The Source for Neurovascular News and Education

May 28, 2024

The likelihood of the phenomenon depends on location and size as well as stent use.


Occlusion rates often increase during the 6 months following aneurysmal coil embolization, a phenomenon a group of Japanese investigators have termed “progressive thrombosis.” In a single-center series, published online recently in the Journal of NeuroInterventional Surgery, they characterize factors linked with its occurrence.


“We have observed that aneurysms treated by insufficient coil embolization and filled with contrast agent immediately after the procedure are often completely occluded at follow-up,” write Yusuke Funakoshi, MD (Kobe City Medical Center General Hospital, Japan), and colleagues. “However, there are limited studies showing progressive thrombosis of aneurysms after coil embolization.”


Funakoshi et al analyzed outcomes of 255 consecutive unruptured aneurysms treated by coil embolization at their institution between January 2011 and June 2017 that had > 6 months of follow-up. Progressive thrombosis as occurring when aneurysms for which neck remnants or dome filling were in evidence immediately after the coiling procedure but were completely obliterated at 6 months


Immediately after coil embolization, 9.4% of aneurysms were completely occluded, 32.2% had neck remnants, and 58.4% had evidence of dome filling. At 6-month digital subtraction angiography, 48.2% of aneurysms were completely occluded, 37.3% had neck remnants, and 14.5% had dome filling. Retreatment for major recanalization was performed in 3.1% of cases.


Location, Size, and Stent Type


Of 231 aneurysms filled with contrast agent after coil embolization, progressive thrombosis occurred in 103 at 6 months. The phenomenon was observed at a high rate in internal carotid artery (ICA)-paraclinoid aneurysms (55.2%) and bifurcation-type aneurysms in the anterior circulation, including ICA-bifurcation, middle cerebral artery, and anterior communicating artery aneurysms (56.3%). Numerically lower rates of progressive thrombosis were seen among aneurysms that occurred in the posterior circulation and the internal carotid artery-posterior communicating artery/internal carotid artery-anterior choroidal artery as well as with non-stenting procedures. In chi-square testing, location was a major factor involved in progressive thrombosis (P = 0.0002), as was procedure type (P = 0.0026).


Other differences between the development of progressive thrombosis and no thrombosis were seen in median aneurysm dome and neck diameter and in median volume embolization ratio.


Factors Associated With Progressive Thrombosis


Progressive Thrombosis

(n = 103)

No Thrombosis

(n = 128)

P Value

Aneurysm Dome

5.8 mm

6.7 mm


Aneurysm Neck

3.8 mm

4.3 mm


Volume Embolization Ratio





The study authors say the literature suggests that progressive thrombosis may occur due to stagnation of blood flow by coil embolization, which leads to local blood coagulation and thrombosis formation in the aneurysm.


Progressive thrombosis can occur in aneurysms after coil embolization depending on aneurysm location and size, and stent use,” Funakoshi and colleagues conclude. “These aneurysms may not need to be packed completely, despite [volume embolization ratio] being a factor in progressive thrombosis. Thus, it is important that the degree of coil embolization and the combination with stents are adjusted depending on the type of aneurysm.”



Funakoshi Y, Imamura H, Tani S, et al. Progressive thrombosis of unruptured aneurysms after coil embolization: analysis of 255 consecutive aneurysms. J NeuroInterv Surg. 2019;Epub ahead of print.



Funakoshi reports no relevant conflicts of interest.