Extended endoscopic transorbital approach with superior-lateral orbital rim osteotomy: cadaveric feasibility study and clinical implications (SevEN-007)

OBJECTIVE The endoscopic transorbital approach (ETOA) has been developed, permitting a new surgical corridor. Due to the vertical limitation of the ETOA, some lesions of the anterior cranial fossa are difficult to access. The ETOA with superior-lateral orbital rim (SLOR) osteotomy can achieve surgical freedom of vertical as well as horizontal movement. The purpose of this study was to confirm the feasibility of the ETOA with SLOR osteotomy. METHODS Anatomical dissections were performed in 5 cadaveric heads with a neuroendoscope and neuronavigation system. ETOA with SLOR osteotomy was performed on one side of the head, and ETOA with lateral orbital rim (LOR) osteotomy was performed on the other side. After analysis of the results of the cadaveric study, the ETOA with SLOR osteotomy was applied in 6 clinical cases. RESULTS The horizontal and vertical movement range through ETOA with SLOR osteotomy (43.8° ± 7.49° and 36.1° ± 3.32°, respectively) was improved over ETOA with LOR osteotomy (31.8° ± 5.49° and 23.3° ± 1.34°, respectively) (p < 0.01). Surgical freedom through ETOA with SLOR osteotomy (6025.1 ± 220.1 mm3) was increased relative to ETOA with LOR osteotomy (4191.3 ± 57.2 mm3) (p < 0.01); these values are expressed as the mean ± SD. Access levels of ETOA with SLOR osteotomy were comfortable, including anterior skull base lesion and superior orbital area. The view range of the endoscope for anterior skull base lesions was increased through ETOA with SLOR osteotomy. After SLOR osteotomy, the space for moving surgical instruments and the endoscope was widened. Anterior clinoidectomy could be achieved successfully using ETOA with SLOR osteotomy. The authors performed ETOA with SLOR osteotomy in 6 cases of brain tumor. In all 6 cases, complete removal of the tumor was successfully accomplished. In the 3 cases of anterior clinoidal meningioma, anterior clinoidectomy was performed easily and safely, and manipulation of the extended dural margin and origin dura mater was possible. There was no complication related to this approach. CONCLUSIONS The authors evaluated the clinical feasibility of ETOA with SLOR osteotomy based on a cadaveric study. ETOA with SLOR osteotomy could be applied to more diverse disease groups that do not permit conventional ETOA or to cases in which surgical application is challenging. ETOA with SLOR osteotomy might serve as an opportunity to broaden the indication for the ETOA.

Development of novel Mixed Reality-Based Simulator for Endoscopic Transnasal Surgery with HoloLens and multiple AR tracker

Background Virtual reality (VR) and mixed reality (MR) are now widely applied for preoperative simulation and intraoperative navigation. Methods We developed an MR-based simulator for endoscopic transnasal surgery (ETNS) with a head-mounted display HoloLens and evaluated its usefulness. This simulator consisted of MR images of patients and an MR endoscope. HoloLens was used for projection of MR images and recognition of markers. The MR images were reconstructed from the preoperative images of patients and superimposed onto the endoscopic training model of the head. The MR endoscope was superimposed onto a three-dimensional (3D) printed replica of an endoscope. The MR endoscopic images from the replica of the endoscope were projected in the operator’s visual field. The MR images followed the manipulation of the replica of the endoscope through a nasal cavity on the training model. To evaluate the developed simulator, the MR endoscopic images were compared with video-recorded actual operative endoscopic views. And face validity and content validity of the simulator were evaluated by senior residents, using a 5-point Likert scale. Result The 3D MR images through HoloLens correlated well with the actual intraoperative views. Although there was an innate learning curve with the simulator, the face validity and the content validity demonstrated effective simulation of an operative field of view with real-time characteristics of the surgical procedure. Conclusions Our developed simulator for ETNS will contribute to learning the unique and the limited surgical fields through the narrow surgical corridor with endoscope, particularly for novice surgeons.

Microsurgical approaches to the cerebellar interpeduncular region: qualitative and quantitative analysis

OBJECTIVE The cerebellar interpeduncular region (CIPR) is a gate for dorsolateral pontine and cerebellar lesions accessed through the supracerebellar infratentorial approach (SCITa), the occipital transtentorial approach (OTa), or the subtemporal transtentorial approach (STa). The authors sought to compare the exposures of the CIPR region that each of these approaches provided. METHODS Three approaches were performed bilaterally in eight silicone-injected cadaveric heads. The working area, area of exposure, depth of the surgical corridor, length of the interpeduncular sulcus (IPS) exposed, and bridging veins were statistically studied and compared based on each approach. RESULTS The OTa provided the largest working area (1421 mm2; p < 0.0001) and the longest surgical corridor (6.75 cm; p = 0.0006). Compared with the SCITa, the STa provided a larger exposure area (249.3 mm2; p = 0.0148) and exposed more of the length of the IPS (1.15 cm; p = 0.0484). The most bridging veins were encountered with the SCITa; however, no significant differences were found between this approach and the other approaches (p > 0.05). CONCLUSIONS To reach the CIPR, the STa provided a more extensive exposure area and more linear exposure than did the SCITa. The OTa offered a larger working area than the SCIT and the STa; however, the OTa had the most extensive surgical corridor. These data may help neurosurgeons select the most appropriate approach for lesions of the CIPR.

Endoscopically Guided Resection of Brainstem Cavernous Malformations Through Miniature Corticotomies

Objective:Targeted surgical precision and minimally invasive techniques are of the utmost importance when it comes to resection of cavernous malformations involving the brainstem region. Minimization of the surgical corridor is desirable but should not compromise the extent of resection. This study provides detailed information on the role of endoscopic techniques in this challenging surgical task.Methods:A retrospective analysis of medical documentation, radiologic studies and detailed intraoperative video-documentation was performed for all consecutive patients, who underwent surgical resection of brainstem cavernous malformations between 2010 and 2020 at the authors’ institution. A case-based volumetry of the corticotomy was performed in relation to the cavernoma’s dimension. Results:A total of 20 procedures have been performed in 19 patients. Neuroendoscopy was implemented in all cases. Mean size of the lesion 5.4 (±5)mm3. Average size of the brainstem corticotomy was 4.5x3.7 (±1.0x1.1)mm with a median relation to the cavernoma’s dimension of 9.99% (1.2%-31.39%). Endoscopic 360° inspection of the resection cavity was feasible in all cases. There were no endoscopy related complications. Mean follow up was 27.8 (12-89) months. Gross-total resection was achieved in all but one cases (95%). Sixteen procedures (80%) resulted in an improved or stable medical condition. Eleven patients (61.1%) showed further improvement 12 months after initial surgery. Conclusion:Experience provided, endoscopic techniques can be safely implemented in surgery for BSCM. Combination of neuroendoscopic visualization and neuronavigation might enable a targeted size of brainstem corticotomy. Endoscopy can be considered as a valuable additive tool to ensure gross total resection of BSCM.

The Tough Fibrous Tissue of The Supracondylar Groove As A Useful Landmark Via The Endoscopic Endonasal Approach To The Lower Clivus

Background: The hypoglossal canal (HGC) is the most important structural landmark for the endoscopic endonasal approach to access the lower clivus (LC). We explored the feasibility of using the tough fibrous tissue covering the supracondylar groove (SCG) as a useful landmark to identify the location of the HGC. Methods: Four cadaveric specimens were dissected and analyzed. The craniovertebral junction (CVJ) region was accessed utilizing 4-mm endoscope with either 0° or 30° lenses. CVJ exposure and the surgical corridor areas were measured. The relationship between the tough fibrous tissue covering the SCG and the HGC was analyzed.Results: Tough fibrous connective tissue was tightly attached the SCG and ran superomedially to inferolaterally. The angle between the horizontal plane and the long axis of the SCG was 30°. Separating the tough tissue inferolaterally, we could locate the external orifice (EO) of the HGC to further accurately isolate the hypoglossal nerve. Conclusion: The tough fibrous connective tissue covered the SCG to the upper part of the HGC EO. The course of the tough fibrous connective tissue was superomedial to inferolateral. Using the tough fibrous connective tissue covering the SCG as a landmark, it was possible to accurately locate the HGC EO via the endoscopic endonasal approach to access the LC.

Endoscopic endonasal and transorbital approaches to petrous apex lesions

OBJECTIVE The petrous apex (PA) is one of the most challenging areas in skull base surgery because it is surrounded by numerous critical neurovascular structures. The authors analyzed the clinical outcomes of patients who underwent endoscopic endonasal approach (EEA) and transorbital approach (TOA) procedures for lesions involving PA to determine the perspectives and proper applications of these two approaches. METHODS The authors included patients younger than 80 years with lesions involving PA who were treated between May 2015 and December 2019 and had regular follow-up MR images available for analysis. Patients with meningioma involving petroclival regions were excluded. The authors classified PA into three regions: superior to the petrous segment of the internal carotid artery (p-ICA) (zone 1); posterior to p-ICA (zone 2); and inferior to p-ICA (zone 3). Demographic data, preoperative clinical and radiological findings, surgical outcomes, and morbidities were reviewed. RESULTS A total of 19 patients with lesions involving PA were included. Ten patients had malignant tumor (chondrosarcoma, chordoma, and osteosarcoma), and 6 had benign tumor (schwannoma, Cushing’s disease, teratoma, etc.). Three patients had PA cephalocele (PAC). Thirteen patients underwent EEA, and 5 underwent TOA. Simultaneous combined EEA and TOA was performed on 1 patient. Thirteen of 16 patients (81.3%) had gross- or near-total resection. Tumors within PA were completely resected from 13 of 16 patients using a view limited to only the PA. Complete obliteration of PAC was achieved in all patients. Postoperative complications included 2 cases of CSF leak, 1 case of injury to ICA, 1 fatality due to sudden herniation of the brainstem, and 1 case of postoperative diplopia. CONCLUSIONS EEA is a versatile surgical approach for lesions involving all three zones of PA. Clival tumor spreading to PA in a medial-to-lateral direction is a good indication for EEA. TOA provided a direct surgical corridor to the superior portion of PA (zone 1). Patients with disease with cystic nature are good candidates for TOA. TOA may be a reasonable alternative surgical treatment for select pathologies involving PA.

Evaluation of the effect of standard neuronavigation and augmented reality on the integrity of the perifocal structures during a neurosurgical approach

OBJECTIVE Intracranial minimally invasive procedures imply working in a restricted surgical corridor surrounded by critical structures, such as vessels and cranial nerves. Any damage to them may affect patient outcome. Neuronavigation systems may reduce the risk of such complications. In this study, the authors sought to compare standard neuronavigation (NV) and augmented reality (AR)–guided navigation with respect to the integrity of the perifocal structures during a neurosurgical approach using a novel model imitating intracranial vessels. METHODS A custom-made box, containing crisscrossing hard metal wires, a hidden nail at its bottom, and a wooden top, was scanned, fused, and referenced for the purpose of the study. The metal wires and an aneurysm clip applier were connected to a controller, which counted the number of contacts between them. Twenty-three naive participants were asked to 1) use NV to define an optimal entry point on the top, perform the smallest craniotomy possible on the wooden top, and to use a surgical microscope when placing a clip on the nail without touching the metal wires; and 2) use AR to preoperatively define an ideal trajectory, navigate the surgical microscope, and then perform the same task. The primary outcome was the number of contacts made between the metal wires and the clip applier. Secondary outcomes were craniotomy size, and trust in NV and AR to help avoid touching the metal wires, as assessed by a 9-level Likert scale. RESULTS The median number of contacts tended to be lower with the use of AR than with NV (AR, median 1 [Q1: 1, Q3: 2]; NV, median 3 [Q1: 1, Q3: 6]; p = 0.074). The size of the target-oriented craniotomy was significantly lower with the use of AR compared with NV (AR, median 4.91 cm2 [Q1: 4.71 cm2, Q3: 7.55 cm2]; and NV, median 9.62 cm2 [Q1: 7.07 cm2; Q3: 13.85 cm2]). Participants had more trust in AR than in NV (the differences posttest minus pretest were mean 0.9 [SD 1.2] and mean −0.3 [SD 0.2], respectively; p < 0.05). CONCLUSIONS The results of this study show a trend favoring the use of AR over NV with respect to reducing contact between a clip applier and the perifocal structures during a simulated clipping of an intracranial aneurysm. Target-guided craniotomies were smaller with the use of AR. AR may be used not only to localize surgical targets but also to prevent complications associated with damage to structures encountered during the surgical approach.

Retractorless brain surgery: technical considerations

Background Retraction is necessary to access deep areas in the brain and skull base, but prolonged and forceful use of fixed retraction might be injurious. Several techniques were developed, in the concept of minimally invasive neurosurgery, to eliminate or minimize the use of fixed retractors. The authors discuss the technical considerations and limits in applying dynamic retraction in brain surgery for a variety of lesions using different approaches. Results We retrospectively collected 123 cases with brain lesions in diverse locations, were dynamic retraction, using the tools in the operator hands and was achieved successfully instead of fixed retraction. Cases with aneurysms were excluded, although retraction was applied during clipping only. Superficial and large masses that do not require fixed retraction as a routine were excluded also. We relied mainly on patient positioning to benefit from the gravity, proper design of the craniotomy, arachnoid dissection, cerebrospinal fluid aspiration, and internal decompression of the mass when possible. Different approaches for different lesions were utilized in our patients, subfrontal or pterional and their modifications in 45.5% of cases, suboccipital in 21.1%, retrosigmoid in 13%, the interhemispheric approach in 10.5%, transcortical to lateral ventricles in 7.3%, and posterior subtemporal in 2.4%. Dynamic retraction with the surgical tools was used successfully in all cases except 7 patients (5.6%) where we had to use fixed retraction transiently. Conclusion Several considerations are helpful and amenable to achieve successful brain surgery without fixed retraction. Utilizing the gravity, unlocking of the brain, choosing the surgical corridor, cerebrospinal fluid suctioning, and mastering of the microsurgical techniques are the keys.

A Laboratory Investigation on a Tailored Skin and Muscle Flap Variant for the Retrosigmoid Approach

Introduction An anatomical study was conducted to test a modified C-shaped flap designed for patients undergoing a keyhole approach and/or minicraniotomy for retrosigmoid approach (KRSA). Materials and Methods Ten heads specimens were used. The surgical technique investigated was based on a 4-cm C-shaped skin incision with medial convexity (placed 8 cm laterally to the external occipital protuberance, with the lower edge terminating 1.5 to 2 cm above the mastoid tip), which followed by careful subperiosteal dissection and completed by reflecting and securing the skin flap layer anteriorly and the muscle flaps superiorly and inferiorly by stitches. Anatomical findings, including depth of surgical corridor till to the cerebellopontine cistern (CPC) as well as the sparing of neurovascular structures, were evaluated in every specimen. Results Twenty surgical approaches to CPC were conducted, resulting in a short working distance to the target (32 mm) without any need for a self-retaining retractor. In every specimen, the integrity of occipital muscles and cutaneous nerves was maintained, and a solid multilayer closure was always achieved. These data suggest that landmarks-based design of this C-shaped incision could be helpful in avoiding damages to the soft tissues encountered during KRSA. Conclusion This modified approach provides a wide surgical corridor to access the CPC while ensuring the minimal invasiveness of the standard S-shaped incision. Compared with the latter, it preserves better the integrity of the surrounding soft tissues and appears less likely to cause any iatrogenic injury to occipital muscles and cutaneous nerves.