Monitoring the evolution of intra-cranial aneurysms that are initially deemed unsuited for treatment can provide important information that can be used in deciding the time point when endovascular or surgical intervention might be necessary. In this study we report how 3D modeling of intra-cranial aneurysms can accurately be used to monitor changes in aneurysm volume on a prospective cohort of aneurysms of the intracranial internal carotid system.
Our study indicates that the rate of aneurysm progression is individual specific but remains relatively low for this cohort of fusiform, dysmorphic aneurysms of the distal internal carotid artery. Indeed, the highest rate of growth we observed is 4.98 % which is a significant change relative to the accuracy of our method (2 +/− 1% (7
)) but still relatively low. This is in agreement with previous knowledge about the natural history of aneurysm growth (6
) and supports the fact that precise 3D tools are required to monitor these aneurysms.
Indeed 3D volume monitoring presents several advantages in comparison to traditional maximal diameter measurements. First, using a 3D approach accounts for changes in patient position and image acquisition direction at different time points (10
). Further, 3D measurements are often more accurate in the detection of structural growth, particularly if that growth is asymmetric (11
). Finally, co-registration of datasets acquired at different time points allows a good overall appreciation of global and local evolution of the aneurysms (). This feature is particularly important in the case of long dysmorphic segments with several bulging areas such as in . In this case, choosing one diameter as a reference for the follow-up can be very misleading and lead to misinterpretation if the growth occurs elsewhere on the pathologic vessel.
Figure 4 Patient with an aneurysm of the intra-cranial internal carotid artery (Patient 4). Left: Registration of the lumen of the baseline study (green) and the most recent study (red). Right: Same patient: Enlargement of the bulging area (arrow) is shown using (more ...)
Figure 5 Patient 2 presenting with a long, fusiform, dysmorphic aneurysm (red part) of the distal internal carotid artery (blue part). The presence of multiple focal bulging areas (arrows) leads to difficulties if the analysis is performed only on 2 dimensional (more ...)
A limitation to our study is the small size of our population. Nevertheless, this study does not intend to provide definitive guidelines for the frequency with which patients should be monitored or to assign change in diameter as the only factor governing rupture risk (as many other cofactors may contribute as decribed in the introduction section) but to illustrate the potential advantages in using a 3D volumetric modeling approach for intra-cranial aneurysm rate of progression.
In conclusion, given the relatively low rate of progression, this study would indicate that patients with dysplastic, fusiform aneurysmal vessel segments of the internal carotid artery that are not saccular in form, should be followed with serial imaging studies, and that quantitative volumetric methods can be helpful in monitoring whether any growth has occurred.