Elsevier

World Neurosurgery

Volume 84, Issue 2, August 2015, Pages 257-266
World Neurosurgery

Original Article
Minimally Invasive Endoscopic Supracerebellar-Infratentorial Surgery of the Pineal Region: Anatomical Comparison of Four Variant Approaches

https://doi.org/10.1016/j.wneu.2015.03.009Get rights and content

Objective

The endoscopic supracerebellar-infratentorial (SCIT) approach is a viable method to access pathology of the posterior incisura, but a narrow working space and frequent instrument conflict can potentially limit its surgical efficacy. Until now, no rigorous studies were available comparing surgical freedom and angle of attack for four previously well-described approaches to pineal region targets.

Methods

Four formalin-fixed cadaver heads were dissected bilaterally (eight sides). A midline approach and three progressively lateral approaches to the pineal region were performed (paramedian, lateral, extreme lateral), and anatomical targets were identified. Utilizing frameless stereotaxy, we calculated surgical freedom using the vector cross-product method for all approaches for the exposed area and for three anatomical targets (pineal gland, ipsilateral superior colliculus, splenium). The mean and maximum possible angles of attack were calculated in the axial and sagittal planes.

Results

Point target surgical freedom, exposed area surgical freedom, and angle of attack for each individual pineal region target can be maximized depending on the medial-to-lateral location of the craniotomy. For endoscopic-controlled approaches, the extreme lateral approach provides the largest surgical freedom when accessing the ipsilateral superior colliculus (P < 0.0001), the lateral approach provides the largest surgical freedom to the pineal gland (P < 0.0001), and the paramedian craniotomy provides the largest surgical freedom when accessing the splenium (P < 0.0001). The extreme lateral approach to the pineal gland provided the largest horizontal angle of attack (P < 0.0001), and the extreme lateral approach to the ipsilateral superior colliculus provided the largest vertical angle of attack (P < 0.001). The microscope provides marginally increased surgical freedom and a better angle of attack to specific anatomical targets in the paramedian and extreme lateral approach compared with those provided by the endoscope, but these differences are negligible during intraoperative application.

Conclusions

Presurgical planning and a detailed understanding of the important neurovascular structures in the pineal region are paramount to safe and successful surgical execution. Our current cadaveric study indicates that the medial-to-lateral location of craniotomy can maximize access to pineal region targets. Furthermore, the endoscope is a viable alternative to the microscope for identifying pathology of the posterior incisura. These differences in surgical freedom and angle of attack to the pineal region may be useful to consider when planning minimal-access 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.

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