Response to Letter by Wong and Poon
We thank Drs Wong and Poon for their interest in our recent work dealing with the utility of diffusion-weighted imaging (DWI) to compare ischemic injury after unprotected versus protected carotid angioplasty and stenting (CAS).
We concur with our colleagues that the proportion of patients with any new ipsilateral DWI lesion after protected CAS (49%) was higher than in those 2 studies cited in their letter.1,2 However, similar to our results other recent studies have observed new DWI lesions in 40%,3 41.5%,4 and 43%5 of the patients after protected CAS. Poppert et al detected new DWI lesions in 54% of their patients after unprotected CAS.6 A closer inspection of the literature thus indicates that with respect to incidence of new DWI lesions after either unprotected or protected CAS a broad range of values have been reported to date. This finding could be related to differences in the sensitivity of the imaging techniques especially in detecting small DWI lesions. Furthermore, because our study comprised all patients treated consecutively from April 1999 to June 2005 at a single academic center it is well perceivable that our results were influenced by a learning curve. In fact, the number of new ipsilateral DWI lesions after protected CAS decreased over the years, which likely reflects an increasing experience with the protection devices (Figure).
Drs Wong and Poon question the clinical significance of new DWI lesions after CAS. Although we acknowledge that the majority of new DWI lesions after CAS were asymptomatic, we clearly found a significant association between the number of new DWI lesions and the incidence of minor or major stroke after CAS. This finding most probably reflects an increased chance that an ischemic lesion will involve an eloquent brain region inducing an evident neurological deficit. In this scenario, it does not seem to be beneficial to determine a cut-off value for the number of new DWI lesions in patients with and without new stroke.
Because clinical events after CAS are relatively uncommon there is a need for additional outcome parameters that occur at a greater frequency to evaluate the potential efficacy of protection devices. Drs Wong and Poon propose to only use DWI lesions, which are also visible on T2-weighted images, as a surrogate marker of ischemic complications in future randomized trials of unprotected versus protected CAS. However, in our study the majority of new DWI lesions were too small (<5 mm in diameter) to be detectable on T2-weighted images. Similarly, only 2 (3.1%) of 64 new DWI lesions were also visible on T2-weighted images in the study of Hauth et al.1 Against the background of these data, it appears unlikely that DWI positive T2-weighted positive lesions are a better surrogate marker for embolic complications after CAS than all DWI lesions, which occur frequently and are closely correlated with clinical outcome.
Hauth EA, Jansen C, Drescher R, Schwartz M, Forsting M, Jaeger HJ, Mathias KD. MR and clinical follow-up of diffusion-weighted cerebral lesions after carotid artery stenting. AJNR Am J Neuroradiol. 2005; 26: 2336–2341.
Pinero P, Gonzalez A, Mayol A, Martinez E, Gonzalez-Marcos JR, Boza F, Cayuela A, Gil-Peralta A. Silent ischemia after neuroprotected percutaneous carotid stenting: a diffusion-weighted MRI study. AJNR Am J Neuroradiol. 2006; 27: 1338–1345.
Maleux G, Demaerel P, Verbeken E, Daenens K, Heye S, Van Sonhoven F, Nevelsteen A, Wilms G. Cerebral ischemia after filter-protected carotid artery stenting is common and cannot be predicted by the presence of substantial amount of debris captured by the filter device. AJNR Am J Neuroradiol. 2006; 27: 1830–1833.
Poppert H, Wolf O, Resch M, Theiss W, Schmidt-Thieme T, Graefin von Einsiedel H, Heider P, Martinoff, Sander D. Differences in number, size and location of intracranial microembolic lesions after surgical versus endovascular treatment without protection device of carotid artery stenosis. J Neurol. 2004; 251: 1198–1203.