Guilherme Carvalhal Ribas

The medial wall of the cavernous sinus: microsurgical anatomy.

OBJECTIVE:This study was conducted to clarify the boundaries, relationships, and components of the medial wall of the cavernous sinus (CS). METHODS:Forty CSs, examined under ×3 to ×40 magnification, were dissected from lateral to medial in a stepwise fashion to expose the medial wall. Four CSs were dissected starting from the midline to lateral. RESULTS:The medial wall of the CS has two parts: sellar and sphenoidal. The sellar part is a thin sheet that separates the pituitary fossa from the venous spaces in the CS. This part, although thin, provided a barrier without perforations or defects in all cadaveric specimens studied. The sphenoidal part is formed by the dura lining the carotid sulcus on the body of the sphenoid bone. In all of the cadaveric specimens, the medial wall seemed to be formed by a single layer of dura that could not be separated easily into two layers as could the lateral wall. The intracavernous carotid was determined to be in direct contact with the pituitary gland, being separated from it by only the thin sellar part of the medial wall in 52.5% of cases. In 39 of 40 CSs, the venous plexus and spaces in the CS extended into the narrow space between the intracavernous carotid and the dura lining the carotid sulcus, which forms the sphenoidal part of the medial wall. The lateral surface of the pituitary gland was divided axially into superior, middle and inferior thirds. The intracavernous carotid coursed lateral to some part of all the superior, middle, and inferior thirds in 27.5% of the CSs, along the inferior and middle thirds in 32.5%, along only the inferior third in 35%, and below the level of the gland and sellar floor in 5%. In 18 of the 40 CSs, the pituitary gland displaced the sellar part of the medial wall laterally and rested against the intracavernous carotid, and in 6 there was a tongue-like lateral protrusion of the gland that extended around a portion of the wall of the intracavernous carotid. No defects were observed in the sellar part of the medial wall, even in the presence of these protrusions. CONCLUSION:The CS has an identifiable medial wall that separates the CS from the sella and capsule of the pituitary gland. The medial wall has two segments, sellar and sphenoidal, and is formed by just one layer of dura that cannot be separated into two layers as can the lateral wall of the CS. In this study, the relationships between the medial wall and adjacent structures demonstrated a marked variability.

Endoscopic anatomy of the pterygopalatine fossa and the transpterygoid approach: development of a surgical instruction model.

Introduction: The pterygopalatine fossa (PPF) is a narrow space located between the posterior wall of the antrum and the pterygoid plates. Surgical access to the PPF is difficult because of its protected position and its complex neurovascular anatomy. Endonasal approaches using rod lens endoscopes, however, provide better visualization of this area and are associated with less morbidity than external approaches. Our aim was to develop a simple anatomical model using cadaveric specimens injected with intravascular colored silicone to demonstrate the endoscopic anatomy of the PPF. This model could be used for surgical instruction of the transpterygoid approach.

Surgical Anatomy of Microneurosurgical Sulcal Key Points

OBJECTIVE: The brain sulci constitute the main microanatomic delimiting landmarks and surgical corridors of modern microneurosurgery. Because of the frequent difficulty in intraoperatively localizing and visually identifying the brain sulci with assurance, the main purpose of this study was to establish cortical/sulcal key points of primary microneurosurgical importance to provide a sulcal anatomic framework for the placement of craniotomies and to facilitate the main sulci intraoperative identification. METHODS: The study was performed through the evaluation of 32 formalin-fixed cerebral hemispheres of 16 adult cadavers, which had been removed from the skulls after the introduction of plastic catheters through properly positioned burr holes necessary for the evaluation of cranial–cerebral relationships. Three-dimensional anatomic and surgical images are displayed to illustrate the use of sulcal key points. RESULTS: The points studied were the anterior sylvian point, the inferior rolandic point, the intersection of the inferior frontal sulcus with the precentral sulcus, the intersection of the superior frontal sulcus with the precentral sulcus, the superior rolandic point, the intersection of the intraparietal sulcus with the postcentral sulcus, the superior point of the parieto-occipital sulcus, the euryon (the craniometric point that corresponds to the center of the parietal tuberosity), the posterior point of the superior temporal sulcus, and the opisthocranion, which corresponds to the most prominent point of the occipital bossa. These points presented regular neural and cranial–cerebral relationships and can be considered consistent microsurgical cortical key points. CONCLUSION: These sulcal and gyral key points can be particularly useful for initial intraoperative sulci identification and dissection. Together, they compose a framework that can help in the understanding of hemispheric lesion localization, in the placement of supratentorial craniotomies, as landmarks for the transsulcal approaches to periventricular and intraventricular lesions, and in orienting the anatomic removal of gyral sectors that contain infiltrative tumors.

The cerebral sulci and gyri

The aim of this study was to describe in detail the microanatomy of the cerebral sulci and gyri, clarifying the nomenclature for microneurosurgical purposes. An extensive review of the literature regarding the historical, evolutionary, embryological, and anatomical aspects pertinent to human cerebral sulci and gyri was conducted, with a special focus on microneuroanatomy issues in the field of neurosurgery. An intimate knowledge of the cerebral sulci and gyri is needed to understand neuroimaging studies, as well as to plan and execute current microneurosurgical procedures.

Study of fetal and postnatal morphological development of the brain sulci

OBJECT The surface of the developing fetal brain undergoes significant morphological changes during fetal growth. The purpose of this study was to evaluate the morphological development of the brain sulci from the fetal to the early postnatal period. METHODS Two hundred fourteen brain hemispheres from 107 human brain specimens were examined to evaluate the timing of sulcal formation, from its appearance to its complete development. These brains were obtained from cadavers ranging in age from 12 weeks of gestation to 8 months of postnatal life. RESULTS The order of appearance of the cerebral sulci, and the number and percentages of specimens found in this study were as follows: longitudinal cerebral fissure at 12 weeks (10/10, 100%); callosal sulcus at 12 weeks (10/10, 100%); hippocampal sulcus at 15 weeks (7/10, 70%); lateral sulcus at 17 weeks (20/22, 90.9%); circular insular sulcus at 17 weeks (18/22, 81.8%); olfactory sulcus at 17 weeks (18/22, 81.8%); calcarine sulcus at 17 weeks (14/22, 63.6%); parietooccipital sulcus at 17 weeks (11/22, 50%); cingulate sulcus at 19 weeks (16/20, 80%); central sulcus at 21 weeks (22/38, 57.9%); orbital sulcus at 22 weeks (9/16, 56.2%); lunate sulcus at 24 ± 2 weeks (12/16, 75%); collateral sulcus at 24 ± 2 weeks (8/16, 50%); superior frontal sulcus at 25 ± 2 weeks (5/6, 83.3%); rhinal sulcus at 25 ± 2 weeks (3/6, 50%); precentral sulcus at 26 ± 3 weeks (2/4, 50%); postcentral sulcus at 26 ± 3 weeks (2/4, 50%); superior temporal sulcus at 26 ± 3 weeks (2/4, 50%); central insular sulcus at 29 ± 2 weeks (4/4, 100%); intraparietal sulcus at 29 ± 2 weeks (2/4, 50%); paraolfactory sulcus at 29 ± 2 weeks (2/4, 50%); inferior frontal sulcus at 30 ± 3 weeks (2/4, 50%); transverse occipital sulcus at 30 ± 3 weeks (2/4, 50%); occipitotemporal sulcus at 30 ± 3 weeks (2/4, 50%); marginal branch of the cingulate sulcus at 30 ± 3 weeks (2/4, 50%); paracentral sulcus at 30 ± 3 weeks (2/4, 50%); subparietal sulcus at 30 ± 3 weeks (2/4, 50%); inferior temporal sulcus at 31 ± 3 weeks (3/6, 50%); transverse temporal sulcus at 33 ± 3 weeks (6/8, 75%); and secondary sulcus at 38 ± 3 weeks (2/4, 50%). CONCLUSIONS The brain is subjected to considerable morphological changes throughout gestation. During fetal brain development the cortex begins to fold in, thereby increasing the cortical surface. All primary sulci are formed during fetal life. The appearance of each sulcus follows a characteristic timing pattern, which may be used as one of the reliable guides pertinent to gestational age and normal fetal development.

Microsurgical anatomy of the optic radiation and related fibers in 3-dimensional images.

BACKGROUND: The fiber dissection technique provides unique 3-dimensional anatomic knowledge of the white matter. OBJECTIVE: To examine the optic radiation anatomy and its important relationship with the temporal stem and to discuss its findings in relation to the approaches to temporal lobe lesions. METHODS: We studied 40 cerebral hemispheres of 20 brains that had been fixed in formalin solution for 40 days. After removal of the arachnoid membrane, the hemispheres were frozen, and the Klingler technique was used for dissection under magnification. Stereoscopic 3-dimensional images of the dissection were obtained for illustration. RESULTS: The optic radiations are located deep within the superior and middle temporal gyri, always above the inferior temporal sulcus. The mean distance between the cortical surface and the lateral edge of the optic radiation was 21 mm. Its fibers are divided into 3 bundles after their origin. The mean distance between the anterior tip of the temporal horn and the Meyer loop was 4.5 mm, between the temporal pole and the anterior border of the Meyer loop was 28.4 mm, and between the limen insulae and the Meyer loop was 10.7 mm. The mean distance between the lateral geniculate body and the lateral margin of the central bundle of the optic radiation was 17.4 mm. CONCLUSION: The white matter fiber dissection reveals the tridimensional intrinsic architecture of the brain, and its knowledge regarding the temporal lobe is particularly important for the neurosurgeon, mostly because of the complexity of the optic radiation and related fibers.

The pterional craniotomy: tips and tricks

This review intended to describe in a didactic and practical manner the frontotemporosphenoidal craniotomy, which is usually known as pterional craniotomy and constitute the cranial approach mostly utilized in the modern neurosurgery. This is, then, basically a descriptive text, divided according to the main stages involved in this procedure, and describes with details how the authors currently perform this craniotomy.

Microsurgical anatomy of the posterior cerebral artery in three-dimensional images.

OBJECTIVE To describe the microsurgical anatomy, branches, and anatomic relationships of the posterior cerebral artery (PCA) represented in three-dimensional images. METHODS Seventy hemispheres of 35 brain specimens were studied. They were previously injected with red silicone and fixed in 10% formalin for at least 40 days. Four of the studied specimens were frozen at -10° to -15 °C for 14 days, and additional dissection was done with the Klinglers fiber dissection technique at ×6 to ×40 magnification. Each segment of the artery was measured and photographed to obtain three-dimensional stereoscopic images. RESULTS The PCA origin was in the interpeduncular cistern at the pontomesencephalic junction level in 23 specimens (65.7%). The PCA was divided into four segments: P1 extends from the PCA origin to its junction with the posterior communicating artery with an average length of 7.7 mm; P2 was divided into an anterior and posterior segment. The P2A segment begins at the posterior communicating artery and ends at the most lateral aspect of the cerebral peduncle, with an average length of 23.6 mm, and the P2P segment extends from the most lateral aspect of the cerebral peduncle to the posterior edge of the lateral surface of the midbrain, with an average length of 16.4 mm; P3 extends from the posterior edge of the lateral surface of the midbrain and ends at the origin of the parieto-occipital sulcus along the calcarine fissure, with an average length of 19.8 mm; and the P4 segment corresponds to the parts of the PCA that run along or inside both the parieto-occipital sulcus and the distal part of the calcarine fissure. CONCLUSIONS To standardize the neurosurgical practice and knowledge, surgical anatomic classifications should be used uniformly and further modified according to the neurosurgical experience gathered. The PCA classification proposed intends to correlate its anatomic segments with their required microneurosurgical approaches.

As bases neuroanatômicas do comportamento: histórico e contribuições recentes

Considering the most recent contributions, the limbic cortical areas, originally known as the greater limbic lobe, besides the cingulated and the parahippocampal gyri also includes the insula and the posterior orbital cortex. In contrast to the nonlimbic cortical areas that project to the basal ganglia (particularly over the dorsal aspects of the striatum, constituted by the caudate nucleus and by the putamen), the limbic cortical areas are characterized by projecting to the hypothalamus and also to the ventral striatum (particularly to the nucleus accumbens). Once all the striatum projects to the globus pallidus which projects to the thalamus and then to the cortex, generating cortical-subcortical reentrant circuits, while the dorsal striatum and pallidum related cortico-subcortical loops are involved with motor activities, the ventral cortical-striatal-pallidal system is particularly related with behavior functions. The extended amygdala (central medial amygdala, stria terminalis or dorsal component, ventral component, and bed nucleus of stria terminalis) receives inputs primarily from the limbic cortical areas, is particularly modulated by the prefrontal cortex, and receives also direct connections from the thalamus that enables the amygdala to generate nonspecific and quick responses through its projections to the hypothalamus and to the brainstem. The ventral striatal-pallidal and the extended amygdala are then two basal forebrain macro-anatomical systems, that together with the basal nucleus of Meynert and with the septal-diagonal band system, constitute the main structures that are particularly connected with the limbic cortical areas, and that altogether project to the hypothalamus and to the brainstem which give rise to the autonomic, endocrine and somatosensory components of the emotional experiences, and that regulate the basic activities of drinking, eating, and related to the sexual behavior.

A ínsula e o conceito de bloco cerebral central

The caracterization of well defined and circumscribed brain regions is particularly useful for the neurosurgical practice once it enhances the tridimensional understanding of its structures and related lesions, and because it induces the development and the utilization of more standard microneurosurgical approaches. In this direction, it is noteworthy that each cerebral hemisphere harbors an evident central core constituted externally by the insula, internally by the basal ganglia and the thalamus, and with the internal capsule within. With a biconvex configuration when seen from above, and located between the sylvian cistern and the supratentorial ventricular cavities, morphologically this central core resembles a head of each brainstem half top, covered by the neocortical mantle of its hemisphere. The central core is attached to the rest of the cerebral hemisphere by isthmi constituted by the different internal capsule fibers. Anteriorly and under the anterior limiting sulcus of the insula there are fibers of the internal capsule anterior limb, superiorly and under the superior limiting sulcus there are the rest of the anterior limb fibers, and the knee and posterior limb fibers that harbors the corticonuclear and the corticospinal tracts, and inferiorly and under the insular inferior limiting sulcus there are the sub- and the retrolentiform internal capsule fibers that enclose the auditory and the optic radiations. Laterally the central core is composed by the insular surface that resembles a shield of the main cerebral subcortical structures. The options of microneurosurgical approaches to the central core related lesions should consider particularly their relationships with the thalamus and with the internal capsule fibers.