British Journal of Radiology (2007) 80, e271-e274
© 2007 British Institute of Radiology
doi: 10.1259/bjr/35231226
Intraplaque haemorrhage mimicking carotid pseudoaneurysm on magnetic resonance angiography
S Goode, MRCS (Eng)
1,2
N Altaf, MRCS (Ed)
1,2
R A Dineen, MRCP
1
S Krishnan, MBBS
1 and
D Auer, PhD
1
1 Department of Academic Radiology, University of Nottingham and 2 Department of Vascular Surgery, Queen's Medical Centre, Nottingham NG7 2UH, UK
Correspondence: Mr Stephen Goode, Department of Academic Radiology, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK. E-mail: msxsg{at}nottingham.ac.uk
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Abstract
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Contrast-enhanced magnetic resonance angiography (CE-MRA) is a commonly used technique to assess the extracranial carotid arteries. We describe two patients (investigated for carotid artery atherosclerotic disease) who underwent CE-MRA. Results suggested pseudoaneurysms of the extracranial carotid arteries. Magnetic resonance direct thrombus imaging (MRDTI) showed that the appearances were due to intraplaque haemorrhage adjacent to the vessel, with the T1-shortening effect of methaemoglobin within the intraplaque haemorrhage mimicking blood flow on the CE-MRA sequence. The cases presented demonstrate this diagnostic pitfall and illustrate the contribution of simple magnetic resonance plaque imaging to establishing the correct diagnosis.
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Introduction
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Extracranial carotid aneurysms are rare. They are usually secondary to atherosclerosis, trauma, or post-operative pseudoaneurysm formation. The management of extracranial carotid aneurysms is different to that of carotid atherosclerotic disease. Accurate detection of aneurysms with magnetic resonance angiography (MRA) has been reported, with increased sensitivity using contrast-enhanced MRA (CE-MRA) [1–4].
In the examination of subacute intracerebral haematoma, the potential misinterpretation of time-of-flight MRA has been noted [5]. Methemoglobin-related T1 shortening within the haematoma may be indistinguishable from intravascular flow signals. This potentially confounding effect is well known in the diagnostic work-up of ruptured intracranial vascular malformations [2].
Here, we report two cases of intraplaque haemorrhage in the extracranial carotid artery mimicking aneurysms where unenhanced carotid plaque imaging, utilizing lipid and blood nulling, allowed us to correctly diagnose histologically confirmed intraplaque haemorrhage.
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Case 1
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A 77-year-old gentleman presented with a 2-week history of recurrent episodes of right amaurosis fugax and left limb weakness lasting less than 1 h. There was no neurological sequel. He had a past medical history of high blood pressure, high cholesterol, previous myocardial infarction and subsequent coronary artery bypass graft surgery (CABG). His blood pressure was satisfactorily managed with simple anithypertensives and he was commenced on aspirin and simvastatin.
A carotid duplex examination demonstrated a plaque causing a stenosis of 80–95% at the origin of the right internal carotid artery (ICA). Additionally, there was an 80–95% stenosis at the origin of the left ICA. An electrocardiogram (ECG) and echocardiogram did not demonstrate a cardiac cause for his symptoms.
MRI was performed using a clinical 1.5T scanner (GE Excite; General Electric, Waukesha, WI) using an 8 channel neurovascular coil. CE-MRA demonstrated bilateral high-grade carotid stenosis at the bifurcation. However, there was marked dilatation at the carotid bulbs bilaterally, suggestive of pseudoaneurysm formation which was seen both on raw images and maximum intensity projection (MIP) images (Figure 1a
).
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Figure 1. (a) Contrast-enhanced magnetic resonance angiography frontal maximum intensity projection view showing focal dilatations at the common carotid artery bifurcations bilaterally (arrows) suggestive of pseudoaneurysms; (b) coronal and (c) axial magnetic resonance direct thrombus imaging images show eccentric high signal at the site of the suspected pseudoaneurysms representing intraplaque haemorrhage; (d) surgical specimen from the right carotid artery opened to demonstrate intraplaque thrombus. VB, vertebral body.
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Additionally, magnetic resonance direct thrombus imaging (MRDTI) was performed as part of a prospective study into the detectability of unstable plaques [6]. The scan consists of a T1 weighted three-dimensional gradient echo sequence with a selective water-excitation radio frequency pulse to abolish fat signal, and the effective inversion time chosen to null the blood signal [7]. An extensive hyperintense signal was shown bilaterally localized within the region, which suggested aneurysmatic dilation seen on CE-MRA. Against the background of previous radiopathological comparison studies [8], this signal was interpreted as typical for an unstable plaque due to intraplaque haemorrhage or thrombus, and a pseudoaneurysm was excluded in the final radiological diagnosis (Figure 1b,c
).
Upon surgical exploration of the right carotid artery, there was no evidence of aneurysmal formation, but there was intraluminal thrombus and intraplaque haemorrhage within the carotid plaque. A carotid endarterectomy was therefore performed. Histopathological examination demonstrated a predominantly eccentric lipid-rich fibrolipid plaque with evidence of intraplaque haemorrhage and thrombus (Figure 1d).
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Case 2
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A 69-year-old man presented with an acute decrease in left visual acuity. He was an ex-smoker for the past 37 years and had a history of left hemispheric stroke 9 years previously, for which he was taking aspirin and simvastatin. On examination, he was found to be hypertensive with normal heart sounds. No new limb weakness or speech disturbance was found and reflexes were normal. Retinoscopy showed a pale retina with occlusion of multiple retinal arteries. A diagnosis of partial left central retinal artery occlusion was made.
Carotid duplex ultrasound failed to demonstrate the left common carotid artery (CCA) bifurcation or the left ICA, which was thought to be due to a high position of the CCA bifurcation. CE-MRA performed 6 weeks after presentation showed occlusion of the left ICA from its origin at the CCA bifurcation. A saccular high-signal structure appeared to arise from the ICA origin suggestive of a pseudoaneurysm (Figure 2a), although on close inspection no definite communication with the lumen was seen. MRDTI showed high-signal material surrounding the ICA origin, consistent with intraplaque haemorrhage/thrombus (Figure 2b). High-signal material could be seen extending along the course of the left ICA consistent with intraluminal thrombus (Figure 2c).
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Figure 2. (a) Contrast-enhanced magnetic resonance angiography lateral maximum intensity projection of the left carotid and vertebral arteries showing "saccular" high-signal structure at the carotid bifurcation and the unopacified left internal carotid artery (ICA). (b) Axial magnetic resonance direct thrombus imaging (MRDTI) image at the bifurcation showing high-signal intraplaque haemorrhage surrounding the ICA origin. (c) MRDTI coronal image demonstrating the intraplaque haemorrhage (large arrow) and a tail of high-signal thrombus extending along the course of the left ICA (small arrows).
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Discussion
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The bifurcation of the CCA is the most commonly reported site of aneurysm formation in the extracranial carotid system, followed by the ICA, with the external carotid artery being the least common location [9, 10]. There are several causes of extracranial carotid aneurysm and the relative frequency of each has changed over time: syphilis and local infections were most common 60 years ago. Instead, atherosclerosis, trauma and previous surgery (pseudoaneurysm) are now believed to be responsible for the majority of extracranial carotid aneurysms in the developed world [11]. These lesions not only put the patient at risk of thromboembolism and progressive enlargement with vessel obliteration, but also rupture with associated haemorrhage. Hence accurate and timely diagnosis is essential.
Although duplex imaging of the extracranial arteries is used as a first-line assessment in patients with suspected carotid disease, there has been a significant increase in the use of MRI (including MRA of the cerebral vascular trees) in the primary assessment of acute strokes and transient ischaemic attacks [12]. Recommended protocols do not include pre-contrast T1 weighted scans of the carotids.
The cases illustrated here suggest that caution is required when diagnosing aneurysmal dilatation of the extracranial carotid arteries on CE-MRA alone. The presence of substrates within or adjacent to the vessel wall which return high-signal material on T1 weighted imaging, such as methaemoglobin within haemorrhagic plaque, can lead to misinterpretation of the angiographic images relying on T1 signal increase related to inflow. The reporting radiologist should bear in mind that intraplaque haemorrhage may mimic flow. Intraplaque haemorrhage is very common in carotid artery disease [13], making this a potentially relevant pitfall for MRA. MRDTI is a short additional sequence that allows the reliable identification of methemoglobin-related T1 hyperintensities [7], and hence rules out the risk of misdiagnosing aneurysm formation. Moreover, the diagnosis of intraplaque haemorrhage is clinically relevant as it predicts the unstable plaque [11, 13, 14] conveying a higher propensity of embolisation [15].
The two cases herein highlight the known fact that pre-existing T1 hyperintensity may mimic flow on both non-contrast-enhanced and contrast-enhanced MRA scans. Routine protocols of CE-MRA are liable to misinterpretation, and awareness of the high incidence of intraplaque haemorrhage is required. Becuase of the emerging evidence of clinical relevance of detecting intraplaque haemorrhage, we recommend the inclusion of pre-contrast, blood-nulled and lipid-suppressed T1 imaging that can be achieved in 3.5 min extra scan time without any additional hardware.
Received for publication August 25, 2006.
Accepted for publication January 12, 2007.
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References
|
|---|
- U-King-Im JM, Trivedi RA, Cross JJ, Higgins NJ, Hollingworth W, Graves M, et al. Measuring carotid stenosis on contrast-enhanced magnetic resonance angiography: diagnostic performance and reproducibility of 3 different methods. Stroke 2004;35:2083–8.[Abstract/Free Full Text]
- Ledgerwood AM and Lucas CE. Mycotic aneurysm of the carotid artery. Arch Surg 1974;109:496–8.[Abstract/Free Full Text]
- Nederkoorn PJ, Elgersma OE, van der Graaf Y, Eikelboom BC, Kapelle LJ, Mali WP. Carotid artery stenosis: accuracy of contrast-enhanced MR angiography for diagnosis. Radiology 2003;228:677–82.[Abstract/Free Full Text]
- Yang CW, Carr JC, Flutterer SF, Morasch MD, Yang BP, Shors SM, et al. Contrast-enhanced MR angiography of the carotid and vertebrobasilar circulations. AJNR Am J Neuroradiol 2005;26:2095–101.[Abstract/Free Full Text]
- Insko EK, Siegelman ES, Stolpen AH. Subacute clot mimicking flow in a thrombosed arterial bypass graft on two-dimensional time-of-flight and three-dimensional contrast-enhanced MRA. J Magn Reson Imaging 2000;11:192–4.[CrossRef][Medline]
- Altaf N, Beech A, Goode SD, Gladman JR, Moody AR, Auer DP, et al. Magnetic Resonance Direct Thrombus Imaging of the carotid plaque is associated with increased thromboembolization. Proceedings of the International Society of Magnetic Resonance in Medicine, Miami 2005. Miami, FL: ISMRM 2005. 13:1063
- Moody AR. Magnetic resonance direct thrombus imaging. J Thromb Haemost 2003;1:1403–9.[CrossRef][Medline]
- Moody AR, Murphy RE, Morgan PS, Martel AL, Delay GS, Allder S, et al. Characterization of complicated carotid plaque with magnetic resonance direct thrombus imaging in patients with cerebral ischemia. Circulation 2003;107:3047–52.[Abstract/Free Full Text]
- McCann RL. Basic data related to peripheral artery aneurysms. Ann Vasc Surg 1990;4:411–14.[CrossRef][Medline]
- Rhodes EL, Stanley JC, Hoffman GL, Cronenwett JL, Fry WJ, et al. Aneurysms of extracranial carotid arteries. Arch Surg 1976;111:339–43.[Abstract/Free Full Text]
- Mofidi R, Crotty TB, McCarthy P, Sheehan SJ, Mehigan D, Keaveny TV. Association between plaque instability, angiogenesis and symptomatic carotid occlusive disease. Br J Surg 2001;88:945–50.[CrossRef][Medline]
- Sunshine JL. CT, MR imaging, and MR angiography in the evaluation of patients with acute stroke. J Vasc Intervent Radiol 2004;15:S47–S55.[Medline]
- Virmani R, Kolodgie FD, Burke AP, Finn AV, Gold HK, Tulenko TN, et al. Atherosclerotic plaque progression and vulnerability to rupture: angiogenesis as a source of intraplaque hemorrhage. Arterioscler Thromb Vasc Biol 2005;25:2054–61.[Abstract/Free Full Text]
- Fisher M, Paganini-Hill A, Martin A, Cosgrove M, Toole JF, Barnett HJ, et al. Carotid plaque pathology: thrombosis, ulceration, and stroke pathogenesis. Stroke 2005;36:253–7.[Abstract/Free Full Text]
- Gaunt ME, Brown L, Hartshorne T, Bell PR, Naylor AR. Unstable carotid plaques: preoperative identification and association with intraoperative embolisation detected by transcranial Doppler. Eur J Vasc Endovasc Surg 1996;11:78–82.[CrossRef][Medline]
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Abstract
Introduction
