Introduction and historical background 25 In both meta-analyses very heterogeneous studies were included, and recanalization rate was not standardized: a small neck remnant and a recurrence within the coil mesh were both regarded as a positive finding, whereas complete occlusion was considered a negative. Most studies evaluating treatment-results in intracranial aneurysms use the difference between complete occlusion, neck remnant and recurrence as described by Roy and Raymond (R&R)416 (Fig 1). More refined grading scales have been proposed,417 but observer variability was found to be substantially better in scales that offer fewer gradations in observer responses.418 Of greatest value in clinical practice is the distinction between neck remnant and residual or recurrent aneurysm, because this last category most likely needs retreatment whereas neck remnant does not. Complete Residual neck Residual aneurysm Figure 1. Aneurysm occlusion classification by Roy and Raymond Recent studies reporting the accuracy of MRA in follow-up of coiled aneurysms use the R&R aneurysm occlusion classification.419-426 If a dichotomization was made between class 1 and 2 of the R&R classification (“complete occlusion” versus “incomplete occlusion”) sensitivity ranged between 72 and 90 % and specificity between 52 and 86%; if, on the other hand, a dichotomization was made between class 2 and 3 (“adequately coiled” versus “inadequately coiled”) sensitivity ranged from 50 to 80% and specificity from 84 to 93%.420-422,426 Thus sensitivity appears to decrease and specificity to increase when a decision is based on adequately versus inadequately coiled as compared to complete versus incomplete occlusion. For an inadequately coiled aneurysm retreatment will usually be considered, but not for an adequately coiled aneurysm. Daugherty et al showed that a substantial variability exists when a group of five experienced neuro- interventional radiologists and interventional neurosurgeons are asked whether a recurrent aneurysm should be retreated:427 After giving their decision to retreat on a five-point scale based on DSA images of 27 coiled aneurysms with recurrence at follow-up, the median Kappa was only 0.27! This reflects the difficulty of establishing a standard of reference for this kind of study. Although not all authors are yet convinced that MRA can replace DSA as the primary modality for follow- up,426 in our hospital, as in many others,423,425,428 it is standard practice. The additional value of CEMRA is still disputed. Advocates of the technique see clear advantages especially in the larger recurrences, where differentiation between class 2 and 3 of the R&R classification, or between retreatment or not, is important.410,422,429-431 Other authors, however, find no additional value.413,420,421,432-435 Recently the advantage of CEMRA over TOF MRA in the follow-up of stent assisted coil embolization was described.436-439 Perhaps at present the best advice is to use both TOF MRA and CEMRA in the follow-up of coiled aneurysms.422 The advantage of 3T MRA over 1.5T for the follow-up of coiled aneurysms is another subject under investigation. In the meta-analyses by Kwee & Kwee414 and Weng et al415 only one study, included in both meta-analyses, used a 3T MRI.440 In more recent publications some find a clear advantage in using
proefschrit Van Zwam inhoud met kaft en stellingen.indd
To see the actual publication please follow the link above