Graham Lennox

Direct magnetic resonance imaging of carotid artery thrombus in acute stroke

Stroke remains a common cause of morbidity and mortality and affects over 100 000 people per year in the UK. Thromboembolism complicating atheromatous disease within the carotid arteries is the major predisposing cause. Management of patients will be assisted if strokes that arise in this way can be distinguished reliably from those caused by emboli of cardiac origin or as a result of intracranial small vessel disease. Early diagnosis is commonly hampered because in any individual patient several potential causes of stroke may co-exist. The effective targeting of new treatments is dependent on the likely natural history of the condition. The ability to identify acute thrombus in association with underlying carotid disease would offer the possibility of identifying symptomatic carotid atheroma. The presumed pathological mechanism of stroke in carotid disease is embolisation of debris from an area of ruptured atheromatous endothelium, a process that is invariably associated with acute thrombus formation. The ability to identify acute carotid thrombus in this clinical setting therefore allows accurate identification of a symptomatic artery. Magnetic resonance imaging (MRI) has already been employed to detect thrombus in patients with acute deep-vein thrombosis. The high signal, short T1, material detected by MRI is likely to represent methaemaglobin, an intermediate breakdown product of haemoglobin that occurs during clot maturation. The MRI protocol comprised diffusion-weighted images, contrast-enhanced carotid angiography, and a novel direct thombus imaging technique. The latter is a T1 weighted 3-D technique that suppresses the signal from fat and nulls that from blood (TR 10·3, TE 4·0, FA 15, TI 20, FOV 3503300, matrix 2563160, 150 partitions, one acquisition, bandwidth 195 Hz/pixel) allowing ease of identification of short T1 species. A diagnosis of carotid territory acute ischaemic stroke was made on the diffusion-weighted images in 20 patients. Contrast-enhanced MR angiography of the carotid arteries demonstrated stenosis or occlusion in 16 patients on the side appropriate to the acute stroke, and in two patients on the contralateral side. Of the 16 patients, 11 had high signal intensity material on the direct thrombus imaging sequence outlining the lumen of the internal Reconstructed transverse section through the neck demonstrating a rim of high signal material within the left internal carotid artery causing a less than 50% narrowing of the vessel This paper is funded by the Italian Ministry of University and Scientific Research

Limitations of clinical diagnosis in acute stroke

Trials in acute stroke have recruited on the basis of clinical diagnosis. Using MRI we have shown that clinical diagnosis is more limited than previously appreciated, thus trials may have been underpowered or confounded.