Introduction: Coil embolization has been increasingly used over the last two decades for the treatment of intracranial aneurysms. Incomplete occlusion and aneurysm recurrence, however, remain disadvantages of this approach.[1-3] Higher packing density (PD) has been shown to have a positive influence on angiographic outcome.[4-8] There are certain situations, however, when the influence of PD has been called into question including the treatment of small[9] and unruptured[4] aneurysms as well as during stent assisted coiling.[10] It would be useful to know in which cases PD is the most influential.

Methods: This is a single center, retrospective review of 384 patients with 405 consecutively treated aneurysms. Exclusion criteria included previous treatment, atypical aneurysms, and non-coiling interventions. The Modified Raymond Roy Occlusion Classification was used to grade aneurysms.[11] Incomplete aneurysm occlusion was defined as Class IIIa or IIIb at any follow-up point. Neck remnants were not included in the incompletely occluded group based on our previous experience.[12]

Results: In the entire study population, PD was associated with incomplete aneurysm occlusion (p=0.008) with 31% being the ideal cut off point. This association persisted in unruptured aneurysms only (0.017) and those treated with stent-assisted coiling (0.037). The association no longer remained significant, however, for small aneurysms (< 7mm; p=0.472), narrow-necked aneurysms (< 4mm, p=0.381), and those aneurysms in which complete coil coverage across the aneurysm neck was achieved (p=0.148).

Conclusions: PD is associated with aneurysm occlusion at follow-up, irrespective of rupture status or stent-assistance. PD may be less important in small, narrow-necked aneurysms and those in which complete coil coverage across the aneurysm neck is achieved. These associations are important to keep in mind when deciding how densely to pack the aneurysm with coils.

Patient Care: The question of when to stop packing the aneurysm with coils frequently arrises toward the end of the procedure. One must always balance the benefit of complete aneurysm occlusion and lower risk of recurrence versus the risk of iatrogenic aneurysm rupture or coil prolapse into the parent artery. The understanding that packing density may be less important in small, narrowed-neck aneurysms as well as those with complete coil coverage across the aneurysm neck has the potential to be useful during coil embolization. In these specific cases it may be appropriate to not over pack the aneurysm. This has the potential to decrease risk and cost.

Learning Objectives: To understand the relationship between packing density and incomplete aneurysm occlusion both in the entire population of aneurysms treated with coiling but also in sub-populations such as small, narrow-necked, unruptured, stent-assisted aneurysms, as well as those with complete coil coverage across the aneurysm neck.

References: 1. Molyneux A, Kerr R, Stratton I, et al. International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised trial. Lancet 2002;360(9342):1267-74 2. Spetzler RF, McDougall CG, Albuquerque FC, et al. The Barrow Ruptured Aneurysm Trial: 3-year results. J Neurosurg 2013;119(1):146-57 doi: 10.3171/2013.3.JNS12683[published Online First: Epub Date]|. 3. Ferns SP, Sprengers ME, van Rooij WJ, et al. Coiling of intracranial aneurysms: a systematic review on initial occlusion and reopening and retreatment rates. Stroke 2009;40(8):e523-9 doi: 10.1161/STROKEAHA.109.553099[published Online First: Epub Date]|. 4. Grunwald IQ, Balami JS, Weber D, et al. Different factors influence recanalisation rate after coiling in ruptured and unruptured intracranial aneurysms. CNS & neurological disorders drug targets 2013;12(2):228-32 5. Leng B, Zheng Y, Ren J, et al. Endovascular treatment of intracranial aneurysms with detachable coils: correlation between aneurysm volume, packing, and angiographic recurrence. J Neurointerv Surg 2013 doi: 10.1136/neurintsurg-2013-010920[published Online First: Epub Date]|. 6. Kawanabe Y, Sadato A, Taki W, et al. Endovascular occlusion of intracranial aneurysms with Guglielmi detachable coils: correlation between coil packing density and coil compaction. Acta neurochirurgica 2001;143(5):451-5 7. Sluzewski M, van Rooij WJ, Slob MJ, et al. Relation between aneurysm volume, packing, and compaction in 145 cerebral aneurysms treated with coils. Radiology 2004;231(3):653-8 doi: 10.1148/radiol.2313030460[published Online First: Epub Date]|. 8. Wakhloo AK, Gounis MJ, Sandhu JS, et al. Complex-shaped platinum coils for brain aneurysms: higher packing density, improved biomechanical stability, and midterm angiographic outcome. AJNR Am J Neuroradiol 2007;28(7):1395-400 doi: 10.3174/ajnr.A0542[published Online First: Epub Date]|. 9. Goddard JK, Moran CJ, Cross DT, 3rd, et al. Absent relationship between the coil-embolization ratio in small aneurysms treated with a single detachable coil and outcomes. AJNR Am J Neuroradiol 2005;26(8):1916-20 10. Chalouhi N, Dumont AS, Hasan D, et al. Is packing density important in stent-assisted coiling? Neurosurgery 2012;71(2):381-6; discussion 86-7 doi: 10.1227/NEU.0b013e31825c36dd[published Online First: Epub Date]|. 11. Mascitelli JR, Moyle H, Oermann EK, et al. An update to the Raymond-Roy Occlusion Classification of intracranial aneurysms treated with coil embolization. J Neurointerv Surg 2014 doi: 10.1136/neurintsurg-2014-011258[published Online First: Epub Date]|. 12. Mascitelli JR, Oermann EK, De Leacy RA, et al. Angiographic outcome of intracranial aneurysms with neck remnant following coil embolization. J Neurointerv Surg 2014 doi: 10.1136/neurintsurg-2014-011226[published Online First: Epub Date]|.