Part 1: Pushing the boundaries of neurointerventional surgery: A historical review of the work of Dr Gerard Debrun

Abstract

French-American neurointerventionalist and pioneer, Dr Gerard Debrun, laid the groundwork for treatments which have become irreplaceable in neurointerventional surgery today. This article aims to outline the career of Dr Debrun while highlighting his accomplishments and contributions to the field of neurointerventional surgery. We selected relevant articles from PubMed authored or co-authored by Dr Debrun between 1941 and 2023. All included articles discuss the accomplishments and contributions of Dr Debrun. Dr Debrun began his career in France by investigating neurointerventional techniques, most notably the intravascular Detachable Balloon Catheter (DBC). His work was recognized by renowned neurosurgeon Dr Charles Drake, who recruited him to London, Ontario. Dr Debrun created the foundation for homemade manufacturing of DBCs, building on one of the largest series for use of DBCs in cerebrovascular disease. Dr Debrun spent time as faculty at Massachusetts General Hospital (MGH) and Johns Hopkins Hospital, before arriving at the University of Illinois Chicago (UIC) where he remained until his retirement. Dr Debrun's subsequent contributions included the calibrated-leak balloon catheter, pioneering of glue embolization, setting the foundation for preoperative AVM embolizations, and as an early adopter of the Guglielmi detachable coil (GDC), including mastering the balloon remodeling technique for wide neck aneurysms. Dr Debrun established the first integrated neurointerventional surgery program at UIC, establishing a well sought-after fellowship program. Dr Debrun lectured extensively and was a prolific writer on neurointerventional surgery throughout this career. His contributions established the foundation for several techniques which have since become standard practice in present-day neurointerventional surgery.

Introduction

Neurointerventional surgery gained a significant role in the treatment of cerebrovascular disorders following its expansion in the 1970s. Cerebral angiography, a staple in the arsenal of the neurointerventionist, can be traced back to as early as the 1920s. The revolutionary advancement was first introduced by Portuguese neurosurgeon Antonio Caetano de Abreu Freire Egas Moniz, who experimented with the implementation of various contrasts to view cerebrovascular architecture via X-ray. The introduction of cerebral angiography provided the framework from which all subsequent advances in neurointerventional surgery would occur. ¹ Over the next 100 years, neurointerventional surgery benefited from significant progression, with each breakthrough establishing a foundation for subsequent discoveries. In 1939, Werner et al. introduced what is considered to be the first endovascular treatment of a large, cavernous carotid aneurysm where intra-aneurysmal occlusion was achieved via silver wire. ² Twenty-five years later in 1964, Luessenhop and Velasquez successfully performed the first micro-catheterization for temporary balloon occlusion of a posterior communicating artery aneurysm. ³

In the 1970s, Dr Gerard Debrun of Hôpital Universitaire Henri-Mondor in Paris began the development of a detachable latex balloon catheter (DBC) technique for the treatment of carotid-cavernous fistulas and giant intracavernous aneurysms. ⁴ His work had been influenced by prior advancements in balloon catheters introduced by Soviet neurosurgeon Dr Fedor Serbinenko. Throughout the 1970s, DBC technology experienced notable expansion, becoming a valuable treatment option for arteriovenous fistulas and cerebral aneurysms until eventually being replaced by the Guglielmi coil in the 1990s. Neurointerventional surgery entered its modern era with the advent of the Guglielmi detachable coil (GDC), developed at UCLA by Italian neurosurgeon Guido Guglielmi. The detachable coil set the basis for many technological advancements used in endovascular neurosurgery today. ⁵

Towards the end of the millennium, Dr Debrun joined the faculty at the University of Illinois Chicago (UIC). As a distinguished neurointerventional surgeon, Dr Debrun helped start the neurointerventional program at UIC, bringing his expertise in the detachable balloon catheter, arteriovenous malformation (AVM) glue embolization, and other endovascular interventions. Throughout his career, Dr Debrun authored and oversaw the publication of over 520 articles and book chapters. The objective of this article is to discuss Dr Gerard Debrun's contributions to the field of neurointerventional surgery and discuss the progression of his work as it established a foundation for future advancements (Figure 1).

Figure 1.

Historical timeline detailing the contributions and accomplishments of Dr Debrun throughout his career.

Methods

Our team selected relevant articles from PubMed authored or co-authored by Dr Debrun, his colleagues, or articles that influenced or were influenced by his work between 1941 and 2023. Various blueprints and patents by Dr Debrun from the archives at UIC were reviewed. All included articles discuss the accomplishments and contributions of Dr Gerard Debrun to the neurointerventional surgical communities.

Discussion

Hôpital Universitaire Henri-Mondor, Paris, France (1960s–1979)

Dr Gerard Debrun received his training in interventional radiology in France where he subsequently became a faculty member at the Hôpital Universitaire in Paris. Throughout the beginning of his tenure at the Hôpital Universitaire, Dr Debrun published extensively on various pathologies requiring the use of interventional radiology techniques. These techniques included arteriography, encephalography, and lymphangiography for use in various disorders and neoplasms of the brain, spinal cord, cardiovascular system, abdomen, lungs, kidneys, and liver. Dr Debrun would eventually focus his investigative efforts on cerebrovascular lesions including, but not limited to, carotid-cavernous fistulas (CCFs), vertebro-jugular fistulas, AVMs, and cerebral aneurysms. During this time, he would begin developing a new type of balloon catheter for the treatment of cerebrovascular lesions.

In 1974, Soviet neurosurgeon Dr Fedor Serbinenko introduced a monumental study in neurointerventional surgery reporting the use of balloon catheters in the occlusion of cerebral vessels in over 300 patients. ⁶ In this study, Serbinenko had employed balloon catheters of varying sizes to occlude the internal carotid artery (ICA), up to the branches of the anterior (ACA), middle (MCA), and posterior cerebral arteries (PCAs). The balloons could be used to temporarily or permanently occlude a vessel depending on the pathology being treated. The use of balloon catheter occlusion of intracranial vessels avoided various existing complications at the time such as decreased cerebral blood supply or undesirable carotid sinus reflex reactions. ⁵

Concurrently, Dr Debrun had been developing his own form of DBC for the treatment of CCFs and vertebro-jugular fistulas. Debrun's detachable catheters were completely homemade, as well as sterilized in-house (Figure 2(a)). He had designed many different molds for the balloons that varied based on size, length, and material, allowing for the personalization of treatment (Figure 2(b)). Based on the patient, their lesion, and subsequent anatomy, Debrun would use the appropriately sized mold to make the most efficacious balloon.

Figure 2.

(a) Dr Debrun's homemade detachable balloon catheters, made and sterilized in-house (Gerard Debrun: Treatment of carotid cavernous and vertebral fistula), Vascular Malformations, edited by R. R. Smith, A. Haerer and E. F. Russel. Raven Press, New York, 1982). (b) Dr Debrun's hand-written design blueprints for the many different balloon molds, varying based on size, length, and material (Courtesy of Department of Neurosurgery).

In 1974, Debrun published a preliminary study discussing results from implementing this unique DBC mechanism in occlusion of CCFs in rabbits. Debrun's DBC mechanism differed from Serbinenko's in that it involved a small latex cover at the end of polyethylene catheters, which could be inflated with simple iodine and released via a thin latex string attached at the base. This DBC enabled occlusion of CCFs and vertebro-jugular fistulas from within the venous side of the fistula while removing the original guiding catheter and preserving ICA flow. In 1975, Dr Debrun traveled to the Burdenko Neurosurgery Institute in Moscow, Russia to collaborate and learn from Serbinenko, leading him to implement components from Serbinenko's research into his own projects. Later that year, Dr Debrun published a study discussing the successful implementation of his latex DBC in the occlusion of CCFs in dogs. This study also demonstrated partial success in implementing the balloon catheter in the treatment of a patient with a vertebro-jugular fistula. ⁷

In 1978, Dr Debrun published a study discussing his findings from DBC implementation in human patients and the advantages/disadvantages encountered with this technique. The study distinguished the efficacy of type I and type II DBCs and the selective purpose for each. ⁸ Type I catheters, like those originally used by Serbinenko, involved a balloon which was not firmly attached to the catheter, was not self-sealing, and detached without requiring a second catheter (Figure 3(a)). Type I catheters posed the risk of detaching prematurely and damaging the vascular lesion, as earlier versions did not have the balloon physically tied to the catheter. Debrun employed type II catheters, which were notably more durable and did not carry the risk of detaching prematurely but required the use of a second catheter to detach the balloon (Figure 3(b)). Using this technique, Debrun and his faculty treated 20 patients with CCFs, 17 of which were post-traumatic. All patients were treated successfully with only one complication and no mortality. In addition, three patients with vertebro-jugular fistulas were also successfully treated with DBCs, all three being asymptomatic at the time of follow-up. ⁸ Debrun's popularization of the use of DBCs in the treatment of CCFs led to its adoption and widespread use at various institutions around the world, leading to multiple publications reviewing the technique.^9,10

Figure 3.

(a) Type I catheters had a detachable balloon which was not firmly attached to the catheter, was not self-sealing, and detached without requiring a second catheter. (b) Type II catheters were notably more durable and did not carry risk of detaching prematurely, but detachment required the use of a second catheter. (Gerard Debrun: Treatment of Carotid Cavernous and vertebral fistula), Vascular Malformations, edited by R. R. Smith, A. Haerer and E.F. Russel. Raven Press, New York, 1982).

Comparatively, various challenges were encountered in the use of DBCs for cerebral arterial aneurysms. Crucially, the balloon was unable to spontaneously enter an aneurysm, as it had with AV fistulas, leading to the risk of leaking when attempting to keep the balloon inflated. More importantly, inflating the intrasaccular balloon to match the aneurysmal volume was difficult and posed significant risk of aneurysmal rupture. This was because it was incredibly difficult to keep the balloon volume consistent with the aneurysm volume to prevent leakage. Of the 14 carotid aneurysms treated, two patients died, and two patients experienced hemiplegia as a complication. ⁸

An additional cerebral lesion where treatment with DBCs was proposed to be advantageous was cerebral AVMs. At this time, complete surgical resection of the malformation was the preferred intervention; therefore, this technique was reserved for cases where surgery was contraindicated. When treating endovascularly, two balloon types could be used. The first was a single-lumen catheter with a detachable, graduated-leak balloon, while the second was a twin-lumen balloon catheter. In the treatment of cerebral AVMs, the first type of catheter was preferred, as the polymerizing agent had a propensity to stick to the catheter of the first type, preventing withdrawal. ⁸

University Hospital, London, Ontario, Canada (1979–1981)

Debrun's work was unparalleled in the world at the time and eventually became recognized by renowned vascular neurosurgeon Dr Charles Drake, who recruited him to the Department of Surgery at the University of Western Ontario in 1979. As Director of Neuroradiology at the University of Western Ontario, Dr Debrun continued his efforts in developing and expanding the applications of the DBC in collaboration with fellow faculty members, Dr Sydney Peerless and Dr Fernando Vineula.

Up until this point, Debrun had been designing and creating the molds for the balloon catheters by himself, without the assistance of manufacturers. In 1979, Polish engineer Leopold Plowiecki of the medical device company Balt Extrusion, would be one of the first to commercially manufacture balloons and their delivery catheters with the help of Dr Serbinenko and Dr Merland from Paris. ¹¹ The Gold Valve detachable balloon was one of the first name-brand balloons available, although this balloon is no longer available in the United States. After this, the Gold Balloon was created by Balt and would become available for use in Europe, becoming one of the only commercially available detachable balloons on the market due to its flexibility for use with various microcatheters. The commercialization of balloon catheters allowed for the continued popularization and use of this technique all around the world.

In 1981, Debrun and his colleagues published a comparison of outcomes between three approaches for detachable balloon occlusion of CCFs: (a) endarterial route; (b) venous route through the jugular vein, the inferior petrosal sinus, and the cavernous sinus; or (c) surgical exposure of the cavernous sinus. ¹² The publication proposed superiority of the endarterial approach due to reduced invasiveness and superior rates of CCF occlusion when compared to the transvenous or open approaches.

A study conducted by Debrun in 1982 corroborated the use of systemic heparinization and aspirin as a premedication strategy in 82 patients undergoing embolization with detachable balloons for prevention of embolic complications. ¹³ At this time, many were assessing the efficacy of heparin-coated catheters and systemic heparinization for use in peripheral endovascular procedures. This study reported the use of premedication with salicylates and systemic heparin in 57 consecutive cases with no thromboembolic complications. When compared against catheter infusion of heparinized saline and aspirin solution (four complications in 25 cases), superiority in premedication with salicylates and systemic heparinization was observed. This led to the proposal of instituting premedication with salicylates and systemic heparin as standard procedure for all prolonged angiographic procedures. ¹⁴ It is now the gold standard to continually flush the endovascular system with heparinized saline, as well as supplementing with the addition of systemic heparinization to decrease clot formation inside the system.

As one of his final projects before being recruited to Massachusetts General Hospital, Debrun conducted a study in 1981 investigating the use of a new type of detachable calibrated-leak balloons for the selective embolization of dural AVMs. The mechanism of a calibrated-leak balloon refers to a leak through the tip of the balloon once it has been inflated to a particular pressure. As the pressure of the balloon continues to increase, the tip will open, allowing for the leakage of contrast material or embolizing agent. ⁸ Experimental testing was initially performed via isobutyl-2-cyanoacrylate (IBCA) embolization of the external carotid artery (ECA) branches in 13 dogs and three patients using a novel system consisting of a small latex balloon attached to a Teflon catheter.^15,16 This novel detachable balloon catheter system differed from the non-detachable, silastic calibrated-leak balloon previously used in IBCA embolization of AVMs by Kerber in 1980. ¹⁷ In 1982, Debrun and his team published a report on 11 out of 46 cases where IBCA embolization was performed via the new detachable calibrated-release balloon catheter. No dissection or rupture of the catheterized artery was observed in this group. ¹⁸ The detachable calibrated-leak balloon system proved to be effective in allowing superselective catheterization of the distal branches of the ECA, while minimizing the risk of dissection and vasospasm. ¹⁶ The calibrated-leak balloon is a balloon attached to the microcatheter with a hole in the distal part of the balloon. IBCA will be injected into the balloon itself, where it will distend the balloon, create a flow arrest, and gradually leak into the distal vascular bed, causing embolization of the lesion, without having the risk of embolization into the lung. The balloon could be detached in place or retrieved depending on the pathology. The capability of this delivery system to catheterize distal branches of the ECA validated IBCA embolization as an alternative to embolization with particles. The liquid property of IBCA facilitated embolization of the AVM nidus, a task which was challenging to accomplish with particle embolization. ¹⁶

Massachusetts General Hospital, Boston, MA (1982–1986)

In 1982, Dr Debrun became chairman of the Division of Neuroradiology at MGH where he worked in collaboration with the cerebrovascular neurosurgical faculty led by Dr Roberto C. Heros. At MGH, Dr Debrun continued the development of the calibrated-leak balloon, improving techniques for supra-selective embolization of cerebral AVMs. While at MGH, Dr Debrun investigated on the use of IBCA as a potential obliterating agent for cerebral aneurysms. The study involved the injection of IBCA into experimental cervical carotid aneurysms in 11 dogs. ¹⁹ Prevention of reflux of IBCA into the artery was proposed by inflating either a latex or a Silastic balloon in the carotid artery at the level of the neck of the aneurysm. The study found that aneurysms arising from the straight portion of an artery could be obliterated successfully with IBCA if a rigid Silastic balloon fully occluded the neck of the aneurysm during the injection of IBCA. Newer latex balloons were not rigid enough and bulged through the neck of the aneurysm, therefore allowing reflux of IBCA into the artery.

Additional investigations assessing the use of detachable balloons in the administration of pharmacological agents, such as 1,3-bis(2-chloroethyl)-N-nitrosourea (Carmustine, BCNU), were conducted at MGH under Debrun. ²⁰ The chemotherapeutic agent, BCNU, had been used extensively in the treatment of glioblastoma by catheter injection into the cervical portion of the ICA. Unfortunately, a complication frequently encountered with this technique was ipsilateral pain and blindness due to backflow of the chemotherapeutic agent. Debrun tried to subvert these complications by administering the BCNU above the ophthalmic artery via calibrated-leak catheters, thus preventing backflow. ²¹ The technique was tested in a cohort of 10 patients, none of whom developed subsequent ocular complications.

Johns Hopkins University, Baltimore, MD (1986–1995)

In 1986, Dr Debrun was recruited to the Department of Neuroradiology at Johns Hopkins where he continued his focus on the treatment of CCFs and aneurysms. One study analyzed the endovascular treatment of unclippable cerebral aneurysms using DBCs for proximal artery occlusion. In the reported series, 37 had carotid artery aneurysms below the level of the ophthalmic artery, 21 aneurysms arose from the supraclinoid portion, six at the basilar artery trunk, and one distal vertebral artery aneurysm. Of the 68 patients with unclippable aneurysms, permanent occlusion was obtained in 65. All 37 patients with aneurysms below the level of the ophthalmic artery were found to have complete obliteration of the aneurysms. ²² These results showed that balloon occlusion of the proximal arteries is a safe and effective technique for the treatment of unclippable aneurysms. One limitation of this study was the inability to use the balloon occlusion technique in the supraclinoid carotid artery, distal vertebral artery, or higher segments due to the immense risk of occluding a perforating artery and causing a major infarction.

In 1988, Dr Debrun published a seminal study assessing the optimal treatment for CCFs based on the Type A-D classification system introduced by Barrow et al. in 1985. ²³ This study provided evidence supporting the use of DBCs as the optimal treatment method for Type A fistulas (direct connection between the ICA siphon and the cavernous sinus through a single arterial tear) by obliterating the connection using the detachable balloon itself. Type B fistulas (fed by meningeal branches of ICA) were not encountered in the study. Type C fistulas (supplied exclusively by ECA feeder vessels) were better treated by embolization of the ECA branches. Type D fistulas (supplied by meningeal feeder vessels from both the ICA and ECA, often bilaterally) proved to be the most challenging, typically requiring the use of both embolization and an open, surgical approach. ²⁴ In 1989, Dr Debrun and his colleagues introduced a novel transvenous approach to the cavernous sinus conducted by advancing a detachable balloon catheter through the superior ophthalmic vein. They described the approach as a safe and effective treatment of CCFs in cases which were not suitable for treatment by standard techniques of endoarterial balloon occlusion or embolization. ²⁴

An issue that occasionally arose while treating CCFs was that a small proportion of the fistulas were unable to be treated by standard endovascular treatment alone. They required the assistance of some form of open surgical approach. This study showed the importance of collaboration between neurosurgery and interventional radiology. Debrun reported ten patients out of a cohort of 143 CCFs that required this assistance. ²⁵ The issues that led to the need of surgical services were categorized as follows: (1) incomplete closure of the fistula due to an issue with the balloon (deflation, migration) with ICA occluded (n = 3), (2) failure to occlude the fistula after both arterial and venous approaches were attempted (n = 1), (3) hairpin loop of cervical ICA (n = 1), (4) failure of previous trapping procedures (n = 3), and (5) failure to cure spontaneous CCF of the dural type and ECA embolization feeder vessels (n = 2). All 10 patients were treated appropriately, although complications, such as contralateral hemiparesis and ocular proptosis, occurred but eventually resolved in all patients. This case series showed that treatment of CCFs is complex, with each case presenting a unique challenge based on the anatomy of the fistula and its surrounding tissues and vessels. ²⁶ Another case study by Masaryk et al. in 1999 highlighted an alternative approach for a patient with a CCF in association with a persistent trigeminal artery. ²⁷ The authors performed a successful detachable balloon embolization with emphasis on the use of a second, non-detachable catheter that stabilized the first device at the time of detachment.

University of Illinois—Chicago, Chicago, IL (1995–2002)

Dr Debrun arrived at UIC in 1995, where he remained until the conclusion of his medical career in the early 2000. Faculty radiologist Dr Glen Dobbin and Neurosurgery Chairman Dr James Ausman played a large role in recruiting Dr Debrun. At UIC, Debrun became a faculty member of the Department of Neurosurgery, bringing in his NeuroInterventional expertise. Dr Debrun and Dr Ausman's partnership at UIC would internationally popularize NeuroInterventional surgery, making it state of the art.

All of the research that Dr Debrun conducted at UIC was done collaboratively between neurosurgery and interventional radiology. During his time here, Dr Debrun further researched the calibrated-leak balloon catheter, while also initially pioneering the use of glue embolization, and setting the foundation for the field of preoperative AVM embolization. Dr Debrun later focused on treatment techniques for wide neck aneurysms, as well as being one of the first ever to use the novel GDC, which had since replaced DBCs as the preferred standard of care. Dr Debrun mastered the balloon remodeling technique using the GDC, while publishing extensively on its use in wide neck aneurysms to promote the technique's efficacy in select cases.

Dr Debrun conducted a 15-year retrospective analysis of 233 cerebral AVMs that were treated with glue embolization. Overall, there were 936 superselective catheterizations of various feeder vessels. This represents one of the largest reports of sequential blood flow reduction in preparation for surgical resection of cerebral AVMs. Of note, Dr Debrun reported on 29 glued microcatheters. Of the 29 glued microcatheters, 27 showed no side effects. This study corroborated evidence that leaving a piece of the catheter in the AVM feeder is safe and usually does not have side effects or complications, although surgery can be conducted to retrieve the tubing if risk of thrombosis is present. ²⁸ The amount of retained catheters in this initial series represent the extent of aggressive embolizations that were performed at that time in large AVMs and has set the foundation for further practices of safe preoperative embolization of AVMs.

Dr Debrun later focused on the treatment of intracranial aneurysms using GDCs. Initially, the neurointerventional team at UIC aimed to categorize aneurysms to develop a criterion for their treatment, while minimizing morbidity and mortality. The geometry of 324 aneurysms that were treated with either GDC or surgically were analyzed to determine outcomes based on criteria considered prior to treatment. Their experience revealed that complete occlusion of an aneurysm using coils was most successful when the dome/neck ratio was more than or equal or to 2/1 and the neck diameter was 5 mm or less, revealing the importance of aneurysm geometry prior to intervention. ²⁹

Dr Debrun published a retrospective analysis on 72 patients at UIC in which balloon-assisted GDC placement had been performed for occlusion of wide-necked intracranial aneurysms. The paper proposed that the remodeling technique, involving release of coils with use of a balloon across the neck of the aneurysm to prevent coil efflux, offered an alternative treatment approach for aneurysms in which initial surgical attempts had been ineffective or for aneurysms that were surgically inaccessible or required challenging surgical approaches. Surgical intervention is also a viable option to treat aneurysms that have been previously treated by GDC placement, as well as those that are persistent or thrombosed. ³⁰ Dr Debrun would subsequently publish a follow-up on these patients in 2002 which demonstrated that the GDC technique was both an effective and safe treatment option for small and wide-necked intracranial aneurysms.^31,32

While at UIC, Dr Debrun and Dr Ausman established the first integrated neurointerventional surgery fellowship program in the United States between Neurosurgery and Radiology, establishing a well sought-after fellowship program. The popularization of neurointerventional surgery would not have been possible without the collaborative effort between neurosurgery and interventional radiology, which would emphasize its multidisciplinary approach, making it a new subsection under neurosurgery and the gold standard for many cerebrovascular pathologies by combining angiography and surgical techniques. ³³ The interplay between specialties raised the quality-of-care standards and emphasized collaborative decision-making, leading to patient-specific treatments and improved outcomes. Dr Debrun's tenure at UIC has been self-described as a distinctly gratifying period in his career due to open acceptance of his endovascular techniques and advancements (Figure 4). After his retirement, Debrun was succeeded by the late Dr Victor Aletich, who continued his legacy.

Figure 4.

Photograph of Dr Gerard Debrun, French-American neurointerventionalist and pioneer in endovascular techniques.

Conclusion

Dr Gerard Debrun is a renowned French neurointerventionalist who began his career at the Hôpital Universitaire Henri-Mondor in Paris. He specialized in the treatment of CCFs, vertebro-jugular fistulas, AVMs, and aneurysms by developing and using the latex DBC. The DBC would offer the first true alternative to the conventional but unfavorable practice of carotid occlusion in CCF treatment. Dr Debrun would go on to implement the DBC in aneurysm occlusion and the subsequent calibrated-leak balloon catheter in the selective angiography and embolization of AVMs. Dr Debrun created the foundation for homemade manufacturing of DBCs, building on one of the largest world series for use of detachable balloons in cerebrovascular diseases.

As his career progressed, he went on to join the faculty at MGH, Johns Hopkins and ultimately UIC, where he focused on techniques involving the novel Gugliemi detachable coil (GDC), which eventually replaced the detachable balloon catheter as the gold standard of care. Although often encountering resistance against his endovascular techniques across various academic institutions, his efforts towards advocating for the collaboration between neurosurgery and interventional radiology allowed for the use of conservative endovascular techniques, laying the groundwork for treatment options which have become irreplaceable in endovascular neurosurgery today.