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Transcranial Doppler sonography evaluation of anterior cerebral artery hypoplasia or aplasia
Journal of the Neurological Sciences 231 (2005) 67 – 70 www.elsevier.com/locate/jns
Transcranial Doppler sonography evaluation of anterior cerebral artery hypoplasia or aplasia Hyung-Min Kwon, Yong-Seok LeeT Department of Neurology, Seoul National University Boramae Hospital, College of Medicine, Seoul National University, 395 Shindaebang 2-dong, Dongjak-gu, Seoul, 156-707, Republic of Korea Received 20 August 2004; received in revised form 16 November 2004; accepted 3 January 2005
Abstract Background and purpose: Transcranial Doppler (TCD) sonography is useful to evaluate intracranial arteries, however, interpretation of the TCD results in anterior cerebral artery (ACA) is difficult because of hypoplasia or aplasia. We try to define useful TCD indices and cut-off values to determine the variations of ACA. Methods: Consecutive patients who underwent TCD and magnetic resonance angiography (MRA) were included. Patients with cerebrovascular abnormality or inadequate temporal windows were excluded. ACA status was classified as normal (NL), hypoplasia (HP), and aplasia (AP) according to MRA. TCD indices of mean flow velocity (MFV), pulsatility index (PI), ACA/middle cerebral artery (MCA) flow velocity ratio (ACA/MCA FVR), and asymmetry index (AI) of ACA were blindly compared with MRA between three groups. Results: Two hundred and forty-one patients were included, and 193 patients (80%) were classified as NL, 34 (14%) as HP and 14 (6%) as AP. MFV was significantly lower in HP and AP ( pb0.001), however, PI and ACA/MCA FVR were not different. AI was significantly different between NL and HP (21.5% vs. 50.4%), NL and AP (21.5% vs. 105.2%) ( pb0.001). Conclusions: MFV of ACA should be interpreted with caution for its frequent anatomical variations. AI is useful to differentiate hypoplasia and aplasia from normal ACA with optimal criteria. D 2005 Elsevier B.V. All rights reserved. Keywords: Transcranial Doppler; Anterior cerebral artery; Hypoplasia; Aplasia
1. Introduction Transcranial Doppler (TCD) is a noninvasive method to assess cerebral circulation, which has several limitations in clinical practice. Anatomical variations of circle of Willis are not uncommon, known as frequent as 12–22% [1–4], and this may confer difficulty in interpretation of the TCD results. Proximal segment of anterior cerebral artery (ACA) is the frequent site for hypoplasia or aplasia [4–6], and interpretation of the TCD results in this segment is sometimes difficult. Studies regarding TCD evaluation of ACA are rare, and only one study representing increased flow velocity of ACA was performed to the patients with angiographically pathologic
condition [7]. There are some studies evaluating ACA status in various pathologic conditions, e.g., hemodynamic studies in early ischemic stroke [8], transcranial Doppler monitoring in angioplasty and stenting of the carotid bifurcation [9], collateral hemispheric flow in patients with carotid artery disease [10], and symptomatic vasospasm diagnosis after subarachnoid hemorrhage [11]. However, these studies also did not consider the variation of normal ACA. Comparing with magnetic resonance angiography (MRA), we try to define useful TCD indices and cut-off values to determine the variations of ACA.
2. Materials and methods T Corresponding author. Tel.: +82 2 840 2492; fax: +82 2 849 2492. E-mail address: [email protected] (Y.-S. Lee). 0022-510X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2005.01.004
Consecutive patients who underwent TCD and MRA during Nov 2001–Oct 2002 were included. Patients with
68
H.-M. Kwon, Y.-S. Lee / Journal of the Neurological Sciences 231 (2005) 67–70
acute stroke, MRA-verified intracranial stenosis, or other cerebrovascular abnormalities (arteriovenous malformation, moyamoya disease, etc.) were excluded. Patients with incomplete temporal windows were also excluded. TCD was performed with 2-MHz pulsed Doppler instrument (Pioneer TC-4040, EME, Germany) according to the standard protocol [12]. MRA was performed by a 1.0-T superconducting magnet with 3-dimensional time-of-flight methods. Status of ACA was classified as normal (NL), hypoplasia (HP), and aplasia (AP) according to MRA by the neuroradiologist, who was blinded to the TCD results. Using a fine ruler, the neuroradiologist measured on the magnified image luminal diameter. HP was defined if the diameter of A1 segment was less than half of the contralateral A1, and AP was defined if A1 segment was invisible (Fig. 1). Mean flow velocity (MFV), pulsatility index (PI), and ACA/MCA (middle cerebral artery) flow velocity ratio (FVR) were blindly compared between NL, HP, and AP group. Asymmetry index (AI) of ACA calculated by
2100|MFVipsi MFVcontra|/(MFVipsi+MFVcontra)(%) was also compared [13]. Statistical significance was tested by one-way analysis of variances (ANOVA) for MFV, PI, ACA/MCA FVR, and AI between three groups (SPSS 11.0 for Windows). After posthoc test (Tukey-B method), they were re-evaluated which variables were significant. Using receiver operation characteristic (ROC) curve, sensitivity, specificity, and cut-off value for HP and AP were calculated.
3. Results Two hundred and forty-one patients (male 51%, mean age; 58.5F13.3 years) were finally included for analysis. Mean time interval between TCD and MRA was 2.3 days. Among them, 193 patients (80%) were classified as NL, 34 patients (14%) as HP, and 14 patients (6%) as AP by MRA criteria. In patients with AP, Doppler signal was not found in
Fig. 1. Representative cases showing MRA and TCD findings of anterior cerebral arteries in normal subject (A), hypoplasia (B), and aplasia (C). Both arrows indicate anterior cerebral arteries.
H.-M. Kwon, Y.-S. Lee / Journal of the Neurological Sciences 231 (2005) 67–70 Table 1 Basic demographic data (n=241)
Age, years (meanFSD) Male sex Hypertension Diabetes mellitus
Normal (n=193)
Hypoplasia (n=34)
Aplasia (n=14)
p-value
58.4F13.6
58.8F11.8
62.3F15.0
0.244
99 (51.3) 96 (50.0) 22 (11.5)
16 (47.1) 12 (38.7) 5 (16.1)
8 (57.1) 9 (64.3) 3 (21.4)
0.807 0.261 0.496
Table 3 Sensitivity and specificity for the diagnosis of hypoplasia and aplasia according to transcranial Doppler criteria Hypoplasia
Numbers in parenthesis mean percentage.
five patients (35.7%). Age, sex, prevalence of hypertension, or diabetes mellitus was not different between three groups (Table 1). MFV of ACA was significantly lower in HP, and lowest in AP (Table 2). PI was lowest in AP, however, statistical significance was not found between three groups. ACA/MCA FVR was not different between groups or between sides. AI was significantly different between NL and HP (21.5% vs. 50.4%), NL and AP (21.5% vs. 105.2%) ( pb0.001). Among TCD criteria, AI over 50% or 100% showed higher specificity for diagnosis of HP or AP (Table 3). Sensitivity and specificity were 50% and 92% for HP (AIN50%), and 43% and 98% for AP (AIN100%).
4. Discussion Mean flow velocity is the most commonly used TCD index to determine the stenosis of cerebral arteries. However, our study reveals that it is not adequate to evaluate ACA status because variations are common (20%) and flow velocity alone may lead to misdiagnosis as occlusion. Also, HP or AP may lead to relative hyperperfusion of contralateral ACA, which may be misinterpreted as stenosis. We identified the frequency and cut-off values of specific ACA variations helpful to differentiate its
69
Sensitivity (%)
Aplasia Specificity (%)
Sensitivity (%)
Specificity (%)
Mean flow velocity b40 cm/s 52.9 b30 cm/s 76.5 b20 cm/s 97.1
23.8 5.2 2.1
14.3 21.4 57.1
23.8 4.7 2.1
Pulsatility index b0.8 50.0 b0.7 76.5 b0.6 85.3 b0.5 94.1
56.0 31.1 9.3 1.6
42.9 50.0 57.1 64.3
56.0 31.1 29.3 1.6
Asymmetry index N50% 50.0 N70% 20.6 N100% 5.9
91.7 95.9 97.9
64.3 42.9 42.9
91.7 95.9 97.9
status. Our results suggest that AI of ACA is useful for the diagnosis of HP or AP of ACA. In the non-dominant ACA, the MFV and AI were different significantly ( pb0.001). But the MFV of ACA has limitation of clinical applications because of low level of specificity (sensitivity 47% and specificity 27% in hypoplasia, sensitivity 57% and specificity 2% in aplasia, respectively). After post-hoc test, only the AI was significant. Therefore, AI of the ACA is the useful index to predict the status of ACA using MFV and to correct the difference due to asymmetry. To be applied in clinical setting, we found optimal sensitivity and specificity according to each AI values. According to ROC curve, AI showed excellent specificity (92% and 98%) for HP and AP with fair sensitivity (Table 3).
Table 2 Mean flow velocity (MFV), pulsatility index (PI), flow velocity ratio (FVR) to MCA, and asymmetry index (AI) of anterior cerebral artery in normal, hypoplasic, and aplasic group
Affected site (ipsilateral) MFV (cm/s) PI ACA/MCA FVRd Non-affected site (contralateral) MFV (cm/s) PI ACA/MCA FVRd AI of the ACA (%)
Normala (n=193)
Hypoplasia (n=34)
52.8F16.3 0.78F0.18 0.90F0.23
41.2F15.8 0.81F0.23 0.89F0.38
20.0F19.0 0.57F0.48 0.40F0.33
b0.001 0.001c b0.001c
50.0F14.7 0.78F0.17 0.88F0.27 21.5F31.1
66.2F16.6 0.78F0.20 0.92F0.28 50.4F36.3
56.1F19.6 0.86F0.21 1.08F0.23 105.2F76.4
b0.001c ns 0.019c b0.001
Aplasia (n=14)
ns: non-significant, MFV: mean flow velocity, PI: pulsatility index. a There is no affected site in normal group. So we divided it into two subgroups (right and left) for the analysis of variance. b Statistical significances were tested by one-way analysis of variances among groups. c After post-hoc test, there was no significance in three groups. d ACA/MCA FVR indicates the ratio of mean flow velocity of anterior cerebral artery to middle cerebral artery in the same side.
p-valueb
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Our study has some limitations. TCD may have potential limitations to evaluate the complex vascular anatomy of the ACA, which may be due to inadequate angle of insonation. In normal ACA group, absent flow was detected in 3 out of 193 (2%). In hypoplastic ACA group, absent flow was detected in 1 out of 34 (3%). False negative may be due to altered angle of insonation between the ultrasound beam and three-dimensional trajectory of the vessel. Aplastic ACA group showed presence of Doppler signal in 9 out of 14 subjects (64%). False positive may be due to MRA characteristic of overestimating hypoplasia as aplasia. So the presence of Doppler signal could not exclude the possibility of AP in the MRA. Other limitation is that MRA is not the diagnostic gold standard for imaging the intracranial circulation. However, MRA of the cerebral arteries is the powerful noninvasive method to demonstrate collateral circulation and to identify hemodynamically relevant anatomic variants of the circle of Willis [14,15]. ACA velocity should be interpreted with caution for its frequent anatomical variations. According to the previous study [7], the positive predictive value in the diagnosis of A1 stenosis was known as 12.5% which is not so high. Therefore, understanding of hemodynamic status such as AI of normal ACA is very useful because of the infrequent occurrence of an intrinsic focal stenosis in the ACA. Analysis of AI for intracerebral arteries was evaluated in the other report [8]. According to the results, upper limits of the confidence intervals are equal to 22% for MCA and 30% for ACA. These data were used as threshold values for the assessment of asymmetry between homologous arteries in analysis of hemodynamic patterns in patients with stroke. Unlike MCA AI, ACA AI is useful in normal condition because ACA more frequently reveals congenital anomaly than MCA. Clinicians must be aware of normal ACA variations and should consider them first when the TCD data disclose high AI (over 50%), particularly if the other basal arteries show no abnormal TCD findings. AI is useful to differentiate hypoplasia and aplasia from normal ACA with optimal criteria. Further studies are needed to determine adequate TCD indices of ACA in pathologic conditions.
References [1] Gillilan LA. Significant superficial anastomoses in the arterial blood supply to the human brain. J Comp Neurol 1959;112:55 – 74. [2] Gillilan LA. Blood supply to primitive mammalian brains. J Comp Neurol 1972;145:209 – 21. [3] Lee RM. Morphology of cerebral arteries. Pharm Ther 1995;66: 149 – 73. [4] Alpers BJ, Berry RG, Paddison RM. Anatomical study of the circle of Willis in normal brain. Arch Neurol Psychiatry 1959;81:409 – 18. [5] Riggs HE, Rupp C. Variation in form of circle of Willis. The relation of the variations to collateral circulation: anatomic analysis. Arch Neurol 19638 – 14. [6] Marinkovic S, Kovacevic M, Milisavljevic M. Hypoplasia of the proximal segment of anterior cerebral artery. Anat Anz 1989;168: 145 – 54. [7] Park KI, Kang DW, Roh JK. Interpretation of increased flow velocity on transcranial Doppler ultrasound. Cerebrovasc Dis 2002;14:61 – 3. [8] Akopov S, Whitman GT. Hemodynamic studies in early ischemic stroke. Serial transcranial Doppler and magnetic resonance angiography evaluation. Stroke 2002;33:1274 – 9. [9] Antonius Carotid Endaterectomy, Angioplasty, and Stenting Study Group. Transcranial Doppler monitoring in angioplasty and stenting of the carotid bifurcation. J Endovasc Ther 2003;10:702 – 10. [10] Anzola GP, Gasparotti R, Magoni M, Prandini F. Transcranial Doppler sonography and magnetic resonance angiography in the assessment of collateral hemispheric flow in patients with carotid artery disease. Stroke 1995;26:214 – 7. [11] Jarus-Dziedzic K, Juniewicz H, Wronski J, Zub WL, Kasper E, Gowacki M, et al. The relation between cerebral blood flow velocities as measured by TCD and the incidence of delayed ischemic deficits. A prospective study after subarachnoid hemorrhage. Neurol Res 2002; 24:582 – 92. [12] Mattle H, Grolimund P, Huber P, Sturzenegger M, Zurbrugg HR. Transcranial Doppler sonographic findings in middle cerebral artery disease. Arch Neurol 1988;12:377 – 82. [13] Zanette EM, Fieschi C, Bozzao L, Roberti C, Toni D, Argentino C, et al. Comparison of cerebral angiography and transcranial Doppler sonography in acute stroke. Stroke 1989;20:899 – 903. [14] Furst G, Steinmetz H, Fischer H, Skutta B, Sitzer M, Aulich A, et al. Selective MR angiography and intracranial collateral blood flow. J Comput Assist Tomogr 1993;17:178 – 83. [15] Stock KW, Wetzel S, Kirsch E, Bongartz G, Steinbrich W, Radue EW. Anatomic evaluation of the circle of Willis: MR angiography versus intraarterial digital subtraction angiography. AJNR 1996;17:1495 – 9.
Transcranial Doppler sonography evaluation of anterior cerebral artery hypoplasia or aplasia Hyung-Min Kwon, Yong-Seok LeeT Department of Neurology, Seoul National University Boramae Hospital, College of Medicine, Seoul National University, 395 Shindaebang 2-dong, Dongjak-gu, Seoul, 156-707, Republic of Korea Received 20 August 2004; received in revised form 16 November 2004; accepted 3 January 2005
Abstract Background and purpose: Transcranial Doppler (TCD) sonography is useful to evaluate intracranial arteries, however, interpretation of the TCD results in anterior cerebral artery (ACA) is difficult because of hypoplasia or aplasia. We try to define useful TCD indices and cut-off values to determine the variations of ACA. Methods: Consecutive patients who underwent TCD and magnetic resonance angiography (MRA) were included. Patients with cerebrovascular abnormality or inadequate temporal windows were excluded. ACA status was classified as normal (NL), hypoplasia (HP), and aplasia (AP) according to MRA. TCD indices of mean flow velocity (MFV), pulsatility index (PI), ACA/middle cerebral artery (MCA) flow velocity ratio (ACA/MCA FVR), and asymmetry index (AI) of ACA were blindly compared with MRA between three groups. Results: Two hundred and forty-one patients were included, and 193 patients (80%) were classified as NL, 34 (14%) as HP and 14 (6%) as AP. MFV was significantly lower in HP and AP ( pb0.001), however, PI and ACA/MCA FVR were not different. AI was significantly different between NL and HP (21.5% vs. 50.4%), NL and AP (21.5% vs. 105.2%) ( pb0.001). Conclusions: MFV of ACA should be interpreted with caution for its frequent anatomical variations. AI is useful to differentiate hypoplasia and aplasia from normal ACA with optimal criteria. D 2005 Elsevier B.V. All rights reserved. Keywords: Transcranial Doppler; Anterior cerebral artery; Hypoplasia; Aplasia
1. Introduction Transcranial Doppler (TCD) is a noninvasive method to assess cerebral circulation, which has several limitations in clinical practice. Anatomical variations of circle of Willis are not uncommon, known as frequent as 12–22% [1–4], and this may confer difficulty in interpretation of the TCD results. Proximal segment of anterior cerebral artery (ACA) is the frequent site for hypoplasia or aplasia [4–6], and interpretation of the TCD results in this segment is sometimes difficult. Studies regarding TCD evaluation of ACA are rare, and only one study representing increased flow velocity of ACA was performed to the patients with angiographically pathologic
condition [7]. There are some studies evaluating ACA status in various pathologic conditions, e.g., hemodynamic studies in early ischemic stroke [8], transcranial Doppler monitoring in angioplasty and stenting of the carotid bifurcation [9], collateral hemispheric flow in patients with carotid artery disease [10], and symptomatic vasospasm diagnosis after subarachnoid hemorrhage [11]. However, these studies also did not consider the variation of normal ACA. Comparing with magnetic resonance angiography (MRA), we try to define useful TCD indices and cut-off values to determine the variations of ACA.
2. Materials and methods T Corresponding author. Tel.: +82 2 840 2492; fax: +82 2 849 2492. E-mail address: [email protected] (Y.-S. Lee). 0022-510X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2005.01.004
Consecutive patients who underwent TCD and MRA during Nov 2001–Oct 2002 were included. Patients with
68
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acute stroke, MRA-verified intracranial stenosis, or other cerebrovascular abnormalities (arteriovenous malformation, moyamoya disease, etc.) were excluded. Patients with incomplete temporal windows were also excluded. TCD was performed with 2-MHz pulsed Doppler instrument (Pioneer TC-4040, EME, Germany) according to the standard protocol [12]. MRA was performed by a 1.0-T superconducting magnet with 3-dimensional time-of-flight methods. Status of ACA was classified as normal (NL), hypoplasia (HP), and aplasia (AP) according to MRA by the neuroradiologist, who was blinded to the TCD results. Using a fine ruler, the neuroradiologist measured on the magnified image luminal diameter. HP was defined if the diameter of A1 segment was less than half of the contralateral A1, and AP was defined if A1 segment was invisible (Fig. 1). Mean flow velocity (MFV), pulsatility index (PI), and ACA/MCA (middle cerebral artery) flow velocity ratio (FVR) were blindly compared between NL, HP, and AP group. Asymmetry index (AI) of ACA calculated by
2100|MFVipsi MFVcontra|/(MFVipsi+MFVcontra)(%) was also compared [13]. Statistical significance was tested by one-way analysis of variances (ANOVA) for MFV, PI, ACA/MCA FVR, and AI between three groups (SPSS 11.0 for Windows). After posthoc test (Tukey-B method), they were re-evaluated which variables were significant. Using receiver operation characteristic (ROC) curve, sensitivity, specificity, and cut-off value for HP and AP were calculated.
3. Results Two hundred and forty-one patients (male 51%, mean age; 58.5F13.3 years) were finally included for analysis. Mean time interval between TCD and MRA was 2.3 days. Among them, 193 patients (80%) were classified as NL, 34 patients (14%) as HP, and 14 patients (6%) as AP by MRA criteria. In patients with AP, Doppler signal was not found in
Fig. 1. Representative cases showing MRA and TCD findings of anterior cerebral arteries in normal subject (A), hypoplasia (B), and aplasia (C). Both arrows indicate anterior cerebral arteries.
H.-M. Kwon, Y.-S. Lee / Journal of the Neurological Sciences 231 (2005) 67–70 Table 1 Basic demographic data (n=241)
Age, years (meanFSD) Male sex Hypertension Diabetes mellitus
Normal (n=193)
Hypoplasia (n=34)
Aplasia (n=14)
p-value
58.4F13.6
58.8F11.8
62.3F15.0
0.244
99 (51.3) 96 (50.0) 22 (11.5)
16 (47.1) 12 (38.7) 5 (16.1)
8 (57.1) 9 (64.3) 3 (21.4)
0.807 0.261 0.496
Table 3 Sensitivity and specificity for the diagnosis of hypoplasia and aplasia according to transcranial Doppler criteria Hypoplasia
Numbers in parenthesis mean percentage.
five patients (35.7%). Age, sex, prevalence of hypertension, or diabetes mellitus was not different between three groups (Table 1). MFV of ACA was significantly lower in HP, and lowest in AP (Table 2). PI was lowest in AP, however, statistical significance was not found between three groups. ACA/MCA FVR was not different between groups or between sides. AI was significantly different between NL and HP (21.5% vs. 50.4%), NL and AP (21.5% vs. 105.2%) ( pb0.001). Among TCD criteria, AI over 50% or 100% showed higher specificity for diagnosis of HP or AP (Table 3). Sensitivity and specificity were 50% and 92% for HP (AIN50%), and 43% and 98% for AP (AIN100%).
4. Discussion Mean flow velocity is the most commonly used TCD index to determine the stenosis of cerebral arteries. However, our study reveals that it is not adequate to evaluate ACA status because variations are common (20%) and flow velocity alone may lead to misdiagnosis as occlusion. Also, HP or AP may lead to relative hyperperfusion of contralateral ACA, which may be misinterpreted as stenosis. We identified the frequency and cut-off values of specific ACA variations helpful to differentiate its
69
Sensitivity (%)
Aplasia Specificity (%)
Sensitivity (%)
Specificity (%)
Mean flow velocity b40 cm/s 52.9 b30 cm/s 76.5 b20 cm/s 97.1
23.8 5.2 2.1
14.3 21.4 57.1
23.8 4.7 2.1
Pulsatility index b0.8 50.0 b0.7 76.5 b0.6 85.3 b0.5 94.1
56.0 31.1 9.3 1.6
42.9 50.0 57.1 64.3
56.0 31.1 29.3 1.6
Asymmetry index N50% 50.0 N70% 20.6 N100% 5.9
91.7 95.9 97.9
64.3 42.9 42.9
91.7 95.9 97.9
status. Our results suggest that AI of ACA is useful for the diagnosis of HP or AP of ACA. In the non-dominant ACA, the MFV and AI were different significantly ( pb0.001). But the MFV of ACA has limitation of clinical applications because of low level of specificity (sensitivity 47% and specificity 27% in hypoplasia, sensitivity 57% and specificity 2% in aplasia, respectively). After post-hoc test, only the AI was significant. Therefore, AI of the ACA is the useful index to predict the status of ACA using MFV and to correct the difference due to asymmetry. To be applied in clinical setting, we found optimal sensitivity and specificity according to each AI values. According to ROC curve, AI showed excellent specificity (92% and 98%) for HP and AP with fair sensitivity (Table 3).
Table 2 Mean flow velocity (MFV), pulsatility index (PI), flow velocity ratio (FVR) to MCA, and asymmetry index (AI) of anterior cerebral artery in normal, hypoplasic, and aplasic group
Affected site (ipsilateral) MFV (cm/s) PI ACA/MCA FVRd Non-affected site (contralateral) MFV (cm/s) PI ACA/MCA FVRd AI of the ACA (%)
Normala (n=193)
Hypoplasia (n=34)
52.8F16.3 0.78F0.18 0.90F0.23
41.2F15.8 0.81F0.23 0.89F0.38
20.0F19.0 0.57F0.48 0.40F0.33
b0.001 0.001c b0.001c
50.0F14.7 0.78F0.17 0.88F0.27 21.5F31.1
66.2F16.6 0.78F0.20 0.92F0.28 50.4F36.3
56.1F19.6 0.86F0.21 1.08F0.23 105.2F76.4
b0.001c ns 0.019c b0.001
Aplasia (n=14)
ns: non-significant, MFV: mean flow velocity, PI: pulsatility index. a There is no affected site in normal group. So we divided it into two subgroups (right and left) for the analysis of variance. b Statistical significances were tested by one-way analysis of variances among groups. c After post-hoc test, there was no significance in three groups. d ACA/MCA FVR indicates the ratio of mean flow velocity of anterior cerebral artery to middle cerebral artery in the same side.
p-valueb
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Our study has some limitations. TCD may have potential limitations to evaluate the complex vascular anatomy of the ACA, which may be due to inadequate angle of insonation. In normal ACA group, absent flow was detected in 3 out of 193 (2%). In hypoplastic ACA group, absent flow was detected in 1 out of 34 (3%). False negative may be due to altered angle of insonation between the ultrasound beam and three-dimensional trajectory of the vessel. Aplastic ACA group showed presence of Doppler signal in 9 out of 14 subjects (64%). False positive may be due to MRA characteristic of overestimating hypoplasia as aplasia. So the presence of Doppler signal could not exclude the possibility of AP in the MRA. Other limitation is that MRA is not the diagnostic gold standard for imaging the intracranial circulation. However, MRA of the cerebral arteries is the powerful noninvasive method to demonstrate collateral circulation and to identify hemodynamically relevant anatomic variants of the circle of Willis [14,15]. ACA velocity should be interpreted with caution for its frequent anatomical variations. According to the previous study [7], the positive predictive value in the diagnosis of A1 stenosis was known as 12.5% which is not so high. Therefore, understanding of hemodynamic status such as AI of normal ACA is very useful because of the infrequent occurrence of an intrinsic focal stenosis in the ACA. Analysis of AI for intracerebral arteries was evaluated in the other report [8]. According to the results, upper limits of the confidence intervals are equal to 22% for MCA and 30% for ACA. These data were used as threshold values for the assessment of asymmetry between homologous arteries in analysis of hemodynamic patterns in patients with stroke. Unlike MCA AI, ACA AI is useful in normal condition because ACA more frequently reveals congenital anomaly than MCA. Clinicians must be aware of normal ACA variations and should consider them first when the TCD data disclose high AI (over 50%), particularly if the other basal arteries show no abnormal TCD findings. AI is useful to differentiate hypoplasia and aplasia from normal ACA with optimal criteria. Further studies are needed to determine adequate TCD indices of ACA in pathologic conditions.
References [1] Gillilan LA. Significant superficial anastomoses in the arterial blood supply to the human brain. J Comp Neurol 1959;112:55 – 74. [2] Gillilan LA. Blood supply to primitive mammalian brains. J Comp Neurol 1972;145:209 – 21. [3] Lee RM. Morphology of cerebral arteries. Pharm Ther 1995;66: 149 – 73. [4] Alpers BJ, Berry RG, Paddison RM. Anatomical study of the circle of Willis in normal brain. Arch Neurol Psychiatry 1959;81:409 – 18. [5] Riggs HE, Rupp C. Variation in form of circle of Willis. The relation of the variations to collateral circulation: anatomic analysis. Arch Neurol 19638 – 14. [6] Marinkovic S, Kovacevic M, Milisavljevic M. Hypoplasia of the proximal segment of anterior cerebral artery. Anat Anz 1989;168: 145 – 54. [7] Park KI, Kang DW, Roh JK. Interpretation of increased flow velocity on transcranial Doppler ultrasound. Cerebrovasc Dis 2002;14:61 – 3. [8] Akopov S, Whitman GT. Hemodynamic studies in early ischemic stroke. Serial transcranial Doppler and magnetic resonance angiography evaluation. Stroke 2002;33:1274 – 9. [9] Antonius Carotid Endaterectomy, Angioplasty, and Stenting Study Group. Transcranial Doppler monitoring in angioplasty and stenting of the carotid bifurcation. J Endovasc Ther 2003;10:702 – 10. [10] Anzola GP, Gasparotti R, Magoni M, Prandini F. Transcranial Doppler sonography and magnetic resonance angiography in the assessment of collateral hemispheric flow in patients with carotid artery disease. Stroke 1995;26:214 – 7. [11] Jarus-Dziedzic K, Juniewicz H, Wronski J, Zub WL, Kasper E, Gowacki M, et al. The relation between cerebral blood flow velocities as measured by TCD and the incidence of delayed ischemic deficits. A prospective study after subarachnoid hemorrhage. Neurol Res 2002; 24:582 – 92. [12] Mattle H, Grolimund P, Huber P, Sturzenegger M, Zurbrugg HR. Transcranial Doppler sonographic findings in middle cerebral artery disease. Arch Neurol 1988;12:377 – 82. [13] Zanette EM, Fieschi C, Bozzao L, Roberti C, Toni D, Argentino C, et al. Comparison of cerebral angiography and transcranial Doppler sonography in acute stroke. Stroke 1989;20:899 – 903. [14] Furst G, Steinmetz H, Fischer H, Skutta B, Sitzer M, Aulich A, et al. Selective MR angiography and intracranial collateral blood flow. J Comput Assist Tomogr 1993;17:178 – 83. [15] Stock KW, Wetzel S, Kirsch E, Bongartz G, Steinbrich W, Radue EW. Anatomic evaluation of the circle of Willis: MR angiography versus intraarterial digital subtraction angiography. AJNR 1996;17:1495 – 9.