The Practice of Skull Base Surgery: Assessing the Current Evidence, Progress, Knowledge Gaps, and Paths to Advance The Discipline for Improved Outcomes

In July 2019, the American Rhinologic Society (ARS) published the International Consensus Statement of Endoscopic Skull-Base Surgery – ICAR:ESBS.

The development of ICAR:ESBS was made possible by the efforts of a multicenter, multinational workgroup of the leading skull-base surgery experts in otolaryngology and neurosurgery. Leading the effort to develop this assessment and consensus statement on the current state of skull-base surgery was Eric W. Wang, MD, associate professor and vice-chair of clinical operations from the Department of Otolaryngology at the University of Pittsburgh School of Medicine, and a member of the multidisciplinary UPMC Center for Cranial Base Surgery.

Joining Dr. Wang in developing the ICAR:ESBS from the University of Pittsburgh and UPMC were Department of Otolaryngology colleague Carl H. Snyderman, MD, MBA, professor and vice-chair of quality and patient safety and director of the UPMC Center for Cranial Base Surgery, and Department of Neurosurgery colleague Paul Gardner, MD, who is the Peter J. Jannetta Professor of Neurological Surgery, executive chair of surgical services, director of the surgical neuroanatomy laboratory, and a director of the UPMC Center for Cranial Base Surgery.

More than 80 individuals contributed their time and expertise over a two-year period to develop ICAR-ESBS.

What is ICAR:ESBS?

The world of endoscopic skull-base surgery has advanced tremendously during the last 30 years. UPMC and the University of Pittsburgh are pioneering leaders in the development, use, and teaching of skull base surgery to multiple generations of surgeons worldwide. This work continues in an effort to achieve optimal patient outcomes for conditions affecting the skull-base.

Spanning more than 200 pages with more than 1,400 citations for analyzed research, this monumental effort clarifies and classifies the current evidence for endoscopic skull-base surgeries. ICAR-ESBS sheds light on endoscopic skull-base surgery's role for a number of indications that include primary cerebrospinal fluid (CSF) rhinorrhea, intradural malignancies, benign orbital and skull-based pathologies, sinonasal malignancies, and clival lesions.

What ICAR-ESBS Is Not

Dr. Wang and colleagues emphasize that ICAR-ESBS is not a clinical practice guideline for endoscopic skull-base surgery. ICAR-ESBS is a comprehensive analysis of the existing literature reflecting the current state of endoscopic skull-base surgery through a rigorous, critical appraisal of evidence levels for its use in hundreds of studies and case reports.

“ICAR-ESBS is an evidence-based assessment of endoscopic skull-base procedures. The reality is that this discipline is very much still growing and learning. ESBS has matured over the years and gained widespread adoption for a variety of indications. In other areas, its efficacy is still a gray area with much work to be done to validate its use,” says Dr. Wang.

Highlights From ICAR:ESBS

The expansive scope of ICAR:ESBS makes it difficult to summarize every aspect of its findings in this short article. However, Dr. Wang explains several highlights of note that should be of interest to both otolaryngology and neurological surgeons. 

Within ICAR:ESBS, each ESBS topic covered in the study is summarized in tables that detail the literature analyzed for each, the relative strengths and weaknesses of specific ESBS approaches for treating various conditions, and the grade level of evidence attributed to each indication. 

Clarifying the Issue of Spontaneous CSF Leaks

Spontaneous cerebrospinal fluid (CSF) leaks occurring in the absence of trauma, prior surgery, iatrogenic injury, or other precipitating factors, have been a vexing issue and one that is, according to Dr. Wang, becoming more prevalent. Spontaneous CSF leaks traditionally have affected more women than men. They are more common in people in their 40s or older, and obesity is a defined risk factor. Historically, there has been debate and discussion about the causes of spontaneous CSF leaks, including possible congenital dehiscences in the bone of the skull base that appear later in life as a spontaneous CSF leak.

"There has been significant debate in the past concerning the condition's etiology, the disease process, and causal implications beyond gender, age, and weight. Looking critically at the evidence related to spontaneous CSF leak, it appears to be a unique clinical entity associated with increased intracranial (IC) pressures and may be on the spectrum of idiopathic intracranial hypertension," says Dr. Wang.  

Section III of ICAR:ESBS outlines the issue of spontaneous CSF leak and its relationship to idiopathic intracranial hypertension (IIH). From an analysis of the existing literature, there is a strong indication that high IC pressures are associated with spontaneous CSF leaks.

While the causes and mechanisms are not entirely understood, the aggregate level of evidence supports a direct relationship between spontaneous CSF leaks and IIH.

"What this suggests, in general, and specifically for high-risk individuals, is that both surgical expertise and postsurgical control of intracranial pressure is paramount for achieving robust, long-term results," says Dr. Wang

The evidence assessment from the ICAR: ESBS strongly supports the clinical disease entity stemming from IIH. 

ESBS: Efficacy in Pituitary Surgery

Tumors affecting the pituitary gland – adenomas – are the most common tumors affecting the skull base for which ESBS techniques may be appropriate for well-selected patients. Similar to CSF leaks, pituitary surgery was an early area where ESBS was adopted and has increased evidence supporting its efficacy and safety.

ICAR:ESBS section IV documents the high rate of surgical success and low rate of complications when ESBS is used to treat pituitary tumors. Evidence from the literature shows high levels of improved visual outcomes and preservation of the pituitary gland. The evidence level for ESBS is less clear, however, with respect to posterior gland function, but it appears relatively comparable to other methods of pituitary tumor removal.

“With pituitary tumors, we see in the literature strong evidence in outcomes with ESBS. Surgeons can obtain good visual results while minimizing secondary dysfunction, which is critical to success,” says Dr. Wang.

Additionally, evidence surrounding reconstructions with ESBS for pituitary surgery is strong, showing low rates of associated cerebrospinal fluid leaks.

"It is likely that in 2020, in the United States, endoscopic procedures for pituitary tumors will continue to outpace microsurgical techniques. This shows the trend of improved outcomes with ESBS for pituitary surgery and higher levels of adoption of the technique by surgeons to achieve these improvements in outcomes. The evidence clearly supports the use of ESBS for pituitary cases." says Dr. Wang.

Identifying Knowledge Gaps

ICAR:ESBS uncovered strong evidence for the use of ESBS that is at least comparable to other approaches in managing CSF rhinorrhea and adenomas of the pituitary. ICAR:ESBS shows that both ESBS reconstructive techniques and the management of CSF leaks have markedly improved over the years. However, there still are many gaps or lack of strong evidence to support the use of ESBS for other pathologies or indications.

Outside of surgery for pituitary tumors and CSF rhinorrhea, the evidence for ESBS for other intradural or intracranial indications is lacking for understanding optimal patient selection parameters, risks around complications, and other areas. The same is true, broadly speaking, for sinonasal malignancies and clival tumors. There is still much work to be done in the area of reconstruction and complications despite significant improvements and advancements being made in these areas.

One factor contributing to the lack of evidence for ESBS to treat specific pathologies is simply the rarity of the conditions in question, which makes large scale studies or single-center trials that could theoretically be powered to provide definitive evidence on the use of ESBS exceedingly difficult to conduct.

In general, surgical trials are notoriously difficult to conduct. Layering into that equation rare diseases compounds the issue.

“I think what ICAR:ESBS shows is that in some respects, endoscopic surgery for skull-base pathologies has come a long way and can be considered a standard of care alongside or as a substitute to other approaches. More importantly, perhaps, stepping back and critically analyzing where we have been and what evidence we have accumulated shows a clear lack of supportive data or higher levels of evidence for many indications like sinonasal malignancies, clival tumors, and others,” says Dr. Wang. “Therefore, how do we overcome some of the limitations to expand our evidence base for ESBS? It will likely take extensive, multi-institutional collaborations to overcome the challenges in studying the use of ESBS for rare conditions.”

Moreover, Dr. Wang continues, collaboration will need to go beyond just partnering on trial designs and sharing data. As the authors of ICAR:ESBS indicate in their conclusion, for many of the pathologies for which ESBS is used or could be considered, there exist no standardized methods for reporting outcomes data on procedures. Overcoming these challenges will take a concerted and collaborative effort.

More About The UPMC Center for Cranial Base Surgery

To learn more about the UPMC Center for Cranial Base Surgery, or to consult with one of the faculty members about a patient case or to inquire about education opportunities for surgeons at UPMC and the University of Pittsburgh, please visit neurosurgery.pitt.edu/centers/cranial-base or call 412-647-6778.

Reference

Wang EW, Zanation AM, Gardner PA, et al. ICAR: Endoscopic Skull-Base Surgery. Int Forum Allergy Rhinol. 2019; 9: S145–S365. hps://doi.org/10.1002/alr.22326.

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