Transpeduncular Approach for Resection of Ruptured Fourth Ventricular Arteriovenous Malformation.

The lateral recess of the fourth ventricle can be challenging to access surgically. We present a case of a previously ruptured arteriovenous malformation (AVM) of the fourth ventricle that was surgically resected via a retrosigmoid craniotomy and transinferior cerebellar peduncular approach. The patient is a 54-year-old female who experienced an intraventricular hemorrhage several months before presentation to our institution. Imaging studies suggested the presence of an AVM located in the right lateral recess of the fourth ventricle. After discussion of all possible treatment options, the patient elected to proceed with surgical resection. To access the lesion, we performed a retrosigmoid craniotomy and entered into the fourth ventricle via s small incision in the inferior cerebellar peduncle. Postoperative imaging demonstrated complete removal of the AVM nidus. Video 1 demonstrates this approach and discusses the anatomic landmarks used to guide resection.

Assessment of Arterial Configurations of the Suprachiasmatic Region from the Endoscopic Endonasal Perspective: A Cadaveric Anatomical Study.

BACKGROUND: Endoscopic endonasal surgery has proved to offer a practical route to treat suprasellar lesions, including tumors and vascular pathologies. Understanding the different configurations of the anterior cerebral communicating artery (ACoA) complex (ACoA-C) is crucial to properly navigate the suprachiasmatic space and decrease any vascular injury while approaching this region through an endonasal approach. METHODS: An endoscopic endonasal transplanum-transtubercular approach was performed on 36 cadaveric heads (72 sides). The variations of the ACoA-C and feasibility of reaching its different components were analyzed. The surgical area exposure of the lamina terminalis was also quantified before and after mobilization of the ACoA-C. RESULTS: The typical ACoA-C configuration was found in 41.6% of specimens. The following 2 main variations were identified: accessory anterior cerebral artery segment 2 (5, 13.9%) and common trunk of anterior cerebral artery with absence of ACoA (5, 13.9%). Of 101 recurrent arteries of Heubner, 96 (95.0%) were identified within 4 mm proximal or distal to the ACoA. The mean lamina terminalis exposure area was 33.1 ± 16.7 mm2, which increased to 59.9 ± 11.9 mm2 after elevating the ACoA. CONCLUSIONS: A considerable amount of variation of the ACoA-C can be found through an endoscopic endonasal transplanum-transtubercular approach. These configurations determine the feasibility of lamina terminalis exposure and the complexity of reaching the ACoA. Assessment of ACoA morphology and its adjacent structures is crucial while approaching the suprachiasmatic through a transnasal corridor.

Principles of Supplemental Motor Area and Cingulate Tumor Resection With Asleep Trimodal Motor Mapping: 2-Dimensional Operative Video.

Resection of intra-axial tumors adjacent to the motor pathways can lead to devastating deficits; however, with an appropriate mapping technique, it can be performed safely. We present the case of a 63-yr-old woman with a diffuse glioma centered in the left supplemental motor area (SMA) and extending throughout the cingulate gyrus. In the video, we demonstrate the principles developed by the senior author for trimodal motor mapping under general anesthesia. Trimodal motor mapping includes direct stimulation of the cortex with a strip electrode, use of the bipolar stimulator for cortical and subcortical mapping, and use of the monopolar stimulator for subcortical motor mapping. We highlight technical principles required to safely resect these tumors, including the key anatomic landmarks and approach to SMA/cingulate lesions, techniques for subpial dissection, and preservation of en passage vessels. Patients with SMA tumors will almost always have a deficit after SMA resection, but if motor pathways are preserved and can be stimulated to produce movement at the end of the case, then the deficit will almost always improve, as was the case with this patient. Initially, postoperatively, she was nonverbal and hemiplegic, but by postoperative day 7 she recovered her speech significantly, was naming three of three objects, and was moving her right side. By 6 wk postoperative, she was ambulating independently and had normal speech. This case demonstrates the principles and techniques necessary for achieving maximal safe resection of tumors adjacent to the motor pathways with the patient under general anesthesia. The patient gave written informed consent for the surgical resection of her tumor and for the publication of this video.

Combined Pterional Transsylvian and Bifrontal Interhemispheric Approach to Ruptured Subcallosal and Pericallosal Brain Arteriovenous Malformation with Skeletonization of the Entire A2 ACA Segment.

A 39-year-old man presented with a large left paramedian frontal lobe intracerebral hemorrhage. Computed tomography angiography and magnetic resonance imaging revealed a tangle of vessels arising from the anterior cerebral arteries (ACAs) and dilated draining veins entering the superior sagittal sinus. Angiography confirmed a Spetzler-Martin grade 3, supplemented 2 arteriovenous malformation (AVM) with predominant supply from branches of the left ACA with superficial and deep drainage (Video 1). The case illustrates an unusual cerebrovascular pathology involving the entire A2 ACA segment. The AVM extended from the A1/2 junction along the entire A2 segment past the genu of the corpus callosum (A3 segment). A combined pterional transsylvian and bifrontal interhemispheric approach was performed. The proximal sylvian fissure and opticocarotid cistern were opened to expose the A1/2 junction. Once proximal control was obtained, the hematoma was evacuated to define the lateral border of the AVM. The interhemispheric fissure was then opened to identify the draining vein and the distal pericallosal arteries. The interhemispheric approach also defined the medial border of the AVM. The A2 ACAs were then skeletonized from the AVM from the A1/2 junction to the pericallosal arteries. Aneurysm clips were used to interrupt large AVM feeders from the A2 arteries, which avoids cautery and heat transmission to the parent vessel. Once the AVM was disconnected and skeletonized from the A2s, the draining vein was clipped and the nidus was removed. Indocyanine green angiography confirmed patency of the A2s and pericallosal arteries. Postoperative angiography demonstrated no residual shunting, and the patient was discharged in good condition.

Microsurgical Techniques for Exposing the Internal Maxillary Artery in Cerebral Revascularization Surgery: A Comparative Cadaver Study.

BACKGROUND: The internal maxillary artery (IMAX) is currently considered one of the main donor vessels in extracranial-to-intracranial bypass surgeries. Four main techniques for harvesting the IMAX have been described: via the anterior medial infratemporal fossa (AMITF), the middle infratemporal fossa (MITF), the anterior lateral middle fossa (ALMF), and the lateral middle fossa (LMF). The advantages and limitations of these techniques have not yet been systematically evaluated and compared. METHODS: Twenty-five cadaver specimens were used to evaluate the harvesting technique. The length and the caliber of the targeted IMAX segments, as well as the depth from the operating plane to the IMAX, surgical time, and surgical area of exposure, were analyzed. RESULTS: The MITF technique provided the greatest operating area of exposure (mean, 3.88 ± 0.97 cm2). The LMF and MITF techniques provided the largest IMAX caliber (mean, 3.1 ± 0.4 mm and 3.0 ± 0.3 mm, respectively). The ALMF technique provided the shallowest operative depth as well as the least time of exposure (21.8 minutes). The MITF technique exposed the longest IMAX segment (mean, 18.8 ± 3.5 mm). CONCLUSIONS: Advantages of the AMITF and MITF techniques include anatomic simplicity, absence of skull base drilling, and greater discretion in muscle dissection. These properties can simplify the anastomosis procedure compared with the ALMF and LMF techniques. Identification of the IMAX pattern is important before selecting the approach for this bypass operation.

Supracerebellar Approach for Resection of a Falcotentorial Dural Arteriovenous Fistula with Pial Tectal Arteriovenous Malformation Component Associated with a Left Parafalcine Meningioma.

A 66-year-old woman presented with a 4.5- × 4-cm left posterior parafalcine meningioma and visual loss in her left eye (Video 1). Prior to meningioma embolization, angiography confirmed an incidental high-risk falcotentorial dural arteriovenous fistula (DAVF) with pial tectal arteriovenous malformation (AVM) and flow-related aneurysms of the superior cerebellar artery (SCA) and posterior cerebral artery (PCA). Arterial supply to the AVM/DAVF consisted of branches of the middle meningeal artery, tentorial branches of the internal carotid arteries, and the PCA and SCA. Drainage into the vein of Galen (VG) and venous reflux into the precentral cerebellar vein (PCCV) were identified. The patient underwent transarterial embolization of the DAVF via the left middle meningeal artery using Onyx with a significant decrease of arterial venous shunting. A semi-sitting supracerebellar approach was performed. The subarachnoid space of the tentorium, cerebellar hemispheres, vermis, quadrigeminal, and ambient cisterns was dissected to reveal the boundaries of the lesion. Indocyanine green video angiography was done before and after in situ occlusion to identify the arterial supply and early venous drainage. The vascular lesion was disconnected circumferentially around the edges of the pial portion of the AVM, and the feeders were carefully cauterized and cut. The vessels on the surface of the brainstem were occluded in situ to prevent any parenchymal transgression. Finally, the drainage into the VG and the venous reflux to the PCCV were ligated. Postoperative angiography showed no residual DAVF or AVM and regression of aneurysms. The patient was discharged with no added deficits, and the meningioma was totally resected several months later.

An Anatomic Feasibility Study for Revascularization of the Ophthalmic Artery, Part I: Intracanalicular Segment.

BACKGROUND: The anatomico-functional complexity of the ophthalmic segment aneurysms is attributable to the presence of critical neurovascular structures in the surgical field. Surgical clipping of the ophthalmic artery (OpA) aneurysms can result in postoperative visual deficit due to the complexity of the aneurysm, vasospasm, or optic nerve manipulation. In this study, we aimed to characterize the feasibility of an intracanalicular OpA (iOpA) revascularization with 2 donor vessels: an intracranial-intracranial (IC-IC) bypass using the anterior temporal artery (ATA) and an extracranial-intracranial (EC-IC) bypass using the superficial temporal artery (STA). We further discuss their potential role in "unclippable" OpA aneurysms. METHODS: Twenty cadaveric specimens were used to evaluate the operative exposure of the intradural and intracanalicular OpA segments using an extradural-intradural intracanalicular approach. The arterial caliber and length at the anastomotic sites and required donor artery lengths were measured. The feasibility of the bypass using both donors was assessed. RESULTS: The average length of the intradural and intracanalicular segment of the OpA was 9.5 ± 1.6 mm. The mean caliber of the iOpA was 1.5 ± 0.2 mm. The mean ATA length required for an ATA-OpA anastomosis was 26.7 ± 8.9 mm, with a mean caliber of 1.0 ± 0.1 mm. The mean length of STA required for the bypass was 89.9 ± 9.7 mm, with a mean caliber of 1.92 ± 0.4 mm. CONCLUSIONS: This study confirms the feasibility of iOpA revascularization using IC-IC and EC-IC bypasses. These techniques could potentially be used for prophylactic or therapeutic neuroprotection from retinal ischemic injury while treating complex OpA aneurysms, infiltrative tumors, or intraoperative arterial injuries.

Stereoscopy in Surgical Neuroanatomy: Past, Present, and Future.

Since the dawn of antiquity, scientists, philosophers, and artists have pondered the nature of optical stereopsis-the perception of depth that arises from binocular vision. The early 19th century saw the advent of stereoscopes, devices that could replicate stereopsis by producing a 3D illusion from the super-imposition of 2D photographs. This phenomenon opened up a plethora of possibilities through its usefulness as an educational tool-particularly in medicine. Before long, photographers, anatomists, and physicians were collaborating to create some of the first stereoscopic atlases available for the teaching of medical students and residents. In fields like neurosurgery-where a comprehensive visuospatial understanding of neuro-anatomical correlates is crucial-research into stereoscopic modalities are of fundamental importance. Already, medical institutions all over the world are capitalizing on new and immersive technologies-such as 3D intraoperative recording, and 3D endoscopes-to refine their pedagogical efforts as well as improve their clinical capacities. The present paper surveys the history of stereoscopy from antiquity to the modern era-with a focus on its role in neurosurgery and medical education. Through the tracking of this evolution, we can discuss potential benefits, future directions, and highlight areas in which further research is needed. By anticipating these factors, we may strive to take full advantage of an emergent field of technology, for our ultimate goal of improving patient care.

Comparative Analysis of Pterional, Supraorbital, Extended Supraorbital, and Transtubercular-Transplanum Approaches for Exposing the Anterior Communicating Artery Complex: A Cadaveric Study.

OBJECTIVE: We aimed to quantify and compare surgical exposure and freedom at the anterior communicating artery (ACoA) complex using pterional (PT), supraorbital (SO), extended supraorbital withorbital osteotomy (SOO), and endonasal endoscopic transtubercular-transplanum (EEATT) approaches. METHODS: Right-sided PT, SO, SOO, and EEATT approaches were performed using 10 cadaveric heads. Surgical exposure and freedom (horizontal and vertical attack angle) at the ACoA complex were measured. The farthest clipping distance from ACoA to A1 (precommunicating segment of the anterior cerebral artery)/A2 (postcommunicating segment of the anterior cerebral artery) was also quantified. RESULTS: There was a significantly greater exposure length of right A1 in the PT approach (12.20 ± 2.48 mm) compared with the EEATT approach (9.52 ± 2.09 mm; P = 0.029). Among the 4 approaches, EEATT provided the shortest clipping distance for right A1 (6.56 ± 1.33 mm; P = 0.001) and the longest clipping distance for right A2 (3.36 ± 1.24 mm; P = 0.003). SO, SOO, and PT approaches (2.9 ± 0.9) had more observations on perforators from ACoA than did the EEATT approach (2.0 ± 0.66; P = 0.029). The EEATT approach (50.90 ± 17.45 mm2) provided better exposure of the superior part of the ACoA complex compared with the SO approach (29.37 ± 17.27 mm2; P = 0.05). PT and SOO approaches provided the greatest horizontal (36.88° ± 5.85°) and vertical (19.37° ± 4.70°) attack angle, respectively. CONCLUSIONS: The SO, SOO, and PT approaches provided a better hemilateral view of the ACoA complex and similar surgical exposure, whereas the EEATT approach offered greater exposure in the upper part of the ACoA complex, with relatively limited exposure of perforators from ACoA and surgical freedom. The EEATT approach can play a role in exposure of lesion involving the ACoA complex.

Replicating Skull Base Anatomy With 3D Technologies: A Comparative Study Using 3D-scanned and 3D-printed Models of the Temporal Bone.

HYPOTHESIS: 3D technologies, including structured light scanning (SLS), microcomputed tomography (micro-CT), and 3D printing, are valuable tools for reconstructing temporal bone (TB) models with high anatomical fidelity and cost-efficiency. BACKGROUND: Operations involving TB require intimate knowledge of neuroanatomical structures-a demand that is currently met through dissection of limited cadaveric resources. We aimed to document the volumetric reconstruction of TB models using 3D technologies and quantitatively assess their anatomical fidelity. METHODS: In the primary analysis, 14 anatomical characteristics of right-side TB from 10 dry skulls were measured. Each skull was 3D-scanned using SLS to generate virtual models, which were measured using mesh processing software. Metrics were analyzed using mean absolute differences and one-sample t tests with Bonferroni correction. In the secondary analysis, an individualized right-side TB specimen (TBi) was 3D-scanned using SLS and micro-CT, and 3D-printed on a stereolithography printer. Measurements of each virtual and 3D-printed model were compared to measurements of TBi. RESULTS: Significant differences between the physical skulls and virtual models were observed for 11 of 14 parameters (p < 0.0036), with the greatest mean difference in the length of petrous ridge (2.85 mm) and smallest difference in the diameter of stylomastoid foramen (0.67 mm). In the secondary analysis, greater mean differences were observed between TBi and virtual models than between TBi and 3D-printed models. CONCLUSION: For the first time, our study provides quantitative measurements of TB anatomy to demonstrate that 3D technologies can facilitate individualized and highly accurate reconstructions of TB, which may benefit anatomy education, clinical training, and preoperative planning.

An Anatomical Feasibility Study for Revascularization of the Ophthalmic Artery. Part II: Intraorbital Segment.

INTRODUCTION: Distal ophthalmic artery (OpA) aneurysms are a rare subset of vascular lesions with lack of optimal treatment. The management of these aneurysms may require complete occlusion of the parent vessel, carrying a risk of permanent visual impairment due to individual variations of extracranial collateral flow to the intraorbital ophthalmic artery (iOpA). OBJECTIVE: To test the feasibility of a superficial temporal artery (STA) to iOpA bypass to prevent acute ischemic retinal injury. Two different transorbital corridors (superomedial and posterolateral approaches) for this bypass were evaluated. METHODS: Each approach was carried out in 10 specimens each (n = 20). The corridors were compared to achieve the optimal exposure of the iOpA until the central retinal artery origin was visualized. An end-to-end anastomosis was performed from STA-to-iOpA. The arterial caliber and length at the anastomotic sites, required donor artery length, and intraorbital surgical area were measured. RESULTS: STA-iOpA bypasses were performed in all specimens. For the posterolateral transorbital approach, the mean caliber of STA was 1.8 ± 0.2 mm, and that of iOpA was 1.7 ± 0.5 mm. The required STA graft length was 78.3 ± 1 mm with lateral iOpA transposition of 8.2 ± 1.1 mm. For the superomedial approach, the average STA length required for an intraorbital bypass was 130.8 ± 14.0 mm. The mean calibers of iOpA and STA were 1.5 ± 0.1 mm and 1.5 ± 0.1 mm, respectively. CONCLUSIONS: This study demonstrates the feasibility of a novel revascularization technique of the iOpA using 2 different transorbital approaches. These techniques can be used in the management of intraorbital lesions such as OpA aneurysms, tumoral infiltrations, or intraoperative injuries.

Intradural and Extradural Ligation of a Left Dural Arteriovenous Fistula of the Sigmoid Sinus Using a Retrosigmoid Approach: 3-Dimensional Operative Video.

Dural arteriovenous fistulas (dAVFs) are acquired dural shunts between an artery and a vein without parenchymal nidus. DAVFs represent 10%-15% of intracranial arteriovenous malformations, and their manifestations vary from asymptomatic to devastating intracranial hemorrhage.1 They are classified according to their drainage and presence/absence of cortical venous reflux (CVR).2,3 The junction between transverse and sigmoid sinus (SS) is the most common location, and their treatment in case of CVR can involve the sacrifice of the sinus. DAVF occlusion may be achieved with both endovascular and surgical technique and frequently with combined techniques. This video demonstrates the management of a left dAVF of the SS in a 54-yr-old male with recent onset of diplopia and imbalance with venous congestion seen in the left cerebellum on T2 sequence MRI. Angiography revealed a Borden grade 2, Cognard grade IIa + b left SS dAVF supplied by the jugular and hypoglossal branches of the neuromeningeal trunk with retrograde filling of the partially thrombosed SS and drainage to the superior petrosal sinus and multiple cerebellar veins. Endovascular repair was not feasible due to high risk of postoperative cranial neuropathy. The patient consented to surgery. A left retrosigmoid craniotomy was performed to achieve intradural ligation of the fistula at the dural edge along the inferior aspect of the tentorium. After drainage occlusion and cauterization of the transmastoid extradural feeders (via mastoidectomy), the SS was entirely exposed and clipped to prevent any further retrograde arteriovenous shunting. The postoperative course was without complication and angiography showed complete occlusion of the dAVF.

Right Retrosigmoid Approach for In Situ Occlusion of Brainstem Arteriovenous Malformation Surrounding the Trigeminal Nerve: 3-Dimensional Operative Video.

Arteriovenous malformations (AVMs) of the trigeminal root entry zone are rare and can be associated with neurovascular compression syndromes as well as intracranial hemorrhage.1 They generally have a small nidus located on and around the pial surface of the brainstem; thus, they are feasible for surgery. Nevertheless, they represent a challenge given the vicinity and involvement of cranial nerves and brainstem perforators.2-4This video demonstrates the case of a 57-yr-old man with new onset of a severe headache without neurological deficit associated with MRI evidence of a vascular malformation around the cisternal right trigeminal nerve. The nerve showed an altered signal on the MRI. Angiography revealed a Spetzler-Martin grade II AVM with a 16-mm nidus supplied by basilar artery perforators, right anterior inferior cerebellar artery, and the superior cerebellar artery (SCA), with drainage into the superior petrosal vein and sigmoid sinus. After an unsuccessful attempted embolization, the patient was referred for and elected microsurgical treatment. With the patient in a lateral position, a right retrosigmoid approach was performed. After cisternal dissection and identification of the nidus, the feeders were occluded by alternating cauterization and clipping to avoid damage to the critical surrounding structures. The AVM in-situ occlusion was carried on without resection, given the involvement of the trigeminal nerve. The intraoperative indocyanine green angiography allowed recognition of the venous drainage and helped to localize and differentiate the feeders from normal perforators. In the immediate postoperative course, the patient suffered from mild numbness with a V2-V3 distribution that progressively improved. Angiography showed no residual AVM.

Clipping of High-Risk Dural Arteriovenous Fistula of the Posterior Fossa: 3-Dimensional Operative Video.

Dural arteriovenous fistulas (DAVFs) represent 10%-15% of all intracranial arteriovenous malformations.1 DAVFs located in the posterior cranial fossa are rare and often present with intracranial hemorrhage and myelopathy.2 Arterial supply could be provided by the meningeal branches of the vertebral artery and external and internal carotid arteries.3 A 68-year-old man presented with progressive lower-extremity weakness (Video 1). Magnetic resonance imaging revealed a patchy longitudinal cord signal abnormality extending from the cervicomedullary junction to C7. A tentorial DAVF supplied by the right posterior meningeal artery with drainage via dorsal and ventral perimedullary veins was identified on angiography. According to the Cognard classification, the patient's DAVF was determined to be high risk as a type V lesion with spinal venous drainage and progressive myelopathy.4 The fistula was embolized with 50% ethanol resulting in near-complete occlusion. However, follow-up angiography revealed a persistent arteriovenous shunt and slightly worsening symptoms for the patient. He underwent a sitting supracerebellar approach with a torcular craniotomy for successful clip ligation of the dural arteriovenous fistula. The patient was discharged with improvements in lower-extremity strength and no residual arteriovenous shunting in postoperative imaging.

Middle Meningeal Artery to Premeatal Anterior Inferior Cerebellar Artery Bypass via Anterior Petrosectomy: An Anatomic Feasibility Study.

BACKGROUND: Anterior inferior cerebellar artery (AICA) aneurysms are rare with no optimal consensus on management strategies. When treatment requires parent artery occlusion, postoperative ischemic or neuropathic complications can occur. This study evaluated the feasibility of direct revascularization of premeatal AICA using the middle meningeal artery (MMA) as the donor through an anterior petrosectomy window. METHODS: Ten specimens were used for surgical simulation of MMA-AICA bypass. MMA was harvested from the dura down to the foramen spinosum. An anterior petrosectomy approach was performed on each specimen, and AICA was exposed up to its origin from the basilar artery. The lateral pontine (A2) segment was mobilized laterally, and the end-to-end anastomosis was completed. Measurements of the required length of the AICA, MMA, and their calibers at the anastomotic site were recorded. RESULTS: MMA-AICA bypass was feasible in all specimens. The mean length of AICA from the origin at the anastomotic site was 7.3 ± 1.7 mm, and mean length of MMA from the foramen spinosum was 34.6 ± 5.1 mm. Mean calibers of MMA were 2.1 ± 0.2 mm at the foramen spinosum and 1.7 ± 0.2 mm at the anastomosis. A2 caliber was 1.6 ± 0.3 mm with average lateral mobilization of 7.6 ± 2.7 mm. CONCLUSIONS: This study establishes the feasibility of MMA-AICA bypass via a middle fossa approach. The matching caliber of the 2 arteries makes end-to-end anastomosis easy to achieve. The MMA is a suitable donor artery that avoids the use of an interposition graft and the complications of extracranial-intracranial bypass.

Construction of Neuroanatomical Volumetric Models Using 3-Dimensional Scanning Techniques: Technical Note and Applications.

BACKGROUND: Visuospatial features of neuroanatomy are likely the most difficult concepts to learn in anatomy. Three-dimensional (3D) modalities have gradually begun to supplement traditional 2-dimensionanl representations of dissections and illustrations. We have introduced and described the workflow of 2 innovative methods-photogrammetry (PGM) and structured light scanning (SLS)-which have typically been used for reverse-engineering applications. In the present study, we have described a novel application of SLS and PGM that could enhance medical education and operative planning in neurosurgery. METHODS: We have described the workflow of SLS and PGM for creating volumetric models (VMs) of neuroanatomical dissections, including the requisite equipment and software. We have also provided step-by-step procedures on how users can postprocess and refine these images according to their specifications. Finally, we applied both methods to 3 dissected hemispheres to demonstrate the quality of the VMs and their applications. RESULTS: Both methods yielded VMs with suitable clarity and structural integrity for anatomical education, surgical illustration, and procedural simulation. CONCLUSIONS: The application of 3D computer graphics to neurosurgical applications has shown great promise. SLS and PGM can facilitate the construction of VMs with high accuracy and quality that can be used and shared in a variety of 3D platforms. Similarly, the technical demands are not high; thus, it is plausible that neurosurgeons could become quickly proficient and enlist their use in education and surgical planning. Although SLS is preferable in settings in which high accuracy is required, PGM is a viable alternative with a short learning curve.

Acquisition of Volumetric Models of Skull Base Anatomy Using Endoscopic Endonasal Approaches: 3D Scanning of Deep Corridors Via Photogrammetry.

OBJECTIVE: In this study we aim to evaluate the feasibility of creating volumetric models of highly intricate skull-base anatomy-previously not amenable to volumetric reconstruction-using endoscopic endonasal approaches. METHODS: Ten human cadaveric heads were dissected through the nasal corridor to expose anterior, middle, and posterior cranial fossi structures and the pterygopalatine and infratemporal fossi. A rigid endoscope with a 30° lens was used to capture the images. Subsequently, a photogrammetry software was used to align, smooth, and texturize the images into a complete 3-dimensional model. RESULTS: An average of 174 photographs were used to construct each model (n = 10). In the end, we achieved high-definition stereoscopic volumetric models of the nasal corridor; paranasal fossae; and anterior, middle and posterior fossae structures that preserved structural integrity. Strategic points of interests were labeled and animated for educational use. CONCLUSIONS: Endoscopic volumetric models represent a new way to depict the anatomy of the skull base; their use with 3-dimensional technologies could potentially improve the visuospatial understanding of narrow surgical corridors for education and surgical-planning purposes.

Characterization of Anatomical Landmarks for Exposing the Internal Carotid Artery in the Infratemporal Fossa Through an Endoscopic Transmasticator Approach: A Morphometric Cadaveric Study.

BACKGROUND: The Eustachian tube and sphenoid spine have been previously described as landmarks for endonasal surgical identification of the most distal segment of the parapharyngeal internal carotid artery (PhICA). However, the intervening space between the sphenoid spine and PhICA allows for error during exposure of the artery. In the present study, we have characterized endoscopic endonasal transmasticator exposure of the PhICA using the sphenoid spine, vaginal process of the tympanic bone, and the "tympanic crest" as useful anatomical landmarks. METHODS: Endonasal dissection was performed in 13 embalmed latex-injected cadaveric specimens. Two open lateral dissections and osteologic analysis of 10 dry skulls were also performed. RESULTS: A novel and palpable bony landmark, the inferomedial edge of the tympanic bone, referred to as the tympanic crest, was identified, leading from the sphenoid spine to the lateral carotid canal. Additionally, the vaginal process of the tympanic bone, viewed endoscopically, was a guide to the PhICA. The sphenoid spine was bifurcate in 20% of the skulls, with an average length of 5.98 mm (range, 3.9-8.2 mm), width of 5.81 mm (range, 3.0-10.6 mm), and distance to the carotid canal of 4.48 mm (range, 2.5-6.1 mm). CONCLUSION: The sphenoid spine and pericarotid space has variable anatomy. Using an endoscopic transmasticator approach to the infratemporal fossa, we found that the closest landmarks leading to the PhICA were the tympanic crest, sphenoid spine, and vaginal process of the tympanic bone.

Revascularization of the Anterior Inferior Cerebellar Artery Using Extracranial and Intracranial Donors: A Morphometric Cadaveric Study.

INTRODUCTION: Anterior inferior cerebellar artery (AICA) aneurysms are rare, accounting for 0.2%-1.3% of all intracranial aneurysms. The standard treatment is often endovascular embolization or neck clipping; however, sacrifice of the parent vessel is sometimes necessary. Addition of revascularization procedures is a subject of controversy. The occipital artery (OA) has been used as a donor for bypass, but recently there has been a trend toward intracranial-intracranial approaches. The posterior inferior cerebellar artery (PICA)-AICA side-to-side bypass may serve as a safe alternative. OBJECTIVE: To characterize the PICA-AICA side-to-side bypass and the OA-AICA end-to-side bypass and review the literature relevant to AICA revascularization. METHODS: We performed a far-lateral approach on 12 cadaveric specimens and analyzed the regional anatomy. On this basis, we performed either an OA-AICA or a PICA-AICA bypass and took morphometric measurements relevant to the technique. RESULTS: PICA-AICA bypass was successful in 6/12 specimens. The length of the flocculopeduncular segment was 42.6 ± 15.8 mm in the specimens in which the bypass was feasible and 26.2 ± 7.2 mm in those in which the bypass was not feasible (P = 0.04). Mean distance between AICA and PICA was 5.3 ± 4 mm in the specimens in which side-to-side bypass was feasible and 11.6 ± 4.2 mm in the specimens in which it was not (P = 0.02). OA-AICA end-to-side bypass was feasible in all the specimens (75% in the flocculopeduncular segment; 25% in the cortical segment). CONCLUSIONS: This is the first cadaveric study analyzing the PICA-AICA side-to-side bypass for AICA revascularization. Our analyses provide evidence for the feasibility of this bypass and document the anatomic variations that may indicate its use.

Comparative Analysis of the Subtonsillar, Far-Lateral, Extreme-Lateral, and Endoscopic Far-Medial Approaches to the Lower Clivus: An Anatomical Cadaver Study.

BACKGROUND: The lower clivus (LC) is one of the most difficult areas to access in neurosurgery. Several microsurgical approaches to the LC have been reported, including the subtonsillar, far-lateral (FL), extreme-lateral (EL), and endoscopic far-medial (Endo-FM). However, no consensus has been reached regarding the optimal approach. We aimed to quantify and compare the surgical exposure and freedom (angle of attack) for various targets at the LC using these 4 surgical approaches. METHODS: The subtonsillar, FL, EL, and Endo-FM approaches were performed on 5 cadaveric specimens (total 10 sides). Surgical exposure and freedom were measured using the neuronavigation system. RESULTS: At the LC, the Endo-FM approach provided the greatest area of exposure (459.3 ± 82.2 mm2). For surgical freedom, the EL approach provided the greatest angle of attack at the jugular foramen (98.1° ± 9.2°) and hypoglossal canal (128.8° ± 26.1°). The Endo-FM was the only approach that provided access to the midline of the LC in all specimens. However, the surgical freedom at the midline (20.9° ± 2.4° at the level of the jugular foramen; 24.2° ± 2.9° at the level of hypoglossal canal) was limited by its deep surgical corridor (104.3 ± 11.2 mm) compared with the EL and FL approaches. CONCLUSION: The Endo-FM approach provided the greatest surgical freedom at the ventral aspect but the least freedom at the lateral aspect. The EL approach provided maximal values for most parameters among the open approaches; however, the craniotomy with the EL approach was the most complicated. Our quantitative results could guide neurosurgeons in preoperative planning for LC lesions, including awareness of the maximum exposure limits and the advantages and disadvantages of each surgical approach.