Microsurgical anatomy of the orbit: the rule of seven.

The orbits are paired structures, located on the anterior part of the face. Morphologically, each orbit is a four sided pyramid with a posterior apex and anterior base. In the orbit, all openings are arranged around the base, apex or between the orbital walls. An anatomical characteristic of the orbit is that structures are arranged in groups of seven: there are seven bones, seven intraorbital muscles and seven nerves in the orbit. Tumors confined within the periorbita in the anterior two thirds of the orbit can often be approached extracranially, but those located in the apical area, and especially those on the medial side of the optic nerve, often require a transcranial approach. Thus, knowledge of orbital osteology is paramount in adequately choosing and performing an orbital approach. Understanding the critical topographical elements in this area helps to classify an orbital lesion and provides for a solid basis in choosing the most adequate intraorbital route for its treatment.

The transzygomatic approach.

We aim to describe the technical details of the transzygomatic approach to intracranial surgery. The incision begins at the level of the inferior border of the zygomatic arch, anterior to the tragus, and extends towards the contralateral pupillary line. A subgaleal and interfascial dissection is performed. Then, the zygomatic arch is vertically sectioned twice and mobilized downwards, together with the masseter muscle. Next, a fronto-temporo-sphenoidal craniotomy is performed and complete exposure of the anterior temporal dura achieved. Thus, the surgical possibilities are: (i) intradural access to the middle fossa; (ii) intradural pretemporal access to the basal cisterns; (iii) intradural transtemporal access to the insular region; and (iv) extradural access to the middle fossa. The transzygomatic approach offers excellent exposure to the floor of the middle fossa and the lateral wall of the cavernous sinus (both intradurally and extradurally). Also, combined with a pretemporal approach, it affords a good view of the interpeduncular cistern; and using a transtemporal approach, it provides good access to the insular region.

Microsurgical anatomy of the sphenoid ostia.

We aimed to determine the position, number and variability of the sphenoid sinus ostia. A total of 32 dry skulls were examined under x6 magnification. The septum and nasal turbinates were removed to expose the anterior wall of the sphenoid sinus. A caliper was used for measurements. We found 2 ostia per skull, except for one (3%), in which the left ostium was absent. The inferior edges of both ostia were found at the same height in only four skulls (12.5%), and the superior edges of both ostia were found at the same height in only one skull (3%). Thus, in 27 skulls (84%) the lower and upper margins of both ostia were at different levels. The distance from the internal edge of the right ostium to the midline was 2.04mm on average (range: 0.3-5.3mm). The distance from the internal edge of the left ostium to the midline was 2.18mm on average (range: 0.2 to 5.1mm). In most skulls, the sphenoid ostia are located at different heights on each side; also a great variability in the distance from the internal border of the ostia to the midline was found. We found this anatomical knowledge useful when performing a transsphenoidal approach to the sella turcica.

Surgical anatomy of the dural walls of the cavernous sinus.

The external structure of each cavernous sinus (CS) is made of four dural walls. The aim of this study was to describe the anatomy of the dural walls of the CS. We studied 42 adult cadaveric heads, fixed with formalin and injected with coloured silicon. The main findings were: (i) the lateral wall of the CS has two layers - the external, which is thick and pearly grey, and the internal, which is semi-transparent and containing the cranial nerves (CNs); (ii) the medial wall of the CS has two areas - sellar and sphenoidal, both made up of one dural layer only; and (iii) the superior wall of the CS is formed by three triangles - oculomotor, clinoid and carotid - CN III may be found in a cisternal space of the oculomotor triangle; and (iv) the posterior wall of the CS is made up of two dural layers - meningeal dura and periostic dura - and this wall is close to the vertical segment of CN VI.

Three-piece orbitozygomatic approach.

OBJECTIVE: To describe the technical details of a 3-piece orbitozygomatic approach. INTRODUCTION: In a 3-piece orbitozygomatic approach, soft tissue exposure is mostly comparable to the classic frontopterional approach. Osseous resection is a 3-piece operation that consists of first performing anterior and posterior cuts along the zygomatic arch, reflecting it down, attached to the masseter. This is followed by a classic frontotemporosphenoidal craniotomy, and finally, an osteotomy of the orbital rim, roof, and lateral wall of the orbit. RESULTS: When compared with its 1- and 2-piece counterparts, 3-piece orbitozygomatic craniotomy, as described here, is a relatively simple operation and is thus advisable when considering an anterior or middle fossa approach. Brain exposure is wide, whereas cerebral retraction is minimal. We recommend avoiding orbit sectioning as deep as the superior orbital fissure. CONCLUSION: The modifications described herein show the technical features of the 3-piece orbitozygomatic approach, which provides excellent brain exposure with less retraction and a good cosmetic result.

Anatomical landmarks for positioning the head in preparation for the transsphenoidal approach: the spheno-sellar point.

The transnasal approach is the most utilized approach to the sellar region. This study was conducted to identify an anatomical landmark on the lateral surface of the head that corresponds to the midpoint of the sellar floor at the level of sphenoidal rostrum. This point, lined up with the nostril, simulates the surgical path and facilitates the transnasal access to the sella turcica. Four adult, formalin-fixed and silicon-injected cadaveric heads, and ten dried skulls were used for laboratory dissection. The heads and skulls were sectioned along the midline; and the spheno-sellar point, corresponding to the midpoint of the sellar floor at the level of sphenoid rostrum, was determined. The spheno-sellar point was plotted on the lateral surface of the skull, and its position measured relative to the external acoustic meatus. Linking the spheno-sellar point with the nostril created the spheno-nostril line. This line represents the surgical path to be taken for direct access to the sphenoid rostrum, and was used to align the cadaveric heads as in surgery. The endonasal transsphenoidal approach was then utilized in one hundred and two adult patients with sellar lesions, using the spheno-sellar point and the spheno-nostril line as the superficial landmarks to guide the approach. The results of this clinical experience are summarized. The spheno-sellar point was found to be located an average of 40.1 mm (SD+/-2.9 mm) anterior and 23.3 mm (SD+/-3.2 mm) superior to the external acoustic meatus. The spheno-nostril line represents the straight surgical path to the sphenoidal rostrum. This landmark was used in 102 correlative transnasal surgeries for sellar lesions of adult patients, and has allowed an easy and straightforward access to the sella. In only 3 cases with poor pneumatisation of the sphenoid sinus (presellar type), the actual location of the surgical instruments had to be confirmed by fluoroscopy. The application of the spheno-sellar point and the spheno-nostril line is a fast, reliable and very simple way to facilitate transsphenoidal surgery, and their use may avoid complications associated with misdirection of this approach. Its use may be limited in cases of poor pneumatisation of the sphenoid sinus, where fluoroscopic guidance could be necessary as a rule.

Microsurgical anatomy and approaches to the cavernous sinus.

OBJECTIVE: The aim of this article is to describe the anatomy of the cavernous sinus and to provide a guide for use when performing surgery in this complex area. Clinical cases are used to illustrate routes to the cavernous sinus and its contents and to demonstrate how the cavernous sinus can be used as a pathway for exposure of deeper structures. METHODS: Thirty cadaveric cavernous sinuses were examined using x3 to x40 magnification after the arteries and veins were injected with colored silicone. Distances between the entrance of the oculomotor and trochlear nerves and the posterior clinoid process were recorded. Stepwise dissections of the cavernous sinuses, performed to demonstrate the intradural and extradural routes, are accompanied by intraoperative photographs of those approaches. RESULTS: The anatomy of the cavernous sinus is complex because of the high density of critically important neural and vascular structures. Selective cases demonstrate how a detailed knowledge of cavernous sinus anatomy can provide for safer surgery with low morbidity. CONCLUSION: A precise understanding of the bony relationships and neurovascular contents of the cavernous sinus, together with the use of cranial base and microsurgical techniques, has allowed neurosurgeons to approach the cavernous sinus with reduced morbidity and mortality, changing the natural history of selected lesions in this region. Complete resection of cavernous sinus meningiomas has proven to be difficult and, in many cases, impossible without causing significant morbidity. However, surgical reduction of such lesions enhances the chances for success of subsequent therapy.

Abordaje orbitocigomático en tres piezas: Nota técnica / Three piece orbito-zygomatic approach

Objetivo. Describir los detalles técnicos del abordaje orbitocigomático en tres piezas. Descripción. La exposición de partes blandas no difiere mayormente de la efectuada en una craneotomía frontopterional. La resección ósea es realizada en tres piezas, en el siguiente orden: 1) dos cortes, uno anterior y otro posterior, sobre el arco cigomático. Luego, dicho arco es llevado hacia abajo, junto con el músculo masetero; 2) craneotomía fronto-temporo-esfenoidal clásica; y 3) resección del reborde orbitario junto con su techo y su pared lateral. Conclusiones. Las modificaciones descriptas en este trabajo permiten realizar, en forma fácil y segura, un abordaje orbitocigomático que permite una excelente exposición cerebral sin retracción, con muy buenos resultados cosméticos.

Microsurgical anatomy of the diaphragma sellae and its role in directing the pattern of growth of pituitary adenomas.

OBJECTIVE: To evaluate the anatomic aspects of the diaphragma sellae and its potential role in directing the growth of a pituitary adenoma. METHODS: Twenty cadaveric heads were dissected and measurements were taken at the level of the diaphragma sellae. RESULTS: The diaphragma sellae is composed of two layers of dura mater. There is a remarkable variation in the morphology of the diaphragm opening. The average anteroposterior distance of the opening was 7.26 mm (range, 3.4-10.7 mm) and the average lateral-to-lateral distance was 7.33 mm (range, 2.8-14.1 mm). CONCLUSION: The variability in the diameter of the opening of the diaphragma sellae could explain the growth of pituitary tumors toward the cavernous sinus or toward the suprasellar region.

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. METHODS: We dissected six PPF in three cadaveric specimens prepared with intravascular injection of colored material using two different injection techniques. An endoscopic endonasal approach, including a wide nasoantral window and removal of the posterior antrum wall, provided access to the PPF. RESULTS: We produced our best anatomical model injecting colored silicone via the common carotid artery. We found that, using an endoscopic approach, a retrograde dissection of the sphenopalatine artery helped to identify the internal maxillary artery (IMA) and its branches. Neural structures were identified deeper to the vascular elements. Notable anatomical landmarks for the endoscopic surgeon are the vidian nerve and its canal that leads to the petrous portion of the internal carotid artery (ICA), and the foramen rotundum, and V2 that leads to Meckel's cave in the middle cranial fossa. These two nerves, vidian and V2, are separated by a pyramidal shaped bone and its apex marks the ICA. CONCLUSION: Our anatomical model provides the means to learn the endoscopic anatomy of the PPF and may be used for the simulation of surgical techniques. An endoscopic endonasal approach provides adequate exposure to all anatomical structures within the PPF. These structures may be used as landmarks to identify and control deeper neurovascular structures. The significance is that an anatomical model facilitates learning the surgical anatomy and the acquisition of surgical skills. A dissection superficial to the vascular structures preserves the neural elements. These nerves and their bony foramina, such as the vidian nerve and V2, are critical anatomical landmarks to identify and control the ICA at the skull base.

Anatomical considerations of the endonasal transsphenoidal approach / Considerações anatômicas na abordagem transesfenoidal endonasal

The sellar contents are separated from the sphenoidal sinus by a tiny sheath of bone that compris es the sellar floor, making the transsphenoidal approach the most used surgical route to intrasellar lesions. The transsphenoidal approach can be initiated in three different ways: 1) cutting the mucosa over the alveolar part of maxilla (sublabial transsphenoidal), 2) cutting long the anterior nasal mucosa adjacent to the columella (transeptal transsphenoidal), and 3) cutting the mucosa over the sphenoidal rostrum (endonasal transsphenoidal). Each cavernous sinus has four dural walls. The lateral, superior and posterior walls are composed of endosteal and periosteal dura leaflets. Unlike the other dural walls, the medial wall is formed of a single, thin dural sheath, an anatomical fact that help explains the lateral expansion of a pituitary adenoma. In the center, the diaphragm sellae has an opening through which the infundibulum courses, linking the pituitary gland to the floor of the third ventricle. The morphology of this opening is quite variable among individuals. On average, the anteroposterior distance of the diaphragm opening was 7.26 mm + 1.99 mm, varying from 3.4 mm up to 10.7 mm. The lateral distance of the diaphragm opening was 7.33 mm + 2.79 mm, varying from 2.8 mm up to 14.1 mm.

Los contenidos de la silla turca se encuentran separados del seno esfenoidal por una delgada lámina de hueso que es el piso selar, haciendo que la vía transesfenoidal sea la ruta quirúrgica más utilizada para lesiones intraselares. El abordaje transesfenoidal puede ser iniciado de tres diferentes maneras: 1) cortando la mucosa sobre la parte alveolar del maxilar superior (sublabial transesfenoidal), 2) cortando la mucosa nasal anterior, adyacente a la columena (transseptal transesfenoidal), y 3) cortando la mucosa sobre el rostro del esfenoides (endonasal transesfenoidal). Cada seno cavernoso tiene 4 paredes urales. Las paredes lateral, superior y posterior están compuestas por dos hojas (endosteal y perióstica), mientras que la pared medial posee una sola hoja dural, muy delgada, un hecho anatómico que podría explicar la expansión lateral de los adenomas hipofisarios. En el centro, el diafragma selar tiene una abertura a través de la cual el infundíbulo transcurre, uniendo la glándula pituitaria con el tercer ventrículo. La morfología de dicha abertura es muy variable. En promedio, la distancia anteroposterior de la abertura es de 7.26 mm + 1.99 mm, variando desde 3.4 mm hasta 10.7 mm. La distancia lateral de la abertura del diafragma es de 7.33 mm + 2.79 mm, variando desde 2.8 mm hasta 14.1 mm.

Localización del surco central en pacientes con tumores cerebrales cercanos a la corteza sensitivo-motora utilizando omega contralateral / Contralateral omega sign for the localization of the central sulcus by patients with cerebral tumors next to the sensory-motor area

Objetivo: Determinar la utilidad de la identificación del surco central contralateral a la lesión, a través de Omega invertida, como método para localizar la corteza sensitivomotora adyacente al proceso tumoral. Método: Desde julio de 2005 hasta abril de 2007, fueron operadas por el primer autor (AC) 15 pacientes con lesiones cercanas o a nivel de la corteza sensitivomotora, utilizando el signo de Omega contralateral a la lesión. Además, fueron estudiados 5 cerebros (10 hemisferios) de cadáveres adultos fijados en formol. Resultados: El surco central separa la corteza motora de la sensitiva. Presenta tres rodillas o curvas. La rodilla media, es la resposable de la forma de Omega invertida que muestra el surco central en un corte axial. En promedio, la altura de Omega fue de 11.2mm +/- 3.35mm, y el ancho, en su base, de 15.7mm +/- 2.48mm. Por otro lado, la distancia promedio desde el borde medial de Omega hasta la línea media fue de 24.5mm +/- 5.35mm. En los 15 casos se estudió detenidamente la resonancia magnética (corte axial) antes de la cirugía, para poder identificar el surco central a través del signo de Omega, en el hemisferio contralateral a la lesión. En todos los casos excepto uno, fue posible identificar dicho signo. De los quince pacientes operados, siete mostraron déficit motor previo a la cirugía (1 plejía, 1 paresia severa, 1 paresia moderada y 4 paresias leves). En todos los casos hubo una mejoría en el postoperatorio. Los ocho pacientes restantes no presentaron déficit motor antes de la cirugía. Luego del procedimiento quirúrgico, dichos enfermos continuaron sin presentar déficit motor. Conclusión: El signo de Omega contralateral puede, fácil y eficientemente, ser utilizado para identificar la relación entre una lesión y el surco central ipsilateral.

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.

Microsurgical approaches to the medial temporal region: an anatomical study.

OBJECTIVE: To describe the surgical anatomy of the anterior, middle, and posterior portions of the medial temporal region and to present an anatomic-based classification of the approaches to this area. METHODS: Twenty formalin-fixed, adult cadaveric specimens were studied. Ten brains provided measurements to compare different surgical strategies. Approaches were demonstrated using 10 silicon-injected cadaveric heads. Surgical cases were used to illustrate the results by the different approaches. Transverse lines at the level of the inferior choroidal point and quadrigeminal plate were used to divide the medial temporal region into anterior, middle, and posterior portions. Surgical approaches to the medial temporal region were classified into four groups: superior, lateral, basal, and medial, based on the surface of the lobe through which the approach was directed. The approaches through the medial group were subdivided further into an anterior approach, the transsylvian transcisternal approach, and two posterior approaches, the occipital interhemispheric and supracerebellar transtentorial approaches. RESULTS: The anterior portion of the medial temporal region can be reached through the superior, lateral, and basal surfaces of the lobe and the anterior variant of the approach through the medial surface. The posterior group of approaches directed through the medial surface are useful for lesions located in the posterior portion. The middle part of the medial temporal region is the most challenging area to expose, where the approach must be tailored according to the nature of the lesion and its extension to other medial temporal areas. CONCLUSION: Each approach to medial temporal lesions has technical or functional drawbacks that should be considered when selecting a surgical treatment for a given patient. Dividing the medial temporal region into smaller areas allows for a more precise analysis, not only of the expected anatomic relationships, but also of the possible choices for the safe resection of the lesion. The systematization used here also provides the basis for selection of a combination of approaches.

Microsurgical anatomy of the oculomotor cistern.

OBJECTIVE: To define the characteristics of the arachnoidal sleeve and cistern that accompany the oculomotor nerve through the cavernous sinus roof. METHODS: Forty cavernous sinuses were examined using 3 to 40x magnification. Information was obtained about the size of the oculomotor cistern and its relationship to the roof of the cavernous sinus and anterior clinoid process. RESULTS: An arachnoidal sleeve and cistern, referred to as the oculomotor cistern, accompanied the oculomotor nerve into the roof of all the cavernous sinuses examined. The oculomotor cistern extends from the oculomotor porus, where the nerve enters the roof of the cavernous sinus, to the area below the tip or the adjacent part of the lower margin of the anterior clinoid process. From the porus, the nerve passes forward and downward to the depth of the cistern where it becomes incorporated into the fibrous lateral wall of the cavernous sinus. The width of the cistern was maximal at the oculomotor porus averaged 5.5 mm (range, 3.0-9.2 mm), and tapered slightly towards the midpoint and deep end of the cistern. The cistern's average length was 6.5 mm (range, 3.0-11.0 mm). The oculomotor nerve usually coursed closer to the anterior than the posterior wall of the cistern at the level of the oculomotor porus. CONCLUSION: The oculomotor cistern, an arachnoidal and dural cuff, accompanies the oculomotor nerve through the cavernous sinus roof to the area just below or anterior to the lower edge of the tip of the anterior clinoid process. The segment of the nerve inside the oculomotor cistern is interposed between its free portion in the interpeduncular cistern and the part of its course where it is incorporated into the fibrous lateral wall of the cavernous sinus. The cistern can be opened to aid in the exposure and mobilization of the nerve in dealing with pathology in the area.

O ponto selar-esfeno: localização anatômica e utilização em 56 casos operados com uma aproximação transporte - esfenoidal endonasal / The spheno-sellar point: anatomical localization and usefulness in 56 operated cases with an endonasal trans-sphenoidal approach

Objetivo: Determinar o relacionamento da localização da parede anterior do seio esfenoidal com a superfície externa do crânio, localizando o ponto selar-esfeno para guiar a aproximação endonasal. Método: Quatro formalinas fixas de cabeças cadavéricas de adulto, injetadas com silicone colorido, e dez crânios secos, foram usados. Os crânios foram divididos ao meio e no ponto selar-esfeno, aquele corresponde à interseção entre a linha vertical que se cruza através da parede anterior do seio esfenoidal e uma linha horizontal que se cruza com o assoalho da turcica do sella, foi localizado. Então, o relacionamento entre o ponto selar-esfeno e a superfície externa do crânio foi estudado, utilizando uma broca e apontando a ponta do ponto selar-esfeno na lateral. Assim, as medidas foram feitas entre a representação externa do ponto selar-esfeno e o meato aditivo externo. 56 pacientes com lesões selares estavam usando aproximadamente o transesfenoidal endonasal e aproximadamente o ponto selar-esfeno como guia para a posicionar a cabeça antes da cirurgia. Resultados: O ponto selar-esfeno fica situado na superfície externa do crânio 4.01 cm adiante e 2.33 cm acima do meato auditivo externo. Este ponto foi útil durante a cirurgia a fim de guiar a aproximação paralela do assoalho do quarto do operando. Conclusão: O ponto selar-esfeno ajuda no planejamento do trajeto cirúrgico durante a aproximação transesfenoidal endonasal e o seu uso pode evitar as complicações associadas com o posicionamento da cabeça.

Referências anatômicas na cirurgia do implante auditivo de tronco cerebral

O implante auditivo de tronco cerebral é uma opção os pacientes surdos que não têm a integridade das vias auditivas preservada. A cirurgia, por sua complexidade anatômica e funcional, requer treinamento específico em laboratório de anatomia por parte do cirurgião. OBJETIVOS: Estudar a anatomia cirúrgica da cirurgia do implante auditivo de tronco cerebral. FORMA DE ESTUDO: Estudo anatômico. MATERIAL E MÉTODO: Neste estudo dissecamos cadáver fresco preparado com solução corante injetada nas artérias e veias intra-cranianas. O local de inserção do eletrodo do implante auditivo de tronco cerebral foi estudado através do acesso translabiríntico. RESULTADOS: A técnica cirúrgica utilizada para a implantação do eletrodo de tronco cerebral é semelhante à utilizada na remoção do shwannoma vestibular. O complexo de núcleo coclear, composto pelo núcleo coclear ventral e dorsal, é o local para a colocação do eletrodo. O núcleo coclear ventral é o principal núcleo de transmissão de impulsos neurais do VIII par e seus axônios formam a principal via ascendente do nervo coclear. Tanto o núcleo ventral como o dorsal não são visíveis durante a cirurgia e sua localização depende de identificação de estruturas anatômicas adjacentes. CONCLUSÃO: A região de implantação do eletrodo do implante auditivo de tronco cerebral apresenta referências anatômicas que permitem sua fácil identificação durante a cirurgia.

Microsurgical anatomy and approaches to the cavernous sinus.

OBJECTIVE: The aim of this article is to describe the anatomy of the cavernous sinus and to provide a guide for use when performing surgery in this complex area. Clinical cases are used to illustrate routes to the cavernous sinus and its contents and to demonstrate how the cavernous sinus can be used as a pathway for exposure of deeper structures. METHODS: Thirty cadaveric cavernous sinuses were examined using x3 to x40 magnification after the arteries and veins were injected with colored silicone. Distances between the entrance of the oculomotor and trochlear nerves and the posterior clinoid process were recorded. Stepwise dissections of the cavernous sinuses, performed to demonstrate the intradural and extradural routes, are accompanied by intraoperative photographs of those approaches. RESULTS: The anatomy of the cavernous sinus is complex because of the high density of critically important neural and vascular structures. Selective cases demonstrate how a detailed knowledge of cavernous sinus anatomy can provide for safer surgery with low morbidity. CONCLUSION: A precise understanding of the bony relationships and neurovascular contents of the cavernous sinus, together with the use of cranial base and microsurgical techniques, has allowed neurosurgeons to approach the cavernous sinus with reduced morbidity and mortality, changing the natural history of selected lesions in this region. Complete resection of cavernous sinus meningiomas has proven to be difficult and, in many cases, impossible without causing significant morbidity. However, surgical reduction of such lesions enhances the chances for success of subsequent therapy.

Para-muscular and trans-muscular approaches to the lumbar inter-vertebral foramen: an anatomical comparison.

Foraminal and extra-foraminal disc herniations comprise up to 11.7% of all lumbar disc herniations. Facetectomy, which had been the classic approach, is now recognized as cause of pain and instability after surgery. Otherwise, posterior lateral approaches through a trans-muscular or a para-muscular technique offer no significant damage to key structures for spinal stability. The surgical anatomy of these approaches has already been described, but they were not compared. In order to quantify the angle of vision towards the intervertebral foramen offered by each technique, 12 fresh cadavers were dissected and studied regarding these approaches. The angle presented by trans-muscular approach was wider in all studied lumbar levels. Surgery through the trans-muscular approach is performed with a better working angle, requiring a smaller resection of surrounding tissues. Therefore, minor surgical trauma can be expected. Our measurements support previously published data that point the trans-muscular approach as the best surgical option.

Microsurgical anatomy of the dural arteries.

OBJECTIVE: The objective was to examine the microsurgical anatomy basic to the microsurgical and endovascular management of lesions involving the dural arteries. METHODS: Adult cadaveric heads and skulls were examined using the magnification provided by the surgical microscope to define the origin, course, and distribution of the individual dural arteries. RESULTS: The pattern of arterial supply of the dura covering the cranial base is more complex than over the cerebral convexity. The internal carotid system supplies the midline dura of the anterior and middle fossae and the anterior limit of the posterior fossa; the external carotid system supplies the lateral segment of the three cranial fossae; and the vertebrobasilar system supplies the midline structures of the posterior fossa and the area of the foramen magnum. Dural territories often have overlapping supply from several sources. Areas supplied from several overlapping sources are the parasellar dura, tentorium, and falx. The tentorium and falx also receive a contribution from the cerebral arteries, making these structures an anastomotic pathway between the dural and parenchymal arteries. A reciprocal relationship, in which the territories of one artery expand if the adjacent arteries are small, is common. CONCLUSION: The carotid and vertebrobasilar arterial systems give rise to multiple branches that supply the dura in a complex and overlapping pattern. A knowledge of the microsurgical anatomy of these dural arteries and their assessment on pretreatment evaluations plays a major role in safe and accurate treatment of multiple lesions.