AANS Neurosurgeon : Peer-Reviewed Research

Volume 20, Number 1, 2011

Incidence of Clipping and Coiling Procedures

Aneurysm Treatment of Medicare Patients, 1996–2006

Scott D. Simon, MD, Tatsuki Koyama, PhD, Joseph S. Cheng, MD, Robert A. Mericle, MD

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Scott D. Simon, MD, Department of Neurosurgery; Tatsuki Koyama, PhD, Department of Biostatistics; Joseph S. Cheng, MD, Department of Neurosurgery; Robert A. Mericle, MD, Department of Neurosurgery, Vanderbilt University School of Medicine, Nashville, Tenn.
Dr. Mericle is a paid physician proctor for eV3 Neurovascular, Irvine, Calif. The other authors reported no conflicts for disclosure.
Correspondence to: ssimon3@ mcvh-vcu.edu
Abbreviations: ACGME, Accreditation Council for Graduate Medical Education; CI, confidence interval; CPT, Current Procedural Terminology
Key Words: aneurysm, cerebrovascular, clipping, coiling, CPT, Medicare
July 31, 2009
Jan. 8, 2010
Portions of this work were presented in digital poster format at the AANS Annual Meeting in San Diego, Calif., May 2–6, 2009.

The development of endovascular procedures has added embolization using coils to surgical clipping as an option for treatment of cerebral aneurysms. To determine trends in incidence of coiling procedures compared to craniotomies for aneurysm clipping, we retrospectively reviewed Medicare data for 1996–2006. The Medicare database collects the CPT codes submitted for Medicare payment. The craniotomy codes for clipping of cerebral aneurysm (61697, 61698, 61700, 61702) and for endovascular embolization (61624) were tabulated for each of the 11 years studied. An ordinary regression model was created to capture the trend in the number of craniotomies performed during the period studied. The number of craniotomies decreased from 3,204 in 1996 to 1,702 in 2006, declining at a rate of 131 per year (95 percent CI). Conversely, the number of endovascular embolizations increased from 808 in 1996 to 5,152 in 2006. The change in the frequency of each type of procedure has significant consequences for neurosurgical training and treatment of cerebral aneurysms.

The development of endovascular procedures has had a significant impact on how cerebral aneurysms are treated (4–6, 8–9). Nonetheless, there has been only one published report of the respective numbers of craniotomies and embolizations for aneurysms of the last few years in the U.S. (1). In that report Andaluz and colleagues examined the Nationwide Inpatient Sample database to determine the relative numbers of clipping and coiling 1993–2003. Their report demonstrated that while the number of embolizations increased, the number of craniotomies for aneurysm remained stable.

We examined Medicare data 1996– 2006 and used these data to speculate on the socioeconomic consequences of the most current trends in aneurysm treatment for neurosurgeons in practice and in training.

Materials and Methods
We retrospectively reviewed the Medicare database for the 11-year period 1996–2006. This database collects the CPT codes submitted for Medicare payment. We began with 1996 data because Gugliemi detachable coils were approved by the Food and Drug Administration in 1995, making 1996 the first full year this device was available in the U.S. for use in endovascular embolization (3). We studied data through 2006 because these were the most recent data available for our study. The CPT codes associated with craniotomy for clipping of cerebral aneurysms are 61697, surgery of complex intracranial aneurysm, intracranial approach, carotid circulation; 61698, surgery of complex intracranial aneurysm, intracranial approach, vertebrobasilar circulation; 61700, surgery of simple intracranial aneurysm, intracranial approach, carotid circulation; and 61702, surgery of simple intracranial aneurysm, intracranial approach, vertebrobasilar circulation.

Embolization of intracranial aneurysm is coded 61624, transcatheter permanent occlusion or embolization (e.g., for tumor destruction, to achieve hemostasis, to occlude a vascular malformation), percutaneous, any method, central nervous system (intracranial, spinal cord). This code obviously applies to more than just aneurysm coiling, but it is the code most commonly used for aneurysm coiling. The general nature of this code makes it difficult to determine the absolute number of aneurysm coilings in a given year. However, it does allow for generalization or identification of trends in the number of intracranial embolizations.

The patient population studied represents all Medicare patients in the U.S. The majority of Medicare patients are 65 and older, but a smaller proportion represents patients younger than 65 with disability.

An ordinary logistic regression model was created to capture the longitudinal trend for the number of craniotomies performed 1996–2006. The rate of change with a 95 percent CI was computed based on the regression model. The number of embolizations and the total number of procedures also were recorded and tabulated. However, formal statistical analysis was not attempted on these endpoints due to the inherent difficulty in determining the absolute number of aneurysm coilings represented by code 61624, which encompasses repeat embolizations as well as embolization of lesions other than aneurysms.

Craniotomies for aneurysm clipping decreased during the period studied. Procedures coded 61700 decreased from 2,942 in 1996 to 865 in 2006, and those coded 61702 decreased from 262 to 42 (Table 1). The introduction of two new codes in 2001 to denote aneurysms of greater complexity led to a decrease in the number of procedures coded 61700 and 61702, but their introduction should not affect the total number, which decreased from 3,204 to 1,702. Our analysis shows that the number of craniotomies for aneurysm clipping decreased by 131 per year, with 95 percent CI: 109 to 154 (Figure 1).

The number of endovascular embolizations increased from 808 to 5,152 during the period studied, representing a six-fold increase in the number of coiling procedures. The percentage of coiled aneurysms climbed from 20.1 percent in 1996 to 67.0 percent in 2006.

Andaluz and colleagues surveyed hospital discharge data 1993–2003 and found the number of embolization procedures doubled while the number of craniotomies for clipping remained stable (1). Our data concur with the rapid increase in endovascular coiling therapy they reported, but differs starkly from their finding of a stable rate of craniotomies for clipping.

The primary reason for this difference is that the data we studied were more recent. Also, our data represent Medicare patients, those 65 and older or on disability, whereas Andaluz and colleagues examined all patients at the hospitals studied. Certain studies have indicated that older patients or those with significant surgical morbidity have better outcomes with endovascular treatment (2, 4–6). Our data suggest that the neurosurgical community has embraced the age of 65 and older as an indication for coiling, and this change in thinking also may account for the decline in craniotomies for clipping in the Medicare population. Given the increasing percentage of the U.S. population that will qualify for Medicare in the coming decade as well as the four times higher prevalence of intracranial aneurysms among older adults, the trend toward an increasing number of endovascular procedures is very likely to continue (6–7).

Whether or not the sharp decline in the number of craniotomies for aneurysm clipping applies to all age groups is beyond the scope of the Medicare data presented here. However, it is possible to extrapolate from the previously reported stable number of craniotomies for clipping in all patients and from our data showing the decreasing number of craniotomies for clipping in the Medicare population that the number of clipping procedures in younger patients must be increasing.

These trends will necessarily affect neurosurgical training. Endovascular training will play a larger role during neurosurgery residency. The current training philosophy that requires all neurosurgeons to learn aneurysm clipping but only a handful of fellowship-trained specialists to learn aneurysm coiling seems outdated. The increasing number of coiling procedures we have described suggests that case volumes will be more than adequate to train all neurosurgeons in treatment of aneurysms via endovascular coiling. The ACGME Residency Review Committee for neurological surgery has recognized this fact and has taken steps to integrate basic endovascular skills training into the residency curriculum (http://www.acgme.org/acWebsite/RRC_160/160_prIndex.asp).

The effect of these trends on the training of residents for clipping of aneurysms is less clear. It is possible that improved imaging might lead to the discovery of more occult aneurysms in young patients and increase the number of elective clippings. It is also possible that as a greater proportion of aneurysms are coiled, fewer clipping cases will be available to train residents.

The number of craniotomies for aneurysm clipping decreased significantly 1996–2006 in the Medicare population, while the number of endovascular embolizations increased in the same population. This change has significant consequences for neurosurgeons with regard to their training and treatment of cerebral aneurysms. Continued monitoring of clipping and coiling trends will aid in determining how to prepare future generations of neurosurgeons with an optimal skill set for treatment of cerebrovascular aneurysms.


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