The Inferolateral Transorbital Endoscopic Approach: A Preclinical Anatomic Study.

BACKGROUND: In recent years, transorbital endoscopic approaches are increasing in popularity as they provide several corridors to reach lateral areas of the ventral skull base through the orbit. The aim of this study is to investigate the feasibility of the inferolateral transorbital endoscopic approach (ILTEA) by detailing the step-by-step dissection, anatomic landmarks, and target anatomic areas. METHODS: Seven cadaveric specimens (14 sides) were dissected in the Laboratory of Endoscopic Anatomy of the University of Brescia. Step-by-step dissection of ILTEA was performed to identify the main anatomic landmarks and corridors. Skin incision, dural incision, and boundaries of craniectomy were measured. Neuronavigation was used to check landmarks, track boundaries of surgical volumes, and measure orbital dislocation. RESULTS: The study on the 14 ILTEAs defined 1 anatomic area ("waterline door") that leads to 4 corridors: Meckel's cave corridor, carotid foramen corridor, petrous corridor, and transdural middle fossa corridor. Crucial anatomic landmarks were identified and analyzed. Orbital dislocation was <10 mm. CONCLUSIONS: ILTEA provides the surgeon with a direct route to the region of the "waterline door," lateral areas of the ventral skull base, and middle cranial fossa. In addition, it allows an optimal view of the intracranial and extracranial portions of the maxillary and mandibular nerves. Further anatomic and clinical studies are needed to validate ILTEA in surgical practice.

Endoscopic endonasal approach to the middle cranial fossa through the cavernous sinus triangles: anatomical considerations.

The lateral limit of endoscopic endonasal surgery has yet to be defined. The aim of this study was to investigate the lateral limit of endoscopic endonasal surgery at the level of the sphenoid sinus. Access from the sphenoid sinus to the middle cranial fossa through the cavernous sinus triangles was evaluated by cadaver dissection. Anatomical analysis demonstrated that the medial temporal dura mater was exposed through the anterior area of the clinoidal triangle, anteromedial triangle, and superior area of the anterolateral triangle, indicating potential corridors to the middle cranial fossa. This study suggests that the cavernous sinus triangles are applicable in selected cases to manage middle cranial fossa lesions by endoscopic endonasal surgery.

Endoscopic anatomy of the skull base explored through the nose.

OBJECTIVE: Different surgical approaches have been used over the years in order to access skull base. The endoscopic endonasal approach represents a direct and minimally invasive approach to the suprasellar, retrosellar, and retroclival space, with the advantage of avoid brain retraction and visualize safely and effectively the surgical target. The present contribution aims to provide anatomical details of the skull base as seen from below (i.e., via an endoscopic endonasal approach). METHODS: Five human cadaver heads were dissected. The anatomical neurovascular structures within the skull base were visualized and carefully described from an endoscopic endonasal view. The advantages and limitations of the endoscopic endonasal route were discussed as well. RESULTS: The entire skull base region, as seen from the endoscopic endonasal viewpoint, has been divided in 4 main regions: anterior skull base, middle skull base, posterior skull base and parasellar area. CONCLUSION: The development of endoscopic techniques has opened different perspectives over the skull base surgery. Endonasal surgery provides access to a wide range of skull base lesions via a natural surgical corridor (i.e., the nasal cavities).

Endoscopic endonasal surgical approach to the oculomotor trigone from the cavernous sinus.

Knowledge of anatomy visualized endoscopically is necessary to perform endoscopic surgical procedures safely. The cavernous sinuses are complicated structures with major blood vessels and nerves seated deeply in the center of the skull base. Anatomical orientation during surgery is essential for deep and narrow skull base surgery. While performing surgery involving the cavernous sinuses, understanding of the structures identifiable via a transsphenoidal view can allow comprehension of the relationship between a lesion and the surrounding structures, thus preventing intraoperative complications. The objective of this study was to dissect the neurovascular structures in the cavernous sinus deeply inside the oculomotor trigone through a transsphenoidal view, and to determine the relationships among anatomical landmarks in the path of surgery. Ten fresh silicone-injected cadaveric heads were evaluated. Four millimeter-diameter rigid endoscopes with 0° and 30° rod-lenses were utilized to perform an endonasal transsphenoidal approach. The detailed position and course of the major components in each cavernous sinus were assessed under panoramic view. We also validated the utility of this approach by successfully excising a huge pituitary adenoma.

Skull base embryology: a multidisciplinary review.

INTRODUCTION: The skull base represents a central and complex bone structure of the skull and forms the floor of the cranial cavity on which the brain lies. Anatomical knowledge of this particular region is important for understanding several pathologic conditions as well as for planning surgical procedures. Embryology of the cranial base is of great interest due to its pronounced impact on the development of adjacent regions including the brain, neck, and craniofacial skeleton. MATERIALS AND METHODS: Information from human and comparative anatomy, anthropology, embryology, surgery, and computed modelling was integrated to provide a perspective to interpret skull base formation and variability within the cranial functional and structural system. RESULTS AND CONCLUSIONS: The skull base undergoes an elaborate sequence of development stages and represents a key player in skull, face and brain development. Furthering our holistic understanding of the embryology of the skull base promises to expand our knowledge and enhance our ability to treat associated anomalies.

Identification of the internal carotid artery at the superior part of the cavernous sinus during endoscopic endonasal cavernous sinus tumor surgery.

BACKGROUND: Identification of the internal carotid artery (ICA) is essential for successful endoscopic endonasal cavernous sinus tumor surgery. This study aimed to develop a method for identifying the ICA in cavernous sinus tumors at the superior part of the cavernous sinus. METHODS: Ten fresh cadavers were studied with a 4-mm 0° and 30° endoscope to identify surgical landmarks of the ICA in the cavernous sinus. Clinical cases of cavernous sinus tumors were surgically treated using an endoscopic transpterygoid approach. RESULTS: Anatomical study indicated the ICA at the superior part of the cavernous sinus can be identified using three steps: 1) exposure of the optic nerve sheath by drilling the optic canal; 2) identification of the proximal orifice of the optic nerve sheath at the transition of the optic nerve sheath and dura mater of the tuberculum sellae; and 3) identification of the clinoid segment of the ICA at the distal dural ring just below the proximal orifice of the optic nerve sheath. Although the ICA was encased and transposed by tumors in preliminary surgical cases, the clinoid segment of the ICA was safely exposed at the superior part of the cavernous sinus using this method. CONCLUSIONS: Dural structures around the cavernous sinus are key to identifying the ICA at the superior part of the cavernous sinus. This method is expected to reduce the risk of ICA injury during endoscopic endonasal surgery for cavernous sinus tumors.

Transventricular fenestration of the lamina terminalis: the value of a flexible endoscope: technical note.

BACKGROUND: Recently, the authors demonstrated the technical feasibility of a transventricular translaminar terminalis ventriculostomy with a rigid endoscope. A major problem with this technique remains the contusion of the fornix at the foramen of Monro. Here, the authors evaluated alternative approaches and techniques, including the use of a flexible endoscope. MATERIAL AND METHODS: Feasibility of two approaches-anterior and posterior of the coronal suture-was evaluated on magnetic resonance images and in cadaveric brains. Two different trajectories were selected. Lamina terminalis (LT) fenestration was performed with a rigid and a flexible endoscope using two approaches in 10 fixed cadaver brains. RESULTS: Using the posterior approach 2 cm behind the coronal suture with the two endoscopes caused moderate to severe damage to foramen and fornix. Using the standard approach (Kocher point) with the flexible endoscope avoided damage of these structures. After completion of the anatomical investigation, the authors successfully performed a transventricular fenestration of the LT with the flexible endoscope in one clinical case. CONCLUSION: Rigid scopes provide brilliant optics and safe manipulation with the instruments. However, with the rigid scope, a transventricular opening of the LT is only possible with acceptance of structural damage to the foramen of Monro and the fornix. In contrast, opening of the LT via a transventricular route with preservation of the anatomical structures can be achieved with a flexible steerable endoscope even via a standard burr hole. Thus, if a standard third ventriculostomy is not feasible, endoscopic opening of the LT might represent an alternative, particularly with a flexible scope in experienced hands.

A 3-dimensional transnasal endoscopic journey through the paranasal sinuses and adjacent skull base: a practical and surgery-oriented perspective.

An endoscopic approach through the transnasal corridor is currently the treatment of choice in the management of benign sinonasal tumors, cerebrospinal fluid leaks, and pituitary lesions. Moreover, this approach can be considered a valid option in the management of selected sinonasal malignancies extending to the skull base, midline meningiomas, parasellar lesions such as craniopharyngioma and Rathke cleft cyst, and clival lesions such as chordoma and ecchordosis. Over the past decade, strict cooperation between otorhinolaryngologists and neurosurgeons and acquired surgical skills, together with high-definition cameras, dedicated instrumentation, and navigation systems, have made it possible to broaden the indications of endoscopic surgery. Despite these improvements, depth perception, as provided by the use of a microscope, was still lacking with this technology. The aim of the present project is to reveal new perspectives in the endoscopic perception of the sinonasal complex and skull base thanks to 3-dimensional endoscopes, which are well suited to access and explore the endonasal corridor. In the anatomic dissection herein, this innovative device came across with sophisticated and long-established fresh cadaver preparation provided by one of the most prestigious universities of Europe. The final product is a 3-dimensional journey starting from the nasal cavity, reaching the anterior, middle, and posterior cranial fossae, passing through the ethmoidal complex, paranasal sinuses, and skull base. Anatomic landmarks, critical areas, and tips and tricks to safely dissect delicate anatomic structures are addressed through audio comments, figures, and their captions.

Endoscopic endonasal surgical approach to the oculomotor trigone from the cavernous sinus.

Knowledge of anatomy visualized endoscopically is necessary to perform endoscopic surgical procedures safely. The cavernous sinuses are complicated structures with major blood vessels and nerves seated deeply in the center of the skull base. Anatomical orientation during surgery is essential for deep and narrow skull base surgery. While performing surgery involving the cavernous sinuses, understanding of the structures identifiable via a transsphenoidal view can allow comprehension of the relationship between a lesion and the surrounding structures, thus preventing intraoperative complications. The objective of this study was to dissect the neurovascular structures in the cavernous sinus deeply inside the oculomotor trigone through a transsphenoidal view, and to determine the relationships among anatomical landmarks in the path of surgery. Ten fresh silicone-injected cadaveric heads were evaluated. Four millimeter-diameter rigid endoscopes with 0° and 30° rod-lenses were utilized to perform an endonasal transsphenoidal approach. The detailed position and course of the major components in each cavernous sinus were assessed under panoramic view. We also validated the utility of this approach by successfully excising a huge pituitary adenoma.

Endoscopic endonasal approach to the middle cranial fossa through the cavernous sinus triangles: anatomical considerations.

The lateral limit of endoscopic endonasal surgery has yet to be defined. The aim of this study was to investigate the lateral limit of endoscopic endonasal surgery at the level of the sphenoid sinus. Access from the sphenoid sinus to the middle cranial fossa through the cavernous sinus triangles was evaluated by cadaver dissection. Anatomical analysis demonstrated that the medial temporal dura mater was exposed through the anterior area of the clinoidal triangle, anteromedial triangle, and superior area of the anterolateral triangle, indicating potential corridors to the middle cranial fossa. This study suggests that the cavernous sinus triangles are applicable in selected cases to manage middle cranial fossa lesions by endoscopic endonasal surgery.

Cranial sutures: a multidisciplinary review.

INTRODUCTION: Progress in cranial suture research is shaping our current understanding of the topic; however, emphasis has been placed on individual contributing components rather than the cranial sutural system as a whole. Improving our holistic view helps further guide clinicians who treat cranial sutural abnormalities as well as researchers who study them. MATERIALS AND METHODS: Information from anatomy, anthropology, surgery, and computed modeling was integrated to provide a perspective to interpret suture formation and variability within the cranial functional and structural system. RESULTS: Evidence from experimental settings, simulations, and evolution suggest a multifactorial morphogenetic process associated with functions and morphology of the sutures. Despite molecular influences, the biomechanical cranial environment has a main role in both the ontogenetic and phylogenetic suture dynamics. CONCLUSIONS: Furthering our holistic understanding of the intricate cranial sutural system promises to expand our knowledge and enhance our ability to treat associated anomalies.

Anatomical landmarks for transoral robotic tongue base surgery: comparison between endoscopic, external and radiological perspectives.

PURPOSE: To describe the transoral viewpoint of the tongue base anatomy, focusing on a superior to inferior perspective, which is less familiar to the head and neck surgeon but, at the same time, worthy to be known given the expanding interest and diffusion of the transoral robotic technique. METHODS: Seven heads were dissected, two with the Da Vinci(®) robotic system, three by means of a transoral endoscopic approach and another two by means of a lateral "traditional" external approach. Ten normal patients, with normal oral cavity and oropharynx, were studied as control samples by means of a 3-T MRI scanner. RESULTS: Major neurovascular elements are placed laterally and deeply within the tongue base. Dissection within intrinsic and genioglossus muscles is safe because the main trunk of the lingual artery lies on the lateral surface of genioglossus muscle, covered by the hyoglossus muscle. The hypoglossal nerve, with its comitant vein, is more lateral, lying on the external surface of the hyoglossus muscle. Radiological evaluation can visualize important details of this complex anatomy. The position of the vessels can be directly identified, whereas major nerves are more difficult to be visualized unless they are surrounded by fibro-fatty tissue. CONCLUSIONS: A medial to lateral dissection of the tongue base can be considered safe. A strict collaboration with the radiologist is helpful in approaching these cases by means of a robotic technique and in improving a true 3D understanding of this complex anatomy.

The temporo-parietal fascial flap in extended transnasal endoscopic procedures: cadaver dissection and personal clinical experience.

Due to progressively expanded indications of endoscopic transnasal surgery, having different reconstructive options in the armamentarium becomes of paramount importance. We herein report our experience with the use of the temporo-parietal fascial flap after extended endoscopic procedures for malignancies of the clival and nasopharyngeal regions. We focus our report on the surgical anatomy of this flap and the technique for its intranasal transposition through an infratemporal corridor. The main steps of the procedure and anatomic landmarks were highlighted, thanks to previous cadaver dissection. Five patients underwent an extended endoscopic resection for malignant tumors: one with persistent clival chordoma, three with recurrent nasopharyngeal carcinomas, and 1 recurrent nasopharyngeal adenoid cystic carcinoma. In all patients a temporo-parietal fascial flap was harvested to protect critical structures or irradiated denuded bone. The Mean harvesting and hospitalization time were 120 min and 5 days, respectively. No major or minor complications were observed. Whenever local flaps are not available for oncologic reasons or previous surgery, the temporo-parietal fascial flap is a safe and relatively easy option to protect the residual skull base and critical structures such as the internal carotid artery and dura of the posterior cranial fossa, after extended endoscopic resections.

Three-dimensional susceptibility-weighted imaging at 7 T using fractal-based quantitative analysis to grade gliomas.

INTRODUCTION: Susceptibility-weighted imaging (SWI) with high- and ultra-high-field magnetic resonance is a very helpful tool for evaluating brain gliomas and intratumoral structures, including microvasculature. Here, we test whether objective quantification of intratumoral SWI patterns by applying fractal analysis can offer reliable indexes capable of differentiating glial tumor grades. METHODS: Thirty-six patients affected by brain gliomas (grades II-IV, according to the WHO classification system) underwent MRI at 7 T using a SWI protocol. All images were collected and analyzed by applying a computer-aided fractal image analysis, which applies the fractal dimension as a measure of geometrical complexity of intratumoral SWI patterns. The results were subsequently statistically correlated to the histopathological tumor grade. RESULTS: The mean value of the fractal dimension of the intratumoral SWI patterns was 2.086 ± 0.413. We found a trend of higher fractal dimension values in groups of higher histologic grade. The values ranged from a mean value of 1.682 ± 0.278 for grade II gliomas to 2.247 ± 0.358 for grade IV gliomas (p = 0.013); there was an overall statistically significant difference between histopathological groups. CONCLUSION: The present study confirms that SWI at 7 T is a useful method for detecting intratumoral vascular architecture of brain gliomas and that SWI pattern quantification by means of fractal dimension offers a potential objective morphometric image biomarker of tumor grade.

Endoscopic far-lateral approach to the posterolateral craniovertebral junction: an anatomical study.

Minimally invasive surgery to the posterolateral craniovertebral junction (CVJ) has not been sufficiently described. The aims of this study were to evaluate the feasibility of an endoscopic far-lateral approach to the posterolateral craniocervical junction and to better understand the related anatomy under distorted endoscopic view. Ten fresh cadavers were studied with 4-mm 0° and 30° endoscopes to develop the surgical approach and to identify surgical landmarks. After making a 3-cm straight incision behind the mastoid process, the superior oblique and rectus capitis posterior major muscles were partially exposed. An endoscope was then introduced and the two muscles were followed inferiorly until the posterior arch of the atlas appeared. The two muscles were removed to create ample working space without violating the posterior atlanto-occipital membrane. The vertebral artery was identified by the landmark of the posterior arch of the atlas, and the atlanto-occipital joint and foramen magnum were exposed. In addition to suboccipital craniectomy, transcondylar, supracondylar, and paracondylar extension by drilling were applicable through the narrow corridor under superb visualization. The intradural neurovascular structures from the acousticofacial bundle to the dorsal root of C2, anterolateral space of the foramen magnum, cerebellomedullary fissure, and fourth ventricle were clearly demonstrated. This endoscopic far-lateral approach offers excellent exposure of surgical landmarks around the posterolateral CVJ with minimal invasiveness. Endoscopic soft tissue dissection is key to creating the surgical corridor. This approach could offer an alternative to the conventional far-lateral approach in selected cases.

Endoscopic extradural subtemporal approach to lateral and central skull base: a cadaveric study.

OBJECTIVE: Endoscopy has provided a less invasive approach to skull base surgery, mainly through endonasal routes, but has been limited in its applications due to potential complications. The aims of this study were to evaluate the feasibility of the purely endoscopic extradural transcranial approach to lateral and central skull base through a subtemporal keyhole and to better understand potential distortions of the related anatomy via endoscopy. METHODS: Ten fresh cadaver heads were studied with 4-mm 0° and 30° endoscopes to develop the surgical approach and to identify surgical landmarks. RESULTS: The endoscopic extradural subtemporal approach was divided into 3 sections after exposure of the extradural space in the middle cranial fossa: 1) exposure of the lateral wall of the cavernous sinus and the preauricular infratemporal fossa; 2) anterior petrosectomy and posterior cranial fossa exploration; and 3) unroofing of the tympanic cavity and exposure of the facial nerve. This keyhole endoscopic technique clearly visualized anatomical landmarks of the lateral and central skull base via an extradural subtemporal route. CONCLUSIONS: The endoscopic extradural subtemporal approach was feasible. This approach could display a wide range of lateral and central skull base structures with minimal invasiveness. The use of extradural space would be key to performing safe and effective endoscopic skull base surgery.

Endoscopic approaches to the trigeminal nerve and clinical consideration for trigeminal schwannomas: a cadaveric study.

OBJECT: The course of the trigeminal nerve straddles multiple fossae and is known to be very complex. Comprehensive anatomical knowledge and skull base techniques are required for surgical management of trigeminal schwannomas. The aims of this study were to become familiar with the endoscopic anatomy of the trigeminal nerve and to develop a minimally invasive surgical strategy for the treatment of trigeminal schwannomas. METHODS: Ten fresh cadavers were studied using 5 endoscopic approaches with the aid of 4-mm 0° and 30° endoscopes to identify surgical landmarks associated with the trigeminal nerve. The endoscopic approaches included 3 transcranial keyhole approaches (the extradural supraorbital, extradural subtemporal, and retrosigmoid approaches), and 2 endonasal approaches (the transpterygoid and the transmaxillary transpterygoid approaches). RESULTS: The trajectories of the extradural supraorbital, transpterygoid, and extradural subtemporal approaches corresponded with the course of the first, second, and third divisions of the trigeminal nerve, respectively. The 3 approaches demonstrated each division in intra- and extracranial spaces, as well as the Meckel cave in the middle cranial fossa. The interdural space at the lateral wall of the cavernous sinus was exposed by the extradural supraorbital and subtemporal approaches. The extradural subtemporal approach with anterior petrosectomy and the retrosigmoid approach visualized the trigeminal sensory root and its neighboring neurovascular structures in the posterior cranial fossa. The transmaxillary transpterygoid approach revealed the course of the third division in the infratemporal fossa. CONCLUSIONS: The 5 endoscopic approaches effectively followed the course of the trigeminal nerve with minimal invasiveness. These approaches could provide alternative options for the management of trigeminal schwannoma.

Computer-assisted and fractal-based morphometric assessment of microvascularity in histological specimens of gliomas.

Fractal analysis is widely applied to investigate the vascular system in physiological as well as pathological states. We propose and examine a computer-aided and fractal-based image analysis technique to quantify the microvascularity in histological specimens of WHO grade II and III gliomas. A computer-aided and fractal-based analysis was used to describe the microvessels and to quantify their geometrical complexity in histological specimens collected from 17 patients. The statistical analysis showed that the fractal-based indexes are the most discriminant parameters to describe the microvessels. The computer-aided quantitative analysis also showed that grade III gliomas are generally more vascularized than grade II gliomas. The fractal parameters are reliable quantitative indicators of the neoplastic microvasculature, making them potential surrogate biomarkers. The qualitative evaluation currently performed by the neuropathologist can be combined with the computer-assisted quantitative analysis of the microvascularity to improve the diagnosis and optimize the treatment of patients with brain cancer.

Endoscopic reconstruction of the middle cranial fossa through a subtemporal keyhole using a pedicled deep temporal fascial flap: a cadaveric study.

BACKGROUND: Reconstruction of the skull base is essential to prevent postoperative leakage of cerebrospinal fluid (CSF). However, a reliable method of reconstructing the middle cranial fossa via a subtemporal keyhole is not available. OBJECTIVE: To determine whether less invasive reconstruction of the middle cranial fossa under endoscopic guidance with a pedicled deep temporal fascia approach via a subtemporal keyhole is feasible and useful. METHODS: The middle cranial fossa in 4 fresh cadaver heads was reconstructed with a 4-mm 0° rigid endoscope. RESULTS: A subtemporal skin incision (subtemporal incision) was followed by 2 small skin incisions (temporal line incisions) made on the superior temporal line. The endoscope was inserted through the temporal line incisions, and then the deep temporal fascia was separated from the superficial temporal fascia and temporal muscle under endoscopic view. A pedicled flap was harvested from the subtemporal incision and applied to the middle cranial fossa after subtemporal keyhole craniotomy. The pedicled deep temporal fascial flap was flexible, long, and large enough to overlay skull base defects. CONCLUSION: This purely endoscopic technique using a pedicled deep temporal fascial flap provided reliable reconstruction of the middle cranial fossa through a subtemporal keyhole. This technique would also be applicable in preventing CSF leakage or treating traumatic, acquired nontraumatic, or congenital encephalocele in the middle cranial fossa.

Transoral robotic surgery of the tongue base in obstructive sleep Apnea-Hypopnea syndrome: anatomic considerations and clinical experience.

BACKGROUND: The purpose of our work was to describe, through cadaveric dissection, the anatomy of the tongue base with a robotic perspective and to demonstrate the feasibility of this approach in case of tongue base hypertrophy in Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS). METHODS: Forty-four patients with OSAHS underwent tongue base resection in the last 2 years. Twenty patients with a 10-month minimum follow-up were evaluated. The anatomic details of 3 tongue bases dissected from above are illustrated. RESULTS: The cadaveric study shows that no constant landmarks are identifiable, with no significant neurovascular structures present in the midline. Clinically, transoral robotic surgery (TORS) for the tongue base was feasible, with no major complications and satisfaction of the majority of patients. Mean apnea hypopnea index (AHI) improvement was 24.6 ± 22.2 SD, mean Epworth Sleepiness Scale (ESS) improvement was 5.9 ± 4.4 SD. CONCLUSION: Tongue base hypertrophy can be safely and effectively managed by TORS in OSAHS. Our midterm data are encouraging and worthy of further evaluation.