Neurointerventional Research between 2003 and 2012: Slow Growth, High Interdisciplinary Collaboration, and a Low Level of Funding

Discussion

The field of neurointerventional therapy was developed originally in 1960 when Lussenhop, a neurosurgeon, and Spence⁶ described the technique of intravascular embolization of brain AVMs by injecting Silastic spheres (Dow Corning, Auburn, Michigan) through a surgically exposed carotid artery. After this monumental effort, neurointerventional therapy has made tremendous progress in recent years. This progress is attributable to continuing advances in imaging modalities, catheters and other devices, and interventional techniques, coupled with recent pharmaceutical and basic science knowledge. At least until the end of the 1990s, there was a bitter turf war regarding which of 3 specialties, neurosurgery, neuroradiology, and neurology, had the right to practice the neurointerventional procedures.

In the future, however, the most appropriate type of physician to perform the procedure in this evolving subspecialty may become less relevant with the ultimate goal of optimized patient care. In 2006, the Accreditation Council for Graduate Medical Education announced the revised program requirements in the United States for fellowship education in endovascular surgical neuroradiology.⁷ Endovascular surgical neuroradiology occupies a unique niche in the area of neurovascular interventions among neuroradiology, neurosurgery, and neurology. In 2007, after much work, the Society of Neurointerventional Surgery (formerly the American Society of Interventional and Therapeutic Neuroradiology) was formed, comprising all specialists interested in neurointervention.⁸ At present, in many neurointerventional centers throughout the world, clinical practice and research are performed by the collaborative effort among physicians with different backgrounds of training.

Given the relatively less invasive nature, rapid technical advances, and the large number of patients, neurointerventional therapy of cerebrovascular disease promises to be a greatly expanding field across many specialty disciplines such as neurosurgery, radiology, and neurology. Therefore, determining the group of physicians most appropriate to perform this specific endovascular procedure is becoming more difficult.^9⇓–11

The results of our study show that the total number of publications has slightly increased from 2003 to 2012. This increase in publications seems to be related to the increasing worldwide prevalence of cerebrovascular diseases and the increasing interest in the neurointerventional treatment from multiple disciplines. The most active discipline was neurosurgery, but we also observed increases in publications from radiology and neurology.

Despite these achievements, there were 2 disappointing features in the publications that focused on the neurointerventional therapy of cerebrovascular diseases. First, only approximately half of the publications were in the form of original articles. This disproportionately low number of original articles suggests that increases in publication may not necessarily be accompanied by an equivalent increase in the growth of the global scientific impact. Second, only 9.0% of all publications received funding. It is possible that the preponderance of case reports and review articles are reducing the percentage of funded articles because these articles are not usually funded. When examining the original articles specifically, 15.2% of published original articles received funding. This funding rate is substantially lower than that in several other specialties, such as interventional radiology (23.0%)¹² and general radiology (26.9%).¹³ These findings are alarming, given that a positive relationship between funding and research productivity has been well established.¹⁴

The United States was the leading country in producing articles on neurointervention, contributing 31.1% of the publications. This relative contribution of the United States is less than that in radiology literature (45.5%).¹³ However, our figure is similar to the productivity in neurosurgery (31.7%) and stroke (27.2%) research of the United States.^15,16 Three Far East Asian countries—Japan, China, and South Korea—collectively accounted for 30.2% of publications. Although the cause of the high research productivity from these countries is likely multifactorial, state-of-the-art equipment and high standard training and education programs in these countries are possible key forces in this achievement.

An interesting feature of our study was that 3 major departments published a relatively small portion (57.8%–69.9%) of articles in their own specialty journals. We surmise that most journals related to neurointervention have an open spirit, providing a publication opportunity for researchers from other disciplines. One of the current trends in scientific publication is publication across disciplines. Several recent studies have addressed the evolution of the departmental affiliations of primary authors in many disciplines.^17⇓–19

Another interesting finding of the study was that half of the publications were the result of interdisciplinary collaboration. Although little attention has been paid to interdisciplinary collaboration in medical research, research on the neurointerventional therapy of cerebrovascular disease can be classified as a high-collaboration area at the specialty level. Many possible explanations exist for this interesting finding. First, some of these authors might even have multiple backgrounds or different specialties. The senior or corresponding author is often the person who plays the most important role on the research team. Second, interdisciplinary collaboration in research may reflect interdisciplinary collaboration in clinical practice for the neurointerventional therapy of cerebrovascular disease. However, it is unclear how many neurointerventional procedures are currently performed by each specialty. Finally, the size of the research group is increasing on all levels—the total number of authors, departments, institutions, and countries. The large research group has clear advantages for funding and other resources in biomedical research.²⁰

Although the results of our study revealed that neurosurgeons, radiologists, and neurologists contributed in important ways to publications relating to neurointervention, we found several interesting differences in the publication pattern among specialties.

First, radiologists produced more original articles, neurosurgeons published more case reports and technical notes, and neurologists published more review articles. In addition, neurologists published their findings in journals with higher Impact Factors. Although it may be tempting to conclude that neurologists' research is superior to that of radiologists and neurosurgeons and, thus, is accepted by more prestigious journals, an alternative explanation is that neurologists published more articles in multidisciplinary journals that have more readers and higher journal IFs. Second, the funding rate of neurology (15.2%) was significantly higher than that observed for radiology (8.7%) and neurosurgery (6.8%). The exact cause of this disparity in funding is unclear and is likely multifactorial. Third, the specialty of the authors who published articles on this topic varied according to the country of origin. For instance, most articles originating from the top 4 most productive countries were published by neurosurgeons. Different national patterns of research output may indicate different clinical practice patterns if research precedes clinical adoption. Last, our results showed more collaboration in publications by first authors affiliated with departments of neurology (65.6%) than those affiliated with departments of radiology (53.1%) and neurosurgery (41.3%). A possible explanation for this finding may relate to the staff composition of neurointerventional centers. Neurologists may be a rather small group in the research team or may have a less prominent role in clinical research.

Several limitations in interpreting the results of this bibliometric study should be kept in mind. First, this study is limited to only articles indexed within the PubMed data base, which does not index all research. While PubMed is generally considered a comprehensive and trusted resource, any bias in PubMed indexing of articles could have potentially influenced the results. Second, it is difficult to identify publications that focus on neurointervention because of its broad nature and varied terminology. Consequently, some articles pertaining to the neurointerventional treatment of cerebrovascular disease may have been excluded accidentally. However, the goal of this study was not to capture all neurointerventional research but rather to examine a large representative sample. Finally, the assignment of the clinical specialty and country was based on the affiliation of the first author. Many publications in our data are the product of a collaborative effort among different specialties or countries, so assigning articles to 1 specialty or country is inherently difficult. However, several studies^21,22 have determined that first authors make the greatest contributions to the research and are considered the best means of assigning credit.