By Maciej Szajner
I must begin by pointing out that the year 2012 should be regarded as an exceptionally important anniversary in the history of interventional neuroradiology. It was 20 years ago that Guglielmi Detachable Coils were introduced for the first time—thus changing the philosophy of treatment of intracranial aneurysms completely. There is still a lack of clarity about the respective roles of endovascular and surgical treatment of aneurysms. Patients in different countries, or even different institutions, are offered various options. However, it is accepted that aneurysm rests and recurrences are more frequent after endovascular treatment than after surgical clipping. In just two decades, a major (r)evolution in medicine has taken place. Now, endovascular coiling is not only an alternative treatment, but regarded as “the gold standard” in the treatment of intracranial aneurysms.
Emerging new embolic agents or devices might increase the long-term efficacy of coiling, possibly at the cost of increased immediate complications. There is a need to identify a target population with lesions that are at higher risk of recurrence, or a subpopulation of patients in whom recurrences are unlikely. Endovascular treatment is definitely less invasive than surgery, but whether this evidence translates into better long-term outcome than surgical or conservative management remains to be proven. The magnitude and clinical significance of this important drawback of endovascular treatment is still poorly documented, because most series have followed-up data for only a limited number of patients, for relatively short periods.
Unfortunately, intracranial aneurysm embolisation appears to be a strongly operator-dependent method. Even the choice of materials used depends on the individual practitioner’s understanding of the lesion and decision-making process. Our knowledge of the long-term natural history of a coiled aneurysm remnant is incomplete. Re-bleeding, though uncommon, is well-recognised. We all have experience with cases of aneurysms that have recurred and been re-treated many times, regardless of very good immediate post-operative angiographic result. Often, such aneurysms initially appear to be easy to treat. Yet in one year or less, we observe coil compaction and recanalisation.
Disconcerting and disappointing, especially because they appeared so simple to treat initially. What was the cause, what made it happen? Do we make them recur by improper use of different materials, or is there anything in the patho-anatomy of certain aneurysms that prevent them from being completely excluded from the circulation?
Some aneurysms may be called “malignant”. As observed by many neurointerventionists, there are several factors concerning aneurysm patho-anatomy and the procedure itself that should be taken into consideration and carefully analysed. Factors previously identified as significant predictors of a recurrence include suboptimal initial angiographic results, treatment after rupture, and aneurysm size.
The size of the sac and the neck as well as location strongly affect the intrinsic haemodynamics or inflow and outflow zones. It seems to be essential to define them well and then to properly carry on the “attack” (with coils, stents, flow-diverters, Onyx or any reasonable combination of those materials). The observations show that deactivation of the inflow zone will almost certainly stop the growth of the aneurysmal sac leading to blood stasis and thrombosis. After all, dispersing the blood stream coming into the sac constitutes the base for the flow-diverter device idea. Recanalisation occurs more frequently in large aneurysms (>10mm), those with large necks (>4mm) and those that show incomplete occlusion at initial treatment. Small aneurysms with small necks are, however, by no means exempt from recanalisation. Dense aneurysm packing is an important factor in reducing recanalisation, and coils should occupy at least 25% of the aneurysm volume to reduce the risk.
Some locations haemodynamically resemble each other: basilar tip, ICA bifurcation (the T), A1/A2 with one side predominance or M1/M2 segments. They all come close to “the T” configuration which may be the major cause of aneurysmal “malignancy”. The neck is usually irregular in shape, blood stream hits it at the strait angle with major energy.
I suppose “malignant” aneurysms exist and it is not only our “influence” but also the individual, haemodynamical features of a particular aneurysm that sometimes make complete endovascular treatment almost impossible. Clearly, the six-month follow-up angiographic study that is commonly recommended is insufficient to detect all recurrences.
A thorough analysis of patho-anatomy of those aneurysms would tell us more and, above all, help to establish the prognostic features that will set the indications for individualised, specific treatment and the correct choice of materials.
Maciej Szajner is assistant professor at the Department of Interventional Radiology and Neuroradiology, Medical Univeristy of Lublin, Lublin, Poland