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Objective: Opening the roof of the interhemispheric microsurgical corridor to access various neurooncological or neurovascular lesions can be demanding because of the multiple bridging veins that drain into the sinus with their highly variable, location-specific anatomy. The objective of this study was to propose a new classification system for these parasagittal bridging veins, which are herein described as being arranged in 3 configurations with 4 drainage routes., Methods: Twenty adult cadaveric heads (40 hemispheres) were examined. From this examination, the authors describe 3 types of configurations of the parasagittal bridging veins relative to specific anatomical landmarks (coronal suture, postcentral sulcus) and their drainage routes into the superior sagittal sinus, convexity dura, lacunae, and falx. They also quantify the relative incidence and extension of these anatomical variations and provide several preoperative, postoperative, and microneurosurgical clinical case study examples., Results: The authors describe 3 anatomical configurations for venous drainage, which improves on the 2 types that have been previously described. In type 1, a single vein joins; in type 2, 2 or more contiguous veins join; and in type 3, a venous complex joins at the same point. Anterior to the coronal suture, the most common configuration was type 1 dural drainage, occurring in 57% of hemispheres. Between the coronal suture and the postcentral sulcus, most veins (including 73% of superior anastomotic veins of Trolard) drain first into a venous lacuna, which are larger and more numerous in this region. Posterior to the postcentral sulcus, the most common drainage route was through the falx., Conclusions: The authors propose a systematic classification for the parasagittal venous network. Using anatomical landmarks, they define 3 venous configurations and 4 drainage routes. Analysis of these configurations with respect to surgical routes indicates 2 highly risky interhemispheric surgical fissure routes. The risks are attributable to the presence of large lacunae that receive multiple veins (type 2) or venous complex (type 3) configurations that negatively impact a surgeon's working space and degree of movement and thus are predisposed to inadvertent avulsions, bleeding, and venous thrombosis.

OBJECTIVE The purpose of this study was to describe in detail the cortical and subcortical anatomy of the central core of the brain, defining its limits, with particular attention to the topography and relationships of the thalamus, basal ganglia, and related white matter pathways and vessels. METHODS The authors studied 19 cerebral hemispheres. The vascular systems of all of the specimens were injected with colored silicone, and the specimens were then frozen for at least 1 month to facilitate identification of individual fiber tracts. The dissections were performed in a stepwise manner, locating each gray matter nucleus and white matter pathway at different depths inside the central core. The course of fiber pathways was also noted in relation to the insular limiting sulci. RESULTS The insular surface is the most superficial aspect of the central core and is divided by a central sulcus into an anterior portion, usually containing 3 short gyri, and a posterior portion, with 2 long gyri. It is bounded by the anterior limiting sulcus, the superior limiting sulcus, and the inferior limiting sulcus. The extreme capsule is directly underneath the insular surface and is composed of short association fibers that extend toward all the opercula. The claustrum lies deep to the extreme capsule, and the external capsule is found medial to it. Three fiber pathways contribute to form both the extreme and external capsules, and they lie in a sequential anteroposterior disposition: the uncinate fascicle, the inferior fronto-occipital fascicle, and claustrocortical fibers. The putamen and the globus pallidus are between the external capsule, laterally, and the internal capsule, medially. The internal capsule is present medial to almost all insular limiting sulci and most of the insular surface, but not to their most anteroinferior portions. This anteroinferior portion of the central core has a more complex anatomy and is distinguished in this paper as the "anterior perforated substance region." The caudate nucleus and thalamus lie medial to the internal capsule, as the most medial structures of the central core. While the anterior half of the central core is related to the head of the caudate nucleus, the posterior half is related to the thalamus, and hence to each associated portion of the internal capsule between these structures and the insular surface. The central core stands on top of the brainstem. The brainstem and central core are connected by several white matter pathways and are not separated from each other by any natural division. The authors propose a subdivision of the central core into quadrants and describe each in detail. The functional importance of each structure is highlighted, and surgical approaches are suggested for each quadrant of the central core. CONCLUSIONS As a general rule, the internal capsule and its vascularization should be seen as a parasagittal barrier with great functional importance. This is of particular importance in choosing surgical approaches within this region.

The relevance of the cerebral venous system is often underestimated during neurosurgical procedures. Damage to this draining system can have catastrophic implications for the patient. Surgical decision-making and planning must consider each component of the venous compartment, from the medullary draining vein to the dural sinuses and extracranial veins. Intraoperative ultrasound (ioUS) permits the real-time study of venous compartments using different modalities, thus allowing complete characterization of their anatomical and functional features. The B-mode (brightness mode) offers a high-resolution anatomical representation of veins and their relationships with lesions. Doppler modalities (color, power, spectral) allow the study of blood flow and identification of vessels to distinguish their functional characteristics. Contrast-enhanced US allows one to perform real-time angiosonography showing both the functional and the anatomical aspects of vessels. In this technical report, the authors demonstrate the different applications of multimodal ioUS in neurosurgery for identifying the anatomical and functional characteristics of the venous compartment. They discuss the general principles and technical nuances of ioUS and analyze their potential implications for the study of various venous districts during neurosurgical procedures.

Objective: The drainage of the superficial middle cerebral vein (SMCV) has previously been classified into 4 subtypes. Extradural procedures and dural incisions during the anterior transpetrosal approach (ATPA) may interrupt the route of drainage from the SMCV. In this study, the authors examined the relationship between anatomical variations in the SMCV and the corresponding surgical modifications to the ATPA that are necessary for venous preservation., Methods: This study included 48 patients treated via the ATPA in whom the SMCV was examined using 3D CT venography. The drainage patterns of the SMCV were classified into 3 types: cavernous or absent (Type 1), sphenobasal (Type 2), and sphenopetrosal (Type 3). Type 2 was subdivided into medial (Type 2a) and lateral (Type 2b), and Type 3 was subdivided into vein (Type 3a), vein and sinus (Type 3b), and sinus (Type 3c). The authors performed 3 ATPA modifications to preserve the SMCV: epidural anterior petrosectomy with subdural visualization of the sphenobasal vein (SBV), modification of the dural incision, and subdural anterior petrosectomy. Standard ATPA can be performed with Type 1, Type 2a, and Type 3a drainage. With Type 2b drainage, an epidural anterior petrosectomy with subdural SBV visualization is appropriate. The dural incision should be modified in Type 3b. With Type 3c, a subdural anterior petrosectomy is required., Results: The frequency of each type was 68.7% (33/48) in Type 1, 8.3% (4/48) in Type 2a, 4.2% (2/48) in Type 2b, 14.6% (7/48) in Type 3a, 2.1% (1/48) in Type 3b, and 2.1% (1/48) in Type 3c. No venous complications were found., Conclusions: The authors propose an SMCV modified classification based on ATPA modifications required for venous preservation.

Objective: Transcortical and transsylvian corridors have been previously described as the main surgical approaches to the insula, but there is insufficient evidence to support one approach versus the other. The authors performed a cadaveric comparative study regarding insular exposure, surgical window and freedom, between the transcortical and transsylvian approaches (with and without cutting superficial sylvian bridging veins). Surgical anatomy and skull surface reference points to the different insular regions are also described., Methods: Sixteen cadaveric specimens were embalmed with a customized formula to enhance neurosurgical simulation. Two different blocks were defined in the study: first, transsylvian without (TS) and with the superficial sylvian bridging veins cut (TSVC) and transcortical (TC) approaches to the insula were simulated in all (16) specimens. Insular surface exposure, surgical window and surgical freedom were calculated for each procedure and related to the Berger-Sanai insular glioma classification (Zones I-IV) in 10 specimens. Second, the venous drainage pattern and anatomical landmarks considered critical for surgical planning were studied in all specimens., Results: In the insular Zone I (anterior-superior), the TC approach provided the best insular exposure compared with both TS and TSVC. The surgical window obtained with the TC approach was also larger than that obtained with the TS. The TC approach provided 137% more surgical freedom than the TS approach. Only the TC corridor provided complete insular exposure. In Zone II (posterior-superior), results depended on the degree of opercular resection. Without resection of the precentral gyrus in the operculum, insula exposure, surgical windows and surgical freedom were equivalent. If the opercular cortex was resected, the insula exposure and surgical freedom obtained through the TC approach was greater to that of the other groups. In Zone III (posterior-inferior), the TC approach provided better surgical exposure than the TS, yet similar to the TSVC. The TC approach provided the best insular exposure, surgical window, and surgical freedom if components of Heschl's gyrus were resected. In Zone IV (anterior-inferior), the TC corridor provided better exposure than both the TS and the TSVC. The surgical window was equivalent. Surgical freedom provided by the TC was greater than the TS approach. This zone was completely exposed only with the TC approach. A dominant anterior venous drainage was found in 87% of the specimens. In this group, 50% of the specimens had good alternative venous drainage. The sylvian fissure corresponded to the superior segment of the squamosal suture in 14 of 16 specimens. The foramen of Monro was 1.9 cm anterior and 4.42 cm superior to the external acoustic meatus. The M2 branch over the central sulcus of the insula became the precentral M4 (rolandic) artery in all specimens., Conclusions: Overall, the TC approach to the insula provided better insula exposure and surgical freedom compared with the TS and the TSVC. Cortical and subcortical mapping is critical during the TC approach to the posterior zones (II and III), as the facial motor and somatosensory functions (Zone II) and language areas (Zone III) may be involved. The evidence provided in this study may help the neurosurgeon when approaching insular gliomas to achieve a greater extent of tumor resection via an optimal exposure.

Object: The central lobe consists of the pre- and postcentral gyri on the lateral surface and the paracentral lobule on the medial surface and corresponds to the sensorimotor cortex. The objective of the present study was to define the neural features, craniometric relationships, arterial supply, and venous drainage of the central lobe., Methods: Cadaveric hemispheres dissected using microsurgical techniques provided the material for this study., Results: The coronal suture is closer to the precentral gyrus and central sulcus at its lower rather than at its upper end, but they are closest at a point near where the superior temporal line crosses the coronal suture. The arterial supply of the lower two-thirds of the lateral surface of the central lobe was from the central, precentral, and anterior parietal branches that arose predominantly from the superior trunk of the middle cerebral artery. The medial surface and the superior third of the lateral surface were supplied by the posterior interior frontal, paracentral, and superior parietal branches of the pericallosal and callosomarginal arteries. The venous drainage of the superior two-thirds of the lateral surface and the central lobe on the medial surface was predominantly through the superior sagittal sinus, and the inferior third of the lateral surface was predominantly through the superficial sylvian veins to the sphenoparietal sinus or the vein of Labbé to the transverse sinus., Conclusions: The pre- and postcentral gyri and paracentral lobule have a morphological and functional anatomy that differentiates them from the remainder of their respective lobes and are considered by many as a single lobe. An understanding of the anatomical relationships of the central lobe can be useful in preoperative planning and in establishing reliable intraoperative landmarks.

Object: The aim of this study was to describe the similarity of configuration between the arachnoid complex in the posterior half of the incisural space and the Liliequist membrane., Methods: Microsurgical dissection and anatomical observation were performed in 20 formalin-fixed adult cadaver heads. The origin, distribution, and configuration of the arachnoid membranes and their relationships with the vascular structures in the posterior half of the incisural space were examined., Results: The posterior perimesencephalic membrane and the cerebellar precentral membrane have a common origin at the tentorial edge and form an arachnoid complex strikingly resembling an inverted Liliequist membrane. Asymmetry between sides is not uncommon. If the cerebellar precentral membrane is hypoplastic on one side or both, the well-developed quadrigeminal membrane plays a prominent part in partitioning the subarachnoid space in the posterior half of the incisural space., Conclusions: The arachnoid complex in the posterior half of the incisural space can be regarded as an inverted Liliequist membrane. This concept can help neurosurgeons to gain better understanding of the surgical anatomy at the level of the tentorial incisura.

Object: Jugular foramen tumors often extend intra- and extracranially. The gross-total removal of tumors located both intracranially and intraforaminally is technically challenging and often requires a combined skull base approach. This study presents a suprajugular extension of the retrosigmoid approach directed through the osseous roof of the jugular foramen that allows the removal of tumors located in the cerebellopontine angle with extension into the upper part of the foramen, with demonstration of an illustrative case., Methods: The cerebellopontine angles and jugular foramina were examined in dry skulls and cadaveric heads to clarify the microsurgical anatomy around the jugular foramen and to define the steps of the suprajugular exposure., Results: The area drilled in the suprajugular approach is inferior to the acoustic meatus, medial to the endolymphatic depression and surrounding the superior half of the glossopharyngeal dural fold. Opening this area exposed the upper part of the jugular foramen and extended the exposure along the glossopharyngeal nerve below the roof of the jugular foramen. In the illustrative case, a schwannoma originating from the glossopharyngeal nerve in the cerebellopontine angle and extending below the roof of the jugular foramen and above the jugular bulb was totally removed without any postoperative complications., Conclusions: The suprajugular extension of the retrosigmoid approach will permit removal of tumors located predominantly in the cerebellopontine angle but also extending into the upper part of the jugular foramen without any additional skull base approaches.

Object: The foramen ovale and its neighboring vascular structures may be seen via external approaches to the skull base. More commonly, however, transcutaneous approaches to the foramen ovale are performed. Although complications with this latter technique are uncommon, studies of the distances to the surrounding extracranial vascular structures are lacking in the literature. The present study aimed to elucidate such anatomical relationships., Methods: Twenty adult cadavers (40 sides) underwent dissection of the region surrounding the foramen ovale at the external skull base. Measurements between the external surface of the foramen ovale and surrounding vascular structures were made., Results: From the nearest aspect of the undersurface of the foramen ovale, the authors found that the mean distances to the middle meningeal artery, maxillary artery, superior bulb of the internal jugular vein, and internal carotid artery at its entrance to and exit from the carotid canal were 3, 19, 20, 9, and 12 mm, respectively. Distances tended to be shorter in females, but this did not reach statistical significance. On the basis of these data, the authors also determined a safe zone while approaching the undersurface of the foramen ovale., Conclusions: Additional knowledge of the neurovascular relationships surrounding the foramen ovale may be useful to the neurosurgeon and may help decrease the potential for complications.

Object: There are few systematic investigations of the dissected surgical anatomy of the diploic venous system (DVS) in the neuroanatomical literature. The authors describe the DVS relative to different common neurosurgical approaches. Knowledge of this system can help avoid potential sources of unacceptable bleeding and may impact healing of the cranium., Methods: Using a high-speed drill with a 2-mm bit, the authors removed the outer layer of the compact bone in the skull to expose the DVS in 12 formalin-fixed cadaver heads. Pterional, supraorbital, and modified orbitozygomatic craniotomies were performed to delineate the relationship of the DVS., Results: The draining point of the frontal diploic vein (FDV) was located near the supraorbital notch. The draining point of the anterior temporal diploic vein (ATDV) was located in all pterional areas; the draining point of the posterior temporal diploic vein (PTDV) was located in all asterional areas. The PTDV was the dominant diploic vessel in all sides. The FDV and ATDV could be damaged during supraorbital, modified orbitozygomatic, and pterional craniotomies. The anterior DVS connected with the sphenoparietal and superior sagittal sinus (SSS). The posterior DVS connected with the transverse and sigmoid sinuses and was the dominant diploic vessel in all 24 sides. Of all the major diploic vessels, the location and pattern of distribution of the FDV were the most constant. The parietal bone contained the most diploic vessels. No diploic veins were found in the area delimited by the temporal squama., Conclusions: The pterional, orbitozygomatic, and supraorbital approaches place the FDV and ATDV at risk. The major anterior diploic system connects the SSS with the sphenoparietal sinus. The posterior diploic system connects the SSS with the transverse and sigmoid sinuses.

Cerebral venous sinus thrombosis (CVST) is a rare clinicopathological entity. The incidence of CVST in children and neonates has been reported to be as high as 7 cases per million people, whereas in adults the incidence is 3-4 cases per million. The predisposing factors to this condition are mainly genetic and acquired prothrombotic states and infection. The clinical picture of CVST is nonspecific, highly variable, and can mimic several other clinical conditions. Diagnosis of CVST is established with the implementation of neuroimaging studies, especially MR imaging and venography. Identification and elimination of the underlying cause, anticoagulation, proper management of intracranial hypertension, and anticonvulsant prophylaxis constitute cornerstones of CVST treatment. Newer treatment strategies such as endovascular thrombolysis and decompressive craniectomy have been recently used in the treatment of patients with CVST with variable success rates. Further clinical research must be performed to delineate the exact role of these newer treatments in the management of severe cases of CVST. The recent advances in the diagnosis and treatment of patients with CVST have significantly lowered the associated mortality and morbidity and have improved the outcome of these patients.

Object: The cerebral venous regulation involved in various physiological and pathological processes has received little attention. Here the authors describe the anatomy of the junction between the cortical vein and the superior sagittal sinus (SSS) and propose a new theory of cerebral venous regulation., Methods: Ten adult human cadaveric heads (20 sides), including five specimens into which stained latex had been injected, were used for anatomical study. Formalin-fixed cadaver heads were dissected to demonstrate the cortical veins along the SSS. The characteristics of the cortical bridging veins and their openings into the SSS were established by anatomical, histological, immunohistochemical, and ultrastructural study of the junction., Results: After their subarachnoid course, the cortical bridging veins penetrated the SSS at different points in the dura mater depending on their rostrocaudal position. The venous endothelium stretched beyond the sinus endothelium. The orientation of the collagen fibers changed at the level of the venous openings, with the luminal diameter becoming narrow and oval-shaped. The major finding was the organization of the smooth-muscle cells at the end of each cortical vein. At this site and particularly in the frontoparietal region, the vessel resembled a myoendothelial "sphincter." The authors hypothesize that this organization is involved in cerebral venous system regulation., Conclusions: The point of convergence between the cortical veins and the SSS is a key area. The authors also hypothesize that the myoendothelial junction acts as a smooth sphincter and that it plays a role in cerebral venous hemodynamics and pathological conditions.

Object: The purpose of this human cadaver study was to determine whether or not an intraosseous skull infusion would access the superior sagittal sinus (SSS) via intradural venous channels. The diploic space of the skull bone contains a sinusoidal vascular network that communicates with the underlying dura mater. Diploic veins in the parasagittal area connect with endothelium-lined intradural channels in the subjacent dura and ultimately with the dural venous sinuses. A significant proportion of cerebrospinal fluid (CSF) absorption is thought to occur via arachnoid granulations in the region of the SSS and especially along the parasagittal dura where arachnoid granulations are surrounded by intradural venous channels (lateral lacunae). The CSF is likely to be conducted from the subarachnoid space into the venous system via the fine intradural channels making up the lateral lacunae., Methods: Infusion of vinyl acetate casting material into the diploic space of the human cadaveric skull resulted in complete filling of the lateral lacunae and SSS. Corrosion casting techniques and examination under magnification were used to characterize the anatomical connections between diploic spaces and dural venous sinuses., Results: Corrosion casting, performed on five formalin-fixed cadavers, clearly showed the anatomical connections between the diploic infusion site and the venous sinuses in the underlying parasagittal dura where some of the CSF is thought to be absorbed., Conclusions: The diploic vascular channels of the human skull may represent an indirect pathway into the dural venous sinuses. Intraosseous skull infusion may represent another possible strategy for diversion of CSF into the vascular system in the treatment of hydrocephalus.

Object: The superior and inferior sagittal sinuses have been well studied. Interestingly, other venous structures within the falx cerebri have received scant attention in the medical literature. The present study was performed to elucidate the presence and anatomy of these midline structures., Methods: The authors examined 27 adult latex- or ink-injected cadaveric specimens to observe the morphological features of the sinuses within the falx cerebri (excluding the inferior and superior sagittal sinuses)., Results: All specimens were found to have an extensive network of small tributaries within the falx cerebri that were primarily concentrated in its posterior one third. In this posterior segment, these structures were usually more pronounced in the inferior two thirds. The portion of the falx cerebri not containing significant falcine venous sinus was termed a "safe area." These vascular channels ranged in size from 0.5 mm to 1.1 cm (mean 0.6 mm); 100% of these vessels communicated with the inferior sagittal sinus. Classification of the structures was then performed based on communication of the falcine venous sinus with the superior sagittal sinus. Type I falcine sinuses had no communication with the superior sagittal sinus, Type II falcine sinuses had limited communication with the superior sagittal sinus, and Type III falcine sinuses had significant communication with the superior sagittal sinus. Seventeen (63%) of 27 specimens communicated with the superior sagittal sinus (Types II and III). Further subdivision revealed 10 Type I, seven Type II, and 10 Type III falcine venous plexuses., Conclusions: There are other venous sinuses in the falx cerebri in addition to the superior and inferior sagittal sinuses. Neurosurgical procedures that necessitate incising or puncturing the falx cerebri can be done more safely via a described safe area. Given that the majority of specimens in the authors' study were found to have a plexiform venous morphology within the falx cerebri, they propose that these channels be referred to as the falcine venous plexus and not sinus. The falcine venous plexus should be taken into consideration by the neurosurgeon.

Object: The purpose of this study was to define the patterns of drainage of the superior petrosal venous complex (SPVC) along the petrous ridge in relation to the Meckel cave and internal acoustic meatus (IAM) and to delineate its effect on the surgical exposures obtained in subtemporal transtentorial and retrosigmoid suprameatal approaches., Methods: The patterns of drainage of the SPVC along the petrous ridge were characterized according to their relation to the Meckel cave and the IAM based on an examination of 30 hemispheres. Subtemporal transtentorial and retrosigmoid suprameatal approaches were performed in three additional cadavers to demonstrate the effect of the drainage pattern on the surgical exposures., Conclusions: The SPVC emptied into the superior petrosal sinus (SPS) within a distance of 1 cm from the midpoint of the Meckel cave. The patterns of drainage of the SPVC were classified into three groups. Type I emptied into the SPS above and lateral to the boundaries of the IAM. The most common type, Type II, emptied between the lateral limit of the trigeminal nerve at the Meckel cave and the medial limit of the facial nerve at the IAM, within an area of approximately 13 mm. Type III emptied into the SPS above or medial to the Meckel cave. The ideal SPVC for a subtemporal transtentorial approach (with or without anterior extradural petrosectomy) seems to be a Type I. In SPVC Type III and those Type II cases in which the SPVC is located near the Meckel cave, the amount of working space is significantly limited in a subtemporal transtentorial approach. In contrast, the ideal type of SPVC for a retrosigmoid suprameatal approach would be a Type III, and the SPVC must be divided in the majority of Type I and II cases for a satisfactory surgical exposure along the Meckel cave and middle fossa dura. The proposed modified classification system and its effect on the surgical exposure may aid in planning the approach directed along the petrous apex and may reduce the probability of venous complications.

Object: The purpose of this study was to determine the ability of software-assisted 3D reconstruction performed using a neuronavigation system to delineate the anatomy and variation patterns of the pineal region venous complex, and then to compare these data with previous anatomical findings., Methods: The authors retrospectively reviewed the neuroimages obtained in 100 patients with intracranial lesions (50 computed tomography [CT] scans obtained with contrast agents and 50 magnetic resonance [MR] images obtained with gadolinium) by using a neuronavigation workstation for 3D reconstruction. Particular attention was given to the internal cerebral vein, basal vein (BV), and the vein of Galen. The various connection patterns between the major vessels were classified and statistically analyzed., Conclusions: The venous system of the pineal region shows a wide range of sex-related variations. In the female patient the absence of a BV (Type 0) is significantly more frequent than in the male. In this study the authors illustrate the ability to depict the venous drainage patterns in the pineal region for all cases studied by using 3D neuronavigation software without the need for additional examinations. This simple tool provides important information for surgical planning and may be of significant help intraoperatively.

Object: The basal vein of Rosenthal (BV) courses from the premesencephalic cistern, through the ambient cistern, and terminates in the quadrigeminal cistern. The aim of this study was to describe and quantitate the surgical anatomy of this structure and specifically to provide landmarks for identifying this vessel along its course. These data may be of use, for example, to surgeons using subtemporal operative approaches through regions where this vessel is concealed., Methods: The authors examined 15 latex-injected adult cadaveric brains (30 sides) to delineate the morphological characteristics of the BV. Dissections of the BV were then performed and measurements were made between this structure and the tentorial incisura at the anterior, middle, and posterior borders of the lateral midbrain. All specimens were found to have a left and right BV with varying morphological characteristics. The mean distance between the BV and posterior cerebral artery at the midpoint of the lateral midbrain was 16 mm. The BV was always found superomedial to the posterior cerebral artery along the lateral aspect of the midbrain, and the BV ranged in diameter from 1 to 5 mm. The BV drained into the vein of Galen in all but two specimens. The mean distances from the tentorial edge to the BV at the anterior, middle, and posterior borders of the lateral midbrain were 11, 1 3, and 4 mm, respectively. No statistically significant differences were found when comparing left and right sides or male and female specimens., Conclusions: The authors hope that these data will help the neurosurgeon operating near the BV to avoid injury to this important structure.

Object: The authors studied the microsurgical anatomy and endoscopic features of the pineal region and third ventricle to describe a combined microsurgical-endoscopic infratentorial-supracerebellar approach to the posterior third ventricle. Such an approach exposes the pineal gland and its complex neurovascular structures so that the third ventricle can be reached through a minimally invasive parapineal incision., Methods: The approach was studied in 10 adult cadaveric heads, six fresh and four formalin fixed, by using an operative microscope with a magnification level of 6 to 40 and the assistance of an endoscope. The endoscope-assisted infratentorial-supracerebellar approach affords a complete view of the third ventricle from a posterior perspective. The third ventricle is entered through a parapineal incision using the natural space between the internal cerebral vein and the vein of Rosenthal located above the superior colliculi., Conclusions: The infratentorial-supracerebellar approach to the third ventricle follows a natural corridor and requires minimal retraction and resection of critical neural structures. With the use of the endoscope, an unsurpassed view into the third ventricle from a posterior perspective is obtained.

Object: Chordae willisii are structures located in the lumen of the superior sagittal sinus (SSS). It is thought that they act as flow-improving structures within the sinuses. There are few anatomical descriptions of chordae willisii, and all previous observations were performed through standard anatomical dissections. The purpose of this study was to visualize and describe structural and topographical features of the chordae willisii with the aid of rigid endoscopy., Methods: Twenty-five SSSs obtained from fresh human cadavers during autopsies were the material for this study. Specimens were flushed with tap water to remove clots. Bridging veins emptying into the sinus were ligated, and continuous flow of a saline solution through the sinus in a physiological direction was achieved by connecting the sinus to an irrigating system. Rigid endoscopes of different diameters (2.7-4.5 mm) and optic (0 and 30 degrees) were inserted into the lumen of the sinus. The endoscope was connected to a digital camera and a video system to allow for recording of the observed structures. Finally, the sinuses were opened and the chordae willisii were dissected using standard anatomical methods. The chordae willisii were observed in all examined specimens. Three different types of the cords were found: lamellar, trabecular, and valvelike types. The most common type was the valvelike (mixed) one, which comprised 45.1% of all cords. The chordae willisii were most commonly observed in the parietooccipital region of the SSS., Conclusions: Witout disturbing any structural relationships, the use of endoscopy allowed visualization and description of intraluminal structures as they behaved physiologically.

Object: The two most common surgical routes to the fourth ventricle are the transvermian and telovelar approaches. The purpose of this study was to compare the microanatomy and exposures gained through these approaches., Methods: Ten formalin-fixed specimens were dissected in a stepwise manner to simulate the transvermian and telovelar surgical approaches. Stealth image guidance was used to compare the exposures and working angles obtained using these approaches. The transvermian and telovelar approaches provided access to the entire rostrocaudal length of the fourth ventricle floor from the aqueduct to the obex. In addition, both approaches provided access to the entire width of the floor of the fourth ventricle. The major difference between the two approaches regarded the exposure of the lateral recess and the foramen of Luschka. The telovelar, but not the transvermian, approach exposed the lateral and superolateral recesses and the foramen of Luschka. The transvermian approach, which offered an incision through at least the lower third of the vermis, afforded a modest increase in the operator's working angle compared with the telovelar approach when accessing the rostral half of the fourth ventricle., Conclusions: The transvermian approach provides slightly better visualization of the medial part of the superior half of the roof of the fourth ventricle. The telovelar approach, which lacks incision of any part of the cerebellum, provides an additional exposure to the lateral recesses and the foramen of Luschka.

Object: The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure., Methods: The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres., Conclusions: The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

Object: The deep cerebral veins may pose a major obstacle in operative approaches to deep-seated lesions, especially in the pineal region where multiple veins converge on the great cerebral vein of Galen. Because undesirable sequelae may occur from such surgery, the number of veins and branches to be sacrificed during these approaches should kept to a minimum. The purpose of this study was to examine venous drainage into the vein of Galen with a view to surgical approaches. If a vein hampering surgical access must be sacrificed, it can therefore be selected according to the smallest draining territory., Methods: The deep cerebral veins and their surrounding neural structures were examined in 50 cerebral hemispheres from 25 adult cadavers in which the arteries and veins had been perfused with red and blue silicone, respectively. Special consideration was given to the size and location of drainage of the vein of Galen and its tributaries., Conclusions: When a surgeon approaches the pineal region, several veins may hamper the access route. From posterior to anterior, these include the following: the superior vermian and the precentral or superior cerebellar veins, which drain into the posteroinferior aspect of the vein of Galen; and the tectal and pineal veins, which drain into its anterosuperior aspect. The internal occipital vein is the main vessel draining into the lateral aspect of the vein of Galen. It may be joined by the posterior pericallosal vein, and in that case has an extensive territory. To avoid intraoperative venous infarction, it is important to use angiography to determine the venous organization before surgery and to estimate the permeability and size of the branches of the deep venous system.

Object: The sphenopetroclival area is the border zone between the middle and posterior cranial fossa. Several authors have studied the microsurgical anatomy of this region and have furnished sometimes contradictory descriptions of this area, which still represents a great challenge for the neurosurgeon. On the basis of previous anatomical data reported in the literature, the authors undertook a new microanatomical analysis of the sphenopetroclival region and report their findings., Methods: Twenty human cadaveric heads were used to reproduce, in the laboratory, different skull base approaches to expose the petroclival area. Measurements were taken in 40 specimens. From this study has emerged the finding that the sphenopetroclival area is a venous space, which the authors have named the "sphenopetroclival venous gulf" (SPCVG). The SPCVG is filled anteriorly by blood from the cavernous sinus (lateral sellar compartment [LSC], medially by blood from the basilar plexus, and laterally by blood from the superior petrosal sinus; this venous gulf is drained by the inferior petrosal sinus. The SPCVG is comparable in shape to an irregular hedron figure. It contains the Dorello canal, the venous segment of the abducent nerve, and the superior sphenopetrosal (Gruber) ligament, the fibers of which are in anatomical continuity with those of the inferior sphenopetrosal (petrolingual) ligament, forming a "falciform ligament.", Conclusions: The structures defining the posterior surface of the SPCVG may represent a helpful surgical corridor through which it is possible to approach the LSC via the posterior fossa. This conceptualization of the SPCVG is an attempt to define univocally the microanatomy of the sphenopetroclival region in its entirety.

Object: In this study the authors performed a retrospective analysis of five cases in which the patients (three women and two men) were treated for intracranial dural arteriovenous fistulas (AVFs) associated with cerebellar hemorrhage. On the basis of their findings, the authors evaluated the characteristics of this unusual symptom., Methods: The dural AVFs were located in the right cavernous sinus in one patient, the left transverse-sigmoid sinus in three patients, and the right superior petrosal sinus (SPS) in one patient. All patients presented with severe headache and/or loss of consciousness. Computerized tomography scans revealed a small cerebellar hemorrhage near the fourth ventricle and hydrocephalus in four cases, and a massive hemispheric cerebellar hemorrhage in the remaining case. The four patients with small hemorrhages underwent ventriculostomy and endovascular treatment; all recovered. The patient suffering from a massive hemorrhage because of a dural AVF in the SPS was treated by suboccipital craniectomy, hematoma evacuation, and removal of the vascular anomaly. This patient remains in a persistent vegetative state. In four cases, results of angiography demonstrated retrograde leptomeningeal venous drainage through the SPS to the anastomotic lateral mesencephalic vein (ALMV) and/or to the vein of the lateral recess of the fourth ventricle (VLR4V). Retrograde leptomeningeal venous drainage to the ALMV and/or VLR4V was responsible for cerebellar hemorrhage in these cases., Conclusions: Thus, it is important to consider dural AVF in cases in which there is even a small hemorrhage near the fourth ventricle accompanied by intraventricular perforation and a decreased level of consciousness.

Object: In the past, access to the fourth ventricle was obtained by splitting the vermis or removing part of the cerebellum. The purpose of this study was to examine the access to the fourth ventricle achieved by opening the tela choroidea and inferior medullary velum, the two thin sheets of tissue that form the lower half of the roof of the fourth ventricle, without incising or removing part of the cerebellum., Methods: Fifty formalin-fixed specimens, in which the arteries were perfused with red silicone and the veins with blue silicone, provided the material for this study. The dissections were performed in a stepwise manner to simulate the exposure that can be obtained by retracting the cerebellar tonsils and opening the tela choroidea and inferior medullary velum., Conclusions: Gently displacing the tonsils laterally exposes both the tela choroidea and the inferior medullary velum. Opening the tela provides access to the floor and body of the ventricle from the aqueduct to the obex. The additional opening of the velum provides access to the superior half of the roof of the ventricle, the fastigium, and the superolateral recess. Elevating the tonsillar surface away from the posterolateral medulla exposes the tela, which covers the lateral recess, and opening this tela exposes the structure forming the walls of the lateral recess.

The behavior of bridging veins at their entrance into the superior sagittal sinus during elevated intracranial pressure (ICP) was investigated in rats using a cranial window and infusion of mock cerebrospinal fluid. The bridging veins became slightly smaller as the ICP rose (maximum reduction 17%). Compression or collapse of the veins was not observed, even at an ICP level of 100 mm Hg, and there was no cuffing of bridging veins upstream of the entrance. Both the scanning electron microscopic investigation based on resin vessel casts and the histological examination of whole-head coronal sections indicated that the narrowest points of the bridging veins are at their entrance to the superior sagittal sinus, caused by the oval aperture with thickened wall structure in the lateral sinus wall to which the bridging veins are connected. The present data thus support the concept that cerebral blood flow during intracranial hypertension is not reduced by venous cuffing or compression of the lateral lacunae and bridging veins; by contrast, the arteriovenous pressure difference seems to remain the determining factor even at high ICP. Thus, blood flow through the brain stops when ICP approaches the level of blood pressure.