Peter Kurucz

Endoscopic anatomical study of the arachnoid architecture on the base of the skull. Part I: The anterior and middle cranial fossa

Abstract Minimally invasive neurosurgery requires a detailed knowledge of microstructures, such as the arachnoid membranes. In spite of many articles addressing arachnoid membranes, its detailed organization is still not well described. The aim of this study is to investigate the topography of the arachnoid in the anterior cranial fossa and the middle cranial fossa. Rigid endoscopes were introduced through defined keyhole craniotomies, to explore the arachnoid structures in 110 fresh human cadavers. We describe the topography and relationship to neurovascular structures and suggest an intuitive terminology of the arachnoid. We demonstrate an “arachnoid membrane system”, which consists of the outer arachnoid and 23 inner arachnoid membranes in the anterior fossa and the middle fossa. The inner membranes are arranged in two “arachnoid membrane groups” in the examined regions. The first is the carotid membrane group, located in the suprasellar region, consisting of seven paired and three unpaired inner membranes and the outer arachnoid on its base. The second is the Sylvian membrane group, composed of three inner membranes of the Sylvian fissure and completed by the outer arachnoid. Our findings should be very helpful in understanding the complex organization of the cranial arachnoid, which is mandatory for the safe and effective use of minimally invasive endoscopic techniques.

Endoscopic approach-routes in the posterior fossa cisterns through the retrosigmoid keyhole craniotomy: an anatomical study

Endoscopy in cerebellopontine angle surgery is an increasingly used technique. Despite of its advantages, the shortcomings arising from the complex anatomy of the posterior fossa are still preventing its widespread use. To overcome these drawbacks, the goal of this study was to define the anatomy of different endoscopic approaches through the retrosigmoid craniotomy and their limitations by surgical windows. Anatomical dissections were performed on 25 fresh human cadavers to describe the main approach-routes. Surgical windows are spaces surrounded by neurovascular structures acting as a natural frame and providing access to deeper structures. The approach-routes are trajectories starting at the craniotomy and pointing to the lesion, passing through certain windows. Twelve different windows could be identified along four endoscopic approach-routes. The superior route provides access to the structures of the upper pons, lower mesencephalon, and the upper neurovascular complex through the suprameatal, superior cerebellar, and infratrigeminal windows. The supratentorial route leads to the basilar tip and some of the suprasellar structures via the ipsi- and contralateral oculomotor and dorsum sellae windows. The central endoscopic route provides access to the middle pons and the middle neurovascular complex through the inframeatal, AICA, and basilar windows. The inferior endoscopic route is the pathway to the medulla oblongata and the lower neurovascular complex through the accessory, hypoglossal, and foramen magnum windows. The anatomy and limitations of each surgical windows were described in detail. These informations are essential for safe application of endoscopy in posterior fossa surgery through the retrosigmoid approach.

Three-dimensional HD endoscopy - first experiences with the Einstein Vision system in neurosurgery

Abstract Lack of stereoscopy and inferior image resolution prevented endoscopes to become standard in Neurosurgery. The new Einstein Vision® system provides a 3D HD non-distorted image. The objective is to evaluate image quality and suitability for neurosurgery. The Einstein Vision® system was used for nine operations including four meningiomas, two aneurysms, one intraspinal lipoma, one lumbar stenosis, and one neuroma of the sciatic nerve. Image quality and suitability were analyzed in a semi-quantitative manner based on each 10 aspects and compared to an operating microscope. The system was successfully used in eight operations. Two operations could be completed with the new system as the only optical tool. In six operations it could be used only for certain parts, and in one operation the 3D effect was significantly disturbed. Overall, the image quality was rated “equal” to the microscope. Two aspects were found to be superior, four aspects equal, and four aspects inferior. Suitability was rated overall as “inadequate”. No aspect was rated superior, two aspects equal, six aspects inferior and two aspects could not be rated. Presently, image quality was found to be equal to the operating microscope but suitability for minimal invasive neurosurgical operation is inadequate.

Endoscopic anatomical study of the arachnoid architecture on the base of the skull. Part II: Level of the tentorium, posterior fossa and the craniovertebral junction

Abstract Interest in surgical anatomy of arachnoid membranes is relatively new and became more important with the development of endoscopic techniques in neurosurgery. In the first part we introduced the term “arachnoid membrane system” and “arachnoid membrane groups” and described them in the anterior and middle cranial fossa. The objective of this second part is to discuss the arachnoid membranes of the tentorial level, posterior fossa and the craniovertebral junction. Rigid endoscopes were introduced through defined keyhole craniotomies to explore the arachnoid in 127 fresh human cadavers. We defined 12 inner membranes that are arranged in three membrane groups. The “tentorial membrane group” consists of five paired membranes forming an almost complete barrier between the supra- and infratentorial spaces. The “clival membrane group” consists of three membranes and completes the separation created by the tentorial group. The superior part of the “perimedullary group” located around the medulla oblongata and consists of three inner membranes. The inferior part located in the craniovertebral junction consisting of four membranes. Intracranial arachnoid membranes are constant and defined structures that are well arranged in distinct groups. These new findings are essential in understanding the three-dimensional architecture of the arachnoid and its importance in endoscopic neurosurgery.

Endoscopic anatomy of the intracisternal oculomotor nerve: a new segmentation based on the topography of the arachnoid membranes

Abstract Objective: The aim of our study was to investigate the detailed endoscopic anatomy of the intracisternal portion of the oculomotor nerve and to update the present knowledge of its related anatomy with the newest research on the topography of the arachnoid membrane system of the skull base. Methods: This study was performed on 50 fresh human cadaveric specimens post-mortem not more than 72 h. In each specimen, the intracranial arterial system was injected with red gelatin solution. We used the endoscope-controlled and endoscope-assisted microsurgical techniques applied through the minimally invasive supraorbital keyhole craniotomy to perform our dissections. Results: We divided the intracisternal oculomotor nerve into three segments in this study. These are the interpeduncular segment, located in the interpeduncular fossa and surrounded by dens arachnoid trabeculae around the thalamoperforating arteries; the tentorial segment, located between the posterior cerebral and superior cerebellar arteries and the posterior petroclinoid fold and surrounded by the elements of the clival and tentorial arachnoid membrane groups; and the trigonal segment located on the surface of the oculomotor trigone between the posterior petroclinoid fold and the dural exit of the nerve into the cavernous sinus and surrounded by the posteriorly located membranes of the carotid membrane group. Conclusions: Our findings support the more accurate understanding of the physiology of the arachnoid membrane system and the pathophysiology of space-occupying lesions in the region of the oculomotor nerve. Therefore, our results may support performing more atraumatic surgery in this area.

The Clival Line as an Important Arachnoid Landmark During Endoscopic Third Ventriculostomy: An Anatomic Study

OBJECTIVE Endoscopic third ventriculostomy (ETV) is a well-accepted treatment option instead of ventriculoperitoneal shunt placement in cases of obstructive hydrocephalus. A sufficient flow from the ventricles to the basal cisterns requires perforation of the arachnoid membranes in the retroclival region. This point is critical to achieve an optimal outcome. The complex arachnoid relations were investigated in the retroclival region from the viewpoint of ETV, and anatomic landmarks were defined for subarachnoid dissections. METHODS Sixty fresh human cadaveric specimens were dissected under macroscopic, microscopic, and endoscopic control. The recordings of 100 operated cases of ETVs were analyzed to ascertain the clinical-anatomic relevance. RESULTS The Liliequist membrane complex and the anterior pontine membranes are located just above and parallel to both sides of the basilar artery. The basal attachment of these membranes forms an inverted U-shaped, white-grey thickening on the outer arachnoid. We refer to this structure as the clival line. During ETV, if arachnoid dissections were performed ventrally to the clival line, the outer arachnoid was opened; this resulted in a limited flow to the subarachnoid spaces (ventriculo-subdural). If the perforation on the arachnoid membranes was dorsal to the clival line, the prepontine cistern could be directly reached through the Liliequist membrane complex. CONCLUSIONS Sufficient arachnoid dissection is essential for a successful ETV. The clival line is an important landmark that helps to perform the subarachnoid dissections correctly and achieve an undisrupted cerebral spinal fluid flow between the ventricles and the basal cisterns.

Primary Obstruction of the Foramen of Luschka: Anatomy, Histology, and Clinical Significance

BACKGROUND The foramen of Luschka is a natural aperture between the fourth ventricle and the subarachnoid space at the cerebellopontine angle. Membranous closure of this foramen is referred to as primary obstruction. Available information about this variant and its role in the development of the cysts of the posterior fossa is contradictory. METHODS The macroscopic and histologic features of the obstructed foramina were examined in 61 formalin-fixed human brains (122 foramina). Three rhomboid lips of various sizes with lateral recess were used for comparison. Five postoperative cases of diverticulum of the foramen of Luschka were included in this study, with 1 case presented in detail to illustrate anatomic and histologic findings. RESULTS Primary obstruction was present in 11 of 122 cases. In 1 case, an enlarged rigid pouch with a thick wall was found. The wall of the membrane in primary obstruction and the rhomboid lip were composed of an inner ependymal, a middle glial, and an outer leptomeningeal layer. CONCLUSIONS The rhomboid lip is a remnant of the roof of the fourth ventricle. Imperforation of the foramen of Luschka results in a pouch in the cerebellopontine angle that contains choroid plexus (Bochdaleks flower basket) and communicates with the fourth ventricle. This pouch has the potential to grow to a diverticulum and cause clinical symptoms. Based on our clinical observations, detailed radiologic and surgical-anatomic criteria were proposed to support the differential diagnosis of a diverticulum of the foramen of Luschka. Treatment strategies were also suggested.

Endoscope-Assisted Microsurgical Removal of an Optic Foramen Meningioma through a Frontolateral Minicraniotomy

A 72-year-old male patient with visual disturbance of the right eye was diagnosed with a small meningioma of the right optic foramen extending to the carotid cistern. The operation was performed through an individually tailored frontolateral minicraniotomy via a curvilinear skin incision behind the hairline. Endoscope-assisted microsurgical technique was used to resect the lesion. The roof of the optic canal was partly removed to get access to the intraforaminal tumor parts. The lesion could be completely removed and the patient showed a satisfactory visual recovery in the follow-up examinations. The link to the video can be found at: https://youtu.be/p8EZx7aryeQ .

Vascular Lesions of the Skull Base

Cerebrovascular diseases of the skull base represent a separate entity. Especially aneurysms located close to the skull base as well as dural arteriovenous fistulas require highly specialized neuroradiological diagnostics and an individualized treatment strategy being exactly tailored to the lesion. For different reasons there has been a shift to endovascular treatment of these vascular lesions of the skull base over the years. Modern supraselective microcatheters and further development and improvement of the different embolization materials nowadays allow a very selective occlusion of arteriovenous malformations. Furthermore, the ongoing development of endovascular coil technology and especially the modern methods of vessel wall reconstruction by stents have pushed back the complex surgical procedures for the microsurgical clipping of skull base aneurysms. But nevertheless, endovascular procedures will not completely replace microsurgical therapy in the foreseeable future. A problem for the younger generation and especially for the practical training of young skull base surgeons is the decreasing number of neurovascular cases due to the increasing number of endovascular cases. Furthermore, often very complex cases that are very difficult to operate on remain for microsurgical therapy.