Endoscopic approaches to intraventriclar lesions and the endoscopic anatomy of the cerebral ventricles are described. A wide visual field, close observation for deep seated lesions and exploration in the wet field are the benefits of endoscopic surgery. In addition, changes in view point help to foster a better understanding of the three-demensional anatomy of the cerebral ventricles. Endoscopic tumor removal is performed via various types of transparent sheathes with specially designed instruments. The ventricles are surrounded by essential structures, which should be kept intact during the surgery. Distortion of the paraventricular structures is often seen in patients with paraventricular tumors. The foramen of Monro, choroid plexus, and thalamostriate vein are the clear landmarks to follow even in distorted anatomy. Understanding the endoscopic anatomy of the cerebral ventricles based on these landmarks assures a correct orientation and safety during the surgical treatment.

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  This article describes the surgical anatomy for various endoscopic procedures to deal with a variety of cerebrospinal fluid pathway obstructions. The procedures are roughly classified into two tasks : the creation of a bypass into the cisterns and the restoration of the obstructed cerebrospinal fluid pathway. A thorough knowledge of the structure and vasculature in the cistern is required for the success of the former and neural fiber and nucleus under the ventricle should be ascertained for the latter. Usually third ventriculostomy is performed behind the clivus, halfway between the infundibular recess and mammillary bodies in the midline. Both the interpeduncular and prepontine cisterns should be inspected through the ventriculostomy with perforation of two leaves of Liliequist's membrane. In temporal ventriculostomy, blunt perforation should be done at the tip of the inferior horn, laterally from the choroidal fissure line to avoid injuring the anterior choroidal artery. In aqueductoplasty, gentle inflation of the balloon to perforate the obstructive membrane is required in order to protect the oculomotor nucleus, medial longitudinal fasciculus and trochlear nerve fiber seated close to the ependymal layer. Finally, because anatomical variations are sometimes observed in cases with hydrocephalus, preoperative high resolution MR-images are essential prior to performing these procedures.

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  Recently, an endoscopic trans-nasal approach has become frequently used for skull base surgery. Depending on the extent of the skull base lesions, an appropriate corridor in the nasal cavity should be chosen to avoid excessive resection of important nasal constructions. For the mid-line approach including pituitary surgery, resection of the vomer and anterior wall of the sphenoid sinus provides sufficient surgical fields without resection of the middle turbinate. In some cases, partial resection of the superior turbinate is required. In cases in which surgical procedures around the carotid prominence and the optic nerve canal in the sphenoid sinus, ethmoidectomy via the middle meatus is necessary. In such cases, partial resection of the superior turbinate is required, but the middle turbinate can be preserved. It is also important to understand the anatomical relation between the sphenoid and posterior ethmoid sinus, especially to an Onodi cell, which if present would be located superiorly to the sphenoid sinus. For more advanced cases, maxillectomy is necessary to access to the lateral aspects of the sphenoid. The round canal and vidian canal are two important landmarks in this approach. When the pedicled mucoperiosteal septal flap is elevated for the reconstruction of the skull base, we should pay attention to the location of the olfactory epithelium and septal branches of the sphenopalatine artery.

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  Although the recent progress in neruoendoscopy including image-guidance techniques has enhanced pituitary surgery via the transsphenoidal route, it still requires the surgeon possess sophisticated skills to overcome conflicts between the lens rod-scope and surgical tools in the narrow surgical corridor. To achieve a safe and reliable technique, a systematic understanding of the anatomical structures of the nasal cavity, sphenoid and ethmoid sinuses, and sellar region are mandatory. The nasal phase is the first step of the procedure, which includes the inferior and middle turbinates, bony septum of the vomer, perpendicular plate of the ethmoid bone and sphenopalatine artery as important landmarks. For the sphenoid phase, the superior turbinate, posterior ethmoid sinus, sphenoid septum, optic prominence, carotid prominence, and opticocarotid recess should be cared for before approaching the sellar floor. Finally, after making an incision into the sellar floor dura matter and medial cavernous sinus wall, such structures as diaphragm sellae, and arachnoid recess should be mentioned. In this article, the authors describe the basis of microsurgical anatomy in a step-by-step way in relation to pure endoscopic endonasal removal of pituitary tumors.

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  Extended skull base surgery based on endoscopic endonasal transsphenoidal surgery (E-ETSS) for various skull base lesions has been reported recently. However, application of E-ETSS without sufficient experience and knowledge of the surgical anatomy may result in severe complications. In the approach to the skull base, making a wide opening in the anterior sphenoid sinus wall through both nostrils with or without superior or middle turbinectomy is important. In opening the skull base, comprehension of anatomical landmarks and having an image of normal anatomy in the endoscopic view are necessary. In this paper, the essential surgical methods and anatomy for anterior, cavernous and clivus lesions are reported with contrast to cadaver studies and surgical cases.

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  Lesions in the posterior cranial fossa are sometimes difficult to observe by microscope since they are often located in a deep and hidden area. We outlined the microsurgery procedure for lesions in the posterior cranial fossa assisted by endoscope. By use of endoscope, the hidden structures such as the perforators and the wall of the aneurysm in the aneurysmal clipping, the offending vessel and the root entry/exit zone in the microvascular decompression, the nerve behind the CP angle tumor, and the view of the fundus of the internal auditory meatus can be recognized in the early stage of the surgical procedure. The endoscope compliments the microscope, and a combination of those two surgical tools improves the safety and certainty of surgery.

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  Percutaneous endoscopic discectomy (PED) is a minimally invasive procedure for decompressing mechanical compression of a nerve root by an intervertebral disc. PED has further evolved as a procedure via a posterior approach for intervertebral foramen decompression of nerve roots and for pinpoint resection, medially or laterally to the intervertebral facet joint. PED is now performed for laminectomy with decompression of the dura and nerve roots in spinal canal stenosis. The macro-and microanatomy of nerve roots must thus be thoroughly understood for decompression surgery. The use of PED has expanded about 4-fold compared to MED. Moreover, because of the clean and bloodless surgical field, structures that have previously been difficult to identify can now be observed, including the sinuvertebral nerves and radicular vessels along the nerve roots.
  During exit out of the intervertebral foramen from the lateral recess, nerve roots change in structure and terminology in 3 stages, as ventral and dorsal roots, spinal nerves, and peripheral nerves. In addition, the microcirculation with the transition from nerve root to the dural canal displays unique characteristics unlike those in other organs. First, veins in the tissues of the spinal canal have no valves. Furthermore, the cauda equina in the lumbar area is a blood flow “watershed” region where blood flows from cephalad to caudal and also from caudal to cephalad. The hemodynamics can thus be greatly affected by standing or other postures. This can lead to the development of intermittent claudication.

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  We report the case of a patient with a non-ruptured aneurysm that had developed and expanded at the site of anastomosis of the superficial temporal artery (STA) and middle cerebral artery (MCA). A 58-year-old man had undergone STA-MCA anastomosis and neck clipping of a right MCA aneurysm 8 years ago. Follow-up magnetic resonance imaging (MRI) was performed every year, and the patency of the bypass was confirmed. We first detected the formation of an aneurysm at the site of the anastomosis by using MRI in 2010. We retrospectively evaluated the MRI results and found a bulge at the site of the anastomosis. The size of the aneurysm increased gradually up to 8 mm. The patient underwent neck clipping of the aneurysm. A part of the aneurysm was excised after neck clipping. Histological examination revealed a true aneurysm. The patient's postoperative course was uneventful. Here, we report a rare case of aneurysm formation and growth at the site of anastomosis, with a review of the literature.

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