Neurology -- Correspondence for Sakaguchi et al., 61 (6) 845-847

Correspondence published:

Mechanical compression of the extracranial vertebral artery during neck rotation: Michael I. Weintraub, MD, FACP, FAAN, PC, Andre Khoury, MD (5 December 2003)

Reply to Weintraub et al: Kazuo Kitagawa, MD, PhD, Manabu Sakaguchi, MD (5 December 2003)

Mechanical compression of the extracranial vertebral artery during neck rotation 5 December 2003

Michael I. Weintraub, MD, FACP, FAAN, PC,
Clinical Professor Neurology, New York Medical College ,
Andre Khoury, MD
Send Correspondence to journal:
Re: Mechanical compression of the extracranial vertebral artery during neck rotation

miwneuro{at}pol.net Michael I. Weintraub, MD, FACP, FAAN, PC, et al.

The recent article by Sakaguchi and colleagues [1] utilizing duplex ultrasonography to diagnose vertebral artery (VA) compression at the Atlas loop was informative yet is not very practical and may provide inaccurate data. As noted by the authors, insonation angulation may falsely lead to a drop in diastolic flow, especially in hypoplastic arteries (HVA). Pulsed gated Doppler ultrasound and colorflow Doppler are also influenced by shadowing and tortuosity and thus may lead to difficulty measuring lumen size or stenosis. It is also highly technician dependent. Thus, duplex ultrasonography with velocity criteria alone is insufficient for accurate hemodynamic assessment.
We have previously reported the use of dynamic MR angiography with angulation and flow analysis techniques (cine phase contrast with peripheral gating and flow compensation) [2,3] and believe this is the non-invasive imaging method of choice. Specifically, it provides accurate volume flow rate (milliliters/min) and velocity (centimeters/sec) and can accurately identify hypoplasia, stenosis, dissection, and occlusion. In a prior study of 160 consecutive patients screened for peri-operative stroke risk by this technique, [3] HVA were identified in 40 cases (25% of the cohort). Hypoplasia was defined by two parameters: A) 2/3 reduced size compared to contralateral VA, and B) Blood flow less than 50 ml/min. (Normal VA flow equals 61-115 ml/min.) This technique also allows for imaging of slow flow and reversal of flow which was present. We also noted that there was an increase of silent posterior circulation infarctions in individuals harboring HVA and feel that this is a biological marker for augmented stroke risk.
The HVA cohort display unique vulnerability with hyperextension and rotation at the Atlanto-axial and Atlanto-occipital junctions. The dramatic pattern of contralateral slow flow occlusion and flow reversal identified by this technique cannot be appreciated by duplex ultrasonography.
The sensitivity, specificity and non-invasive nature is attractive for precise in-vivo assessment of perfusion and velocity changes with hyperextension and rotational positions.
Regardless of one�s choice of technology, it is clear that the vertebral artery is vulnerable to critical neck positions and represents an independent risk factor for posterior circulation and stroke. [4]
References
1. Sakaguchi M, Kitagawa K, Hougaku H, et al: Mechanical Compression of the Extracranial Vertebral Artery During Neck Rotation. Neurology 2003; 61: 845-847.
2. Weintraub, MI, Khoury A,: Critical Neck Positions as an Independent Risk Factor for Posterior Circulation and Stroke: MR Angiographic Analysis. J Neuroimaging 1995; 5: 16-22.
3. Weintraub, MI, Khoury A,: Cerebral Hemodynamic Changes Induced by Simulated Tracheal Intubation: A Possible Role in Perioperative Stroke? Magnetic Resonance Angiography and Flow Analysis in 160 Cases. Stroke 1998; 29: 1644-1649.
4. Weintraub, MI: Beauty Parlor Stroke Syndrome: Report of Five Cases. JAMA 1993; 269: 2085-2086.

Reply to Weintraub et al 5 December 2003

Kazuo Kitagawa, MD, PhD,
Osaka University, Dept. of Internal Medicine and Therapeutics
2-2 Yamadaoka, Suita, Osaka 565-0871, Japan,
Manabu Sakaguchi, MD
Send Correspondence to journal:
Re: Reply to Weintraub et al

kitagawa{at}medone.med.osaka-u.ac.jp Kazuo Kitagawa, MD, PhD, et al.

Dr. Weintraub and Khoury [1] previously reported the effects of neck position on vertebral artery perfusion using a dynamic magnetic resonance angiography (MRA) technique. We agree that dynamic MRA has the advantage of quantitative measurement of blood flow in both vertebral and basilar arteries. Weintraub et al are concerned about the insonation angle and shadowing in duplex US. Although ECVA is tortuous in the atlas loop segment, we measured the ECVA flow at the C4 to C6 level (not at the atlas portion) where the vessel passes straight. [2] Because we can keep the incident angle between the beam and ECVA, the difference in angles between the two positions, the neutral position and head rotation, was less than a few degree even in hypoplastic VA. Furthermore, between the spines, ECVA can be clearly identified without any shadow as shown in our article. [2] However, diagnosis of vessel compression may be difficult in cases of VA ending in posterior inferior cerebellar artery (PICA) because diastolic component of blood flow in such vessels is small in the neutral neck position. [3]
The difference between US and MRA is the cost and the time required for each examination. The cost of the US is inexpensive, so US examination is suitable for screening the patients. Although at least a few minutes with one�s neck kept in certain position are required for MRA [1], ten seconds is long enough to detect flow change in ECVA with US examination. [2] In a patient with vertebrobasilar ischemia during neck rotation, keeping the neck in such a neck position for more than a minute is ethically unacceptable. Therefore, we believe that US examination is very useful in identifying ECVA compression in the atlas loop segment, especially in patients with vertigo, faintness or blurred vision during neck rotation. US examination would be also useful for screening the ECVA compression in critical neck position during general anesthesia. However, it remains unclear if mechanical compression of ECVA during neck rotation without any symptom represents an independent risk factor for stroke in posterior circulation.
References
1. Weintraub, MI, Khoury A. Critical neck positions as an independent risk factor for posterior circulation and stroke: MR angiographic analysis. J Neuroimaging 1995;5:16-22.
2. Sakaguchi M, Kitagawa K, Hougaku H, Hashimoto H, nagai Y, Yamagami H, Ohtsuki T, Oku N, Hashikawa K, Matsushita K, Matsumoto M, Hori M. Mechanical compression of the extracranial vertebral artery during neck rotation. Neurology 2003;61:845-847.
3. Kimura K, Yasaka M, Moriyasu H, Tsuchiya T, Yamaguchi T. Ultrasonographic evaluation of vertebral artery to detect vertebrobasilar axis occlusion. Stroke 1994;25:1006-1009.