Microsurgical Anatomy of the Cavernous Sinus: Measurements of the Triangles in and around It

The Connective Tissue Architecture of the Cavernous Sinus: An Anatomical Study and Unifying Conceptualization

OBJECTIVE

The aim of this study was to synthesize existing knowledge regarding the anatomy of the cavernous sinus (CS), critically evaluate the current anatomical hypotheses concerning its walls, to conduct anatomical dissections, and develop a comprehensive understanding of the connective tissue structure of the CS.

METHODS

We performed systematic dissections on 15 fresh adult cadavers. Specifically, 5 specimens were approached laterally, 5 were sectioned in the axial plane, and 5 were dissected using endoscopic endonasal techniques.

RESULTS

Based on histological and embryological data, we formulated several anatomical concepts and examined them through dissection studies. 1) An uninterrupted periosteum envelops all surfaces of the skull and establishes a periosteal dural layer within the cranial cavity. 2) All structures of the neuraxis are encased by a meningeal layer of dura mater. 3) Cranial nerves (CNs) are ensheathed by 1 layer of meningeal layer as they pierce it. This meningeal layer invaginates along the course of the nerves to various lengths forming the corresponding CN cisterns before fusing with the nerve's perineurium. 4) Fibers of the periosteal layer that are strained between the nearby bony structures form a thin periosteal "ligamentous" layer. This layer is mostly attenuated but becomes more robust in named "ligaments". These ligaments covered by meningeal layer of dura form "dural folds" such as anterior and posterior petroclinoidal folds. Consequently, the lateral wall of the CS is composed of the following elements: 1) the meningeal layer associated with the mesial temporal lobe; 2) a thin periosteal "ligamentous" layer; and 3) the meningeal layers corresponding to CNs III, IV, and V1 originating from the posterior cranial fossa. The medial wall of the CS is constituted by a single layer of periosteal dura inferiorly and a meningeal layer superiorly. The superior wall of the CS is exclusively formed by the periosteal layer of the anterior clinoid process at the anterior aspect of the clinoidal triangle (referred to as the carotidooculomotor membrane). In contrast, the posterior aspect of the oculomotor triangle consists of both a meningeal layer and a thin "periosteal ligamentous layer" that extends between 3 more substantial periosteal condensations: the anterior and posterior petroclinoidal ligaments and the interclinoidal ligament. The posterior wall of the CS is comprised of the meningeal layer of the dura mater from the posterior cranial fossa, along with a periosteal layer that envelops the clivus and petrous apex, contributing to the formation of the posterior petroclinoidal and Gruber's ligaments. Finally, a single layer of periosteal dura delineates both the anterior and inferior walls of the CS.

CONCLUSIONS

The dural anatomy of the CS involves an intricate interplay between the meningeal and periosteal dural layers, which is elucidated more effectively through the application of fundamental principles informed by embryological development.

Mullan's triangle or anteromedial triangle of the middle cranial fossa: a cadaveric study with its surgical importance

BACKGROUND

Surgical approaches to the cavernous sinus (CS) and middle cranial fossa (MCF) can be challenging, particularly for young neurosurgeons. The anteromedial (Mullan's) triangle is a triangle by the side of the CS and constitutes part of the floor of the MCF. The contents include the sphenoid sinus, superior ophthalmic vein, and sixth cranial nerve. The literature contains very little research that has precisely defined and measured the anteromedial triangle while considering anatomical variances minimally.

METHODOLOGY

The present study was conducted on the skulls of 25 adult human cadavers which were dissected to expose the anteromedial (Mullan's) triangle on both sides. After precisely defining the triangle on each side, measurements of the three borders were taken, and using Heron's formula, the area of each triangle was calculated.

RESULTS

On average, the length of the medial border was 12.5 (+ 3.1 mm); the length of the lateral border was 9.9 (+ 3.1 mm); the length of the base was 10.75 (+ 2.4 mm) and the area of the anteromedial triangle was 43.9 (+ 15.06 mm2).

CONCLUSION

Precise anatomical knowledge of the Mullan's triangle enables the treatment of disorders in often deformed anatomy or difficult-to-access structures. That is the reason it is important to gain a thorough understanding of the surgical anatomy and to adopt a safe procedure.

A primer to vascular anatomy of the brain: an overview on anterior compartment

PURPOSE

Knowledge of neurovascular anatomy is vital for neurosurgeons, neurologists, neuro-radiologists and anatomy students, amongst others, to fully comprehend the brain's anatomy with utmost depth. This paper aims to enhance the foundational knowledge of novice physicians in this area.

METHOD

A comprehensive literature review was carried out by searching the PubMed and Google Scholar databases using primary keywords related to brain vasculature, without date restrictions. The identified literature was meticulously examined and scrutinized. In the process of screening pertinent papers, further articles and book chapters were obtained through analysis and additional assessing of the reference lists. Additionally, four formalin-fixed, color latex-injected cadaveric specimens preserved in 70% ethanol solution were dissected under surgical microscope (Leica Microsystems Inc, 1700 Leider Ln, Buffalo Grove, IL 60089 USA). Using microneurosurgical as well as standard instruments, and a high-speed surgical drill (Stryker Instruments 1941 Stryker Way Portage, MI 49002 USA). Ulterior anatomical dissection was documented in microscopic images.

RESULTS

Encephalic circulation functions as a complex network of intertwined vessels. The Internal Carotid Arteries (ICAs) and the Vertebral Arteries (VAs), form the anterior and posterior arterial circulations, respectively. This work provides a detailed exploration of the neurovascular anatomy of the anterior circulation and its key structures, such as the Anterior Cerebral Artery (ACA) and the Middle Cerebral Artery (MCA). Embryology is also briefly covered, offering insights into the early development of the vascular structures of the central nervous system. Cerebral venous system was detailed, highlighting the major veins and tributaries involved in the drainage of blood from the intracranial compartment, with a focus on the role of the Internal Jugular Veins (IJVs) as the primary, although not exclusive, deoxygenated blood outflow pathway.

CONCLUSION

This work serves as initial guide, providing essential knowledge on neurovascular anatomy, hoping to reduce the initial impact when tackling the subject, albeit the intricate vasculature of the brain will necessitate further efforts to be conquered, that being crucial for neurosurgical and neurology related practice and clinical decision-making.

Anteromedial Petrous (Gardner's) Triangle: Surgical Anatomy and Relevance for Endoscopic Endonasal Approach to the Petrous Apex and Petroclival Region

BACKGROUND AND OBJECTIVES

Triangular corridors have been used as reliable surgical entry points for open transcranial approaches to the petrous apex (PA) and petroclival region (PCR). The endoscopic endonasal approaches have grown rapidly in the last decade, and the indications have advanced. The knowledge of accurate and reliable anatomic landmarks through endoscopic endonasal route is essential and remain to be established. The purpose of this study was to describe the feasibility and surgical exposure of the anteromedial petrous (Gardner's) triangle as a novel corridor to the PA and PCR.

METHODS

Five anatomic specimens were dissected. The PA and PCR were accessed through endoscopic endonasal approaches and contralateral transmaxillary approach. The limits of the anteromedial petrous (Gardner's) triangle were identified and dissected and associated measurements performed.

RESULTS

The dissection was divided into 6 steps. The limits of the anteromedial petrous (Gardner's) triangle were identified and defined by the paraclival internal carotid artery anterolaterally, the abducens nerve posteromedially, and the petroclival synchondrosis inferiorly. Three lines were established following the limits of the triangle. The mean distance of the anterolateral limit was 10.03 mm (SD = 0.94), of the posteromedial limit was 20.06 mm (SD = 2.90), and of the inferior limit was 17.99 mm (SD = 2.99). The mean area was 87.56 mm 2 (SD = 20.06). The 3 anatomic landmarks with a critical role to safely define the triangle were the pterygosphenoidal fissure, the petrosal process of the sphenoid bone, and the petroclival synchondrosis.

CONCLUSION

The anteromedial (Gardner's) triangle is a well-defined bone corridor which provides access to the entire petrous bone and petroclival junction through endoscopic endonasal route. Regardless of the anatomic variations or tumor location, the landmarks of the abducens nerve, paraclival internal carotid artery, and petroclival synchondrosis are key for understanding lateral access to tumors extending from the clivus.

Anterolateral surgical triangle of the cavernous sinus: a cadaveric study of neurosurgical importance

BACKGROUND

The anterolateral triangle around the cavernous sinus is a surgical skull base triangle used as a neurosurgical landmark essential to skull-based surgeries. There are few reports of its measurements with little attention paid to anatomical variations.

METHODOLOGY

A total of 15 adult human cadaveric skulls were dissected to expose the anterolateral triangle on both sides. The triangle was defined and measurements of the three borders were taken precisely and the area of each triangle was calculated using Heron's formula.

RESULTS

On an average, the length of the anteromedial border is 11.4 (+ 2.2 mm); the length of the posteromedial border is 8.7 (+ 2.6 mm); the length of the lateral border is 13.06 (+ 2.6 mm) and the area of the anterolateral triangle is 48.05 (+ 17.5 mm2).

CONCLUSION

Concise understanding of anterolateral triangle is essential to skull-based surgeries; comprehending its anatomy helps with better surgical planning and provides insight into local pathology.

The anterolateral triangle as window on the foramen lacerum from transorbital corridor: anatomical study and technical nuances

OBJECTIVE

Neurosurgical indications for the superior eyelid transorbital endoscopic approach (SETOA) are rapidly expanding over the last years. Nevertheless, as any new technique, a detailed knowledge of the anatomy of the surgical target area, the operative corridor, and the specific surgical landmark from this different perspective is required for a safest and successful surgery. Therefore, the aim of this study is to provide, through anatomical dissections, a detailed investigation of the surgical anatomy revealed by SETOA via anterolateral triangle of the middle cranial fossa. We also sought to define the relevant surgical landmarks of this operative corridor.

METHODS

Eight embalmed and injected adult cadaveric specimens (16 sides) underwent dissection and exposure of the cavernous sinus and middle cranial fossa via superior eyelid endoscopic transorbital approach. The anterolateral triangle was opened and its content exposed. An extended endoscopic endonasal trans-clival approach (EEEA) with exposure of the cavernous sinus content and skeletonization of the paraclival and parasellar segments of the internal carotid artery (ICA) was also performed, and the anterolateral triangle was exposed. Measurements of the surface area of this triangle from both surgical corridors were calculated in three head specimens using coordinates of its borders under image-guide navigation.

RESULTS

The drilling of the anterolateral triangle via SETOA unfolds a space that can be divided by the course of the vidian nerve into two windows, a wider "supravidian" and a narrower "infravidian," which reveal different anatomical corridors: a "medial supravidian" and a "lateral supravidian," divided by the lacerum segment of the ICA, leading to the lower clivus, and to the medial aspect of the Meckel's cave and terminal part of the horizontal petrous ICA, respectively. The infravidian corridor leads medially into the sphenoid sinus. The arithmetic means of the accessible surface area of the anterolateral triangle were 45.48 ± 3.31 and 42.32 ± 2.17 mm2 through transorbital approach and endonasal approach, respectively.

CONCLUSION

SETOA can be considered a minimally invasive route complementary to the extended endoscopic endonasal approach to the anteromedial aspect of the Meckel's cave and the foramen lacerum. The lateral loop of the trigeminal nerve represents a reliable surgical landmark to localize the lacerum segment of the ICA from this corridor. Nevertheless, as any new technique, a learning curve is needed, and the clinical feasibility should be proven.

A New Perspective on the Cavernous Sinus as Seen through Multiple Surgical Corridors: Anatomical Study Comparing the Transorbital, Endonasal, and Transcranial Routes and the Relative Coterminous Spatial Regions

Background: The cavernous sinus (CS) is a highly vulnerable anatomical space, mainly due to the neurovascular structures that it contains; therefore, a detailed knowledge of its anatomy is mandatory for surgical unlocking. In this study, we compared the anatomy of this region from different endoscopic and microsurgical operative corridors, further focusing on the corresponding anatomic landmarks encountered along these routes. Furthermore, we tried to define the safe entry zones to this venous space from these three different operative corridors, and to provide indications regarding the optimal approach according to the lesion's location. Methods: Five embalmed and injected adult cadaveric specimens (10 sides) separately underwent dissection and exposure of the CS via superior eyelid endoscopic transorbital (SETOA), extended endoscopic endonasal transsphenoidal-transethmoidal (EEEA), and microsurgical transcranial fronto-temporo-orbito-zygomatic (FTOZ) approaches. The anatomical landmarks and the content of this venous space were described and compared from these surgical perspectives. Results: The oculomotor triangle can be clearly exposed only by the FTOZ approach. Unlike EEEA, for the exposure of the clinoid triangle content, the anterior clinoid process removal is required for FTOZ and SETOA. The supra- and infratrochlear as well as the anteromedial and anterolateral triangles can be exposed by all three corridors. The most recently introduced SETOA allowed for the exposure of the entire lateral wall of the CS without entering its neurovascular structures and part of the posterior wall; furthermore, thanks to its anteroposterior trajectory, it allowed for the disclosure of the posterior ascending segment of the cavernous ICA with the related sympathetic plexus through the Mullan's triangle, in a minimally invasive fashion. Through the anterolateral triangle, the transorbital corridor allowed us to expose the lateral 180 degrees of the Vidian nerve and artery in the homonymous canal, the anterolateral aspect of the lacerum segment of the ICA at the transition zone from the petrous horizontal to the ascending posterior cavernous segment, surrounded by the carotid sympathetic plexus, and the medial Meckel's cave. Conclusions: Different regions of the cavernous sinus are better exposed by different surgical corridors. The relationship of the tumor with cranial nerves in the lateral wall guides the selection of the approach to cavernous sinus lesions. The transorbital endoscopic approach can be considered to be a safe and minimally invasive complementary surgical corridor to the well-established transcranial and endoscopic endonasal routes for the exposure of selected lesions of the cavernous sinus. Nevertheless, peer knowledge of the anatomy and a surgical learning curve are required.

The Pterygosphenoidal Triangle: Surgical Anatomy and Case Series in Endoscopic Endonasal Skull Base Surgery

BACKGROUND

Safe exposure of the lacerum segment of the carotid artery remains a challenge in endoscopic endonasal surgery.

OBJECTIVE

To introduce the pterygosphenoidal triangle as a novel and reliable landmark for facilitating access to the foramen lacerum.

METHODS

Fifteen colored silicone-injected anatomic specimens were dissected using an endoscopic endonasal approach to the foramen lacerum region in a stepwise manner. Twelve dried skulls were studied and 30 high-resolution computed tomography scans were analyzed to measure the borders and angles of the pterygosphenoidal triangle. Surgical cases incorporating the foramen lacerum exposure between July 2018 and December 2021 were reviewed to provide surgical outcomes of the proposed surgical technique.

RESULTS

The pterygosphenoidal triangle is delineated by the pterygosphenoidal fissure medially and the vidian nerve laterally. The palatovaginal artery is located at the base of the triangle anteriorly, while the apex is formed by the pterygoid tubercle posteriorly, which leads to the anterior wall of the foramen lacerum and lacerum internal carotid artery. In the reviewed surgical cases, 39 patients underwent 46 foramen lacerum approaches for resection of pituitary adenoma (12 patients), meningioma (6 patients), chondrosarcoma (5 patients), chordoma (5 patients), or other lesions (11 patients). There were no carotid injuries or ischemic events. Near-total resection was achieved in 33 (85%) of 39 patients (gross-total in 20 [51%]).

CONCLUSION

This study details the pterygosphenoidal triangle as a novel and practical anatomic surgical landmark for safe and effective exposure of the foramen lacerum in endoscopic endonasal surgery.

Comparison of Accessibility to Cavernous Sinus Areas Throughout Endonasal, Transorbital, and Transcranial Approaches: Anatomic Study With Quantitative Analysis

BACKGROUND

The cavernous sinus (CS) is accessed through several approaches, both transcranially and endoscopically. The transorbital endoscopic approach is the newest proposed route in the literature.

OBJECTIVE

To quantify and observe the areas of the CS reach from 2 endoscopic and 1 transcranial approaches to the CS in the cadaver laboratory.

METHODS

Six CSs were dissected through endoscopic endonasal, transorbital endoscopic, and transcranial pterional approaches, with previous implanted references for neuronavigation during the dissection. Point registration was used to mark the CS exposure and limits through each approach for later area and volume quantification through a computerized technique.

RESULTS

The endoscopic endonasal approach reaches most of the CS except part of the sinus's superior, lateral, and posterior regions. The area exposed through this approach was 210 mm 2 , and the volume was 1165 mm 3 . The transcranial pterional approach reached the superior and part of the lateral sides of the sinus, not allowing good access to the medial side. The area exposed through this approach was 306 m 2 , whereas the volume was 815 m 3 . Finally, the transorbital endoscopic approach accessed the whole lateral side of the sinus but not the medial one. The area exposed was the greatest, 374 m 2 , but its volume was the smallest, 754 m 3 .

CONCLUSION

According to our results, the endonasal endoscopic approach is the direct route to access the medial, inferior, and part of the superior CS compartments. The transorbital approach is for the lateral side of the CS. Finally, the transcranial pterional approach is the one for the superior side of the CS.

Microanatomical study of arachnoid granulations and meningeal architecture around Meckel's cave

Although the microanatomy of Meckel's cave (MC) has been well studied, there are still controversies regarding the meningeal architecture of the space. Moreover, there are only general mentions of the arachnoid granulations near MC in just a few sources. This study is aimed at determining the frequency, location, and anatomical variability of the main clusters of arachnoid granulations around MC. The dissection involved 26 isolated specimens of MC fixed in formalin (neutral buffered, 10%). This number included five freshly harvested specimens examined histologically. Additional paraffin block with MC horizontal section was taken from our neuroanatomical collection. Carefully selected anatomical and histological techniques were applied to assess the complex relationships between the arachnoid granulations and adjacent structures. Arachnoid granulations were found around MC in all specimens with different anatomical variations. The main clusters of arachnoid granulations were close to the trigeminal ganglion and its divisions. The dorsolateral wall of MC was a thick layer formed by interweaving bundles of collagen fibers arranged in various directions. The entire MC was surrounded by a dural sleeve (envelope). This sleeve separated MC from the lateral sellar compartment. At its anterior (rostral) end, it formed a cribriform area pierced by individual fascicles of the trigeminal nerve's primary divisions. The connective tissue forming the sleeve was not only continuous with the epineurium but also shifted to the perineuria surrounding individual nerve fascicles. The meningeal architecture around MC has a complex and multilayer arrangement with a collagenous sleeve closely related to the trigeminal ganglion. Arachnoid granulations are typically found around MC.

The Learning Curve in Skullbase Surgery Part 2–From the Microsurgical Lab Training to the Operative Room

In this second part, the authors review and suggest a methodology for studies in skull base surgery and training in microsurgical laboratory, based on their experiences and reflections. Not only are the foundations for the acquisition of microsurgical skills presented, but also what is needed to be an effective skullbase surgeon with good results. The present article reflects in particular the philosophy of professor Evandro de Oliveira and also serves to present to the neurosurgical community a new state-of-the-art laboratory for hands-on courses in Brazil, at the Faculdade Evangélica Mackenzie do Paraná.

Abordajes quirúrgicos de los meningiomas petroclivales Parte 2: revisión narrativa y lo que aprendimos con 30 casos

Antecedentes:

La resección quirúrgica de los meningiomas petroclivales es un desafío debido a su ubicación profunda y su relación con las estructuras neurovasculares vitales. Por lo general, son lesiones benignas, pero pueden involucrar o infiltrar huesos en la base del cráneo, la duramadre y el tronco encefálico. Esto hace que la extirpación total sea muy difícil o imposible sin causar déficits neurológicos. El objetivo de este estudio es revisar los abordajes quirúrgicos utilizados para tratar los meningiomas petroclivales y las lecciones que hemos aprendido en el manejo quirúrgico de 30 casos.

Métodos:

Serie de casos de 30 meningiomas petroclivales. Al comienzo de nuestra serie, utilizamos el abordaje petroso para todos los casos, pero con la adquisición de experiencia comenzamos a indicar cada vez más el abordaje retrosigmoideo, reservando los abordajes petrosos y cráneo-orbitocigomático para casos seleccionados.

Resultados:

Debido a la dificultad de acceso, los meningiomas petroclivales generalmente requieren diferentes abordajes quirúrgicos y presentan diferentes dificultades quirúrgicas. Hay tres abordajes principales: fronto-orbito-cigomático y variantes; petroso y variantes; y retrosigmoideo, pudiendo ser combinados. La elección del abordaje quirúrgico generalmente se basa en la ubicación y extensión del tumor, la forma del cráneo y la participación de las estructuras venosas, y la experiencia del cirujano.

Conclusión:

Los meningiomas petroclivales son raros y complejos en la base del cráneo. Elegir el abordaje correcto es crucial para un resultado quirúrgico exitoso.

Clinical analysis of cavernous sinus anatomy, pathologies, diagnostics, surgical management and complications - comprehensive review

For decades, the cavernous sinus (CS) has been the subject of debates and scientific studies aimed at elucidating its anatomical variability, and at choosing the best method for accessing it so that optimal diagnoses and related surgical treatments can be decided. The present review considers a series of issues related to the CS. The anatomy of the CS and its features is explored first, and the most important structures, spaces and morphological variations are considered. This is followed by CS pathology and selected diagnostic methods that have proved useful in therapy, and then the management of these pathologies is discussed. Examples of therapeutic steps that have proved helpful in specific cases are taken from the literature. Finally, the various surgical accesses and complications that can be encountered during invasive interventions in the CS area are discussed. The aim of this study is to summarize up-to-date anatomical and clinical knowledge about the CS, citing the most informative scientific papers and aggregating their results. Morphological variations of the CS are common but have not been well described in the literature.

A Patient With Large Cavernous Hemangioma in the Cavernous Sinus Straddling the Saddle With Bilateral Optic Nerve Compression

BACKGROUND

This report describes the removal of a giant cavernous hemangioma while protecting the blood vessels and nerves to the greatest degree of safety, relieving the intracranial space, and relieving the symptoms of the patient.

METHODS

Large cavernous hemangioma crossing into the cavernous sinus in a saddle surgery procedure was retrospectively analyzed, summarizing many cross-regional giant cavernous hemangioma treatments.

RESULTS

The patient underwent non-en bloc resection of the tumor with rapid removal. The internal carotid artery and adjacent nerves were safely preserved.

CONCLUSION

Large cavernous hemangiomas spanning from the cavernous sinus to the area of the butterfly saddle require complete evaluation, and appropriate surgical entry should be selected. With the surgeon having rich surgical experience, the operation can protect the patient's neurological function.

Abordajes quirúrgicos de meningiomas petroclivales parte 1: anatomía microquirúrgica

Antecedentes:

Los meningiomas petroclivales son tumores benignos cuyo tratamiento microquirúrgico es uno de los mayores retos de la neurocirugía. El conocimiento profundo de la anatomía microquirúrgica y los abordajes quirúrgicos para el tratamiento de estos tumores es la primera etapa de aprendizaje para un manejo ideal. Este artículo se divide en dos partes: la primera parte presentará los resultados de la anatomía microquirúrgica relevantes para el manejo de los meningiomaspetroclivales. En la segunda parte, los autores correlacionan esta anatomía con 30 casos de meningiomas petroclivales operados por el autor principal (GRI).

Métodos:

Se disecaron ocho cabezas de cadáveres utilizando un microscopio quirúrgico en el laboratorio de microcirugía de la University of Arkansas for Medical Sciences. En los cerebros y en todas las cabezas, se inyectó silicona de colores para resaltar la diferencia entre las arterias y las venas. Los cadáveres fueron colocados en un fijador craneal tipo Mayfield, simulando el posicionamiento quirúrgico de los abordajes craneo-órbito-cigomatico, petrosectomía anterior y posterior y retrosigmoideo. Otras ocho cabezas de cadáveres fueron formolizadas y con los vasos inyectados con silicona de colores. Se realizaron los abordajes petroso anterior, petroso posterior y craneo-órbito-cigomático.

Resultados:

En el manejo de los meningiomas petroclivales se utilizan tres abordajes quirúrgicos principales: abordaje pterional y sus variantes, abordaje petroso y sus variantes y abordaje retrosigmoideo. Los abordajes endonasales endoscópicos extendidos tienen factores limitantes para su uso en este tipo de procedimiento. Para racionalizar la elección del abordaje quirúrgico, dividimos el clivus en tercios superior, medio e inferior.

Conclusíon:

Varios abordajes quirúrgicos dan acceso a la regiónpetroclival. El conocimiento práctico de la anatomía de esta región adquirido en el laboratorio de microcirugía es parte fundamental del cirujano que se propone operar meningiomas petroclivales.

How I do it: Surgical Resection of a Recurrent Chondromyxoid Fibroma by Micro-Endoscopic Combination Technique

BACKGROUND

The surgical resection of the tumor spreading into the cavernous sinus (CS) is complicated and challenging.

METHOD

We report a left recurrent CS chondromyxoid fibroma occupying the clival-petrous apex-parasellar-suprasellar area, which was totally removed by the micro-endo combination technique via the middle cranial fossa extradural approach.

CONCLUSION

This case demonstrates the value of the micro-endoscopic combination technique for complicated skull base surgery.

Review of the Petroclinoid Ligament

An ossified left petroclinoid ligament was found during routine dissection of the skull base in an adult male cadaver. The petroclinoid ligament is clinically and surgically important given its anatomical relationships to cranial nerves III, V, and VI, so its ossification is a risk factor for injuries due to trauma, increased intracranial pressure, and vascular and tumor compression resulting in abducens and oculomotor palsies. The causes of petroclinoid ligament ossification are yet to be completely elucidated although several reports have associated them with age-related and physiological processes. Assessing the integrity of the petroclinoid ligament is important during skull base surgical interventions to avoid postoperative complications. Therefore, this paper reviews the petroclinoid ligament and its variation, the ossified petroclinoid ligament.

Temporary Clipping of the Intracavernous Internal Carotid Artery: A Novel Technique for Proximal Control

BACKGROUND

Securing proximal control in complex paraclinoid aneurysm surgery through traditional techniques may be challenging and risky in certain situations. Advancements of anatomical knowledge of the cavernous sinus (CS) and hemostasis have made it more accessible as a surgical option.

OBJECTIVE

To describe the technique of temporary clipping of the horizontal segment of the intracavernous internal carotid artery (IC-ICA) in preparation for permanent clipping of complex paraclinoid aneurysms.

METHODS

Through an extradural pretemporal approach, the lateral wall of the CS is exposed. The dura between the trochlear nerve and V1 is opened, and access is made to the horizontal segment of the IC-ICA. After circumferential dissection, the temporary clip can be introduced to the artery, and the extradural clinoidectomy can be continued under secured proximal control.

RESULTS

Seven patients with complex paraclinoid aneurysms were treated between May 2013 and May 2016 by the senior author. Temporary clipping of the IC-ICA was performed in all cases. Average time to achieve proximal control was 22.6 min (22.6 ± 13.8). One patient developed transient oculomotor palsy postoperatively. There were no other complications.

CONCLUSION

When the exposed clinoidal segment of the internal carotid artery does not offer sufficient proximal space for temporary clipping, the extradural approach can be extended to the horizontal portion of the IC-ICA. In our experience, this technique is a quick, reliable, and safe alternative to the classical modalities of temporary occlusion.

Cranio-Orbital Pretemporal Approach for Resection of Right Superior Orbital Fissure/Orbital Renal Cell Metastasis: 2-Dimensional Operative Video

Orbital metastatic lesions are rare entities^1-3 best treated with radical surgical resection with preservation/improvement of neurological and visual function.^1-9 Renal cell metastases, in particular, respond less favorably to radiation.⁹ To our knowledge, an operative video of microsurgical resection of a renal cell carcinoma metastasis to the superior orbital fissure and orbit has not been reported.

A patient presented with worsening right eye vision as demonstrated on preoperative visual field testing and found to have a 3 × 1 × 1 cm lesion in the orbit and superior orbital fissure. The patient was placed supine and stealth neuronavigation was used to aid in tumor localization and extension. A cranio-orbital craniotomy and pretemporal exposure^2,10,11 were performed to allow extradural dissection of the dura propria off the lateral wall of the cavernous sinus. Right-sided extradural cranial nerves II, III, IV, V1, and V2 were identified, and a high-speed diamond drill was used to perform extradural anterior clinoidectomy and optic nerve decompression. Microsurgical resection of the intraorbital tumor components was performed by the senior author (KIA) to delineate the plane between tumor and periorbita. An oval-shaped dural opening was made to resect the dura involved by tumor, confirmed on histological analysis, followed by closure via dural allograft. The patient's right-sided visual field improved markedly after surgery.

Metastatic renal cell carcinoma of the orbit should be resected while preserving and improving preoperative neurological and visual function. The orbitocranial pretemporal approach offers wide visualization to achieve surgical resection.

The patient provided written consent and permission to publish her image.

Microsurgical anatomy of the cranial nerve-centric triangles of the posterior cranial base: cadaveric and radiological anatomical study

Tumors in the posterior fossa can be situated either dorsal and lateral, ventral and medial, or occupying both regions in relation to the cranial nerves, with the latter position being especially challenging. In an effort to organize neurovascular complexes contained within, anatomically based triangles have been proposed to serve as guiding landmarks for locating critical neurovascular structures. The objectives of this study were to: (1) provide a review of historical anatomically based vascular-centric triangles of the posterior fossa based on respective neurovascular complexes; (2) introduce a more organized alternative system of triangles with the conceptualization of a projection system from superficial to deep; and (3) propose and describe two new triangles of the posterior fossa: Petrous-Acousticofacial and Acousticofacial-Trigeminal. Five cadavers were studied. Neurovascular complexes were described with the use of anatomically guided cranial nerve-centric triangles, each of which was formed by cranial nerves, petrous bone, brainstem, tentorium, and superior petrosal vein. All triangles were measured and anatomical boundaries confirmed by neuronavigation. Two circumferential frameworks were created to correlate superficial and deep anatomy: (1) Outer circumference and (2) Inner circumference. Posterior fossa was divided into the following: (1) Superior complex-corresponds to the sub-asterional region, which was projected to the trigeminal nerve; (2) Middle complex-corresponds to the mastoid emissary vein foramen, which was projected to the facial and vestibulocochlear nerves; and (3) Inferior complex-corresponds to the posterior condylar canal, which projects to the lower cranial nerves. Neuronavigation confirmed these landmarks. Two new triangles were proposed: (1) The Petrous-Acousticofacial triangle, and (2) The Acousticofacial-Trigeminal triangle. Triangles provide a useful anatomical guide to the posterior fossa. We have introduced an organized schema, as well as proposed two new triangles, with the intent to minimize manipulation of neurovascular structures.

Gross and Micro-Anatomical Study of the Cavernous Segment of the Abducens Nerve and Its Relationships to Internal Carotid Plexus: Application to Skull Base Surgery

The present study aims to provide detailed observations on the cavernous segment of the abducens nerve (AN), emphasizing anatomical variations and the relationships between the nerve and the internal carotid plexus. A total of 60 sides underwent gross-anatomical study. Five specimens of the AN were stained using Sihler’s method. An additional five specimens were subjected to histological examination. Four types of AN course were observed: a single nerve along its entire course, duplication of the nerve, division into separate rootlets at the point of contact with the cavernous part of the internal carotid artery (ICA), and early-branching before entering the orbit. Due to the relationships between the ICA and internal carotid plexus, the cavernous segment of the AN can be subdivided into a carotid portion located at the point of contact with the posterior vertical segment of the cavernous ICA and a prefissural portion. The carotid portion of the cavernous AN segment is a place of angulation, where the nerve always directly adheres to the ICA. The prefissural portion of the AN, in turn, is the primary site of fiber exchange between the internal carotid plexus and either the AN or the lateral wall of the cavernous sinus.

Microsurgical Anatomy of the Inferomedial Paraclival Triangle: Contents, Topographical Relationships and Anatomical Variations

The inferomedial triangle is one of the two surgical triangles in the paraclival subregion of the skull base. It is delineated by the posterior clinoid process, the dural entrance of the trochlear nerve and the dural entrance of the abducens nerve. The aim of the present article is to describe the anatomical variations within the inferomedial triangle. Measurements of the triangle’s borders and area were supplemented by detailed observations of the topographical anatomy and various arrangements of its contents. Nine adult cadaveric heads (18 sides) and 28 sagittal head sections were studied. The mean area of the inferomedial triangle was estimated to be 60.7 mm². The mean lengths of its medial, lateral and superior borders were 16.1 mm, 11.9 mm and 10.4 mm, respectively. The dorsal meningeal artery was identified within the inferomedial triangle in 37 out of 46 sides (80.4%). A well-developed petrosphenoidal ligament of Grüber was identified within the triangle on 36 sides (78.3%). Although some structures were variable, the constant contents of the inferomedial triangle were the posterior petroclinoid dural fold, the upper end of the petroclival suture, the gulfar segment of the abducens nerve and the posterior genu of the intracavernous internal carotid artery.

The Inferolateral Surgical Triangle of the Cavernous Sinus: A Cadaveric and MRI Study with Neurosurgical Significance

BACKGROUND

The inferolateral triangle is a surgical skull base triangle used as a neurosurgical landmark. There are few reports of its measurements with little attention paid to anatomic variations.

METHODS

The inferolateral triangle was measured in 10 adult human cadaveric heads via dissection then direct measurement and 5 participants undergoing neuroimaging using tracing features.

RESULTS

In the cadavers, mean lengths (mm) of the superior, anterior, and posterior borders were 17.0 (±5.5), 12.9 (±1.7), and 17.8 (±3.3), respectively, with mean area of 97.85 (±28.17) mm². In the participants, mean lengths (mm) of the superior, anterior, and posterior borders were 17.35 (±4.01), 14.36 (±1.36), and 18.01 (±2.43), respectively, with mean area of 113.6 (±25.46) mm². No statistical difference in triangle areas between groups was found.

CONCLUSIONS

Intimate understanding of the inferolateral triangle is essential to skull-based surgery; knowing its anatomy and variations aids in surgical planning and understanding of regional pathology.

The anterior incisural width as a preoperative indicator for intradural space evaluation: An anatomical investigation

Background:

The opticocarotid triangle (OCT) and the carotico-oculomotor triangle (COT) are two anatomical triangles used in accessing the interpeduncular region. Our objective is to evaluate if the anterior incisural width (AIW) is an indicator to predict the intraoperative exposure through both triangles.

Methods:

Twenty sides of 10 cadaveric heads were dissected and analyzed. The heads were divided into the following: Group A – narrow anterior incisura and Group B – wide anterior incisura – using 26.6 mm as a cutoff distance of the AIW. Subsequently, the area of the COT and the OCT in the transsylvian approach was measured, along with the maximum widths through the two trajectories in modified superior transcavernous approach.

Results:

The COT in the wide group was shown to have a significantly larger area compared with the COT in the narrow group (38.4 ± 12.64 vs. 58.3 ± 15.72 mm, P < 0.01). No difference between the two groups was reported in terms of the area of the OCT (50.9 ± 19.22 mm vs. 63.5 ± 15.53 mm, P = 0.20), the maximum width of the OCT (6.6 ± 1.89 vs. 6.5 ± 1.38 mm, P = 1.00), or the maximum width of the COT (11.7 ± 2.06 vs. 12.2 ± 2.32 mm, P = 0.50). Clinical cases were included.

Conclusion:

An AIW <26.6 mm is an unfavorable factor related to a limited COT area in a transsylvian approach for pathologies at the interpeduncular fossa. Preoperative identification and measurement of a narrow AIW can suggest the need to add a transcavernous approach.

Paratrigeminal, Paraclival, Precavernous, or All of the Above? A Circumferential Anatomical Study of the C3-C4 Transitional Segment of the Internal Carotid Artery

BACKGROUND

Although the term paraclival carotid pervades recent skull base literature, no clear consensus exists regarding boundaries or anatomical segments.

OBJECTIVE

To reconcile various internal carotid artery (ICA) nomenclatures for transcranial and endoscopic-endonasal perspectives, we reexamined the transition between lacerum (C3) and cavernous (C4) segments using a C1-C7 segments schema. In this cadaveric study, we obtained a 360°-circumferential view integrating histological, microsurgical, endoscopic, and neuroradiological analyses of this C3-C4 region and identified a distinct transitional segment.

METHODS

In 13 adult, silicone-injected, formalin-fixed cadaveric heads (26 sides), transcranial-extradural-subtemporal and endoscopic-endonasal CT-guided dissections were performed. A quadrilateral area was noted medial to Meckel's cave between cranial nerve VI, anterolateral and posterolateral borders of the lateral-paratrigeminal aspect of the precavernous ICA, and posterior longitudinal ligament. Endoscopically, a medial-paraclival aspect was defined. Anatomical correlations were made with histological and neuroradiological slides.

RESULTS

We identified a distinct precavernous C3-C4 transitional segment. In 18 (69%) specimens, venous channels were absent at the quadrilateral area, on the paratrigeminal border of the precavernous ICA. A trigeminal membrane, seen consistently on the superior border of V2, defined the lateral aspect of the cavernous sinus floor. The medial aspect of the precavernous ICA corresponded with the paraclival ICA.

CONCLUSION

Our study revealing the juncture of 2 complementary borders of the ICA, endoscopic endonasal (paraclival) and transcranial (paratrigeminal), reconciles various nomenclature. A precavernous segment may clarify controversies about the paraclival ICA and support the concept of a "safe door" for lesions involving Meckel's cave, cavernous sinus, and petrous apex.

Anatomical study of presigmoid-retrolabyrinthine approach based on temporal bone high-resolution CT

BACKGROUND

The surgical approach of acoustic neuroma includes translabyrinthine, transcranial fossa, suboccipital retrosigmoid sinus, and presigmoid retrolabyrinthine approach. Aims/Objective: To provide the anatomical basis for the surgical selection of presigmoid retrolabyrinthine approach by measuring the anatomical parameters of retrolabyrinthine space of the petrous bone by high-resolution CT.

MATERIAL AND METHODS

A retrospective study of 208 high-resolution CT (HRCT) images of 104 patients examined in our hospital were analyzed retrospectively. Forty-nine males and 55 females were included in this study. Lines were drawn on the HRCT to measure the morphological data for pre-operational assessment.

RESULT

Morphological data were retracted from HRCT, for preoperational assessment.

CONCLUSION AND SIGNIFICANCE

Using the standard postprocessing images of temporal bone HRCT can predict the size of the retrolabyrinthine space and the degree of exposure to the inner auditory canal, providing an important anatomical index for the choice of presigmoid retrolabyrinthine approach.

Anterolateral Triangle: A Cadaveric Study with Neurosurgical Significance

The anterolateral triangle is one of 10 surgical triangles of the cavernous sinus and serves as an important anatomic landmark for the skull base surgeon. There are few studies in the English literature that have precisely defined and measured the borders of the anterolateral triangle and little agreement has been made regarding the nomenclature within the English literature. A total of 12 midsagittally hemisected adult human cadaveric head halves were dissected to expose the anterolateral triangle. The triangle was defined and measurements of the anterior, posterior, and lateral borders were taken. The mean lengths and standard deviations of the anterior, posterior, and lateral borders were 8.3 ± 2.2 mm, 5.9 ± 2.0 mm, and 11.5 ± 2.9 mm, respectively. The mean area and standard deviation were 20.46 ± 9.30 mm². The anterolateral triangle is helpful in understanding and planning surgical approaches to the cavernous sinus and middle cranial fossa. As such, normal anatomic relationships and the sizes of the anterolateral triangle must first be recognized to better access the pathologic changes within and around this region.

Review of Surgical Anatomy of the Tumors Involving Cavernous Sinus

The lesions involving cavernous sinus (CS) and lateral sellar region includes tumors, vascular lesions, infection, inflammation, and trauma. Tumors associated with CS cause significant distortion of the microanatomy posing an additional surgical challenge to the neurosurgeons. The surgical approach and microsurgical anatomy with respect to the origin and growth of the tumor within the CS region have not been comprehensively described in recent years. We conducted a review of literature concerning CS and associated tumors, complied through MEDLINE/OVID and using cross-references of articles on PubMed with the keywords cavernous sinus, CS tumors, pituitary adenoma, meningioma, schwannoma, chordoma, CS hemangiomas, extradural, interdural, intradural, skull base, gamma knife radiosurgery, endoscopic endonasal approach. Based on the tumor origin and growth pattern, the tumors associated with CS can be classified into three categories: Type-I: tumor originating from CS, Type-II: originating from lateral wall of CS, and Type-III: extraneous origin and occupying CS. The review focuses on approach to a tumor within each type of tumor in the CS region. The emphasis is that the tumor growth pattern and significant distortion of the CS anatomy caused by the tumor growth should be considered while planning the optimal surgical approach for tumors in this region to ensure complete tumor resection with minimal neurovascular morbidity.

Intracranial Anatomical Triangles: A Comprehensive Illustrated Review

There are multiple anatomical triangles of the skull base. However, to our knowledge, there has been no comprehensive review of these geometric landmarks. To allow for a safe and consistent approach to lesions of the skull base such as those near the internal carotid artery, internal acoustic meatus, and cavernous sinus, a comprehensive review of the variations with illustrations is required. This article provides an overview of the anatomical borders, dimensions, and surgical implications as well as illustrations of the major skull base triangles.

Cavernous Sinus Involvement by Pituitary Adenomas: Clinical Implications and Outcomes of Endoscopic Endonasal Resection

Background  Parasellar invasion of pituitary adenomas (PAs) into the cavernous sinus (CS) is common. The management of the CS component of PA remains controversial. Objective  The objective of this study was to analyze CS involvement in PA treated with endoscopic endonasal approaches, including incidence, surgical risks, surgical strategies, long-term outcomes, and our treatment algorithm. Methods  We reviewed a series of 176 surgically treated PA with particular attention to CS involvement and whether the CS tumor was approached medial or lateral to the internal carotid artery. Results  The median duration of follow-up was 36 months. Macroadenomas and nonfunctional adenomas represented 77 and 60% of cases, respectively. CS invasion was documented in 23% of cases. CS involvement was associated with a significantly diminished odds of gross total resection (47 vs. 86%, odds ratio [OR]: 5.2) and increased the need for subsequent intervention (4 vs. 40%, OR: 14.4). Hormonal remission was achieved in 15% of hormonally active tumors. Rates of surgical complication were similar regardless of CS involvement. Conclusion  Our tailored strategy beginning with a medial approach and adding lateral exposure as needed resulted in good outcomes with low morbidity in nonfunctional adenomas. Functional adenomas involving the CS were associated with low rates of hormonal remission necessitating higher rates of additional treatment.

Ten Triangles around Cavernous Sinus for Surgical Approach, Described by Schematic Diagram and Three Dimensional Models with the Sectioned Images

For the surgical approach to lesions around the cavernous sinus (CS), triangular spaces around CS have been devised. However, educational materials for learning the triangles were insufficient. The purpose of this study is to present educational materials about the triangles, consisting of a schematic diagram and 3-dimensional (3D) models with sectioned images. To achieve the purposes, other studies were analyzed to establish new definitions and names of the triangular spaces. Learning materials including schematic diagrams and 3D models with cadaver's sectioned images were manufactured. Our new definition was attested by observing the sectioned images and 3D models. The triangles and the four representative surgical approaches were stereoscopically indicated on the 3D models. All materials of this study were put into Portable Document Format file and were distributed freely at our homepage (anatomy.dongguk.ac.kr/triangles). By using our schematic diagram and the 3D models with sectioned images, ten triangles and the related structures could be understood and observed accurately. We expect that our data will contribute to anatomy education, surgery training, and radiologic understanding of the triangles and related structures.

Relative Projective Location of Three Bottom Apexes of Petrous Bone on Skull

The complex anatomy of petrous part of temporal bone makes the craniotomy around this area challenging. To avoid damaging the interior structures of petrous part of temporal bone, the authors used computed tomography to get the projection of the petrous part of temporal bone on skulls, making the external contours of petrous part clear, thus protecting its interior structure as a reference in craniotomy. The objective of this study was to find out the three-dimensional location of 4 points of petrous part of temporal bone. Parameters of 120 patients (240 observations) between 25 and 65 years who were free of abnormalities and pathological changes in temporal bone were measured on high-resolution spiral multiple slice computed tomographic multiple planar reconstruction images that were parallel to the base plane. The data were analyzed by SPSS, statistical software with the comparison between sides and sexes. The authors found the accurate locations that 4 points of petrous part of temporal bone with mastoidale as the origin. Then the authors connect the 3 vertexes of underside and the petrous apex and lengthen it until intersect with skulls to get the external landmarks. In the end, the authors get the safe range that can be applied to the clinical surgery.

Gamma knife radiosurgery in patients with persistent acromegaly or Cushing's disease: long-term risk of hypopituitarism

INTRODUCTION

For patient with a recurrent or residual acromegaly or Cushing's disease (CD) after resection, gamma knife radiosurgery (GKRS) is often used. Hypopituitarism is the most common adverse effect after GKRS treatment. The paucity of studies with long-term follow-up has hampered understanding of the latent risks of hypopituitarism in patients with acromegaly or CD. We report the long-term risks of hypopituitarism for patients treated with GKRS for acromegaly or CD.

METHODS

From a prospectively created, IRB-approved database, we identified all patients with acromegaly or CD treated with GKRS at the University of Virginia from 1989 to 2008. Only patients with a minimum endocrine follow-up of 60 months were included. The median follow-up is 159·5 months (60·1-278). Thorough radiological and endocrine assessments were performed immediately before GKRS and at regular follow-up intervals. New onset of hypopituitarism was defined as pituitary hormone deficits after GKRS requiring corresponding hormone replacement.

RESULTS

Sixty patients with either acromegaly or CD were included. Median tumour volume at time of GKRS was 1·3 cm(3) (0·3-13·4), and median margin dose was 25 Gy (6-30). GKRS-induced new pituitary deficiency occurred in 58·3% (n = 35) of patients. Growth hormone deficiency was most common (28·3%, n = 17). The actuarial overall rates of hypopituitarism at 3, 5 and 10 years were 10%, 21·7% and 53·3%, respectively. The median time to hypopituitarism was 61 months after GKRS (range, 12-160). Cavernous sinus invasion of the tumour was found to correlate with the occurrence of a new or progressive hypopituitarism after GKRS (P = 0·018).

CONCLUSIONS

Delayed hypopituitarism increases as a function of time after radiosurgery. Hormone axes appear to vary in terms of radiosensitivity. Patients with adenoma in the cavernous sinus are more prone to develop loss of pituitary function after GKRS.

Endoscopic endonasal study of the cavernous sinus and quadrangular space: Anatomic relationships

BACKGROUND

The quadrangular space permits an anterior entry into Meckel's cave while obviating the need for cerebral or cranial nerve retraction. This avenue is intimately associated with the cavernous sinus; thus, from this ventral perspective, it is feasible to visualize the anteromedial, anterolateral, and Parkinson triangles.

METHODS

Twenty middle cranial fossae were dissected endonasally under direct endoscopic visualization. Measurements of the surface area of the quadrangular space and the ventrally accessible cavernous sinus triangles were performed using 3 coordinates under image-guided navigation.

RESULTS

The surface area of the quadrangular space was 16.36 mm(2) (±2.89 mm(2) ). The anterolateral triangle was the largest (47.27 ± 5.37 mm(2) ), whereas Parkinson's was the smallest (22.46 ± 5.54 mm(2) ); the anteromedial triangle presented an average surface area 36.07 mm(2) (±4.15 mm(2) ).

CONCLUSION

The trajectory of the internal carotid artery (ICA) significantly impacts the quadrangular space area and may be a potential parameter for defining the feasibility of this corridor. © 2016 Wiley Periodicals, Inc. Head Neck 38: E1680-E1687, 2016.

Surgical management of trigeminal schwannomas: defining the role for endoscopic endonasal approaches

OBJECT

Because multiple anatomical compartments are involved, the surgical management of trigeminal schwannomas requires a spectrum of cranial base approaches. The endoscopic endonasal approach to Meckel's cave provides a minimal access corridor for surgery, but few reports have assessed outcomes of the procedure or provided guidelines for case selection.

METHODS

A prospectively acquired database of 680 endoscopic endonasal cases was queried for trigeminal schwannoma cases. Clinical charts, radiographic images, and long-term outcomes were reviewed to determine outcome and success in removing tumor from each compartment traversed by the trigeminal nerve.

RESULTS

Four patients had undergone endoscopic resection of trigeminal schwannomas via the transpterygoid approach (mean follow-up 37 months). All patients had disease within Meckel's cave, and 1 patient had extension into the posterior fossa. Gross-total resection was achieved in 3 patients whose tumors were purely extracranial. One patient with combined Meckel's cave and posterior fossa tumor had complete resection of the extracranial disease and 52% resection of the posterior fossa disease. One patient with posterior fossa disease experienced a sixth cranial nerve palsy in addition to a corneal keratopathy from worsened trigeminal neuropathy. There were no CSF leaks. Over the course of the study, 1 patient with subtotal resection required subsequent stereotactic radiosurgery for disease progression within the posterior fossa.

CONCLUSIONS

Endoscopic endonasal approaches appear to be well suited for trigeminal schwannomas restricted to Meckel's cave and/or extracranial segments of the nerve. Lateral transcranial skull base approaches should be considered for patients with posterior fossa disease. Further multiinstitutional studies will be necessary for adequate power to help determine relative indications between endoscopic and transcranial skull base approaches.

Endoscopic endonasal anatomical study of the cavernous sinus segment of the ophthalmic nerve

OBJECTIVES/HYPOTHESIS

This cadaveric study analyzes the endoscopic endonasal anatomy of the ophthalmic division of the trigeminal nerve (V1 ), from the middle fossa to its orbital entry via the superior orbital fissure. Anatomical relationships with the surrounding cranial nerves and blood vessels are described, with emphasis on their clinical correlation during surgery in this region. Our objective was to describe the anatomical relationships of the ophthalmic division of the trigeminal nerve.

STUDY DESIGN

Cadaveric study.

METHODS

Thirty middle cranial fossae, in adult human cadaveric specimens, were dissected endonasally under direct endoscopic visualization. During the dissection, we noted the relationships of the V1 nerve with the other trigeminal branches, as well as with the oculomotor and trochlear nerves, the paraclival and cavernous portions of the internal carotid artery, and the superior orbital fissure (SOF).

RESULTS

The V1 nerve is the most superior trigeminal branch and runs upward and obliquely, along the middle portion of the lateral wall of the cavernous sinus. The V1 nerve joins the oculomotor and trochlear nerves to exit the cavernous sinus and enter the orbit through the SOF. Ten percent of the specimens displayed the trochlear nerve running along as a mate of the V1 nerve. The V1 nerve borders two key triangles in the lateral wall of the cavernous sinus, and the Parkinson's and anteromedial triangles.

CONCLUSIONS

In this study, the V1 nerve was a constant and reliable landmark, thus allowing the identification of the anteromedial triangle. This potential space can serve as an adequate window to access the temporal lobe. Knowledge of this anatomy is essential when planning and executing endonasal surgery in this region.

LEVEL OF EVIDENCE

NA.

Endoscopic, endonasal variability in the anatomy of the internal carotid artery

BACKGROUND

Classic three-dimensional schemas of the internal carotid artery (ICA) for transcranial approaches do not necessarily apply to two-dimensional endoscopic views. Modifying an existing ICA segment classification, we define endoscopic orientation for the lacerum (C3) to clinoid (C5) segments through an endonasal approach.

METHODS

In 20 cadaveric heads, we classified endoscopic appearance based on shape and angulation of C3 to C5 segments. Distances were measured between both arteries, and between the ICA and pituitary gland.

RESULTS

We identified 4 common ICA patterns: types I through III matched side-to-side, whereas type IV was asymmetric. In 80% of specimens, the pituitary gland had direct contact with the ICA. In 20% of specimens, a space existed between the pituitary gland and the cavernous segment. Access to the posterior aspect of the cavernous sinus medial to the cavernous segment was possible without retraction of the artery or pituitary gland. Spaces between the lacerum and cavernous segments were trapezoid (80%) and hourglass (20%).

CONCLUSIONS

Distinguishing which ICA type courses between the lacerum and clinoid segments can help clarify the relationships between the artery and its surrounding structures during endoscopic approaches. Adapting the classic terminology of ICA segments provided consistency of endoscopic relevance, defined potential endoscopic corridors, and highlighted the critical step of arterial contact.

Volumetry and analysis of anatomical variants of the anterior portion of the petrous apex outlined by the kawase triangle using computed tomography

Background Anterior petrosectomy has become an increasingly used approach for petroclival lesions. This study measures the volume and the anatomical variants of the anterior portion of the petrous apex outlined by the Kawase triangle using computed tomography (CT). Methods This was a transversal retrospective study. We assessed the anterior petrous apex portion outlined by the Kawase triangle in consecutive patients > 18 years of age from CT scans of temporal bone stored in an archive system. The volumetry was performed on a workstation. Results A total of 154 petrosal apex were analyzed in 77 patients (36 men). The average volume of the region outlined by the Kawase triangle was 1.89 ± 0.52 cm(3). The volume average in men was 2.01 ± 0.58 cm(3), and the average in women was 1.79 ± 0.41 cm(3). Intra- and interobserver agreement were both excellent, and there was little variance. Nineteen petrous apex demonstrated anatomical variations. In 18 cases it was pneumatized, and in one case a vascular or nerve-like structure was identified, a report we did not find in the literature. Conclusion The volumetry of the petrous apex anterior portion outlined by the Kawase triangle can be made by CT with excellent intra- and interobserver agreement and reproducibility. There are anatomical variants in this region that are relevant to surgery.

Surgical outcomes using a medial-to-lateral endonasal endoscopic approach to pituitary adenomas invading the cavernous sinus

OBJECT

This study details the extent of resection and complications associated with endonasal endoscopic surgery for pituitary tumors invading the cavernous sinus (CS) using a moderately aggressive approach to maximize extent of resection through the medial CS wall while minimizing the risk of cranial neuropathy and blood loss. Tumor in the medial CS was aggressively pursued while tumor in the lateral CS was debulked in preparation for radiosurgery.

METHODS

A prospective surgical database of consecutive endonasal pituitary surgeries with verified CS invasion on intraoperative visual inspection was reviewed. The extent of resection as a whole and within the CS was assessed by an independent neuroradiologist using pre- and postoperative Knosp-Steiner (KS) categorization and volumetrics of the respective MR images. The extent of resection and clinical outcomes were compared for medial (KS 1-2) and lateral (KS 3-4) lesions.

RESULTS

Thirty-six consecutive patients with pituitary adenomas involving the CS who had surgery via an endonasal endoscopic approach were identified. The extent of resection was 84.6% for KS 1-2 and 66.6% for KS 3-4 (p = 0.04). The rate of gross-total resection was 53.8% for KS 1-2 and 8.7% for KS 3-4 (p = 0.0006). Six patients (16.7%) had preoperative cranial neuropathies, and all 6 had subjective improvement after surgery. Surgical complications included 2 transient postoperative cranial neuropathies (5.6%), 1 postoperative CSF leak (2.8%), 1 reoperation for mucocele (2.8%), and 1 infection (2.8%).

CONCLUSIONS

The endoscopic endonasal "medial-to-lateral" approach permits safe debulking of tumors in the medial and lateral CS. Although rates of gross-total resection are moderate, particularly in the lateral CS, the risk of permanent cranial neuropathy is extremely low and there is a high chance of improvement of preexisting deficits. This approach can also facilitate targeting for postoperative radiosurgery.

Microsurgical localization of the cochlea in the extended middle fossa approach

Objective In the extended middle fossa approach, a portion of the petrous bone known as Kawase's rhomboid can be drilled to expose the posterior fossa through a middle fossa corridor. During this bony resection, the cochlea is placed at risk. The objective of this study was to objectively detail the position of the cochlea in relation to reliable surgical landmarks. Methods Eleven cadaveric specimens were dissected-including six cadaveric heads and five dry temporal bones by means of an anterior petrosectomy with skeletonization of the cochlea. Three anatomic measurements describing the location of the cochlea in relation to the extrapolated intersection of the greater superficial petrosal nerve (GSPN) and facial nerve were recorded. These measurements were then correlated with thin-cut temporal bone computed tomography scans from 25 patients with morphologically normal inner ears. Results In the cadaveric specimens, the anterior border of the membranous basal turn of the cochlea was located an average of 7.56 mm (6.4 to 8.9 mm) anterior to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the GSPN. The medial border of the membranous cochlea (medial margin of basal turn) was located an average of 8.2 mm (6.9 to 8.9 mm) medial to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the facial nerve. The average maximum distance from the extrapolated junction of the GSPN and facial nerve to the membranous cochlea was 9.3 mm (8.2 to 10.3 mm). These anatomic measurements correlated well with radiologic measurements of the same parameters. Conclusion When drilling Kawase's rhomboid, it is useful to locate the extrapolated junction of the GSPN and the facial nerve. Drilling of the anteromedial petrous bone outside of a radius of 12.5 mm from the extrapolated junction of GSPN and facial nerve appears to be associated with a low degree of risk to the cochlear apparatus.

Anatomia microcirúrgica das artérias infratentoriais: um estudo estereoscópico

CONTEXTO: O espaço infratentorial do crânio é uma região que possui complexa rede de artérias que vascularizam o tecido cerebelar e o tronco encefálico. Sua complexa anatomia tridimensional deve ser profundamente entendida pelo neurocirurgião vascular e pelo radiologista intervencionista. OBJETIVO: Descrever as principais artérias do espaço infratentorial e seu trajeto, bem como sua relação com a topografia das estruturas neurais. MÉTODOS: Foram estudados 30 cérebros humanos, fixados em formalina e 6 cabeças de cadáveres dissecadas, utilizando-se microscópico cirúrgico com 3X a 40X de aumento. Os cérebros e todas as cabeças foram injetados com siloxanos polimerizados ou polisiloxanos (silicone) colorido. As dissecções anatômicas foram documentadas utilizando-se técnica para obtenção de imagens tridimensionais (3D), objetivando a produção de impressões estereoscópicas. RESULTADOS: São descritos o trajeto, segmentos e ramos das artérias basilar, cerebelar superior, cerebelar anteroinferior, cerebelar posteroinferior e vertebral. CONCLUSÃO: A anatomia das artérias infratentoriais é complexa e as imagens estereoscópicas apresentadas são um importante instrumento de documentação, pois permitem uma noção de profundidade da anatomia estudada.

Acousticofacial-glossopharyngeal triangle: an anatomic model for rapid surgical orientation

The cerebellopontine angle (CPA) poses a surgical challenge due to the complexity and variation of its associated structures. This study examined the relationship between the glossopharyngeal nerve (CN IX) and the acousticofacial complex (AFC). Retrosigmoid suboccipital dissections were preformed on 10 cadaveric specimens. A triangle formed by the AFC, CN IX, and the skull base was consistently observed. The cisternal portions of the AFC and CN IX formed two sides of the triangle. The base was formed by a line traversing the respective dural portals of these nerves at the skull base. Triangular proportions were utilized to predict distances from five points along the course of CN IX to a corresponding point along the course of the AFC. Predicted distances were not statistically different when compared with cadaveric measurements in all 10 specimens (p > 0.05). A table of predicted distances between CN IX and the AFC at all five points along CN IX was developed, revealing a quantitative model to predict the native location of the AFC in the lateral pontine cistern. The triangle and predicted location of the AFC can serve as points of reference for the identification and preservation of these structures in CPA surgery.

Interdural haemorrhage of the posterior fossa due to infraclinoidal carotid artery aneurysm rupture

Several anatomical studies indicate that the intracranial pachimeninges consist of two dural layers joined together, which divide while bordering the venous sinuses, therefore located in an interdural space. We present here an uncommon case of haematoma due to rupture of an infraclinoidal internal carotid artery aneurysm. The dome of the aneurysm leaned against the posterior wall of the cavernous sinus and, following laceration, pierced the inner dural layer and caused its detachment from the periosteal layer, thus determining a truly interdural haematoma which progressively involved the whole posterior fossa. A 42-year-old female was admitted to our institution with a recent history of thunderclap headache and right ophthalmoparesis. Two cerebral computerised scan tomographies performed elsewhere tested negative for subarachnoid haemorrhage. A cerebral magnetic resonance imaging (MRI) showed a thin collection of blood adjacent to the clivus and all along the wall of the posterior fossa and foramen magnum. A right infraclinoid internal carotid artery aneurysm was also diagnosed, subsequently better highlighted on angiography. The patient underwent surgery with aneurysm clipping. Post-operative course was uneventful, and control angiography showed complete exclusion of the aneurysm from blood circulation. The patient was discharged 5 days later. At 3 months follow-up ophthalmoplegia had disappeared, and the patient had fully recovered. The possibility of a truly interdural location, particularly in cases of non-traumatic parasellar or clival haematomas, must be included in the differential diagnosis of posterior fossa extra-axial haemorrhages. MRI is the test of choice for diagnostic purposes.