Original ArticleMinimally Invasive Endoscopic Supracerebellar-Infratentorial Surgery of the Pineal Region: Anatomical Comparison of Four Variant Approaches
Introduction
The supracerebellar-infratentorial (SCIT) approach is an effective method to access pathology of the posterior incisural space. The midline SCIT approach was originally reported by Victor Horsley in 1910 (10) and popularized by Stein et al. for pineal region tumors 17, 18. Several variations with progressively more lateral extensions have since been described: Yaşargil performed a paramedian SCIT approach for cavernomas of the parahippocampal gyrus (23), and Van den Bergh et al., as well as our group, described the extreme lateral SCIT approach for pineal region tumors and cavernous malformations 21, 22. Although microscope-controlled and endoscope-assisted methods have been mainstays of neurosurgical utility for access (3), as approach-related morbidity and brain retraction injury have become increasingly recognized (16), minimally invasive access to the pineal region using a fully endoscopic approach has steadily gained acceptance and reliability. Ruge et al. described the first purely endoscopic SCIT approach for fenestration of quadrigeminal region arachnoid cysts (13), and our group described the first successful case of a fully endoscopic SCIT resection of a pineal cyst 9, 20. Several groups have since validated this approach for various intracranial lesions of the pineal region (15). This approach requires a smaller skin incision and craniotomy, and the endoscope can be tunneled to the pineal region with minimal brain retraction while providing excellent illumination and visualization, particularly around corners. However, a narrow working space and instrument conflict when manipulating critical neurovascular structures with endoscopic tools are often sources of great frustration for surgeons new to this method.
Surgical freedom is an increasingly important concept in endoscopic skull base surgery and is defined as the ease by which the surgeon can move the hands when manipulating instruments in the operative field 4, 5. Restricted surgical freedom can result in increased surgeon fatigue and frustration, increased operative time, and limitations on the ability to perform delicate intraoperative tasks 4, 5, 24. Our personal experience has taught us that surgical freedom for endoscopic SCIT approaches varies, depending on both the anatomical target and the medial to lateral location of the craniotomy. To date, there have been no rigorous assessments comparing the surgical freedom afforded by different permutations of the endoscopic SCIT approach. Additionally, no group has directly compared the endoscopic SCIT approach to the microscopic SCIT approach. We previously established a quantitative method of assessing the surgical freedom and angles of attack permitted by a given endoscopic exposure using stereotaxy, allowing for a more rigorous and objective method of comparison 5, 24. In this analysis, we applied the same methodology to determine the optimal endoscopic approach for several pineal region anatomical targets.
Section snippets
Methods
Four silicon-injected, formalin-fixed cadaveric heads were dissected bilaterally, with a total of eight anatomical sides exposed for final analysis. We sequentially performed a midline approach and three different variations of the minimally invasive endoscopic SCIT approach: a paramedian approach, a lateral approach, and an extreme lateral approach. All dissections were performed using a rigid 0° endoscope (Karl Storz, Tuttlingen, Germany) with standard endoscopic instruments. The microscope
Surgical Freedom for the Exposed Area
Surgical freedom, which represents the maximal area through which a surgeon could move a hand, was calculated for all anatomical targets; these findings are summarized in Table 1. In summary, among the four SCIT approaches, the extreme lateral approach provided the largest surgical freedom (mean ± SD, 142.2 ± 7.1 cm2) compared with the midline approach (104.5 ± 8.3 cm2), lateral approach (115.2 ± 6.6 cm2), and paramedian approach (103.5 ± 8.3 cm2) (P < 0.0001) (Table 1). This can be explained
Discussion
The endoscopic SCIT approach is a relatively new method to access pathology of the posterior incisural space. Although the endoscope minimizes approach-related tissue disruption and brain retraction without compromising visualization, instrument conflict during dissection can lead to surgeon frustration, increased operative time, and increased risk of incomplete resection and complications. Our current report uses a previously validated method of assessing surgical freedom and angle of attack,
Conclusions
The endoscopic SCIT is an increasingly popular approach to access pathology of the posterior incisura, and purely endoscope driven approaches are increasing in popularity. Presurgical planning and a detailed understanding of the important neurovascular structures in this region are paramount to safe and successful surgical execution. Our current cadaveric study highlights the important differences in the various endoscopic SCIT approaches to the pineal region, including a quantitative analysis
Acknowledgments
We thank Karl Storz and the Newsome Family Endowment for their support of the Barrow Neurological Institute Skull Base Laboratory.
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Conflict of interest statement: The authors have no conflicts of interest to disclose.