Dual-Port 2D and 3D Endoscopy: Expanding the Limits of the Endonasal Approaches to Midline Skull Base Lesions with Lateral Extension

Objective To investigate a novel dual-port endonasal and subtemporal endoscopic approach targeting midline lesions with lateral extension beyond the intracavernous carotid artery anteriorly and the Dorello canal posteriorly. Methods Ten dual-port approaches were performed on five cadaveric heads. All specimens underwent an endoscopic endonasal approach from the sella to middle clivus. The endonasal port was combined with an anterior or posterior endoscopic extradural subtemporal approach. The anterior subtemporal port was placed directly above the middle third of the zygomatic arch, and the posterior port was placed at its posterior root. The extradural space was explored using two-dimensional and three-dimensional endoscopes. Results The anterior subtemporal port complemented the endonasal port with direct access to the Meckel cave, lateral sphenoid sinus, superior orbital fissure, and lateral and posterosuperior compartments of the cavernous sinus; the posterior subtemporal port enhanced access to the petrous apex. Endoscopic dissection and instrument maneuverability were feasible and performed without difficulty in both the anterior and posterior subtemporal ports. Conclusion The anterior and posterior subtemporal ports enhanced exposure and control of the region lateral to the carotid artery and Dorello canal. Dual-port neuroendoscopy is still minimally invasive yet dramatically increases surgical maneuverability while enhancing visualization and control of anatomical structures.     

The anterior cavernous sinus space

Summary The anterior cavernous sinus space is the venous space anterior to the cavernous carotid artery. It is tetrahedral in shape with the anterior apex at the superior orbital fissure. The superomedial wall is formed by the base of the anterior clinoid process. The inferomedial wall is formed by the sphenoid bone. The lateral wall consists of two layers of dura with the oculomotor, trochlear, ophthalmic and abducens nerves in the inner layer. Medially, the posterior wall consists of the cavernous carotid artery. Laterally, it communicates with the lateral cavernous sinus space. Paraclinoid and carotid cave aneurysms may occupy this space and its microanatomy is important in the surgery of these aneurysms.     

Drainage Pathway of the Superior Petrosal Vein Evaluated by CT Venography in Petroclival Meningioma Surgery

Objectives This study aimed to clarify the drainage location of the superior petrosal vein (SPV) in relation to Meckel''s cave and the internal acoustic meatus (IAM) and to discuss its significance in petroclival meningioma surgery.Design Prospective clinical study.Setting Hospital-based.Participants Five patients with petroclival meningioma and 50 patients (primarily unruptured supratentorial aneurysm patients, with a few hemifacial spasm patients) with no posterior fossa lesions.Main Outcome Measures On computed tomography venography (CTV), the drainage site was classified into three patterns based on its relationship to Meckel''s cave and the IAM: Meckel''s cave type, Intermediate type, and Meatal type.Results In all patients, the SPV was patent and emptied into the superior petrosal sinus (SPS). In patients without posterior fossa lesions, 35% had Meckel''s cave type, 54% had Intermediate type, and 11% had Meatal type. Of the five patients with petroclival meningioma, three had Intermediate type, and two had Meckel''s cave type.Conclusion The SPV is a significant vein that should be preserved to prevent venous complications. Preoperative knowledge of the SPV drainage site is helpful for planning the approach and preserving the SPV in petroclival meningioma surgery.     

Anterior clinoidectomy

Background

The optic nerve within the optic canal, the parophthalmic segment of the carotid artery, and the oculomotor nerve in the superior orbital fissure all lay against the anterior clinoid process. Bone resection uncovers these structures.

Method

For extradural resection of the anterior clinoid process and surrounding bone, two key steps are recommended: bony opening of the superior orbital fissure, and transection of the orbitotemporal periosteal fold.

Conclusion

Anterior clinoidectomy is technically challenging. Following a sequence of surgical steps to expose clearly-defined surgical landmarks helps to make this procedure simple and safe.

Key points

? Pterional craniotomy ? Complete extradural anterior clinoidectomy ? Slit dura (3 mm) to drain cerebrospinal fluid ? Peel dura from orbital roof and lateral wall ? Bony opening of superior orbital fissure to use it as surgical corridor ? Drilling of optic canal ? Transection of orbitotemporal periosteal fold ? Hollow anterior clinoid process and piece-meal resection ? Transection of falciforme ligament to free optic nerve ? Replace falciforme ligament by extradural free pericranial flap     

The Superior Transvelar Approach to the Fourth Ventricle and Brainstem

Objective The superior transvelar approach is used to access pathologies located in the fourth ventricle and brainstem. The surgical path is below the venous structures, through the superior medullary velum. Following splitting the tentorial edge, near the tentorial apex, the superior medullary velum is split in the cerebello-mesencephalic fissure. Using the supracerebellar infratentorial, transtentorial or parietal interhemispheric routes, the superior medullary velum is approached. Splitting this velum provides a detailed view of the fourth ventricle and its floor.Materials and Methods A total of 10 formalin-fixed specimens were dissected in a stepwise manner to simulate the superior transvelar approach to the fourth ventricle. The exposure gained the distance from the craniotomy site and the ease of access was assessed for each of the routes. We also present an illustrative case, operated by the senior author (AN).Results The superior transvelar approach provides access to the entire length of the fourth ventricle floor, from the aqueduct to the obex, when using the parietal interhemispheric route. In addition, this approach provides access to the entire width of the floor of the fourth ventricle; however, this requires retracting the superior cerebellar peduncle. Using the supracerebellar infratentorial route gives a limited exposure of the superior part of the fourth ventricle. The occipital interhemispheric route is a compromise between these two.Conclusion The superior transvelar approach to the fourth ventricle provides a route for approaching the fourth ventricle from above. This approach does not require opening the posterior fossa in the traditional way, and provides a reasonable alternative for accessing the superior fourth ventricle.     

“Round-the-Clock” Surgical Access to the Orbit

Objective To describe an algorithm to guide surgeons in choosing the most appropriate approach to orbital pathology. Methods A review of 12 selected illustrative cases operated on at the neurosurgical department of University of Pittsburgh Medical Center over 3 years from 2009 to 2011 was performed. Preoperative coronal magnetic resonance imaging and/or computed tomography views were compared using a “clock model” of the orbit with its center at the optic nerve. The rationale for choosing an external, endoscopic, or combined approach is discussed for each case. Results Using the right orbit for demonstration of the clock model, the medial transconjunctival approach provides access to the anterior orbit from 1 to 6 o''clock; endoscopic endonasal approaches provide access to the mid and posterior orbit and orbital apex from 1 to 7 o''clock. The lateral micro-orbitotomy gives access to the orbit from 8 to 10 o''clock. The frontotemporal craniotomy with orbital osteotomy accesses the orbit from 9 to 1 o''clock; addition of a zygomatic osteotomy to this extends access from 6 to 8 o''clock. Conclusions Combined, the approaches described provide 360 degrees of access to the entire orbit with the choice of the optimal approach guided primarily by the avoidance of crossing the plane of the optic nerve.     

Lateral Transorbital Neuroendoscopic Approach to the Lateral Cavernous Sinus

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.     

The Significance of Intraoperative Electromyographic “Lateral Spread” in Predicting Outcome of Microvascular Decompression for Hemifacial Spasm

Objectives During microvascular decompression (MVD) of the facial nerve for hemifacial spasm (HFS), an abnormal muscle response can be recorded upon stimulation of the facial nerve, also known as the lateral spread response. This response may vanish after MVD and has been associated with a successful outcome. The purpose of this study was to determine if resolution of lateral spread correlated with the elimination of HFS in a single surgeon''s experience. Design and Setting (1) Retrospective analysis of 38 patients undergoing MVD with intraoperative electromyography for HFS. (2) Meta-analysis of studies from the literature. Main Outcome Measure Presence or absence of HFS and any complications. Results Lateral spread response was seen in 36 patients; 20 patients had full resolution. Of these, 15 patients became HFS free, and 5 five patients still had some degree of HFS. Sixteen patients had a persistent lateral spread response despite a technically successful MVD; 11 of these became spasm free, and 5 still suffered from some degree of facial twitching. Analyzing 16 studies reporting a total of 1301 patients, a significant correlation (p < 0.0001) between response cessation and resolution of HFS was found. Conclusion The role of monitoring lateral spread response as a predictor for clinical outcome is limited.     

A New Segment of the Trochlear Nerve: Cadaveric Study with Application to Skull Base Surgery

Objectives The trochlear nerve is important to preserve during approaches to the skull base. Traditionally, this nerve has been divided into cisternal, cavernous, and orbital segments. However, the authors anecdotally observed an additional segment during routine cadaveric dissections. Therefore, they performed this study to better elucidate this anatomy. Design Twenty latex-injected cadaveric sides (10 adult cadavers) were dissected with the aid of an operating microscope. Standard microdissection techniques were used to examine the course of the distal cisternal and precavernous segments of the trochlear nerve. Setting Cadaver laboratory. Main Outcome Measures Measurements were made using a microcaliper. Digital images were made of the dissections. Results The authors identified a previously undescribed segment of the trochlear nerve in all specimens. This part of the nerve coursed between the entrance of the trochlear nerve into the posterior corner of the oculomotor trigone to the posterior wall of the cavernous sinus. This segment of trochlear nerve was, on average, 4 mm in length. Conclusions The authors have identified a new segment of the trochlear nerve not previously described. They propose that this be referred to as the trigonal segment. Knowledge of the microanatomy of the trochlear nerve is useful to skull base surgeons.     

眶上裂及其周围结构的显微解剖和手术学意义

目的研究眶上裂及其周围结构的显微解剖,并分析其手术学意义,以期为相关手术入路、病理解剖和影像学研究提供显微解剖学资料。方法利用8具经福尔马林固定的成人头颅湿标本和5具成人头颅干标本,在显微镜下对眶上裂及其周围的骨性结构、硬膜结构、韧带、神经和血管进行解剖,并进行多角度观察、拍摄和描述。结果眶上裂的空间分成外侧部、中间部和下部;动眼神经、滑车神经、展神经、眼神经和眼上静脉从眶上裂的外侧部或中间部穿过;神经血管与软组织共同封闭眶上裂;眶上裂外侧韧带和直肌间韧带是重要的解剖标志。结论只有经过精细的显微解剖操作和观察才能全面掌握眶上裂及其周围结构的解剖知识,进而有助于临床手术操作。     

An alternative extradural exposure to the anterior clinoid process: the superior orbital fissure as a surgical corridor

OBJECTIVE: Dolenc has pioneered the extradural approach to the anterior clinoid process (ACP) in approaching the cavernous sinus, clinoidal space, and orbital apex. A key step is the division of the frontotemporal dural fold (FTDF). Less experienced surgeons may not be as versatile in their three-dimensional understanding of the superior orbital fissure and thus may risk injury to its contents. Through our cadaveric and subsequent clinical experience, we have devised a modification of the approach that permits safer handling of the contents of the superior orbital fissure. METHODS: In five consecutive injected cadaveric heads (10 sides), we performed on one side a traditional extradural exposure of the ACP. On the other side, we performed our alternative dissection. Instead of exposing the ACP from medial to lateral and dividing the frontotemporal dural fold along the assumed path of safety, we followed the edge of the lesser wing from lateral to medial, uncovered the superior orbital fissure, and peeled the outer layer of the cavernous sinus medial to the foramen rotundum along the greater wing, thus uncovering the inferolateral surface of the ACP. This allowed dural division under full visualization. RESULTS: The alternative method proved easier and more reliable in every case. We applied this technical modification in seven patients with no complications. Specifically, there was no injury to the oculomotor, lacrimal, frontal, or trigeminal nerves or branches. We present detailed anatomic expositions of the injected specimens. CONCLUSION: This technical modification of the extradural approach of Dolenc is a simple, safe, and valuable adjunct to the exposure of the ACP. We recommend its use particularly by relatively inexperienced surgeons.     

Banked Fascia Lata in Sellar Dura Reconstruction after Endoscopic Transsphenoidal Skull Base Surgery

Objectives Cerebrospinal fluid (CSF) leakage is an undesirable complication of transsphenoidal skull base surgery. The issue of the most appropriate sellar dura repair remains unresolved, although a multilayer technique using autologous fascia lata is widely used. We describe the novel application of a homologous banked fascia lata graft as an alternative to an autologous one in the reconstruction of sellar dura defects in endoscopic transsphenoidal surgery. Design The clinical records of patients who underwent endoscopic transsphenoidal surgery at our department from June 2012, when we started using homologous fascia lata, up to July 2014 were reviewed retrospectively. The data concerning diagnosis, reconstruction technique, and surgical outcome were analyzed. Results We treated 16 patients successfully with banked fascia lata. Twelve patients presented intraoperative CSF leakage, and four patients were treated for postoperative rhinoliquorrhea. Banked fascia lata was used in a single-to-multilayer technique, depending on the anatomical features of the defect and of the sellar floor. No complications or failures in sella reconstruction occurred. Conclusion A banked fascia lata graft proved reliable and safe in providing an effective sellar dura reconstruction. Used in a multilayer strategy, it should be considered a viable alternative to an autologous fascia lata graft.     

Plagiocephaly. Craniofacial asymmetry with variable curling-up

The plagiocephaly syndrome is an asymmetrical cranial deformity due to premature synostosis of a coronal hemi-suture. The predominant alteration is at the spheno-frontal suture. The classification is attempted between the isolated plagiocephaly (P) an plagiocephaly with hypertelorism, on one side, that are to be distinguished from complex asymmetrical cranio-facial deformities. The frontal P. are differentiated from occipital P (pachycephaly) and from mixed hemi-cranial P. The deformity affects the fronto-orbital region situated anterior to the synostosis. The coronal suture incurves around a pivot formed by the lateral orbital pillar and the pterion, giving rise to a set of facial and cranial deformities, variable according to the precocity and the topography of the synostosis. Investigating the syndrome is clinical and radiological. The deformity reveals itself in 88% of cases, the affects are mainly orbital and ophthalmologic. The authors insist on the necessity of a bilateral orbito-fronto-nasal osteotomy, as a therapeutic act that gives better harmony on short and long term; on the other hand, they draw the attention to the importance of abolishing the synostocic lock by the resection of the lesser wing of the sphenoid extended till the superior orbital fissure and the resection of the outher periosteal layer of the dura matter which allows a remodeling effect the growing brain. The results and complications are evaluated on 44 operated children.     

To Preserve or Not to Preserve the Orbit in Paranasal Sinus Neoplasms: A Meta-Analysis

Context The effect on survival of orbital evisceration on patients with paranasal sinus neoplasms has not been well established. Objective To review systematically the available literature concerning survival in patients who undergo surgery for paranasal sinus neoplasm with and without preservation of the eye. Data Source A retrospective meta-analysis of English and non-English articles using Medline and the Cochrane database. Eligibility Criteria Studies analyzing 5-year survival rates in patients who had orbital evisceration compared with orbital preservation for the treatment of paranasal sinus neoplasms were included in the final analysis. Data Extraction Independent review by two authors using predefined data fields. Data Synthesis A meta-analysis of four articles involving 443 patients was performed using the DerSimonian-Laird random-effects method. Results Our analysis revealed a total effect size of 0.964 in favor of preservation of the eye; however, these results are not robust, having a true effect size anywhere from 0.785 to 1.142 with a 95% confidence interval. Limitations Only retrospective observational studies were included because a prospective randomized study cannot be performed in this population. Conclusion Our study supports the notion that in select patients preservation of the eye may yield a different outcome when compared with orbital evisceration.     

New Dried Human Amniotic Membrane Is Useful as a Substitute for Dural Repair after Skull Base Surgery

Objectives Cerebrospinal fluid (CSF) leakage is an undesirable complication of skull base surgery. We used dried human amniotic membrane (AM) as a patch graft for dural repair to determine its efficacy in preventing CSF leakage.Design Frontoparietal craniotomy and removal of dura were performed in 20 Wistar rats. A dried AM was placed to cover the dural defect without suturing in 16 animals. In four animals, an expanded polytetrafluoroethylene was implanted. At 2 weeks and 1, 3, and 6 months, histological examination was performed. Dried AM was also used as a substitute in 10 patients who underwent skull base surgery, after approval by the Ethics Committee of the University of Toyama.Results At 2 weeks after implantation, thick connective tissue completely enclosed the dried AM. At 1 month after implantation, the connective tissue became thin and the implanted AM shortened. At 3 and 6 months after implantation, histological examination revealed disappearance of the dried AM and formation of membranous tissue. In the clinical study, neither CSF leakage nor clinical adverse reactions directly related to the dried AM were observed.Conclusion Dried human AM appears to be an ideal substitute for dura, since it is replaced by natural tissue.     

The Reverse-Flow Facial Artery Buccinator Flap for Skull Base Reconstruction: Key Anatomical and Technical Considerations

Objective To highlight key anatomical and technical considerations for facial artery identification, and harvest and transposition of the facial artery buccinator (FAB) flap to facilitate its future use in anterior skull base reconstruction. Only a few studies have evaluated the reverse-flow FAB flap for skull base defects. Design Eight FAB flaps were raised in four cadaveric heads and divided into thirds; the facial artery''s course at the superior and inferior borders of the flap was measured noting in which incisional third of the flap it laid. The flap''s reach to the anterior cranial fossa, sella turcica, clival recess, and contralateral cribriform plate were studied. A clinical case and operative video are also presented. Results The facial artery had a near vertical course and stayed with the middle (⅝) or posterior third (⅜) of the flap in the inferior and superior incisions. Seven of eight flaps covered the sellar/planar regions. Only four of eight flaps covered the contralateral cribriform region. Lastly, none reached the middle third of the clivus. Conclusions The FAB flap requires an understanding of the facial artery''s course, generally seen in the middle third of the flap, and is an appropriate alternative for sellar/planar and ipsilateral cribriform defects.     

The Extended Nasoseptal Flap for Skull Base Reconstruction of the Clival Region: An Anatomical and Radiological Study

Objective Reconstruction of large clival defects after an endoscopic endonasal procedure is challenging. The objective is to analyze the morphology, indications, and limitations of the extended nasoseptal flap, which adds the nasal floor and inferior meatus mucosa, compared with the standard nasoseptal flap, for clival reconstruction. Design Twenty-seven sides of formalin-fixed anatomical specimens and 13 computed tomography (CT) scans were used. Under 0-degree endoscopic visualization, a standard flap on one side and an extended flap on the other side were performed, as well as exposure of the sella, cavernous sinus, and clival dura mater. Coverage of both flaps was assessed, and they were incised and extracted for measurements. Results The extended flap has two parts: septal and inferior meatal. The extended flaps are 20 mm longer and add 774 mm² of mucosal area. They cover a clival defect from tuberculum to foramen magnum in 66.6% cases and from below the sella in 91.6%. They cover both parasellar and paraclival segments of the internal carotid arteries. The lateral inferior limits are the medial aspect of the hypoglossal canals and Eustachian tubes. CT scans can predict the need or limitation of an extended nasoseptal flap. Conclusions The nasal floor and inferior meatus mucosa adds a significant area for reconstruction of the clivus. A defect laterally beyond the hypoglossal canals is not likely covered with this variation of the flap. Preoperative CT scans are useful to guide the reconstruction techniques.     

C-shaped Incision for Far-Lateral Suboccipital Approach: Anatomical Study and Clinical Correlation

Background The standard incision for far-lateral suboccipital approaches has been the classic “reverse hockey stick.” Although that incision provides ample exposure, concern has been raised that excessive muscle dissection and skin elevation might lead to accumulation of cerebrospinal fluid (CSF) under the flap with increased risk of CSF leak. We hypothesize that the C-shaped incision can minimize the amount of muscle dissection and provide optimal exposure and surgical outcomes. Objective To describe the anatomical dissection for the C-shaped incision and clinical application of the C-shaped incision for the far-lateral approach. Methods A retrospective analysis of all the patients operated on at our center using this approach for the treatment of aneurysm of the posterior inferior cerebellar artery (PICA) from 2005 to 2011. Results of clinical and operative outcome are evaluated. Surgical techniques are described in detail. Cadaveric dissections using the C-shaped incision were performed to assess the exposure of the far-lateral suboccipital area. Results Eleven consecutive patients who had undergone this procedure were selected. All patients underwent clipping of PICA aneurysms. Nine patients (82%) presented with ruptured aneurysms and subarachnoid hemorrhage. All of them underwent suboccipital craniectomy and C1 laminectomy. The dura mater was closed in a watertight fashion in 10 patients (91%). No CSF leak or pseudomeningocele were reported. In nine SAH patients, two (22%) had postoperative dysphagia and required long-term percutaneous endoscopic gastrostomy tube placement. One patient (11%) had chronic respiratory failure and required a tracheostomy. Three patients (33%) developed hydrocephalus and required a ventriculoperitoneal shunt. Conclusions The C-shaped incision is a valid alternative to the classic reverse hockey-stick incision to gain exposure for far-lateral craniotomies. Knowing the anatomy and dissection techniques can provide an easy and safe route to address anterior lateral cranial-cervical lesions. Our results suggest the C-shaped incision is reliable in preventing CSF leak and the formation of pseudomeningocele.     

Modified One-piece Supraorbital Approach for Orbital Tumors: Widely Preserved Orbital Roof in a Self-fitting Flap

Objectives The one-piece supraorbital approach is a rational approach for the removal of orbital tumors. However, cutting the roof through the orbit is often difficult. We modified the technique to facilitate the osteotomy and improve the cosmetic effect. Design Three burr holes are made: the first, the MacCarty keyhole (burr hole 1), exposes the anterior cranial fossa and orbit; the second is placed above the supraorbital nerve (burr hole 2); and the third on the superior temporal line. Through burr hole 2, a small hole is created on the roof, 10 mm in depth. Next the roof is rongeured through burr hole 1 toward the preexisting small hole. Seamless osteotomies using a diamond-coated threadwire saw and the preexisting four holes are performed. Lastly the flap is removed. On closure, sutures are passed through holes in the cuts made with the threadwire saw, and tied. Results We applied our technique to address orbital tumors in two adult patients. The osteotomies in the roof were easy, and most parts of the roof were repositioned. Conclusions Our modification results in orbital osteotomies with greater preservation of the roof. Because the self-fitting flap does not require the use of fixation devices, the reconstruction is cosmetically satisfactory.     

Interhemispheric Endoscopic Fenestration of the Lamina Terminalis through a Single Frontal Burr Hole

Objective We evaluate the feasibility and safety of performing a novel interhemispheric endoscopic fenestration of the lamina terminalis (IEFLT) through a single frontal burr hole immediately lateral to the superior sagittal sinus. Methods Five cadaveric heads underwent IEFLT. Sequential burr holes were made beginning above the glabella and progressed cranially to caudally until the frontal sinus. An endoscope was inserted, and interhemispheric dissection of the arachnoid membranes was completed with endoscopic instruments in a straight direction from the point of entry to the lamina terminalis (LT). Angled optics (0 and 30 degrees) were used to study the neurovascular structures and surgical landmarks. Results The IEFLTs were successfully completed in all specimens and allowed for good visualization of the inferior portion of the LT. The arachnoid dissections were achieved uneventfully. The endoscope provided good surface control of the LT and excellent stereoscopic visualization of the neurovascular complexes. Improved circumferential visualization of the superior part of the anterior portion of the third ventricle was attained. Conclusion IEFLT is a potential alternative to the classic endoscopic third ventriculostomy and a simpler alternative to the subfrontal EFLT, although surgical maneuverability is still limited due to the size of the probe in relation to the narrow surgical corridor.