Comparison of clipping and coiling in elderly patients with unruptured cerebral aneurysms

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The comparative effectiveness of the 2 treatment options—surgical clipping and endovascular coiling—for unruptured cerebral aneurysms remains an issue of debate and has not been studied in clinical trials. The authors investigated the association between treatment method for unruptured cerebral aneurysms and outcomes in elderly patients.


The authors performed a cohort study of 100% of Medicare fee-for-service claims data for elderly patients who had treatment for unruptured cerebral aneurysms between 2007 and 2012. To control for measured confounding, the authors used propensity score conditioning and inverse probability weighting with mixed effects to account for clustering at the level of the hospital referral region (HRR). An instrumental variable (regional rates of coiling) analysis was used to control for unmeasured confounding and to create pseudo-randomization on the treatment method.


During the study period, 8705 patients underwent treatment for unruptured cerebral aneurysms and met the study inclusion criteria. Of these patients, 2585 (29.7%) had surgical clipping and 6120 (70.3%) had endovascular coiling. Instrumental variable analysis demonstrated no difference between coiling and clipping in 1-year postoperative mortality (OR 1.25, 95% CI 0.68–2.31) or 90-day readmission rate (OR 1.04, 95% CI 0.66–1.62). However, clipping was associated with a greater likelihood of discharge to rehabilitation (OR 6.39, 95% CI 3.85–10.59) and 3.6 days longer length of stay (LOS; 95% CI 2.90–4.71). The same associations were present in propensity score–adjusted and inverse probability–weighted models.


In a cohort of Medicare patients, there was no difference in mortality and the readmission rate between clipping and coiling of unruptured cerebral aneurysms. Clipping was associated with a higher rate of discharge to a rehabilitation facility and a longer LOS.

ABBREVIATIONSAD = adjusted difference; FFS = fee-for-service; HRR = hospital referral region; IPW = inverse probability weighting; ISAT = International Subarachnoid Aneurysm Trial; IV = instrumental variable; LOS = length of stay; ZIP = Zone Improvement Plan.

Article Information

INCLUDE WHEN CITING Published online May 20, 2016; DOI: 10.3171/2016.1.JNS152028.

Correspondence Kimon Bekelis, Section of Neurosurgery, Dartmouth-Hitchcock Medical Center, One Medical Center Dr., Lebanon, NH 03755. email:

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Percent of Medicare beneficiaries treated for ruptured cerebral aneurysms using coiling (2007–2012). Each dot represents 1 HRR; the higher the dot, the higher the percentage. Each blue dot represents the percent of Medicare beneficiaries treated for unruptured cerebral aneurysms with coiling in 1 of 306 HRRs in the US. Red dots indicate the regions with the 5 lowest and 5 highest rates, whose names are listed to the left. Reproduced from Bekelis K. Variation in the Care of Surgical Conditions: A Dartmouth Atlas of Health Care Series. Lebanon, NH, 2014. Published with permission. Figure is available in color online only.

  • View in gallery

    Kaplan-Meier estimates of survival for patients with unruptured cerebral aneurysms after surgical clipping or endovascular coiling. Both unadjusted (less-bold lines) and adjusted (bold lines) estimates are presented. Shaded areas represent 95% confidence intervals. Adjustment was performed with an IPW logistic regression model. Figure is available in color online only.


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