Published ahead of print on April 7, 2011
doi: 10.3174/ajnr.A2492

American Journal of Neuroradiology 32:E91, May 2011
© 2011 American Society of Neuroradiology

N. Anzalone^a
aDepartment of Neuroradiology
Scientific Institute HS Raffaele
Milan, Italy

M. Cadioli^b
bPhilips Medical System
Best, the Netherlands

The article by Naggara et al¹ on the added value of high-resolution MR imaging in the diagnosis of vertebral artery dissection shows an interesting comparison between routine clinical MR imaging examinations as performed in their institution and high-resolution imaging acquired with dedicated coils and different techniques. The study enhances the difficult diagnostic task of demonstrating the presence of a mural hematoma along the tortuous course of the vertebral artery together with the problem of differentiating it from a normal venous plexus.

The use of a multiparametric approach with different sequences together with dedicated coils increases the diagnostic accuracy in the article by Naggara et al.¹ This article showed cases in which normal venous plexuses have been interpreted as mural hematomas with routine examinations and cases in which a vessel wall dissection was shown with the use of a high-resolutiontechnique in vessels considered normal at routine examination.

In their study, the authors compared 2 different settings in which the same cases were studied first with contrast-enhanced MR angiography (CE-MRA) and T1-weighted imaging (T1WI) sequences with a regular coil and then with high-resolution T1WI, T2-weighted imaging (T2WI), proton attenuation–weighted imaging, and time-of-flight (TOF) techniques with a superficial dedicated coil. As a consequence, the advantage of high signal intensity and high resolution obtained with dedicated coils is coupled with the advantage of performing added sequences.

The limitation of the CE-MRA acquisition in showing the vessel wall is known² and is related to the use of short parametersthat are required to perform first-pass studies; moreover, regarding the study of vertebral arteries, superimposition of venous structures and of venous plexuses can be present when the acquisition is not perfectly timed with the contrast bolus. The information we may obtain from CE-MRA is then similar to that obtained from digital subtraction angiography (ie, that of an indirect vessel stenosis determined by the invisible mural hematoma).

Fat-suppressed T1WI, as used by the authors of the study, may show the methemoglobin hematoma but may be disturbed by flow-related enhancement as the authors state in the “Discussion” section, and the use of a presaturation band may be insufficient due to the very low, almost stagnant, flow in the venous plexuses.

The advantage of the high-resolution multiparametric approach performed with dedicated coils in the study relates to the possibility of comparing the different behaviors of mural hematomas using T1WI and T2WI and the added value of a 3D TOF sequence—that is, sensitivity to high flow, presaturation of veins, and inflow-effect–based. In our experience, venous plexuses around vertebral arteries are never evident with this acquisition. Moreover because TOF techniques are T1WI, they are sensitive to the presence of methemoglobin and can show the mural hematoma if it is in the subacute phase.

An interesting aspect shown by the study is that venous plexuses at T1WI performed with dedicated coils are isointense with neck tissues, probably related to the use of a black-blood acquisition and/or gating association, not used in the fat-suppressed T1WI acquired routinely.

Again it seems that the use of more appropriate sequences, probably more than that of a dedicated coil, helps in the diagnosis of vertebral artery dissection.

Nevertheless, it is also true that the use of a high-resolution acquisition is important, especially for the study of vertebralarteries, frequently small in caliber.

The study of vertebral arteries is challenging, especially when dissection is suspected and appropriately designed examinations are needed. A multiparametric approach, with T1WI, T2WI, and TOF MRA followed by CE-MRA may be useful to identify the vessel pathology and differentiate hematomas and venous structures. High-resolution images with dedicated coils may be difficult to obtain in the acute phase, when most of the examinations are required.

References

1. Naggara O, Louillet F, Touzé E, et al. Added value of high-resolution MR imaging in the diagnosis of vertebral artery dissection. AJNR Am J Neuroradiol 2010;31:1707–12[Abstract/Free Full Text]
2. Flis CM, Jager HR, Sidhu PS. Carotid and vertebral artery dissections: clinical aspects, imaging features and endovascular treatment. Eur Radiol 2007;17:820–34[CrossRef][Medline]

Reply

Published ahead of print on April 7, 2011
doi: 10.3174/ajnr.A2512

American Journal of Neuroradiology 32:E92, May 2011
© 2011 American Society of Neuroradiology

O. Naggara^a, J.-F. Meder^a and C. Oppenheim^a
aUniversité Paris-Descartes
INSERM U894
Service Imagerie Morphologique et Fonctionnelle
Paris, France

We thank N. Anzalone and M. Cadioli for acknowledging the importance of our study on the added value of high-resolution (HR) MR imaging for the diagnosis of vertebral artery dissection (VAD).¹ An early and reliable identification of VAD is important in preventing ischemic brain lesions. The diagnosis of cervical artery dissection is currently based on 1) a suggestive clinical presentation, 2) exclusion of atherosclerosis, and 3) supportive radiologic evidence. Obtaining radiologic evidence of VAD may be a real challenge, given the highly tortuous course of vertebral arteries, the great variability in normal-vessel caliber, the presence of the thick bony covering, and adjacent veins. The emergence of HR rapid imaging methods has enabled MR imaging to noninvasively image the fine internal structure of cervical artery walls. There is now solid evidence that HR MR imaging can identify the major components of atherosclerotic plaque (ie, lipid core, mural hemorrhage, calcifications, and the fibrous cap).² Thisenables differentiating stable and unstable atherosclerotic plaques.³

Beyond atherosclerosis, HR MR imaging can be used further in case of suspicion of cervical artery dissection, providing an excellent visualization of the cervical artery mural hematoma on both carotid and vertebral arteries.^4–6We demonstrated the usefulness of HR MR imaging in patients who are suspected of having VAD, for whom conventional imaging work-up is inconclusive. However, one can question how far we should go with HR. Because of the limited accessibility of HR MR imaging and the long scanningtime inherent to the technique, the idea is not to perform HR MR imaging in all patients with VAD but rather to improve ourimaging protocols to get supportive imaging evidence in most patients. This is already feasible by using 3T MR magnets with standard multichannel head and neck coils. The bonus signal intensity–to-noise ratio of 3T can be targeted at improving spatial resolution without the need of an additional dedicated surface coil. In daily practice, 3T fat-suppressed T1- and T2-weighted sequences with 3-mm section thickness challenge the HR obtained by using a dedicated surface coil with a 1.5T MR imaging unit (ie, 500 x 500 µm x 3 mm) to image the walls of the cervical arteries. HR MR imaging at 1.5T prefigures tomorrow’s 3T imaging.

References

1. Naggara O, Louillet F, Touzé E, et al.Added value of high-resolution MR imaging in the diagnosis of vertebral artery dissection. AJNR Am J Neuroradiol 2010;31: 1707–12[Abstract/Free Full Text]
2. Yuan C, Mitsumori LM, Ferguson MS, et al.In vivo accuracy of multispectral magnetic resonance imaging for identifying lipid-rich necrotic cores and intraplaque hemorrhage in advanced human carotid plaques. Circulation2001;104: 2051–56[Abstract/Free Full Text]
3. Takaya N, Yuan C, Chu B, et al.Association between carotid plaque characteristics and subsequent ischemic cerebrovascular events: a prospective assessment with MRI—initial results. Stroke 2006;37: 818–23[Abstract/Free Full Text]
4. Naggara O, Oppenheim C, Toussaint JF, et al.Asymptomatic spontaneous acute vertebral artery dissection: diagnosis by high-resolution magnetic resonance images with a dedicated surface coil. Eur Radiol 2007;17: 2434–35[CrossRef][Medline]
5. Bachmann R, Nassenstein I, Kooijman H, et al.High-resolution magnetic resonance imaging (MRI) at 3.0 Tesla in the short-term follow-up of patients with proven cervical artery dissection. Invest Radiol 2007;42: 460–66[CrossRef][Medline]
6. Naggara O, Touzé E, Marsico R, et al.High-resolution MR imaging of periarterial edema associated with biological inflammation in spontaneous carotid dissection. Eur Radiol 2009;19: 2255–60[CrossRef][Medline]