The primary common goal of both endovascular and surgical treatment of a ruptured intracranial aneurysm is to protect the patient from rebleeding. According to the recent report of International Subarachnoid Aneurysm Trial (ISAT) II, the rebleeding incidence after coiling and clipping during four years of mean follow-up interval was 3.3% and 1.2%, respectively2
. Although the major clinical concern after endovascular treatment of the aneurysms is focused on the long-termed anatomical durability, more than half of the rebleeding events were observed within 30 days of the procedure2
Sluzewski et Al. reported six cases of early rebleeding out of their 431 ruptured aneurysm coiling procedures (1.4%)4
. The incidence is comparable to that of ISAT II, which leaves 1.8% of incidence when a case of early rebleeding from another aneurysm was excluded. It is of note that five of the six early rebleeds reported by them were small (<6 mm), originated from the AcomA and developed within the first 16 days 4
. Unlike the cases of late rebleeding, which usually occur in large aneurysm 1,5
, most of the reported cases of early rebleeding occurred in small aneurysms 4,6
. It is a well-known fact that intraprocedural ruptures also frequently occur in small aneurysms7,8
. Both of the undesired incidents are probably due to inherent limitations of current endovascular coiling device and technology8,9
The presumed causes of frequent early rebleeding in the small aneurysm are the following. Firstly, as generally assumed, one possible explanation can be the relatively low coil packing ratio achieved with the current coiling technique. When the aneurysm has a small sac, it is generally not easy to obtain enough packing density, which is believed to be about 30%10
, further effort to obtain more packing density might cause inevitable trauma to the otherwise thin and friable wall of the small aneurysm and compromise of parent artery. Although studies on the relation between packing density and late recanalization of aneurysm have reported contradictory findings 10,11
, we can not deny the possible relation between higher early rebleeding rate and low packing density especially in small aneurysms.
A second possible explanation is early lysis of the partially thrombosed part of the aneurysmal sac formed in the intraprocedural period, which is regarded as the reason for a good angiographic embolization result even after filling of the aneurysms with just a single coil as our cases. Multiple manipulations of the coil loops, tip of the microcatheter in the small aneurysmal sac is enough to provoke early intra-aneurysmal thrombosis in spite of the proper antithrombotic strategy not only because of the mechanical causes but also up-regulated coagulation system. In addition, the microcatheter itself within the anterior cerebral artery proximal to aneurysm, the volume of fresh blood supplied is lower originally than that of distal internal cerebral artery or middle cerebral artery, could be a factor reducing that to the aneurysmal sac. Relatively low packing ratio in some of the completely embolized small aneurysms in Goddard et Al's series and some of the aneurysms treated with just one or two coils in Kwon et Al's series can be explained by this mechanism 11,12
. Intra-aneurysmal thrombosis occurring during the procedure would serve as a good source of intra-aneurysmal tissue reaction, which is a prerequisite for successful aneurysm healing if subsequent fibrous organization of the primary thrombus ensued 13
. However, large amounts of fresh thrombus tend to dissolve with time by the endogenous thrombolytic effect causing early recanalization of the aneurysm. Apart from thrombus formation during the procedure, the other side of the coin that can be given more weight is the existence of preprocedural intraaneurysmal thrombus after rupture. During initial endovascular treatment of our two patients, we noticed a distal coil loop beyond the margin of the index aneurysm. At first, we thought a disastrous accident had happened. However, there was no evidence of intraprocedural rupture such as contrast media leakage or abruptly increased blood pressure. Post-procedural CT finding or symptoms of the patients were not aggravated. After rebleeding, the first patient retreated with additional embolization, initially estimated an extruded coil loop was located inside an enlarged aneurysm. In microsurgical view of the second patient, all the coil loops could be observed inside the sac through the translucent aneurysmal wall.
We believe this phenomenon -the tip of the iceberg-
can be one cause of early rebleeding after endovascular treatment of ruptured small ACoA aneurysm. In addition, we missed the change in coil shape on plain radiographic performed before discharge of the second patient. Loosening of the first coil loop is evidently demonstrated on serial skull radiographies (Figure -). Simple skull radiography of in the short-term interval seems to have an advantage to tack the change in presumed extruded coil loop in such cases. Our two patients underwent successful retreatment and fortunately we did not lose any patient contrary to other reports 4,6
Simple radiograms performed immediately after embolization (A), 10 days (B) and 30 days (C) after initial endovascular treatment show serial changes in the presumed extruded coil loop in the second patient.