The introduction of endoscopy, in conjunction with the technical development of endoscopy such as high definition and 3D, has had a significant impact on the field of endonasal transsphenoidal surgery. Currently, endoscopic surgery is applied for the resection of not only sellar tumors but also parasellar tumors such as anterior skull base tumors, intraorbital tumors, cavernous sinus tumors, infratemporal fossa tumors, clival tumors, and others. Endoscopic endonasal surgery is expected to be used more frequently in the near future. In this paper, based on our own experiences and after reviewing the recent publications, we summarize the indications for endoscopic surgery, focusing on pituitary tumors, craniopharyngiomas, and tuberculum sellae meningiomas.

  In pituitary tumor surgery, operative results by endoscopic and microscopic surgery are comparable for small tumors located in the sellar, while endoscopic surgery is superior to microscopic surgery for large tumors with extrasellar extension. Fully endoscopic surgery is more likely to be performed for giant pituitary adenoma cases for which craniotomy was previously preferred. However, tumors with significant anterior and lateral extension, multilobular suprasellar extension, and firm tumors can be limitations for endoscopic surgery. For craniopharyngiomas, retrochiasmatic tumors extending into the third ventricle can be good candidates for endoscopic surgery. In addition, the tumor-third ventricular relationship in craniopharyngiomas is another important factor to consider when deciding upon an indication for endoscopic surgery. The indication for an endoscopic approach for tuberculum sellae meningioma is limited to small anterior midline tumors for the purpose of decompression of the optic apparatus. In summary, although the efficacy of endoscopic surgery is well established, significant suprasellar and lateral extension and vascular encasement can be limitations for endoscopic surgery.

  For safe and effective endoscopic surgery, patient selection is important depending on the surgeons’ operative techniques and experiences. Also, it is important to note that observation and manipulation are different, and it is necessary to acquire surgical techniques to prevent postoperative cerebrospinal fluid leaks.

  Parasellar meningiomas are mainly divided into two categories, clinoidal and tuberculum sellae meningiomas. Both types of tumors have a characteristic symptom of preoperative visual impairment. Generally, a transsylvian approach with anterior clinoidectomy is chosen as treatment for clinoidal meningiomas. The extent of removal is influenced by the cavernous sinus invasion of the tumor. Preoperative visual deterioration occurs in 54-92% of cases, of which 23.3-40% show improvement after removal of the clinoidal meningioma. Tuberculum sellae meningiomas are characterized by optic canal extension, and craniotomy is predominantly chosen as the treatment. However, the transsphenoidal approach has gradually become the preferred treatment owing to the development of endoscopic endonasal surgery. The anterior interhemispheric or transsylvian approach is chosen as the surgical corridor of transcranial surgery. Gross total resection is achieved in 90.3-96% of cases, with 51-70% showing improvement in vision.

  Secure surgical planning for the removal of a parasellar meningioma is mandatory to achieve both maximum tumor removal and preservation of visual function.

  This is a review paper on the differential diagnosis and neurosurgical strategy for intraorbital lesions. A wide variety of processes produce intraorbital space-occupying lesions within the orbital cavity. These include vascular lesions, congenital lesions, inflammatory diseases, lymphoproliferative diseases, and benign and malignant neoplasms. Surgical strategy depends on each pathology, and total removal is the best treatment for non-lymphocytic tumors. To perform less invasive yet aggressive removal, neurosurgeons should be aware of the advantages and disadvantages of the various surgical approaches including the trans-orbital, lateral, transcranial approaches, and the rapidly developing endoscopic approaches. In some cases with involvement to important paraorbital structures, collaboration with ENT and/or plastic surgeons is required. In this paper, several representative cases among 111 cases with various intraorbital pathologies are illustrated, and the key radiological and surgical points are provided to help readers better understand the best treatment for intraorbital lesions.

  Vestibular schwannoma surgery is one of the most challenging fields, and achieving both maximal tumor removal and preservation of facial and/or hearing functions is difficult. Therefore, intraoperative monitoring, surgical technique based on the microsurgical anatomy and sufficient experience in this field are mandatory to obtain excellent surgical results. The author considers that the key points of removing large vestibular schwannomas (VS) are continuous facial nerve monitoring, deep and wide opening of the internal auditory canal, 7 gates for removing a tumor, 3 planes in tumor dissection, V-cut technique, and lifting up the tumor from the cerebellopontine (CP) angle cistern, from his personal surgical experience of 1,490 CP angle tumors including 1,074 VS. In this article, surgical points for trigeminal and jugular foramen schwannomas, CP angle and skull base meningiomas, and CP angle epidermoid cysts are also described.

  Fourth ventricle tumors are generally classified into two groups from the point of view of benign or malignant nature, or pediatric or adult tumors. But based on a surgical perspective, it is more important to classify whether the tumor is a true fourth ventricle tumor or not. Ependymomas, hemangioblastomas and choroid plexus papillomas are representative true fourth ventricle tumors. On the other hand, medulloblastomas and pilocytic astrocytomas are tumors that originate from the surrounding cerebellar hemisphere or cerebellar vermis, which extend to the fourth ventricle. In surgery of true fourth ventricle tumors, the cerebello-medullary fissure approach including the incision of the taenia and wide opening of the tela choroidea is effective in exposing both the tumor and the fourth ventricle floor. However, for medulloblastoma resection, using the uvulo-tonsillar space without dissection of the cerebello-medullary fissure is often effective. Key anatomical landmarks for surgery near the fourth ventricle are the inferior velum and the tela choroidea.

  In this manuscript, we present typical MRI findings of fourth ventricle tumors and our surgical procedures.

  Placing a neck bridging stent or a flow diverter has enabled the endovascular treatment for a wide-necked cerebral aneurysm by changes in intra-aneurysmal local hemodynamics. Computer-aided design (CAD) has been applied to an intracranial stent to simulate endovascular treatment effects using computational fluid dynamics (CFD). However, CFD analysis with CAD techniques needs enormous time. The aim of this study was to investigate the hemodynamic changes after placing intracranial stents using CFD with porous media modeling.

  The patient-specific geometry models of three unruptured internal carotid artery aneurysms with different sizes were acquired by using three-dimensional (3D) computed tomographic angiography. For each Digital Imaging and Communications in Medicine (DICOM) data, the 3D neck model was made using a Boolean subtraction of aneurysm-deleted model from original geometry model. We obtained 3D stent domain (3DSD) by the transformation in which 3D neck model was offset by a thickness of particle diameter, which corresponds to that of Enterprise VRD (Johnson & Johnson Codman, Miami, FL, USA). Volume coverage ratio (VCR) was defined as the stent volume ratio in 3DSD. Filtration of blood through a virtual 3DSD was described by Darcy’s law (porous media modeling). Hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI), oscillatory velocity index (OVI), relative residence time (RRT), and flow velocity (FV) at dome were calculated by the CFD analysis. CFD simulation was achieved by changing the VCR every 10% from 0% (VCR 0.00) to 50% (VCR 0.50).

  As VCR increased, WSS and FV at dome decreased, and RRT increased in all cases. OSI and OVI in small (Case 1) and medium-sized (Case 2) aneurysms peaked at VCR 0.30 or 0.20 and then decreased, while those in a large aneurysm (Case 3) re-increased at VCR 0.5 after the first peaking and decreasing.

  CFD analysis using porous media simulation revealed that an increase in VCR induced stagnant and disturbed blood flow in a short time. However, hemodynamics in a large aneurysm may be different from that of small and medium-sized aneurysms. CFD may be useful to determine the therapeutic strategy for endovascular neurosurgeons.

  A 28-year-old woman was admitted to the hospital for headache and visual field abnormality. Magnetic resonance imaging (MRI) showed a tumor in the right temporal lobe, with heterogeneous enhancement in gadolinium-enhanced T1-weighted imaging. Craniotomy and tumor resection were performed, and the histopathological findings showed predominantly high cellularity, which included proliferation of atypical astrocytic tumor cells, small spindle cells, and epithelioid/rhabdoid cells, accompanied by pseudopalisading necrosis and microvascular proliferation. Mitotic figures were frequently observed. However, there are also several areas of low cellularity, where piloid tumor cells proliferated forming fascicular or loose reticular structures, accompanied by Rosenthal fibers and eosinophilic granular bodies. Tumor cells were negative for IDH-1, and the BRAF V600E mutation was detected. Postoperatively, the patient underwent local brain radiotherapy (60 Gy, 2 Gy/day) and chemotherapy with temozolomide and bevacizumab and did not have a recurrence within a year after surgery. Herein, we report the findings from a unique case of PA with BRAF V600E mutation and anaplastic features. We plan to perform further genetic analysis and collect follow-up information.