British Journal of Radiology (2006) 79, e108-e111
© 2006 British Institute of Radiology
doi: 10.1259/bjr/89019153
Non-visualization of the internal carotid artery with a normal ipsilateral common carotid artery Doppler waveform: a finding suggesting congenital absence of the ICA on colour Doppler ultrasound
C Yilmaz, MD
1
B Utebay, MD
1
S Kalaycioglu, MD
2
G Onat, MD
1 and
A Solak, MD
2
1 Sosyal Sigortalar Kurumu, Izmir Teaching Hospital, Department of Radiology, Bozyaka, Izmir, 2 Sifa Medical Center, Department of Radiology, Basmane, Izmir, Turkey
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Abstract
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We report a case of congenital absence of the left internal carotid artery (ICA) that presented with left-sided facial numbness. On MRI of the brain, occlusion of the left cavernous ICA was suggested. On colour Doppler ultrasound (CDS), the left ICA was not visualized and the ipsilateral common carotid artery (CCA) showed normal flow in systole and diastole. Combined with the correct identification of the left external carotid artery (ECA), these findings were suggestive of congenital absence of the ICA rather than occlusion. The final diagnosis of congenital absence of the ICA was confirmed with CT of the skull base.
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Introduction
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The absence of an internal carotid artery (ICA) is a very rare anomaly occurring in less than 0.01% of the population [1]. Doppler ultrasound findings have only been reported in a few cases. In our case of left-sided congenital absence, the common carotid artery (CCA) showed normal findings at Doppler waveform analysis, whereas the external carotid artery (ECA) exhibited prominent diastolic flow on the affected side. To the best of our knowledge, these Doppler waveform patterns have not been described in previously reported cases of congenital absence of the ICA.
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Case report
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A 39-year-old woman presented with left sided facial numbness. MRI of the brain revealed loss of the signal void of the left cavernous ICA and was interpreted as an occlusion or a high grade stenosis (Figure 1
). At CDS, the left carotid bifurcation was not seen and instead, the CCA terminated in a single artery. The left CCA revealed a normal Doppler waveform (Figure 2a). Despite a careful search, no evidence of an occluded carotid artery was observed. The left ECA (Figure 2b,c) demonstrated prominent antegrade diastolic flow with a positive response to temporal tapping. The diameters of the vertebral arteries were normal measuring 4.1 mm and 3.9 mm on the left and right side, respectively. Thereafter, CT of the skull base revealed a diminutive canal on the left side consistent with congenital absence of the ICA (Figure 3). Finally, 3D time-of-flight cranial magnetic resonance angiography (MRA) was performed to exclude an aneurysm of the circle of Willis. No aneurysm was detected (Figure 4).
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Figure 1. A 39-year-old woman with left-sided facial numbness. Cranial MRI shows loss of the left cavernous internal carotid artery (ICA) flow void (arrow). Note the normal flow void of the right cavernous ICA (arrowhead).
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Figure 2. (a) The left common carotid artery (CCA) demonstrates normal flow throughout systole and diastole. (b) The single vessel beyond the carotid bulb shows prominent diastolic flow; not a typical feature of the external carotid artery (ECA). (c) A longitudinal colour Doppler ultrasound demonstrates a branching artery (arrow) which correctly identifies the single artery as the ECA.
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Figure 3. Consecutive CT images through the skull base reveal a diminutive left carotid canal(black arrows). The right carotid canal is normal (white arrows).
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Figure 4. A transverse 3D time of flight MR angiogram fails to visualize the left intracranial internal carotid artery(ICA). Note the normal right intracranial ICA (arrow). No aneurysm of the circle of Willis is seen.
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Discussion
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Congenital absence of the ICA is a rare condition. Only about 100 cases have been reported in the literature [1]. Unilateral absence is thought to be the result of an intrauterine mechanical and haemodynamic stress, such as an exaggerated folding of the embryo towards one side and constriction by amniotic bands [2]. The cause of bilateral absence is not yet known [2].
In cases of unilateral absence of the ICA, collateral circulation is sufficient to maintain cerebral function with little or no neurological damage. However, congenital absence of the ICA may be associated with transient ischaemic attacks [1]. In our case, the presenting symptom was facial numbness which disappeared 2 months after the initial presentation. Therefore, we believe that this symptom was unrelated to congenital absence of the ICA.
Congenital absence of the ICA can be incorrectly diagnosed as occlusion [3]. The differentiation is important because congenital absence of the ICA is associated with an increased incidence of circle of Willis aneurysm that may warrant further evaluation [4]. On CDS, the vast majority of ICA occlusions are associated with a markedly diminished or reversed diastolic flow with reduced peak systolic velocities of the ipsilateral CCA [5, 6]. Although a chronically occluded ICA may be associated with a normal ipsilateral CCA Doppler waveform, this is a rare finding, and thus failure to visualize the ICA associated with a normal ipsilateral CCA Doppler waveform should argue against occlusion of the ICA and prompt further evaluation with CT of the skull base to confirm congenital absence.
Doppler waveform analysis is also used to distinguish between the ICA and ECA. Normally, the ECA waveforms have little flow in diastole whereas the ICA waveforms have a large amount flow throughout diastole. In case of occlusion (or absence) of the ICA and occasionally in patients with a patent ICA, the Doppler waveforms of the ECA and its branches may resemble the ICA and may lead to erroneous vessel identification. In the present case, the ECA showed prominent flow throughout diastole, therefore, differentiation between the ECA and ICA was not possible on Doppler waveform analysis. Although the ECA also responded to temporal tapping (a finding suggesting the ECA), this feature alone may not be a reliable criterion to distinguish between the ECA and ICA since the temporal tap effect may also be seen in 33% of the ICAs [7]. In our case, the most reliable criterion for correct identification of the ECA was the demonstration of an extracranial branching artery on longitudinal colour Doppler images. Although extracranial branches of the ICA have also been reported, these are extremely rare and demonstration of an extracranial branching artery beyond the CCA should strongly suggest the ECA.
Our case differs from those of Dinç et al and Midkiff et al, who previously reported on three cases of absence of the ICA [8, 9]. Contrary to the present case, both the CCA and ECA demonstrated a high-resistance Doppler waveform on the affected side in their reports. We believe that the relatively low-resistance flow pattern of the ECA seen in our case resulted from collateralization through the ECA even though we lack the concrete evidence to substantiate this assertion. Similarly, the normal diastolic flow of the left CCA seen in the present case may reflect diversion of blood through the ECA with no major obstacle, such as an occluded ICA.
As the carotid canals in the skull base form secondary to the presence of the embryonic ICA, presence of an ICA is a prerequisite for a carotid canal to develop. Absence or hypoplasia of a carotid canal on skull base CT is thus indicative of a congenital abnormality [1, 10]. In case of an absent carotid canal on CT of the skull base, agenesis is the correct term. If the carotid canal is hypoplastic two possibilities exists; the ICA is either hypoplastic or aplastic [1]. Although not clinically significant, aplasia is the correct term in our case since both CDS and MR angiography failed to show even a small ICA, thus excluding hypoplasia.
In summary, we conclude that non-visualization of the ICA associated with a normal Doppler waveform of the ipsilateral CCA should suggest congenital absence of the ICA rather than occlusion. CT of the skull base confirms the diagnosis.
Received for publication January 24, 2005.
Revision received November 11, 2005.
Accepted for publication November 14, 2005.
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References
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Abstract
Introduction
