Endoscopic Intradural Subtemporal Keyhole Approach with Neuronavigational Assistance to the Suprasellar, Petroclival, and Ventrolateral Brainstem Regions: An Anatomic Study

History, Current Techniques, and Future Prospects of Surgery to the Sellar and Parasellar Region

The sellar and parasellar region can be affected by diverse pathologies. The deep-seated location and surrounding critical neurovascular structures make treatment challenging; there is no singular, optimal approach for management. The history and development of transcranial and transsphenoidal approaches by pioneers in skull base surgery were largely aimed at treating pituitary adenomas, which are the most common lesions of the sella. This review explores the history of sellar surgery, the most commonly used approaches today, and future considerations for surgery of the sellar/parasellar region.

Endoscopic Subtemporal Epidural Key-Hole Approach: Quantitative Anatomic Analysis of Three Surgical Corridors

BACKGROUND

The endoscope-assisted subtemporal key-hole epidural approach (ESKEA) has been recently described. The aim of this study was to measure working volumes and exposure of key areas of the middle cranial fossa provided by this approach.

METHODS

Four fresh frozen cadaver heads were dissected to analyze 3 modular corridors (1A, 1B, and 2) harvested through ESKEA. A step-by-step dissection was performed, and key anatomic landmarks were recorded. A GTxEyesII-ApproachViewer was used to quantify the working volume and exposure of 4 different regions (sphenoorbital, parasellar, superior petrous apex, and squamopetrous). For each corridor, 3 incremental degrees of temporal dural retraction (5, 10, and 15 mm) were tested.

RESULTS

The working volume of all corridors progressively increased with degree of retraction: Corridors 1A, 1B, and 2 showed a gain in working volume of 21%, 27%, and 19% from 5 mm to 10 mm retraction, respectively, and a gain of 40%, 45%, and 44% from 5 mm to 15 mm retraction, respectively. The sphenoorbital area was exposed (27%-45%) through corridor 1A, and exposure significantly increased with the degree of retraction. Corridor 1B provided optimal exposure of parasellar areas (86%-100%) and superior petrous apex (70%-87%) regardless of the degree of retraction. The squamopetrous area was satisfactorily addressed through corridor 2 (88%) only with the highest degree of retraction.

CONCLUSIONS

ESKEA can be conceived as a modular approach: the 3 surgical corridors have specific working volumes, which are clearly influenced by the degree of temporal lobe retraction, and provide exposure of different middle cranial fossa areas.

Evolution and Stagnation of Image Guidance for Surgery in the Lateral Skull: A Systematic Review 1989-2020

Objective: Despite three decades of pre-clinical and clinical research into image guidance solutions as a more accurate and less invasive alternative for instrument and anatomy localization, translation into routine clinical practice for surgery in the lateral skull has not yet happened. The aim of this review is to identify challenges that need to be solved in order to provide image guidance solutions that are safe and beneficial for use during lateral skull surgery and to synthesize factors that facilitate the development of such solutions. Methods: Literature search was conducted via PubMed using terms relating to image guidance and the lateral skull. Data extraction included the following variables: image guidance error, imaging resolution, image guidance system, tracking technology, registration method, study endpoints, clinical target application, and publication year. A subsequent search of FDA 510(k) database for identified image guidance systems and extraction of the year of approval, intended use, and indications for use was performed. The study objectives and endpoints were subdivided in three time phases and summarized. Furthermore, it was analyzed which factors correlated with the image guidance error. Factor values for which an error ≤0.5 mm (μ_error + 3σ_error) was measured in more than one study were identified and inspected for time trends. Results: A descriptive statistics-based summary of study objectives and findings separated in three time intervals is provided. The literature provides qualitative and quantitative evidence that image guidance systems must provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial application during surgery in the lateral skull. Spatial tracking accuracy and precision and medical image resolution both correlate with the image guidance accuracy, and all of them improved over the years. Tracking technology with accuracy ≤0.05 mm, computed tomography imaging with slice thickness ≤0.2 mm, and registration based on bone-anchored titanium fiducials are components that provide a sufficient setting for the development of sufficiently accurate image guidance. Conclusion: Image guidance systems must reliably provide an accuracy ≤0.5 mm (μ_error + 3σ_error) for their safe and beneficial use during surgery in the lateral skull. Advances in tracking and imaging technology contribute to the improvement of accuracy, eventually enabling the development and wide-scale adoption of image guidance solutions that can be used safely and beneficially during lateral skull surgery.

Intradural Subtemporal Keyhole Approach with Neuronavigational Assistance to the Petroclival and Ventrolateral Brainstem Regions: Quantitative Analysis of Anatomic Exposure and Surgical Freedom

OBJECTIVE

The purpose of this study was to evaluate the advantages of endoscopy and navigational assistance in the intradural subtemporal keyhole approach and the intradural Kawase approach by studying anatomic exposure and surgical freedom in the posterior cranial fossa.

METHODS

Twenty endoscopic intradural subtemporal keyhole approaches (EISKA) were performed on 10 cadaveric heads. An intradural Kawase approach and a navigation-assisted intradural Kawase approach were then carried out on a random side of each specimen. Related anatomic structures were observed through a 0° endoscope and a microscope. Anatomic exposure and surgical freedom were measured by transparent graph paper and analyzed.

RESULTS

Compared with the microsurgical technique, the superior, inferior, and medial limits of the endoscopic anatomic exposure increased by 2.9, 15.65, and 10.2 mm, whereas the surgical freedom increased by 2.9, 7.55, and 6 mm (P < 0.05) in the intradural subtemporal keyhole approach. In the intradural Kawase approach and the navigation-assisted intradural Kawase approach, the endoscopic anatomic exposure and surgical freedom also increased (P < 0.05). Using a frameless navigational device, the inferior limit of the anatomic exposure increased 3.8 mm by endoscopy and 3.5 mm by microscopy, whereas the surgical freedom increased by 2.7 and 2.2 mm, respectively (P < 0.05).

CONCLUSIONS

The EISKA provides greater anatomic exposure and surgical freedom primarily in the superior, inferior, and medial directions of the brainstem region. Maximum anatomic exposure and surgical freedom of the posterior cranial fossa was obtained by navigational assistance with fewer complications.