29.1 Introduction

Surgical training methods have evolved significantly over the last century. Early training was through an informal apprenticeship model, characterized by observation at the side of the “master.” The trainee’s appointment was by mutual agreement, the duration of the experience was often open ended, technical “hands-on” training was not assured, and cost was generally borne by the trainee. The development of formal residency programs allowed for more structured training, though pyramidal programs were initially common, in which a certain number of trainees showing inadequate progress would be dismissed annually.s. Literatur In order to create consistency, governing boards were established to provide training oversight and certification of graduates. Over time, the benefit of formalized instruction has been reinforced, in part, by relationships that have been identified between training and postoperative outcomes.s. Literatur ^,​ s. Literatur This chapter will provide an overview of the past, present, and potential future of vestibular schwannoma (VS) microsurgical training, as well as insight into the advantages of a focused surgical education regimen.

29.2 History of Vestibular Schwannoma Surgical Training

Surgical resection has historically been the standard of VS management. However, initial attempts at tumor extirpation were fraught with complications. Limitations in visibility, aseptic technique, anesthetic care, and hemostasis led to significant perioperative morbidity and mortality.s. Literatur Through the work of pioneering neurosurgeons such as Harvey Cushing, Walter Dandy, and Vilhelm Magnus, mortality rates dropped significantly. Consequently, questions began to arise regarding the factors associated with the improvement in outcomes. When visited by Magnus in 1928, Cushing was reported to have “had harsh judgment to pronounce on those surgeons who without the requisite experience undertook these operations, which in the hands of an inexperienced surgeon were desperate remedies indeed.”s. Literatur Over time, standardization emerged in terms of surgical approaches, operative techniques, and perioperative management, leading to widespread improvements in postoperative outcomes.

As in any medical discipline, new advances alter the existing management paradigm. In the early 1960s, largely through the efforts of William House, transtemporal approaches to the lateral skull base were refined. The operating microscope was introduced into tumor resection, and electrophysiology of the auditory and vestibular system was also developed, augmenting the breadth of knowledge in the nascent field of neurotology. As mortality rates associated with VS microsurgery steadily dropped, emphasis was placed on the reduction of morbidity.s. Literatur ^,​ s. Literatur ^,​ s. Literatur Specifically, postoperative cranial nerve function became paramount. Increased attention was given to facial nerve outcomes, postoperative vestibular rehabilitation, and techniques to preserve hearing with tumor removal, reinforcing the importance of comprehensive, specialized training in lateral skull base surgery.

29.3 Modern Training for Vestibular Schwannoma Surgery

Demand for training in lateral skull base surgery naturally led to the expansion of training opportunities. Many early neurotologists obtained their experience under the tutelage of Dr. William House, participating in the fellowship sponsored by the House Ear Institute.s. Literatur By the late 1980s, there were approximately 30 fellowships in otology with differing amounts of emphasis on treatment of lateral skull base tumors. Efforts to standardize neurotology training began in response to the large number of fellowship programs and a subspecialty certificate in neurotology was approved by the Accreditation Council for Graduate Medical Education (ACGME) in 1995. Accreditation of training programs required a 2-year training period with concentrated experience in lateral skull base surgery. Key elements for accreditation included association with a residency program, board-certified faculty, adequate case volume for trainees, and available time for research. The first certification examination was given in 2004 with a 10-year time-limited certificate. Established practitioners were eligible for certification early in the process, but now certificates are only issued to graduates of accredited programs. At present, there are 19 accredited programs, producing between 14 and 16 fellows annually. Nearly all fellowship positions are filled through a subspecialty match.

The ACGME has established minimum case numbers for neurotology fellows that include performance of 25 lateral skull base approaches, 20 tumor resections, 2 temporal bone resections, and 10 repairs of skull base defects with local tissue flaps or grafts. Other skull base cases, including repair of cerebrospinal fluid otorrhea and repair of superior canal dehiscence, account for another five cases. Clinical experience requires the diagnosis of 20 VSs, 3 temporal bone paragangliomas, and 2 facial nerve tumors.

Despite the established minimums, the emphasis in residency training is not on total number of cases, but rather on proficiency in achieving technical, professional, and cognitive milestones. The adoption of this form of analysis recognizes that trainees do not display equal ability to learn. Some trainees are “naturals” who rapidly internalize surgical concepts and can mimic techniques readily. Others who are less adept take longer to achieve proficiency despite a larger volume of cases. In either case, the ability of the trainee to gather, integrate, communicate, and apply data to clinical practice may best predict commitment to self-assessment and continued process improvement.

Though the American Board of Neurologic Surgery (ABNS) does not have provisions for subspecialty certification, fellowship training in skull base surgery is available following neurosurgery residency. The Society of Neurological Surgeons (SNS), often referred to as the “Senior Society,” serves as an accrediting body for neurosurgical fellowships in a variety of disciplines, including neurosurgical oncology and cerebrovascular surgery. Fellowships are generally 1 year in length, and candidates are required to have completed an ACGME accredited (or Canadian equivalent) neurosurgery residency. At present, there are eight neurosurgical oncology fellowships accredited by the SNS. Neurosurgical fellowships specifically focused on skull base tumor surgery are currently not separately accredited.

29.4 How Does Experience Affect Outcomes in Vestibular Schwannoma Surgery?

Unquestionably, dedicated training in skull base microsurgery can provide a wealth of experience with the complex anatomy and pathophysiology encountered during VS resections. With gradated autonomy of the learner, a more safe transition from strict observation to independent tumor resection can be achieved. As was initially noted by Cushing and Magnus, outcomes in VS surgery may be tied to surgeon experience. After it was established that facial nerve function could be preserved during VS surgery, research began to evaluate the factors that govern successful preservation. In 1996, Moffat et al reported a single center’s experience with 300 VS resections.s. Literatur When analyzing this cohort of patients, it became apparent that better facial nerve outcomes were achieved with increasing surgeon experience. In particular, it was noted that 52% of the first 50 consecutive surgical patients in this center achieved a House–Brackmann (HB) grade I–III, while 92% of the last 50 patients evaluated had equivalent facial outcomes in the absence of a significant difference of tumor size between the two groups. Moreover, it was noted that the learning curve was more pronounced with the translabyrinthine approach relative to the retrosigmoid approach, though more recent work has identified that the existence of a learning curve is not necessarily approach-specific.s. Literatur Nearly 20 years following the aforementioned work, Moffat et al performed a follow-up study of 652 patients undergoing VS microsurgery from the same center to evaluate the factors that influenced postoperative facial nerve function.s. Literatur The positive correlation between experience and outcome was again observed, and specifically, it was noted that the learning curve was steepest for the first 50 cases performed through any approach. Additionally, it was reported that surgical patients were approximately four times more likely to have “satisfactory” facial nerve outcomes (HB I–III) following 10 years of surgeon experience. To quantify the learning curve further, research by Buchmans. Literatur and Welling,s. Literatur respectively, considered the number of cases that need to be performed to achieve consistently good postoperative facial nerve function. Welling demonstrated that HB I outcomes are more likely to be achieved after the first 20 surgical cases, whereas Buchman found that approximately 60 cases are needed before outcomes mirror those of more experienced teams. More recently, Wang et al utilized the cumulative summation test for learning curve (LC-CUSUM) to establish that approximately 56 cases are necessary before newly formed surgical teams are able to consistently achieve “satisfactory” outcomes (HB I–III).s. Literatur

Similar to facial nerve outcomes, many factors have been shown to influence rates of hearing preservation in VS microsurgery.s. Literatur With regard to surgeon experience, one study attempted to primarily evaluate trends in hearing preservation microsurgery over time at a single center. In 2001, Kanzaki et al reported on 127 hearing preservation surgeries over a 24-year period.s. Literatur All cases were performed through a middle cranial fossa approach using electrocochleography or auditory brainstem response for cochlear nerve monitoring. In the last 5 years of data collection, higher rates of Gardner–Robertson grade I hearing preservation were achieved on univariate analysis compared to rates for patients with earlier surgical dates (67 vs. 33%, p < 0.05). Though it is likely that surgeon experience does play a role in the probability of hearing preservation during VS surgery, the relative influence of this variable compared to tumor size, tumor location, surgical approach, and the quality of preoperative hearing remains unclear.

The experience of a particular hospital or surgical team likely plays a role in postoperative outcomes, as well. In 2004, Slattery et al evaluated the California Hospital Discharge Database (CHDD) for the period 1996 to 1998 to establish a relationship between hospital volume and VS microsurgical outcomes.s. Literatur Hospitals were categorized into four groups on the basis of the average number of VS resections performed annually. Patients undergoing surgery at the highest volume centers, performing an average of 185 cases per year, were 14.8 times more likely to have routine discharges from the hospital than those patients in centers performing 5 or fewer cases per year (95% confidence interval, 8.2–26.6). Similar findings were also reported by Mahboubi et al when evaluating the CHDD for the period 1997 to 2011.s. Literatur In Maryland, Ward et al found that VS patients undergoing surgery at a high-volume center had a lower likelihood of postoperative readmission as well as urgent or emergent admission.s. Literatur Also noteworthy was the finding that between 1990 and 2009, there was a decrease in the absolute number and relative percentage of cases treated at low-volume centers. It is suspected by the authors of this chapter that trends toward centralization of VS management will continue, and through these trends, multidisciplinary collaborations between neurosurgery, neurotology, audiology, speech pathology, vestibular therapy, facial plastic surgery, and radiation oncology will allow for the optimization of care for VS patients in the future.s. Literatur