Usefulness of cone-beam computed tomography-reformatted epidurography in percutaneous epidural adhesiolysis: A pilot study.

BACKGROUND: Conventional epidurography (CE) is thought to have insufficient usefulness on percutaneous epidural adhesiolysis (PEA). We aimed to evaluate the association between the outcome of PEA and cone-beam computed tomography-reformatted epidurography (CBCT-RE). METHODS: After ethics board approval and written informed consent were obtained, we performed 30 PEA in 26 participants, and evaluated their post-PEA image findings. Two independent radiologists categorized and recorded the occurrence of contrast in the intracanal ventral and extraforaminal regions on CE, and in the dorsal canal (DC), ventral canal (VC), dorsal foramen (DF), and ventral foramen (VF) on CBCT-RE. Reproducibility was assessed using intraclass correlation coefficients (ICCs). Baseline characteristics along with contrast distribution patterns of CE and CBCT-RE were analyzed in terms of their association with symptom relief at 1 month after PEA. RESULTS: The rate of patients with symptoms relief >50% after PEA was 63.3%. The inter-reader agreement was higher for CBCT-RE (ICC = 0.955) than for CE (ICC = 0.793). Participants with contrast coexisting in VC and DF adjacent to the irritated nerve root on CBCT-RE ( p = 0.015) had a significantly better response after PEA than those without contrast at these locations on CBCT-RE, independent of baseline characteristics (adjusted odds ratio: 11.414 [ p = 0.012]). CONCLUSION: CBCT-RE with identifying contrast distribution patterns is useful for predicting outcome of PEA.

Endoscopically assisted presigmoid retrolabyrinthine approach to the lateral mesencephalic sulcus: a cadaveric study with comparison to the variant supracerebellar infratentorial approaches.

The supracerebellar infratentorial (SCIT) approach is commonly used to gain access to the lateral mesencephalic sulcus (LMS), which has been established as a safe entry point into the posterolateral midbrain. This study describes a lateral variant of the SCIT approach, the supreme-lateral SCIT approach, for accessing the LMS through the presigmoid retrolabyrinthine craniectomy and quantitatively compares this approach with the paramedian and extreme-lateral SCIT approaches. Anatomical dissections were performed in four cadaveric heads. In each head, the supreme-lateral SCIT approach was established on one side, following a detailed description of each step, whereas the paramedian and supreme-lateral SCIT approaches were established on the other side. Quantitative measurements of the exposed posterolateral midbrain, the angles of LMS entry, and the depth of surgical corridors were recorded and compared between the three SCIT approach variants. The supreme-lateral (67.70 ± 23.14 mm2) and extreme-lateral (70.83 ± 24.99 mm2) SCIT approaches resulted in larger areas of exposure anterior to the LMS than the paramedian SCIT approach (38.61 ± 9.84 mm2); the supreme-lateral SCIT approach resulted in a significantly smaller area of exposure posterior to the LMS (65.24 ± 6.81 mm2) than the other two variants (paramedian = 162.75 ± 31.98 mm2; extreme-lateral = 143.10 ± 23.26 mm2; both P < .001). Moreover, the supreme-lateral SCIT approach resulted in a surgical corridor with a shallower depth and a smaller angle relative to the horizontal plane than the other two variants. The supreme-lateral SCIT approach is a more lateral approach than the extreme-lateral SCIT approach, providing a subtemporal approach with direct LMS visualization. The supreme-lateral SCIT offers the benefits of both subtemporal and SCIT approaches and represents a suitable option for the management of selected midbrain pathologies.

Biomechanical evaluation of a novel tri-blade titanium implantable vertebral augmentation device.

BACKGROUND CONTEXT: Titanium implantable vertebral augmentation device (TIVAD) are regarded as having potential in the treatment of vertebral compression fractures (VCFs). However, improper design in current TIVADs results in the inability to effectively restore VCF height and maintain stability. There is still an unmet clinical need for improvement. PURPOSE: The authors tested a newly developed a TIVAD (Tri-blade fixed system) that can provide enough endplate collapse support to restore the vertebral body height in a safe retraction mechanism for VCFs using minimally invasive surgery (MIS). STUDY DESIGN: The performed biomechanical tests included blade expansion force, lifetime of cement embedded and vertebral height restoration efficiency of porcine osteoporosis VCFs for its feasibility. METHODS: A cylinder with 3 surface cuts that form blades that can be expanded into a conical space was designed (Tri-blade fixed system). The 3 blades can be expanded outward with angles between blades as 105°/ 105°/150° for lower left/lower right/upper arms, respectively that reach 15mm in height and 14.8 mm in width. A frame was specifically designed to measure the contact force using force sensing resistors during blade expansion. The Tri-blade fixed system was embedded into a cement block to perform fatigue testing under 2000N pressure (5*106 cycles) for understanding the device lifetime limitation. The Tri-blade system was then inserted into porcine osteoporosis VCFs to examine the vertebral height restoration efficiency. RESULTS: The average maximum contact force for the top, bottom left and right blades were 299.0N, 283.5N and 279.3N, respectively with uniformly outward expansion forces. The fatigue test found that there were no obvious cracks or damage to the cement block. The porcine osteoporosis vertebral body at the anterior, middle, and posterior heights can be restored to 21.9%, 12.6% and 6.4%, respectively. CONCLUSIONS: This study developed a novel TIVAD with conical shape that can provide a more stable structure with sufficient/uniform expansion force, passing the fatigue test with bone cement and high effective in vertebral height restoration tests for porcine osteoporosis VCFs. CLINICAL SIGNIFICANCE: The new 3D Tri-blade TIVAD may offer a new treatment option for VCFs.

Risk factors of postoperative hydrocephalus following decompressive craniectomy for spontaneous intracranial hemorrhages and intraventricular hemorrhage.

INTRODUCTION: Hydrocephalus is a complication of spontaneous intracerebral hemorrhage; however, its predictive relationship with hydrocephalus in this patient cohort is not understood. Here, we evaluated the incidence and risk factors of hydrocephalus after craniectomy. METHODS: Retrospectively studied data from 39 patients in the same hospital from 2016/01 to 2020/12 and analyzed risk factors for hydrocephalus. The clinical data recorded included patient age, sex, timing of surgery, initial Glasgow Coma Scale score, intracerebral hemorrhage (ICH) score, alcohol consumption, cigarette smoking, medical comorbidity, and blood data. Predictors of patient outcomes were determined using Student t test, chi-square test, and logistic regression. RESULTS: We recruited 39 patients with cerebral herniation who underwent craniectomy for spontaneous supratentorial hemorrhage. Persistent hydrocephalus was observed in 17 patients. The development of hydrocephalus was significantly associated with the timing of operation, cigarette smoking, and alcohol consumption according to the Student t test and chi-square test. Univariate and multivariate analyses suggested that postoperative hydrocephalus was significantly associated with the timing of surgery (P = .031) and cigarette smoking (P = .041). DISCUSSION: The incidence of hydrocephalus in patients who underwent delayed operation (more than 4 hours) was lower than that in patients who underwent an operation after less than 4 hours. nonsmoking groups also have lower incidence of hydrocephalus. Among patients who suffered from spontaneous supratentorial hemorrhage and need to receive emergent craniectomy, physicians should be reminded that postoperative hydrocephalus followed by ventriculoperitoneal shunting may be necessary in the future.

Endoscope-assisted Manipulation of Chronic Subdural Hematomas Provides a Novel Solution for Eliminating the Septum and Inner Membrane Leading to Reduced Recurrence.

BACKGROUND/AIM: Canonical burr-hole craniostomy (BHC) with drainage is the primary treatment for chronic subdural hematomas. However, complicated situations such as organized clots or compartmentation may result in recurrent chronic subdural hematoma (CSDH). Herein, we introduce a novel technique by applying an endoscope for tearing the inner membrane and septum, in addition to evacuating the hematoma in the subdural space where in-line visualization is not possible. PATIENTS AND METHODS: Two hundred and twenty-nine cases of CSDH were enrolled in this study. Of these, 13 patients were treated endoscopically. The 0-degree and 30-degree, 2.7 mm endoscope was applied after a BHC. The arachnoid knife for microsurgery was used to tear the inner membrane to open the compartments. RESULTS: Non-endoscope-assisted operated (non-Endo group) and endoscope-assisted membranectomy patients (Endo group) demonstrated no differences in sex, age, body mass index, trauma, other diseases, or use of anticoagulation agents. Although the surgery time spent for the Endo patients was longer (128.53±49.56 min) than that for the non-Endo group (65.18±32.89 min), no recurrence was found among the Endo group, whereas a higher rate was observed in the non-Endo group. CONCLUSION: Novel endoscope-assisted membranectomy is a powerful technique capable of reducing recurrence and improving surgical outcomes.

The Role of Power Doppler Ultrasonography in Caudal Epidural Injection.

Background and Objectives: Although the ultrasound-guided technique is used in caudal epidural injections, severe complications can happen if ultrasound cannot identify the occurrence of intravascular injection. To determine intraepidural and intravascular injection during caudal epidural injections, we used power Doppler ultrasonography (PDU) when injecting medications into the epidural space. Materials and Methods: This is a retrospective study that enrolled a total of 277 patients with refractory low back pain or degenerative disc from January 2019 to December 2019. The injectate flow of caudal epidural injections was examined with the assistance of PDU and confirmed by fluoroscopy. Four flow patterns were identified by PDU in our study: the "Earthworm sign," the "Patch sign," the "Tubular sign" and the "Absent flow sign." The accuracy of PDU in identifying intraepidural and intravascular injections was determined by fluoroscopy images recorded during each injection. Results: We evaluated 277 patients (mean age, 68.6 ± 13.2 years; 106 men). The "Patch sign" showed a sensitivity of 88.76% and a specificity of 80% in predicting epidural injection without intravascular injection. The "Earthworm sign" demonstrated a sensitivity of 70% and a specificity of 100% in detecting intravascular injection. The "Tubular sign" showed a specificity of 100% and a sensitivity of 9.4% in predicting successful epidural injection. The absence of a flow signal showed a sensitivity of 1.87% and a specificity of 90% in predicting successful epidural injection. Conclusions: Ultrasound-guided caudal epidural injection can accurately determine intraepidural and intravascular injections with the assistance of PDU and is thus a good alternative technique to fluoroscopy-guided caudal epidural injection.

Case Report: Nerve Root Entrapment Due to Epidural Fibrosis in a Patient With Failed Back Surgery Syndrome: Value of 2-18F-Fluorodeoxyglucose Simultaneous Positron Emission Tomography-Magnetic Resonance Imaging.

Failed back surgery syndrome (FBSS) is a highly prevalent condition in patients after spine surgery. Although magnetic resonance imaging (MRI) is the gold standard for the diagnosis of epidural fibrosis, it is sometimes difficult to determine if epidural fibrosis contributes to radiculopathy. Herein, we share our experience in locating radiculopathy lesions using simultaneous positron emission tomography (PET)/MRI. 2-[18F]-FDG (18F-fluorodeoxyglucose) simultaneous PET/MRI maps of body glucose metabolism detected using PET can be used to correlate anatomical details provided by MRI to offer a very clear picture of neural inflammation due to extensive epidural fibrosis. More applications of 2-[18F]-FDG simultaneous PET/MRI in low back pain and other musculoskeletal diseases should be further investigated in the future.

From GWAS to drug screening: repurposing antipsychotics for glioblastoma.

BACKGROUND: Glioblastoma is currently an incurable cancer. Genome-wide association studies have demonstrated that 41 genetic variants are associated with glioblastoma and may provide an option for drug development. METHODS: We investigated FDA-approved antipsychotics for their potential treatment of glioblastoma based on genome-wide association studies data using a 'pathway/gene-set analysis' approach. RESULTS: The in-silico screening led to the discovery of 12 candidate drugs. DepMap portal revealed that 42 glioma cell lines show higher sensitivities to 12 candidate drugs than to Temozolomide, the current standard treatment for glioblastoma. CONCLUSION: In particular, cell lines showed significantly higher sensitivities to Norcyclobenzaprine and Protriptyline which were predicted to bind targets to disrupt a certain molecular function such as DNA repair, response to hormones, or DNA-templated transcription, and may lead to an effect on survival-related pathways including cell cycle arrest, response to ER stress, glucose transport, and regulation of autophagy. However, it is recommended that their mechanism of action and efficacy are further determined.

Surgical application of endoscopic-assisted minimally-invasive neurosurgery to traumatic brain injury: Case series and review of literature.

BACKGROUND/PURPOSE: Adequate decompression is the primary goal during surgical management of patients with traumatic brain injury (TBI). Therefore, it may seem counterintuitive to use minimally-invasive strategies to treat these patients. However, recent studies show that endoscopic-assisted minimally-invasive neurosurgery (MIN) can provide both adequate decompression (which is critical for preserving viable brain tissue) and maximize neurological recovery for patients with TBI. Hence, we reviewed the pertinent literature and shared our experiences on the use of MIN. METHODS: This was a retrospective multi-center study. We collected data of 22 TBI patients receiving endoscopic-assisted MIN within 72 hours after the onset, with Glasgow Coma Scale (GCS) scores of 6-14 and whose hemorrhage volume ranging from 30 to 70 mL. RESULTS: We have applied MIN techniques to a group of 22 patients with traumatic ICH (TICH), epidural hematoma (EDH), and subdural hematoma (SDH). The mean pre-operative GCS score was 7.5 (median 7), and mean hemorrhage volume was 57.14 cm3 Surgery time was shortened with MIN approaches to a mean of 59.6 min. At 6-month follow-up, the mean GCS score had improved to 12.3 (median 15). By preserving more normal brain tissue, MIN for patients with TBI can result in beneficial effects on recoveries and neurological outcomes. CONCLUSION: Endoscopic-assisted MIN in TBI is safe and effective in a carefully selected group of patients.

GRPEL2 Knockdown Exerts Redox Regulation in Glioblastoma.

Malignant brain tumors are responsible for catastrophic morbidity and mortality globally. Among them, glioblastoma multiforme (GBM) bears the worst prognosis. The GrpE-like 2 homolog (GRPEL2) plays a crucial role in regulating mitochondrial protein import and redox homeostasis. However, the role of GRPEL2 in human glioblastoma has yet to be clarified. In this study, we investigated the function of GRPEL2 in glioma. Based on bioinformatics analyses from the Cancer Gene Atlas (TCGA) and the Chinese Glioma Genome Atlas (CGGA), we inferred that GRPEL2 expression positively correlates with WHO tumor grade (p < 0.001), IDH mutation status (p < 0.001), oligodendroglial differentiation (p < 0.001), and overall survival (p < 0.001) in glioma datasets. Functional validation in LN229 and GBM8401 GBM cells showed that GRPEL2 knockdown efficiently inhibited cellular proliferation. Moreover, GRPEL2 suppression induced cell cycle arrest at the sub-G1 phase. Furthermore, GRPEL2 silencing decreased intracellular reactive oxygen species (ROS) without impending mitochondria membrane potential. The cellular oxidative respiration measured with a Seahorse XFp analyzer exhibited a reduction of the oxygen consumption rate (OCR) in GBM cells by siGRPEL2, which subsequently enhanced autophagy and senescence in glioblastoma cells. Taken together, GRPEL2 is a novel redox regulator of mitochondria bioenergetics and a potential target for treating GBM in the future.

Endovascular aortic repair is a cost-effective option for in-hospital patients with abdominal aortic aneurysm.

BACKGROUND: To investigate the cost-effectiveness of endovascular aortic repair (EVAR) versus open aortic repair (OAR) for abdominal aortic aneurysm (AAA) using incremental costs per decreased in-hospital mortality rate gained through our patients' cohort. METHODS: Medical records and healthcare costs of patients with AAA hospitalized between 2010 and 2015 were extracted from the National Health Insurance Research Database (NHIRD) of Taiwan. Multiple regression analysis was applied to adjust for confounding factors and to compare the differences in postoperative clinical outcomes between patients who received EVAR and OAR. The incremental cost-effectiveness ratio (ICER) of EVAR was determined based on the healthcare cost obtained from the analyzed data. RESULTS: A total of 2803 AAA patients were identified (n = 559 with ruptured AAA and n = 2244 unruptured AAA). Patients with ruptured AAA who underwent EVAR compared with OAR patients had shorter hospital and intensive care unit (ICU) stays (all p < 0.05). For patients with unruptured AAA, those who received EVAR compared with OAR, the adjusted odds ratio (aOR) of postoperative complications and in-hospital mortality were 0.371 and 0.447 (all p < 0.05). The total direct surgical costs and medical expenses during hospitalization in all AAA patients were higher for the EVAR group; however, ICER was <1 per capita gross domestic product. Stratification by age groups further suggested that ICER for patients with unruptured AAA who received EVAR, compared with OAR, decreased with age. CONCLUSION: Total direct medical costs were higher for AAA patients receiving EVAR regardless of rupture status; however, the cost is offset by lower odds of postoperative complications and in-hospital mortality. The observed decrease in ICER with age and EVAR use warrants further analysis. Our findings further validate the use of EVAR over OAR. These results provides supporting evidence for physicians and patients with AAA to inform shared decision making regarding endovascular or OAR options.

Unusual Cerebral Aneurysm after Stereotactic Radiosurgery to Treat Trigeminal Neuralgia.

Stereotactic radiosurgery is a treatment option for trigeminal neuralgia. This procedure is minimally invasive, but tumor development and facial numbness have been reported. Here, we report an unusual presentation after stereotactic radiosurgery to treat trigeminal neuralgia. A 60-year-old man demonstrated typical signs for type 1 trigeminal nerve neuralgia and was treated with medication for 5 years. Owing to an intolerance to that medication, he received stereotactic radiosurgery with 66 Gy. During a 9-year follow-up exam, dizziness with a spinning sensation was reported and a right superior cerebellar thrombosed aneurysm was diagnosed. He received transarterial embolization with coiling of aneurysm and subsequently reported no complications on follow-up exams. Although stereotactic radiosurgery is a promising treatment for trigeminal neuralgia, aneurysm development may be considered a possible complication. Long-term follow-up care of these patients should be considered. To understand the relationship between radiosurgery and the potential development of a cerebral aneurysm, further research is needed.

Endoscopic transcanal transpetrosal approach to the petroclival region: a cadaveric study with comparison to the Kawase approach.

This study introduces expanded application of the endoscopic transcanal approach with anterior petrosectomy (ETAP) in reaching the petroclival region, which was compared through a quantitative analysis to the middle fossa transpetrosal-transtentorial approach (Kawase approach). Anatomical dissections were performed in five cadaveric heads. For each head, the ETAP was performed on one side with a detailed description of each step, while the Kawase approach was performed on the contralateral side. Quantitative measurements of the exposed area over the ventrolateral surface of the brainstem, and of the angles of attack to the posterior margin of the trigeminal nerve root entry zone (CN V-REZ) and porus acusticus internus (PAI) were obtained for statistical comparison. The ETAP provided significantly larger exposure over the ventrolateral surface of the pons (93.03 ± 21.87 mm2) than did the Kawase approach (34.57 ± 11.78 mm2). In contrast to the ETAP, the Kawase approach afforded greater angles of attack to the CN V-REZ and PAI in the vertical and horizontal planes. The ETAP is a feasible and minimally invasive procedure for accessing the petroclival region. In comparison to the Kawase approach, the ETAP allows for fully anterior petrosectomy and larger exposure over the ventrolateral surface of the brainstem without passing through the cranial nerves or requiring traction of the temporal lobe.

Quantitative comparison of endoscopically assisted endonasal, sublabial and transorbital transmaxillary approaches to the anterolateral skull base.

OBJECTIVES: The aim of this anatomical study is to make quantitative comparison among three endoscopic approaches, encompassing contralateral endonasal transseptal transmaxillary transpterygoid approach (contralateral EEA), endoscopic sublabial transmaxillary transalisphenoid (Caldwell-Luc) approach and endoscopic transorbital transmaxillary approach through inferior orbital fissure (ETOA), to the anterolateral skull base for assisting preoperative planning. DESIGN & PARTICIPANTS: Anatomical dissections were performed in four adult cadaveric heads bilaterally using three endoscopic transmaxillary approaches described above. SETTING: Skull Base Laboratory at the National Defense Medical Center. MAIN OUTCOME MEASURES: The area of exposure, angles of attack and depth of surgical corridor of each approach were measured and obtained for statistical comparison. RESULTS: The ETOA had significantly larger exposure over middle cranial fossa (731.40 ± 80.08 mm2 ) than contralateral EEA (266.60 ± 46.74 mm2 ) and Caldwell-Luc approach (468.40 ± 59.67 mm2 ). In comparison with contralateral EEA and Caldwell-Luc approach, the ETOA offered significantly greater angles of attack and shorter depth of surgical corridor (P < .05 for all comparisons). CONCLUSIONS: The ETOA is the superior choice for target lesion occupying multiple compartments with its epicentre located in the middle cranial fossa or superior portion of infratemporal fossa.

Association of early vertebroplasty with risk of hip replacement: A nationwide population-based cohort study in Taiwan.

Studies show that vertebral fractures could predict the risk of hip fractures. We aimed to evaluate the potential benefits of whether the timing of vertebroplasty (VP) for vertebral fracture associated with the risk of hip fracture for hip replacement.We identified 142,782 patients from the Taiwan National Health Insurance Database with thoracolumbar vertebral fracture (International Classification of Diseases, Ninth Revision, Clinical Modification:805.2-805.9) who were followed up from 2000 to 2013. These patients were divided into those who underwent VP (VP group) (International Classification of Diseases, Ninth Revision, Clinical Modification : 78.49) within 3 months and those who did not (non-VP group). After adjusting for the confounding factors, the Cox proportional hazards analysis was used to estimate the effect of early VP on reducing the risk of hip fracture. The difference in the risk of hip replacement, between the VP group and non-VP group was estimated using the Kaplan-Meier method with the log-rank test.In the 14-year follow-up, the cumulative incidence rate of hip replacement in the VP group was lower than that in the non-VP group (0.362% and 0.533%, respectively, long-rank P < .001). There was a significant difference between the 2 groups since the first-year follow-up.Our study showed that early VP performed to avoid progression of the kyphotic changes following thoracolumbar vertebral fracture may reduce the risk of hip fracture. These results, obtained from retrospective data, indicate that a prospective study is warranted.

Endoscopic transorbital approach to anterolateral skull base through inferior orbital fissure: a cadaveric study.

BACKGROUND: Endoscopic transorbital approach (eTOA) has been announced as an alternative minimally invasive surgery to skull base. Owing to the inferior orbital fissure (IOF) connecting the orbit with surrounding pterygopalatine fossa (PPF), infratemporal fossa (ITF), and temporal fossa, the idea of eTOA to anterolateral skull base through IOF is postulated. The aim of this study is to access its practical feasibility. METHODS: Anatomical dissections were performed in five human cadaveric heads (10 sides) using 0-degree and 30-degree endoscopes. A stepwise description of eTOA to anterolateral skull base through IOF was documented. The anterosuperior corner of the maxillary sinus in the horizontal plane of the upper edge of zygomatic arch was defined as reference point (RP). The distances between the RP to the foramen rotundum (FR), foramen ovale (FO), and Gasserian ganglion (GG) were measured. The exposed area of anterolateral skull base in the coronal plane of the posterior wall of the maxillary sinus was quantified. RESULTS: The surgical procedure consisted of six steps: (1) lateral canthotomy with cantholysis and preseptal lower eyelid approach with periorbita dissection; (2) drilling of the ocular surface of greater sphenoid wing and lateral orbital rim osteotomy; (3) entry into the maxillary sinus and exposure of PPF and ITF; (4) mobilization of infraorbital nerve with drilling of the infratemporal surface of the greater sphenoid wing and pterygoid process; (5) exposure of middle cranial fossa, Meckel's cave, and lateral wall of cavernous sinus; and (6) reconstruction of orbital floor and lateral orbital rim. The distances measured were as follows: RP-FR = 45.0 ± 1.9 mm, RP-FO = 55.7 ± 0.5 mm, and RP-GG = 61.0 ± 1.6 mm. In comparison with the horizontal portion of greater sphenoid wing, the superior and inferior axes of the exposed area were 22.3 ± 2.1 mm and 20.5 ± 1.8 mm, respectively. With reference to the FR, the medial and lateral axes of the exposed area were 11.6 ± 1.1 mm and 15.8 ± 1.6 mm, respectively. CONCLUSIONS: The eTOA through IOF can be used as a minimally invasive surgery to access whole anterolateral skull base. It provides a possible resolution to target lesion involving multiple compartments of anterolateral skull base.

Endoscopic transorbital transtentorial approach to middle incisural space: preclinical cadaveric study.

BACKGROUND: Endoscopic transorbital approach is a novel development of minimally invasive skull base surgery. Recently, anatomical studies have started to discuss the expanded utilization of endoscopic transorbital route for intracranial intradural lesions. The goal of this cadaveric study is to assess the feasibility of endoscopic transorbital transtentorial approach for exposure of middle incisural space. METHODS: Anatomical dissections were performed in four human cadaveric heads (8 sides) using 0- and 30-degree endoscopes. A stepwise description of endoscopic transorbital transtentorial approach to middle incisural space and related anatomy was provided. RESULTS: Orbital manipulation following superior eyelid crease incision with lateral canthotomy and cantholysis established space for bone drilling. Extradural stage consisted of extensive drilling of orbital roof of frontal bone, lessor, and greater wings of sphenoid bone. Intradural stage was composed of dissection of sphenoidal compartment of Sylvian fissure, lateral mobilization of mesial temporal lobe, and penetration of tentorium. A cross-shaped incision of tentorium provided direct visualization of crural cistern with anterolateral aspect of cerebral peduncle and upper pons. Interpeduncular cistern, prepontine cistern, and anterior portions of ambient and cerebellopontine cisterns were exposed by 30-degree endoscope. CONCLUSION: The endoscopic transorbital transtentorial approach can be used as a minimally invasive surgery for exposure of middle incisural space. Extensive drilling of sphenoid wing and lateral mobilization of mesial temporal lobe are the main determinants of successful dissection. Further studies are needed to confirm the clinical feasibility of this novel approach.