The article studies as regards PCOM treatment by flow diverter almost concern with patency of PCOM after PED deployment [13, 14] or discuss failure/low occlusion of PCOM aneurysms associated with a fetal origin posterior cerebral artery after flow diverter [15,16,17,18]; few articles discuss the clinical and radiological outcome of fetal and non-fatal PCOM artery aneurysms [6]. Our study describes the clinical and radiological outcomes of PCOM aneurysms treated with flow diverter stent (PED type) in two tertiary institutes. This study has data regarding the anatomical variants and clinical presentation that give better ideas to assess the post-procedure complications and clinical and radiographic outcomes of PCOM aneurysms treated by PED stent.
Endovascular coiling remained the treatment of choice of most of the intracranial aneurysms, but it has low rates of occlusion in complex and large-sized aneurysms [19]. FD offered an alternate treatment option for those complex and large/giant aneurysms [20].
In our series, procedure-related complications occurred in five patients (two ischemic, two TIA, and one ipsilateral distal hemorrhage) with persisting major neurological deficits in two patients (4.2%) and no procedure-related mortality.
The post-procedure complications after PCOM treatment in Roy et al. [18] study occurred only in one patient who suffered from seizure with no major neurological complications. Daou et al.’s [14] study has no ischemic or hemorrhagic complications, and the same is reported by Kühn et al. [6].
As a meta-analysis including 3125 patients, the overall complications 17.0% with mortality rate 2.8%, and the neurological morbidity 4.5% [21], the authors concluded that the use of FD stents in aneurysms treatment yielded satisfactory results with regard to the complications and the mortality rate. In Trivelato et al.’s [22] study, the major strokes or mortality rate was 3.45%. Likewise, in Adeeb et al.’s [23] study, the symptomatic thromboembolic complications were 12% and symptomatic hemorrhagic complications 8% with no mortality; they concluded that the incidence of complications after PED is greater in giant and large aneurysms compared to smaller sized aneurysms.
Distal intraparenchymal hemorrhage is the most dreaded complication of flow diversion. In our study, only one active smoker, hypertensive patient with large PCOM aneurysm who suffered from ipsilateral parenchymal hemorrhage required surgical evacuation and complained from contralateral homonymous superior quadrantanopia, because of the effect of hemorrhage on Meyer’s loop in the temporal lobe.
Distal parenchymal hemorrhage more in anterior circulation aneurysms was treated by FD [24]; the exact mechanism of bleeding is not clearly understood and may be explained by alteration of the parent artery morphology and decrease in the local compliance of the vascular segment affecting the aneurysm hemodynamics [25]; the presence of risk factors as smoking and hypertension with endovascular microvascular damage as well as the use of antiplatelet therapy increases the bleeding risks.
Delayed aneurysm rupture after FD is one of the serious complications with disastrous consequences and is more common in symptomatic and large/giant aneurysms [26]. In the current study, no delayed rupture occurred, it may be attributed to small sample size, and most of the treated aneurysms in our series were small-sized (59.6%).
In contrast to hemorrhage after FD, ischemic complications are more common in treated posterior circulation aneurysms [27] and also more common in large and giant aneurysms [26, 28]. In our study, two patients suffered from thromboembolic events on the 1st day and the 6th month after FD procedures respectively. The first is due to improper deployment of PED and resulting in ipsilateral ICA occlusion. The second patient harboring large aneurysm was treated by two PED stents and developed intra-stent stenosis 6 months after treatment; it attributed to interruption of anti-platelet therapy, and also the use of multiple stents with intra-procedure microvascular injuries changes the hemodynamic and promotes the incidence of ischemic complications [29].
Complete aneurysm occlusion in the present study was achieved in 41/46 aneurysms 89.1% of treated aneurysms and re-treatment required in two aneurysms. The relatively high rate of complete aneurysm occlusion in our study is in line with the findings of previous series especially those concerned with PCOM aneurysm after PED stent: in Roy et al.’s [18] study, complete or near-complete occlusion was achieved in 85.4%, Daou et al. [14] reported 86.7% complete or near-complete obliteration at 6-month follow-up, Kühn et al. [6] observed complete or near-complete occlusion in 91.5% at 3 to 9 months, and Brinjikji et al. [13] realized 81.8% complete or near-complete occlusion at the last follow-up.
Progressive aneurysm occlusion over time was observed in many studies as in Dornbos et al. [30] and Saatci et al.’s [9] studies; in our series complete occlusion progress from 61.1% at 6–12 months to 74.5% at 24 months, the exact mechanism of progressive occlusion over time may be explained by progressive intra-saccular thrombus formation over time and shrinkage of the aneurysm with the inflammatory process reaction.
Failure of complete occlusion in our study was observed in six aneurysms; incorporated vessels and large size aneurysm were statistically significant factors associated with low occlusion rate, and among those with incorporated vessels, one aneurysm has a fetal origin of the PCOM artery which was identified as a predictor for low occlusion, but in our study, its non-statistical significant as a low number of cases with fetal origin was included in our series.
The presence of incorporated artery increases difficulties in endovascular treatment of the aneurysm; flow diverters provided a solution for those aneurysms [31]; we identified that incorporated vessels from the aneurysmal sac/neck is an independent predictor of incomplete aneurysm occlusion, the same announced in many studies [14, 22, 32,33,34,35]. It is explained by pressure gradient kept by incorporated branch toward the aneurysm that reduced the flow diversion effect of the stent and in PCOM aneurysm theoretical explanation by retrograde filling of the sac via the posterior circulation resulting in residual aneurysm filling after treatment [22].
A lager aneurysmal size is associated with low occlusion rate the same realized in many studies [9, 27, 32, 34, 36, 37]. Fetal origin PCOM artery almost always associated with failure of aneurysm occlusion [14,15,16,17]; it explains by high demand flow in large-caliber fetal PCOM artery keep the flow to it and disrupt the flow diversion effect.