Developing the Endovascular and Neurovascular Specialists of the Future

CAMERON G. MCDOUGALL

Training matters. As with other medical and surgical subspecialties, producing adequate numbers of individuals competently trained in endovascular surgical neuroradiology (ESN) requires creating an appropriate training infrastructure. The American Council for Graduate Medical Education (ACGME) defines ESN as “a subspecialty that uses catheter technology, radiologic imaging, and clinical expertise to diagnose and treat diseases of the central nervous system.” This subspecialty exists as a distinct entity because the ACGME recognizes that “the unique clinical and invasive nature of this subspecialty requires special training and skills.”¹ Inherent in this definition is the understanding that ESN is more than a set of technical skills. If ESN is to endure as a distinct entity, training programs must create not only competent clinicians for today’s needs but also thoughtful physicians capable of leading and developing the subspecialty in the future.

Questions regarding what constitutes a competently trained individual and how a trainee acquires such competency are considered in this chapter. The topics covered include a brief look at the development of ESN as a distinct discipline, a discussion of data that might influence the establishment of training standards, the standards as they currently exist, and finally, some thoughts regarding training objectives for the future.

It is clear that endovascular techniques are maturing into an integral component in the overall management of neurovascular disease. These techniques likely will continue to improve and be increasingly used in the near future. Previous chapters in this monograph have discussed the wide and expanding role of ESN. The impact of the changes brought about by endovascular techniques should not be underestimated. Currently about half of all cerebral aneurysms in North America and Europe receive endovascular treatment. Carotid stenting has recently been approved in the United States. Over time, it will replace carotid endarterectomy for most patients. Undoubtedly, stenting techniques will rapidly be adapted to the vertebral and intracranial arteries. Likewise, endovascular stroke therapies are increasingly promising for the treatment of acute ischemic stroke. Despite the short history of ESN, much has been accomplished, and there is every reason to expect even more rapid development in the future.

Endovascular techniques were first introduced in a report by Luessenhop and Spence in 1960.² Similar pioneering work was initiated in the former Soviet Union and in Europe by individuals such as Serbinenko³ and Debrun and coworkers,^4,5 who began to report their work in English language publications in the late 1960s and early 1970s. Simultaneously, in America, groups such as Hieshima and coworkers,⁶ Kerber and coworkers,^7,8 and Berenstein and Kricheff^9,10 were beginning to publish their own work on developing endovascular techniques for the neurovascular system. This novel situation of neuroradiologists treating neurovascular conditions previously managed by neurologists and neurosurgeons was the beginning of ESN. Fundamentally, the three specialties were linked in this endeavor because each possessed only a portion of the skills and knowledge necessary for clinical success.

Developing Training Standards

The definition of what constitutes training is always changing. In the United States, training requirements for a medical specialty or subspecialty typically are defined by the ACGME. These requirements are discussed later in this chapter. In practice, many specialty areas often find themselves at odds with one another with respect to the management of conditions that overlap specialty fields. In this setting, involved organizations often promulgate “guidelines” or “standards” that are believed to define accepted medical practices with respect to a given condition.

Inevitably, establishing training standards is controversial. There is no assurance that standards established by one specialty organization will be agreed to or respected by a second organization. Ultimately, a balance must be struck between ensuring clinical competency and the practical constraints of time, expense, and resources. Training must occur in an environment where adequate supervision is available to ensure that the well-being of patients is not compromised. Trainees must have adequate components of cognitive knowledge and technical expertise. Technical proficiency in ESN begins with mastery of cerebral and spinal angiography. All catheter-based neurovascular interventions begin and end with diagnostic angiography. Many of the risks of angiography overlap with those of the international procedures. In addition to the technical elements of performing angiography, interpretation of the diagnostic studies demands in-depth knowledge of neurovascular anatomy and pathology. With respect to the purely technical components of diagnostic neuroangiography, appropriate training and experience enhance the safety of this procedure. Permanent neurological deficits related to diagnostic cerebral angiography have ranged from 0.3 to 5.7%.^8,11–24

In a prospective study examining 1000 patients undergoing cerebral angiography, 1% of the patients suffered a neurological deficit, and the deficit persisted in half of them. This study was performed in a high-volume teaching hospital where the cerebral angiography was performed by dedicated neuroradiologists. In this study, 9 of 10 patients suffering neurological complications had a history of prior stroke or transient ischemic attack. This finding suggests that patients with clinically significant atherosclerosis have a significantly increased risk for neurological complications.¹⁵ Cases with neurological complications were also associated with increased procedural time and increased doses of contrast.

Addressing the learning curve for cerebral angiography, Dion et al noted that the fluoroscopy time needed for cerebral angiography decreased linearly until 100 diagnostic cases had been performed.¹¹ This finding is particularly relevant because operator risk factors for ischemic complications include increased procedural and fluoroscopy time, increased number of catheters used, and performance of arch aortography.^18,21 These factors are typically related to the operator’s experience. An analysis of 5000 angiograms showed that the neurological complication rate of fellowship-trained specialists is 0.5%; this is slightly less than that of nonfellowship-trained angiographers and much less than the 2.8% complication rate seen with trainees under supervision.^18–20

Evaluation of the complication rates associated with trainees suggests that an individual may need to perform 200 angiograms to gain sufficient clinical competence.¹¹ Learning curves are equally long for cerebrovascular interventions, for example, for carotid angioplasty and stenting²³ and coil embolization of intracranial aneurysms.²⁵

As a relatively new field of endeavor, the parent specialties of ESN have yet to establish specific training standards that require defined numbers of procedures. However, it is likely that these standards will develop as training needs become more refined. The American College of Radiology has published guidelines regarding standards for the performance of diagnostic cervicocerebral angiography in adults.²⁶

A collaborative panel of the American Society of Interventional and Therapeutic Neuroradiology, the American Society of Neuroradiology, and the Society of Interventional Radiology published explicit and detailed guidelines for the performance of cervical carotid angioplasty and stent placement.²⁷ As a prerequisite to carotid stenting, the recommendations require the operator to have sufficient angiographic experience to perform cervicocerebral angiography safely and to obtain appropriate stent training. The operator can meet the diagnostic portion of the training if he or she has performed at least 200 diagnostic cervicocerebral angiograms or alternatively 100 angiograms plus a documented experience in peripheral vascular interventions as required by the American Heart Association. After the requirements for cervicocerebral angiography have been met, carotid stent training can be accomplished with the following experience: noncarotid stenting (25 cases) plus a comprehensive carotid stenting course (16 hours) in addition to four supervised cases with acceptable outcomes. Alternatively, the trainee may perform 10 supervised carotid stent cases as the primary operator with acceptable success.

Parallels can be taken from other fields of expertise. Influential societies overseeing catheter-based coronary interventions, such as the American College of Cardiology (ACC), have acknowledged the learning curve involved in interventional procedures. The ACC requires individuals to complete diagnostic coronary angiography training before training for coronary interventions.²⁸ One year of dedicated training is mandated. During this time, the trainee must perform a minimum of 300 coronary angiograms, after which he or she may start training for interventional procedures. An additional 8 months and 250 procedures are required to complete the technical component of an interventional cardiology training program.²⁸

In a similar fashion, recent collaboration among neuroscience specialties has led to the recognition of the need for “adequate cognitive training” for those who would perform catheter-based cervicocerebral diagnostic and interventional procedures. This cognitive training includes four critical components: (1) formal training that imparts an adequate depth of cognitive knowledge of the brain and its associated pathophysiological vascular processes; (2) adequate procedural skill achieved by repetitive supervised training by a qualified instructor; (3) diagnostic acumen achieved by studying, performing, and correctly interpreting a large number of diagnostic procedures with proper tutelage; and (4) adequate diagnostic procedural skills and knowledge.

Although these principles—understanding the end organ, knowing how to recognize its pathological state, and possessing the technical abilities necessary to perform the required diagnostic and therapeutic procedures— may seem almost intuitive, specific criteria must be defined and met to achieve these laudable objectives. At the time of this writing, these specific criteria remain the subject of debate.

The American Council for Graduate Medical Education Training Requirements

In recognition of the complexity and level of specialization required to perform neurovascular interventions safely, the ACGME has recognized ESN as a distinct subspecialty. This recognition was propelled through years of effort on the part of many individuals, most notably R.T. Higashida, L.N. Hopkins, A. Berenstein, V.V. Halbach, and C. Kerber.^1,29 Although debate continues regarding training standards for particular components of ESN, the ACGME has defined training program requirements for this subspecialty. The training requirements as stated in this document are the result of a consensus among specialties and they may require modification over time.

Details of the ACGME training requirements are available online.¹ The program permits entry to appropriately trained individuals from a background of neurology, neurosurgery, or neuroradiology. All candidates are required to have at least 12 months of training, preferably consecutively, in neuroradiology. The details of the objectives for this “preparatory training” before starting an ESN fellowship are itemized by the ACGME on the downloadable document. During this period of preparation, candidates must gain skills and knowledge in catheter techniques. Both neurosurgical and neurology candidates must acquire a minimum of 3 months training in basic radiology skills. Neurology candidates also must complete a minimum of 3 months of neurosurgical experience and have completed an ACGME-accredited 1-year vascular neurology program. Neuroradiologists must spend 3 months of clinical experience in an ACGME-accredited neurological surgery program. Some of these preparatory requirements may be obtained during electives throughout the respective residency programs.

With respect to the 1-year requirement for ESN after the preparatory year, the specific details again can readily be reviewed online or downloaded.¹ The program requires training and experience in the following areas: signs and symptoms of disorders amenable to diagnosis and treatment by endovascular surgical neuroradiology techniques, neurological examinations to evaluate patients with neurological disorders, the pathophysiology and natural history of these disorders, the indications and contraindications to endovascular surgical neuroradiology procedures, the clinical and technical aspects of endovascular surgical neuroradiology procedures, medical and surgical alternatives, preoperative and postoperative management of endovascular patients, neurointensive care management, the fundamentals of imaging physics and radiation biology, and the interpretation of radiographic studies pertinent to the practice.

Training that includes instruction in the material relevant to ESN under the following categories is also required: basic anatomical and physiological knowledge; technical aspects of endovascular surgical neuroradiology; pharmacology; the coagulation cascade; brain and spinal cord arteriovenous malformations; fistulas of the brain, spine, and spinal cord; head and neck vascular malformations; ischemic stroke; cerebral aneurysms; tumors of the head, neck, spine, and central nervous system; revascularization for occlusive vascular diseases; embolization for epistaxis or other causes of hemorrhage; invasive functional testing; and balloon test occlusion.

The sponsoring institution must have a patient population sufficient to provide a variety and experience commensurate with the training objectives. The minimum number of therapeutic endovascular surgical neuroradiology procedures required by the ACGME to provide this experience is 100 cases per year.

Considerations for the Future

In the end, the inescapable conclusion is that ESN is a clinical subspecialty. It involves the management of patients with neurovascular and related diseases. Practitioners cannot effectively work as technicians and leave the clinical decision-making to allied clinicians. Rather they must accept an equal role with other neurovascular team members, and as such, they must be fully responsible for their treatment decisions. This can only happen if trainees are equipped with sufficient clinical skills to allow them to make sound decisions. Conversely, if training programs focus excessively but narrowly on the procedures or the technology alone, the larger picture will be missed. Although the subspecialty is driven by technology, it is essential to avoid being seduced by technology: Technology is not the end goal, it is only a means to the end. The goal is continual improvement in patient care. Residency and fellowship programs must fashion specialists who are knowledgeable about the conditions that they treat, comfortable with the latest techniques in treating these conditions, and confident enough to develop ever more innovative therapies for the betterment of our patients.

Acknowledgment

The author is greatly indebted to J. J. Connors III for his assistance in preparing this manuscript.

References

1. Program ACGME. Requirements for Residency Education in Endovascular Surgical Neuroradiology. Chicago, IL: American Council for Graduate Medical Education; 2003. Available at: www.acgme.org/acWebsite/downloads/RRC_progReq/422pr403.pdf. Accessed December 15, 2005

2. Luessenhop AJ, Spence WT. Artificial embolization of cerebral arteries. Report of use in a case of arteriovenous malformation. JAMA 1960;172:1153–1155

3. Serbinenko FA. Balloon catheterization and occlusion of major cerebral vessels. J Neurosurg 1974;41(2):125–145

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5. Debrun G, Lacour P, Caron JP, et al. Detachable balloon and calibrated-leak balloon techniques in the treatment of cerebral vascular lesions. J Neurosurg 1978;49(5):635–649

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7. Kerber C. Balloon catheter with a calibrated leak. A new system for superselective angiography and occlusive catheter therapy. Radiology 1976;120(3):547–550

8. Kerber CW, Cromwell LD, Drayer BP, Bank WO. Cerebral ischemia. I. Current angiographic techniques, complications, and safety. AJR Am J Roentgenol 1978;130(6):1097–1103

28. Creager MA, Cooke JP, Olin JW, et al. Revised Recommendations for Training in Adult Cardiovascular Medicine Core Cardiology Training II (COCATS 2; Revision of the 1995 COCATS Training Statement). Bethesda, MD: American College of Cardiology; 2003. Available at: http://www.acc.org/clinical/training/COCATS2.pdf.6-4-2003 Accessed December 15, 2005

29. Higashida RT, Hopkins LN, Berenstein A, Halbach VV, Kerber C. Program requirements for residency/fellowship education in neuroendovascular surgery/interventional neuroradiology: a special report on graduate medical education. AJNR Am J Neuroradiol 2000;21(6):1153–1159