A beginner's guide to grading of carotid artery stenosis by Doppler Ultrasound, CT and MR angiography - A correlative multimodality approach.

Transcription

1 A beginner's guide to grading of carotid artery stenosis by Doppler Ultrasound, CT and MR angiography - A correlative multimodality approach. Poster No.: C-2335 Congress: ECR 2012 Type: Educational Exhibit Authors: A. Jain, J. Webb ; Ayr/UK, Liverpool/UK Keywords: Head and neck, CT-Angiography, MR-Angiography, UltrasoundColour Doppler, Technical aspects, Ischemia / Infarction DOI: /ecr2012/C Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 25

2 Learning objectives 1) Review the radiological anatomy of carotid arteries on Ultrasound, CT and MR. 2) Illustrate various degrees of carotid artery stenosis detected by each modality, as used for decision making in patients' selection for carotid endarterectomy. 3) Discuss common pitfalls of grading using multimodality approach. Background Narrowing of carotid artery is responsible for approximately 15-20% of all ischaemic strokes. It refers to internal carotid artery, with "internal" frequently dropped in the interested brevity. Common carotid artery is rarely involved other than at bifurcation. Figure 1 showing normal apperance of the carotid bifurcation. Warning symptoms ('brain claudication') can be present beforehand in the form of transient ischaemic attack (TIA). If untreated, 5% of patients with TIA will progress to having ischaemic stroke within 1 week and 12% within 2 weeks. Surgical treatments to reduce the narrowing of internal carotid artery and prevent further stroke have been employed since Most widely use are CEA, others Stenting Carotid artery stenting (CAS) offers an alternative approach to carotid endarterectomy (CEA) in both symptomatic and asymptomatic individuals. The National Institute for Health and Clinical excellence (NICE) UK, supports CAS in symptomatic patients. The role of CAS in asymptomatic carotid artery stenosis is however not yet proved. Other treatment options include Angioplasty and ICA-ECA by-pass. The bifurcation of the common carotid artery is predisposed to becoming the site of atheromatous plaque formation through its geometry and the rheologic properties of the blood entering it. Page 2 of 25

3 The role of CEA has been cemented by the results of the two iconic randomised studies, NASCET & ECAS. NASCET demonstrated that in patients with a >=70% stenosis, carotid endarterectomy reduced the risk of any ipsilateral stroke from 26% to 9% at 2 years (P<0.001). Both studies used the gold standard imaging modality grading the internal carotid artery namely digital subtraction angiography (DSA), but employing a different method of calculating the stenosis. However, diagnostic DSA is invasive and has been largely abandoned, in favour of carotid Doppler ultrasound, magnetic resonance & computed tomography angiogram. Translating the degree of stenosis from DSA, to ultrasound particularly, has been a source of some confusion and guidance has been produced to address this and introduce uniform methods of grading of internal carotid artery stenosis. Method of calculating the stenosis used by NASCET investigators is the recommended one, however Ultrasound is intrinsically suited to using ECAS method (Fig 2). Images for this section: Page 3 of 25

4 Fig. 1: Branching of the CCA into ICA and ECA Page 4 of 25

5 Fig. 2: NASCET and ECAS method of calculation of stenosis. Page 5 of 25

6 Imaging findings OR Procedure details IMAGING FINDINGS The appropriate choice of candidates for carotid surgery is of paramount importance. Favourable results of randomised CEA trials can only be extrapolated if the degree of narrowing has been correctly determined. The choice of imaging modality to determine the degree oficanarrowing prior to a potential surgical treatment is decided locally. It is acceptable to make decisions on proceeding to CEA based solely on the degree of ICA narrowing determined by Carotid Doppler Ultrasound, providing there is an agreement from Vascular Surgeons and the Doppler study is of sufficient quality (favourable subject, experienced operator). If there is doubt about the findings of Doppler US and a significant narrowing or occlusion is suspected, then either MR or CT angiogram has to be performed. If there is a disagreement between the findings of Ultrasound and either MR or CT angiogram, DSA is carried out as a gold standard. It may be chosen by an imaging department to proceed to MRA or CTA without prior Ultrasound and it is a logical choice if the patient is already undergoing an emergency brain imaging to extend the scan to include carotid arteries. Contrast MRA with gadolinium (CEMRA) is considered the most accurate method of non invasive imaging. Another MR angiographic method - TOF (time of flight)- may be employed, particularly, if there are contraindications to intravenous contrast. CAROTID DOPPLER ULTRASOUND Protocol: The protocols can vary slightly between various departments. For the protocol that we follow in our institute refer to Figure 3. The normal apperance on doppler ultrasound are shown in figure 4, 5 and figure 6. MRA Protocol: For the protocol that we follow in our institute refer to Figure 7. Page 6 of 25

7 The normal apperance on MRA are shown in figure 8. CTA Protocol: For the protocol that we follow in our institute refer to Figure 9. The normal apperance on CTA are shown in figure 10. CAROTID DOPPLER ULTRASOUND Image 11 to 13 shows approximately 50% stenosis on Doppler imaging. Image 14 shows 90% stenosis on Doppler imaging. MRA Image 15 shows approximately 50% stenosis on MRA. CTA Image 16 and 17 shows approximately 30% stenosis on CTA. Image 18 shows approximately 70% stenosis on CTA. Images for this section: Page 7 of 25

8 Fig. 3: Carotid doppler protocol. Page 8 of 25

9 Fig. 9: CTA protocol. Page 9 of 25

10 Fig. 7: MRA protol that we follow in our institute. Page 10 of 25

11 Fig. 12: Colour flow imaging showing approx 50% stenosis. Page 11 of 25

12 Fig. 13: Doppler image showing approx 50% stenosis with waveform and the PSV calculated. Page 12 of 25

13 Fig. 15: MRA showing 50% stnosis of the left ICA. Page 13 of 25

14 Fig. 18: CTA sag reformat image shows calcification in the ICA causing 70% stenosis. Page 14 of 25

15 Fig. 16: CTA showing 30% stenosis due to calcification at the origin of the ICA. Page 15 of 25

16 Fig. 11: Grey scale image of the CCA with a plaque in keeping with 50% stenosis. Page 16 of 25

17 Fig. 10: Normal CTA apperances with sagittal reformat images. Page 17 of 25

18 Fig. 8: Normal MRA apperances. Note the bifurcation and the detail of the posterior circulation and the circle of Willis. Page 18 of 25

19 Fig. 6: Normal colour flow and doppler of the ICA. Page 19 of 25

20 Fig. 5: Normal colour flow and doppler of the CCA. Page 20 of 25

21 Fig. 4: Normal grey scale image of the common carotid artery. Page 21 of 25

22 Fig. 14: Colour doppler showing 90% stenosis of the ICA, with alteration of waveform and velocity. Page 22 of 25

23 Fig. 2: NASCET and ECAS method of calculation of stenosis. Page 23 of 25

24 Fig. 17: CTA axial shows 30% stenosis left ICA due to calcified plaque. Page 24 of 25

25 Conclusion The reporting Radiologist must be familiar with the established grading criteria and appearances of stenosis on MR and CT angiograms. Furthermore have an understanding of Doppler Ultrasound, including scanning protocol, thus helping their clinician colleagues to choose appropriate patients' management. Personal Information References 1) NICE carotid artery stenting: a summary of the 2011 guidelines, 29 Nov ) Alvarez-Linera J, Benito-León J, Escribano J, et al.prospective evaluation of carotid artery stenosis: elliptic centric contrast-enhanced MR angiography and spiral CT angiography compared with digital subtraction angiography.ajnr Am J Neuroradiol2003;24: ) Patel SG, Collie DA, Wardlaw JM, et al. Outcome, observer reliability, and patient preferences if CT angiography, MR angiography, or Doppler ultrasound were used, individually or together, instead of digital subtraction angiography before carotid endarterectomy.j Neurol Neurosurg Psychiatry2002;73: ) Randoux B, Marro B, Koskas F, et al. Carotid artery stenosis: prospective comparison of CT, three-dimensional gadolinium-enhanced MR, and conventional angiography.radiology2001;220: Page 25 of 25