internal carotid artery(ICA) is a rare finding that can lead to the false diag-nosis of an ICA occlusion. We present the case of ayoung woman with agenesis of the left ICA. Diagnosiswas made noninvasively by color Doppler imaging(CDI) in combination with high-resolution CT ofthe base of the skull. Magnetic resonance angiogra-phy confirmed the diagnosis. CDI in combination withCT of the base of the skull allows the diagnosis ofICA agenesis without the use of invasive proce-dures. © 1998 John Wiley & Sons, Inc. J Clin Ultra-sound 26:213–216, 1998.

Keywords: agenesis; internal carotid artery; transcra-nial color Doppler ultrasonography

Agenesis of the internal carotid artery (ICA) isa rare finding. We present the case of a pa-

tient with unilateral agenesis of the ICA assessedby color Doppler imaging (CDI), magnetic reso-nance angiography (MRA), and CT. The values ofthe different imaging modalities and the differen-tial diagnosis are discussed.

CASE REPORT

A 32-year-old white woman complained of head-ache when consulting her neurologist as an out-patient. The neurologist found Horner’s syn-drome involving the right eye, and MRA wasperformed to rule out an ICA dissection. MRA ofthe extracranial carotid artery circulation did not

visualize the left ICA. The patient was admittedto University Hospital Aachen with a diagnosis ofacute left ICA dissection. On admission, the neu-rologic findings were completely normal exceptfor Horner’s syndrome contralateral to the absentICA. On the left side, CDI revealed a significantlysmaller lumen of the common carotid artery(CCA) (3.2 mm on the left versus 6.6 mm on theright) and an absent ICA. Both vertebral arterieshad a diameter of 5 mm. CDI revealed an absenceof flow signals in the region in which the intra-cranial portion of the left ICA is normally locatedand demonstrated large posterior communicatingarteries, a sign of collateral flow. High-resolutionCT of the base of the skull revealed the absence ofthe left carotid canal. MRA using 3-dimensionalinflow techniques with maximum intensity pro-jections and reconstructions confirmed the exis-tence of the intracranial collateral flow throughenlarged posterior communicating arteries. Nocause for the Horner’s syndrome was found. Thepatient’s headache disappeared the day after im-aging and was therefore classified as a tensionheadache.

DISCUSSION

To our knowledge, this is the first case of ICAagenesis diagnosed noninvasively with CDI andhigh-resolution CT of the base of the skull. Agen-esis of the ICA is a rare anomaly. Since it was firstdescribed by Tode in 1787,1 about 100 cases havebeen reported in the literature, 27 of them with

Correspondence to: U. Sliwka

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bilateral agenesis of the ICA.2 Most of these re-ports were based on postmortem studies.

Two theories exist about the development ofthe carotid arteries. One theory suggests that theCCA and the proximal part of the ICA arise fromthe 3rd aortic arch.3,4 The other theory is thatonly the proximal part of the ICA arises from the 3rd aortic arch and that the CCA and external

carotid artery develop from the aortic sac. In boththeories, agenesis of the ICA is always accompa-nied by absence of the carotid canal. The reasonfor this is that the early development of the ICAin the 4th embryonic week is necessary for theICA canal in the bone of the skull to develop in the

FIGURE 1. Color Doppler sonogram of the left carotid bifurcationdemonstrating the absence of the internal carotid artery (arrows). Incombination with the reduced lumen of the common carotid arteryand the large vertebral arteries on both sides, this finding is suspi-cious for agenesis of the internal carotid artery.

FIGURE 2. Transcranial color Doppler imaging of the circle of Williswith transtemporal insonation. Axial sonogram shows the posteriorcommunicating arteries with a wide lumen and collateral flow (ar-rows).

FIGURE 3. Transcranial color Doppler imaging of the carotid canalwith transtemporal insonation. Sagittal sonogram shows flow signalsin the right carotid canal. There are no flow signals in the region inwhich the left carotid canal is normally located (‘‘fehlende’’ and ar-row).

FIGURE 4. MR angiogram showing collateral flow from the vertebro-basilar territory. Both communicating posterior arteries are markedby arrows.

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5th–6th weeks of fetal life. In consequence, a hy-poplastic carotid canal results from a hypoplasticICA, and the finding of a carotid canal is clearproof that an ICA exists. In our patient, the diag-nosis of ICA agenesis could be confirmed by theabsence of a carotid canal on CT of the base of theskull.

CDI gave important hints for the correct diag-nosis. First, the significantly reduced lumen di-ameter of the CCA on the affected side is a typicalfeature of ICA hypoplasia or aplasia. Lumen re-duction is not visible in ICA occlusions of athero-sclerotic origin or after dissections but may beseen in Takayasu’s arteritis or other inflamma-tory processes involving the supra-aortic arteries.However, inflammatory diseases often affect sev-eral arteries, and inflammatory changes can beproven by laboratory tests; in contrast, ICA agen-esis is not accompanied by such findings. Anotherhint was the nonvisualization of the left ICA. Theabsence of an ICA on CDI without atheroscleroticchanges in the vessel wall is typical of ICA dis-section, but the pattern of occlusion is differentfrom that in ICA agenesis. In dissection, theproximal part of the occluded vessel resembles awedge, a typical Doppler signal is often present

along the dissected vessel, and the occluded lu-men of the ICA may be visible on B-mode sonog-raphy. In ICA agenesis, the relatively small CCAin comparison to the other side has no bifurcation,and there is no sign of an ICA on B-mode sonog-raphy. The detection of large communicating ar-teries also suggested the correct diagnosis. Thebilateral presence of large vertebral arteries pro-vides an indirect indication of long-standing col-lateral flow owing to either vascular occlusion or acongenital abnormality. In acute ICA dissectionsor occlusions, the blood flow velocity in the verte-bral arteries may increase as a sign of collateralflow, and the vessels may become enlarged. In thesagittal view in our patient, no flow signals couldbe detected by CDI in the region in which the leftintracranial ICA is normally located. In the axialview, the communicating posterior arteries werevisible bilaterally, with a larger lumen on the leftthan on the right as a sign of excellent collateralflow. In healthy individuals, these arteries are in-visible or very small on CDI, as described byKlotzsch et al.5 In our patient, large communicat-ing posterior arteries suggested that the visiblecollateral flow was long-standing, ie, the result ofa congenital abnormality. CT of the base of theskull provided the final proof for the diagnosis ofICA agenesis: the absence of the carotid canal onthe left side, a clear sign of a congenital abnor-mality.

MRA with time-of-flight angiography and 3-dimensional reconstructions confirmed the CDIand CT findings. However, the possibility of athrombus in the ICA could not be ruled out usingMRA. In addition, standard MRA does not supplydata about flow direction. Therefore, collateralflow from the vertebrobasilar circulation to thecarotid artery circulation via a communicatingposterior artery may be suspected from MRA butmust be confirmed by transcranical CDI.

Because of the increased incidence of intracra-nial aneurysms in patients with ICA agenesis, theuse of intra-arterial digital subtraction angiogra-phy is under discussion, but it is not necessary forthe diagnosis of ICA agenesis. It is currently notknown whether agenesis of the ICA is associatedwith an increase in cerebral ischemia. In the lit-erature, there is no clear association between ICAagenesis and cerebrovascular events. Therefore,the clinical consequences of the diagnosis of ICAagenesis remain unclear. In our patient, Horner’ssyndrome was seen on the opposite side of theICA agenesis and therefore was not associatedwith the agenesis.

In conclusion, we believe that the combinationof CDI and CT of the base of the skull provides

FIGURE 5. High-resolution CT scan of the base of the skull revealingthe absence of the left carotid canal (arrow).

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sufficient evidence for the diagnosis of ICA agen-esis. In our case, MRA noninvasively supportedthe findings of CDI but provided no additionalinformation for the diagnosis.

REFERENCES

1. Fisher AGT: A case of complete absence of bothinternal carotid arteries, with a preliminary noteon the development history of stapedial artery. JAnat 1914;48;37.

2. Sunada I, Inoue T: Bilateral internal carotid artery

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3. Padget DH: The development of the cranial arter-ies in the human embryo. Contributions to Embry-ology at the Carnegie Institute 1948;32:205.

4. Huber G: Intracranial carotid anastomosis andpartial aplasia of an internal carotid artery. Neu-roradiology 1980;20:207.

5. Klotzsch C, Popescu O, Berlit P: Assessment of theposterior communicating artery by transcranialcolor-coded duplex sonography. Stroke 1996;27:486.

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