OBJECTIVE Different surgical routes have been used over the years to achieve adequate decompression of the optic nerve in its canal including, more recently, endoscopic approaches performed either through the endonasal corridor or the transorbital one. The present study aimed to detail and quantify the amount of bone removal around the optic canal, achievable via medial-to-lateral endonasal and lateral-to-medial transorbital endoscopic trajectories.

METHODS Five human cadaveric heads (10 sides) were dissected at the Laboratory of Surgical Neuroanatomy of the University of Barcelona (Spain). The laboratory rehearsals were run as follows: 1) preliminary preoperative CT scans of each specimen, 2) anatomical endoscopic endonasal and transorbital dissections and Dextroscope-based morphometric analysis, and 3) quantitative analysis of optic canal bone removal for both endonasal and transorbital endoscopic approaches.

RESULTS The endoscopic endonasal route permitted exposure and removal of the most inferomedial portion of the optic canal (an average of 168°), whereas the transorbital pathway allowed good control of its superolateral part (an average of 192°). Considering the total circumference of the optic canal (360°), the transorbital route enabled removal of a mean of 53.3% of bone, mainly the superolateral portion. The endonasal approach provided bone removal of a mean of 46.7% of the inferomedial aspect. This result was found to be statistically significant (p < 0.05). The morphometric analysis performed with the aid of the Dextroscope (a virtual reality environment) showed that the simulation of the transorbital trajectory may provide a shorter surgical corridor with a wider angle of approach (39.6 mm; 46.8°) compared with the simulation of the endonasal pathway (52.9 mm; 23.8°).

CONCLUSIONS Used together, these 2 endoscopic surgical paths (endonasal and transorbital) may allow a 360° decompression of the optic nerve. To the best of the authors' knowledge, this is the first anatomical study on transorbital optic nerve decompression to show its feasibility. Further studies and, eventually, surgical case series are mandatory to confirm the effectiveness of these approaches, thereby refining the proper indications for each of them.

OBJECTIVE: Exposure of the cavernous sinus is technically challenging. The most common surgical approaches use well-known variations of the standard frontotemporal craniotomy. In this paper the authors describe a novel ventral route that enters the lateral wall of the cavernous sinus through an interdural corridor that includes the removal of the greater sphenoid wing via a purely endoscopic transorbital pathway.

METHODS: Five human cadaveric heads (10 sides) were dissected at the Laboratory of Surgical NeuroAnatomy of the University of Barcelona. To expose the lateral wall of the cavernous sinus, a superior eyelid endoscopic transorbital approach was performed and the anterior portion of the greater sphenoid wing was removed. The meningo-orbital band was exposed as the key starting point for revealing the cavernous sinus and its contents in a minimally invasive interdural fashion.

RESULTS: This endoscopic transorbital approach, with partial removal of the greater sphenoid wing followed by a "natural" ventral interdural dissection of the meningo-orbital band, allowed exposure of the entire lateral wall of the cavernous sinus up to the plexiform portion of the trigeminal root and the petrous bone posteriorly and the foramen spinosum, with the middle meningeal artery, laterally.

CONCLUSIONS: The purely endoscopic transorbital approach through the meningo-orbital band provides a direct view of the cavernous sinus through a simple and rapid means of access. Indeed, this interdural pathway lies in the same sagittal plane as the lateral wall of the cavernous sinus. Advantages include a favorable angle of attack, minimal brain retraction, and the possibility for dissection through the interdural space without entering the neurovascular compartment of the cavernous sinus. Surgical series are needed to demonstrate any clinical advantages and disadvantages of this novel route.

Background: The availability of minimal access instrumentation and endoscopic visualization has revolutionized the field of minimally invasive skull base surgery. The transorbital endoscopic approach using an eyelid incision has been proposed as a new minimally invasive technique for the treatment of skull base pathology, mostly extradural tumors. Our study aims to evaluate the anatomical aspects and potential role of the transorbital endoscopic approach for exposure of the sylvian fissure, middle cerebral artery and crural cistern.

Methods: An anatomical dissection was performed in four freshly injected cadaver heads (8 orbits) using 0- and 30-degree endoscopes. First, an endoscopic endonasal medial orbital decompression was done to facilitate medial retraction of the orbit. An endoscopic transorbital approach through an eyelid incision, with drilling of the posterior wall of the orbit and lesser sphenoidal wing, was then performed to expose the sylvian fissure and crural cisterns. A stepwise anatomical description of the approach and visualized anatomy is detailed.

Results: A superior eyelid incision followed by orbital retraction provided a surgical window of approximately 1.2 cm (range 1.0-1.5 cm) for endoscopic transorbital dissection. The superior (SOF) and inferior (IOF) orbital fissures represent the medial limits of the approach and are identified in the initial part of the procedure. Drilling of the orbital roof (lateral and superior to the SOF), greater sphenoidal wing (lateral to the SOF and IOF) and lesser sphenoidal wing exposed the anterior and middle fossa dura. A square-shaped dural opening provided visualization of the posterior orbital gyri, sylvian fissure and temporal pole. Intradural dissection allowed exposure of the sphenoidal portion of the sylvian fissure, M1, MCA bifurcation and M2 branches and lenticulostriate perforators. Dissection of the medial aspect of the sylvian and carotid cisterns with a 30-degree endoscope allowed exposure of the mesial temporal lobe and crural cistern.

Conclusions: The transorbital endoscopic approach allows successful exposure of the sphenoidal portion of the sylvian fissure and M1 and M2 segments of the middle cerebral artery. Angled endoscopes may provide visualization of the mesial temporal lobe and crural cistern. Although our anatomical study demonstrates the feasibility of intradural dissection and closure via an endoscopic transorbital approach, further studies are necessary to evaluate its role in the clinical scenario.

Background: Anterior and posterior ethmoid arteries supply the paranasal sinuses, septum, and lateral nasal wall. Precise identification of these arteries is important during anterior skull base procedures, endoscopic sinus surgery, and ligation of ethmoid arteries for epistaxis refractory to standard treatment. There is controversy in the literature regarding the prevalence of supernumerary ethmoid arteries.

Objective: This study examined the prevalence of supernumerary ethmoid arteries by using direct visualization after transorbital endoscopic dissection.

Methods: Nineteen cadaveric specimens were evaluated by using a superior lid crease (blepharoplasty) incision and an endoscopic approach to the medial orbital wall. Ethmoid arteries were identified as they pierced the lamina papyracea coplanar with the skull base and optic nerve. The distances from the anterior lacrimal crest to the ethmoid arteries and optic nerve were measured with a surgical ruler under endoscopic guidance.

Results: Thirty-eight cadaveric orbits were measured. Overall, there were three or more ethmoid arteries (including anterior and posterior arteries) in 58% of orbits, with 8% of the total sample that contained four or more ethmoid arteries. The average number of ethmoid arteries was 2.7. Bilateral supernumerary ethmoid arteries were noted in 42% of the specimens. The distance between the anterior lacrimal crest and the anterior ethmoid, posterior ethmoid, and optic nerve averaged 20, 35, and 41 mm, respectively. The average distance to the supernumerary or middle ethmoid artery was 29 mm.

Conclusion: This study found supernumerary ethmoid arteries in 58% of cadaveric specimens, a prevalence much higher than previously reported. Recognition of these additional vessels may improve safety during endoscopic sinus surgery and skull base surgery, and may permit more effective ligation for refractory epistaxis originating from the ethmoid system.

Objective To design and assess the quality of a novel lateral retrocanthal endoscopic approach to the lateral cavernous sinus. Design Computer modeling software was used to optimize the geometry of the surgical pathway, which was confirmed on cadaver specimens. We calculated trajectories and surgically accessible areas to the middle fossa while applying a constraint on the amount of soft tissue retraction. Setting Virtual computer model to simulate the surgical approach and cadaver laboratory. Participants The authors. Main Outcome Measures Adequate surgical access to the lateral cavernous sinus and adjacent regions as determined by operations on the cadaver specimens. Additionally, geometric limitations were imposed as determined by the model so that retraction on soft tissue structures was maintained at a clinically safe distance. Results Our calculations revealed adequate access to the lateral cavernous sinus, Meckel cave, orbital apex, and middle fossa floor. Cadaveric testing revealed sufficient access to these areas using <10 mm of orbital retraction. Conclusions Our study validates not only the use of computer simulation to plan operative approaches but the feasibility of the lateral retrocanthal approach to the lateral cavernous sinus.

Transnasal endoscopic surgery has remained at the forefront of surgical management of sinogenic complications involving the frontal sinus, orbit, and anterior skull base. However, the difficulty in accessing certain areas of these anatomical regions can potentially limit its use. Transorbital neuroendoscopic surgery (TONES) was recently introduced to transgress the limits of transnasal endoscopic surgery; the access that it provides could add additional surgical pathways for treating sinogenic complications involving the frontal sinus, orbit, and anterior cranial fossa. We describe a prospective series of 13 patients who underwent TONES for the management of various sinogenic complications, including epidural abscess, orbital abscess, and fronto-orbital mucocele or mucopyocele, as well as subperiosteal abscess presenting with orbital apex syndrome. The primary outcome measurement was the efficacy of TONES in treating these pathologies. TONES provided effective access to the frontal sinus, orbit, and the anterior cranial fossa. All patients demonstrated postoperative resolution of initial clinical symptoms with well-hidden surgical scars. There were no ophthalmologic complications or recurrence of pathology. Based on our experience, TONES appears to provide a valuable addition to the current surgical armamentarium for treating selected complications of sinusitis.