Imaging Follow-Up of Intracranial Aneurysms Treated by Endovascular Means

Aneurysm treatment is dedicated to prevention of rupture (for unruptured aneurysms) or rebleeding (for ruptured aneurysms). Endovascular embolization has become the firstline treatment for intracranial aneurysms in the majority of cases in many institutions. This minimally invasive approach achieved lower morbidity and mortality rates when compared with surgical management. However, although successful in improving patient care, its durability has been noted to be its Achilles’ heel since the earliest application of this technology. Indeed, after endovascular treatment (EVT) ≈20% of patients will experience aneurysm or neck reopening after traditional endovascular coiling, necessitating retreatment in about half of them to maintain long-term protection over bleeding. Despite this issue, low rates of bleeding have been reported after EVT of ruptured aneurysms, and its clinical superiority over surgery seems to be maintained over time according to the longterm clinical follow-up of the International Subarachnoid Aneurysm Trial (ISAT) cohort. In the Cerebral Aneurysm Rerupture after Treatment (CARAT) study, the bleeding rate after coil embolization was 0.11% (mean follow-up time, 4.4 years), whereas in the International Subarachnoid Aneurysm Trial, the annual risk of bleeding after coil-treated aneurysms was 0.08%. In a large single-center study, the Barrow Ruptured Aneurysm Trial (BRAT), no bleeding was observed after 6 years in the coiling arm, but 4.6% of these patients were retreated. Thus, one may question the clinical usefulness of performing imaging follow-up, balancing the small risk of bleeding after EVT with the cost-effectiveness of follow-up. Although the primary end points of these studies were clinical, it is important to note that the majority of EVT patients had imaging follow-up performed at the discretion of the treating physician. For example, in the ISAT trial, 88.2% of the patients in the EVT arm (881 patients) had follow-up angiograms, generally performed 6 months after treatment and repeated at varying intervals. Moreover, during the follow-up of the patients enrolled in these studies, it was noticed that some patients underwent retreatment without any bleeding, so that bleeding may have been more common if these aneurysms were not followed. For example, 8.3% of the EVT patients in ISAT received late retreatment without prior rebleeding, whereas only 0.6% of them were retreated lately because of rebleeding. Several mechanisms have been proposed to explain aneurysm recurrence, including coil compaction, aneurysm growth, coil migration through the aneurysm wall, coil penetration into the thrombus material of a partially thrombosed aneurysm, and abnormal inflammatory reaction of the aneurysm wall leading to growth. Because recurrence is the main weakness of EVT, innovative technologies have been developed during the past decade to improve the long-term stability of EVT. New technologies were developed to improve aneurysm occlusion and coil density within the aneurysm sac and to treat complex aneurysms (large and/or wide-neck and/or bifurcation aneurysms) often prone to recur after simple coil embolization. Several options became progressively available in addition to standard coil embolization with bare platinum coils, widening considerably the treatment options the neurointerventionist can offer: surface-modified coils (such as polyglycolic/polylactic acid coated coils or hydrogel coated coils), balloon-assisted coiling, stent-assisted coiling, flow diverters, and recently flow disrupters. Each treatment option has its own advantages and drawbacks. The physical properties of the material used will be crucial to determine the best modality for performing the follow-up. Another concern for all patients harbouring an intracranial aneurysm is the appearance of newly detected (ie, de novo) aneurysms in ≈5% to 10% of patients. However, although many of them will be of small size, some will carry enough risk of bleeding to require treatment. Then, imaging must be able to detect and follow them. The possibility of aneurysm recurrence and of newly detected aneurysms, with the idea of providing an early Imaging Follow-Up of Intracranial Aneurysms Treated by Endovascular Means Why, When, and How?