Human Cadaver Heads Research Articles

Inaccuracy of buccal bone thickness estimation on cone-beam CT due to implant blooming: An ex-vivo study.

The aim of this article was to evaluate the accuracy of buccal bone thickness measurements around implants on CBCT. Forty-four Osseospeed EV implants (3.6 in Ø) were placed guided and flapless in five fresh frozen human cadaver heads. The buccal peri-implant bone was measured clinically via guided bone sounding. Post-op CBCTs were taken with two different CBCT scanners (NewTom® and Accuitomo® ) on which the buccal bone was measured. Consequently, after implant removal, a new CBCT was made without implant artefacts (image reference standard) on which the real buccal bone thickness was scored. Due to an average blooming (artificial increase of implant diameter) percentage of 12%-15%, the buccal peri-implant bone thickness was underestimated by 0.3mm on both CBCT devices. Immediately adjacent to the implant blooming area, a doubtful zone of about 0.45mm was observed in which the buccal bone was not always visible. Buccal bone that was thick enough to fall outside this doubtful zone could always be visualized. The findings in this study may help the clinician in the decision-making process whether or not to intervene surgically in areas with ambiguous CBCT results.

The "Valva Cerebri": Morphometry, Topographic Anatomy and Histology of the Rhomboid Membrane at the Craniocervical Junction.

The arachnoid membranes' anatomy is a controversial topic in the literature, and the rhomboid membrane at the craniovertebral junction is an element of this system that has been described poorly. Hence, the objective of our study was to examine this membrane's anatomy and histology. A total of 45 fresh formalin-fixed human cadaveric heads were examined, and anatomic dissections and histologic examinations using standard staining methods were performed. The membrane was found to be a constant structure. It has a rhomboid shape and is located on the medulla oblongata and upper cervical spine's ventral surface within the subarachnoid space. Its average craniocaudal length is 49 mm and the short axis is 26 mm. The cranial apex is attached to the vertebral arteries' junction, and the caudal apex reaches the level of C4. The lateral apices are attached to the dura mater at the level of the denticulate ligament's second insertion. The C1 spinal nerves perforate the membrane, while the C2 roots are located dorsal to it. The membrane is attached strongly to the underlying pia mater. Histologically, it has a typical arachnoid structure, in which its adhesions to the vertebral arteries as well as to the pia mater could be verified histologically. This is the first detailed examination of the rhomboid membrane. Our results suggest that the membrane serves a valve-like function between the spinal and cranial subarachnoid spaces. Based on our findings, further hydrodynamic studies should clarify the membrane's physiological role. Clin. Anat. 32:56-65, 2019. © 2019 Wiley Periodicals, Inc.

A minimally invasive endoscope assisted retrosigmoid approach for removal of arachnoid cysts in the internal auditory canal: a step by step description

IntroductionArachnoid cyst in the internal auditory canal is a quite rare pathology but due to its compressive action on the nerves in this district should be surgically removed. Several surgical techniques have been proposed but no surgeons have used the minimally assisted endoscope retrosigmoid approach for its removal. ObjectiveTo investigate the feasibility of using a minimally invasive endoscope assisted retro-sigmoid approach for surgical removal of arachnoid cysts in the internal auditory canal. MethodsMinimally invasive endoscope assisted retrosigmoid approach allows to access to the internal auditory canal through a minimally invasive retrosigmoid approach that combines the use of a microscope and an endoscope. It is performed in six steps: soft tissue step, bone step, dura step, cerebellopontine angle step (performed using an endoscope and a microscope), microscope-endoscope assisted arachnoid cysts removal and closure. We tested minimally invasive endoscope assisted retrosigmoid approach for removal of arachnoid cysts in the internal auditory canal on two human cadaveric heads (specimens) of subjects affected from audio-vestibular disorders and with arachnoid cysts in the internal auditory canal confirmed by magnetic resonance imaging. ResultsThe mass was completely and successfully removed from the two specimens with no damage to the nerves and/or vessels in the surgical area. ConclusionThe results of our study are encouraging and support the feasibility of using minimally invasive endoscope assisted retrosigmoid approach for removal of arachnoid cysts in the internal auditory canal. While further clinical in-vivo studies are needed to confirm the accuracy and safety of using the minimally invasive endoscope assisted retrosigmoid approach for this specific surgery, our group has successfully used the minimally invasive endoscope assisted retrosigmoid approach in the treatment of microvascular compressive syndrome, schwannoma removal and vestibular nerve resection.

Erratum. Quantitative analysis of the surgical exposure and surgical freedom between transcranial and transorbital endoscopic anterior petrosectomies to the posterior fossa.

Object This study proposes a variation of the transorbital endoscopic approach (TOEA) that uses the lateral orbit as the primary surgical corridor, in a minimally invasive fashion, for the posterior fossa (PF) access. The versatility of this technique was quantitatively analyzed in comparison with the anterior transpetrosal approach (ATPA), which is commonly used for managing lesions in the PF. Methods Anatomical dissections were carried out in 5 latex-injected human cadaveric heads (10 sides). During dissection, the PF was first accessed by TOEAs through the anterior petrosectomy, both with and without lateral orbital rim osteotomies (herein referred as the lateral transorbital approach [LTOA] and the lateral orbital wall approach [LOWA], respectively). ATPAs were performed following the orbital approaches. The stereotactic measurements of the area of exposure, surgical freedom, and angles of attack to 5 anatomical targets were obtained for statistical comparison by the neuronavigator. Results The LTOA provided the smallest area of exposure (1.51 ± 0.5 cm2, p = 0.07), while areas of exposure were similar between LOWA and ATPA (1.99 ± 0.7 cm2 and 2.01 ± 1.0 cm2, respectively; p = 0.99). ATPA had the largest surgical freedom, whereas that of LTOA was the most restricted. Similarly, for all targets, the vertical and horizontal angles of attack achieved with ATPA were significantly broader than those achieved with LTOA. However, in LOWA, the removal of the lateral orbital rim allowed a broader range of movement in the horizontal plane, thus granting a similar horizontal angle for 3 of the 5 targets in comparison with ATPA. Conclusions The TOEAs using the lateral orbital corridor for PF access are feasible techniques that may provide a comparable surgical exposure to the ATPA. Furthermore, the removal of the orbital rim showed an additional benefit in an enhancement of the surgical maneuverability in the PF.

Intracochlear Pressure Transients During Cochlear Implant Electrode Insertion: Effect of Micro-mechanical Control on Limiting Pressure Trauma.

Use of micro-mechanical control during cochlear implant (CI) electrode insertion will result in reduced number and magnitude of pressure transients when compared with standard insertion by hand. With increasing focus on hearing preservation during CI surgery, atraumatic electrode insertion is of the utmost importance. It has been established that large intracochlear pressure spikes can be generated during the insertion of implant electrodes. Here, we examine the effect of using a micro-mechanical insertion control tool on pressure trauma exposures during implantation. Human cadaveric heads were surgically prepared with an extended facial recess. Electrodes from three manufacturers were placed both by using a micro-mechanical control tool and by hand. Insertions were performed at three different rates: 0.2 mm/s, 1.2 mm/s, and 2 mm/s (n = 20 each). Fiber-optic sensors measured pressures in scala vestibuli and tympani. Electrode insertion produced pressure transients up to 174 dB SPL. ANOVA revealed that pressures were significantly lower when using the micro-mechanical control device compared with insertion by hand (p << 0.001). No difference was noted across electrode type or speed. Chi-square analysis showed a significantly lower proportion of insertions contained pressure spikes when the control system was used (p << 0.001). Results confirm previous data that suggest CI electrode insertion can cause pressure transients with intensities similar to those elicited by high-level sounds. Results suggest that the use of a micro-mechanical insertion control system may mitigate trauma from pressure events, both by reducing the amplitude and the number of pressure spikes resulting from CI electrode insertion.

The medial wall of the cavernous sinus. Part 1: Surgical anatomy, ligaments, and surgical technique for its mobilization and/or resection.

The medial wall of the cavernous sinus (CS) is often invaded by pituitary adenomas. Surgical mobilization and/or removal of the medial wall remains a challenge. Endoscopic endonasal dissection was performed in 20 human cadaver heads. The configuration of the medial wall, its relationship to the internal carotid artery (ICA), and the ligamentous connections in between them were investigated in 40 CSs. The medial wall of the CS was confirmed to be an intact single layer of dura that is distinct from the capsule of the pituitary gland and the periosteal layer that forms the anterior wall of the CS. In 32.5% of hemispheres, the medial wall was indented by and/or well adhered to the cavernous ICA. The authors identified multiple ligamentous fibers that anchored the medial wall to other walls of the CS and/or to specific ICA segments. These parasellar ligaments were classified into 4 groups: 1) caroticoclinoid ligament, spanning from the medial wall and the middle clinoid toward the clinoid ICA segment and anterior clinoid process; 2) superior parasellar ligament, connecting the medial wall to the horizontal cavernous ICA and/or lateral wall of the CS; 3) inferior parasellar ligament, bridging the medial wall to the anterior wall of the CS or anterior surface of the short vertical segment of the cavernous ICA; and 4) posterior parasellar ligament, which anchors the medial wall to the short vertical segment of the cavernous ICA and/or the posterior carotid sulcus. The caroticoclinoid ligament and inferior parasellar ligament were present in most CSs (97.7% and 95%, respectively), while the superior and posterior parasellar ligaments were identified in approximately half of the CSs (57.5% and 45%, respectively). The caroticoclinoid ligament was the strongest and largest ligament, and it was typically assembled as a group of ligaments with a fan-like arrangement. The inferior parasellar ligament was the first to be encountered after opening the anterior wall of the CS during an interdural transcavernous approach. The authors introduce a classification of the parasellar ligaments and their role in anchoring the medial wall of the CS. These ligaments should be identified and transected to safely mobilize the medial wall away from the cavernous ICA during a transcavernous approach and for safe and complete resection of adenomas that selectively invade the medial wall.

Endoscopic transorbital approach to anterolateral skull base through inferior orbital fissure: a cadaveric study

Endoscopic transorbital approach (eTOA) has been announced as an alternative minimally invasive surgery to skull base. Owing to the inferior orbital fissure (IOF) connecting the orbit with surrounding pterygopalatine fossa (PPF), infratemporal fossa (ITF), and temporal fossa, the idea of eTOA to anterolateral skull base through IOF is postulated. The aim of this study is to access its practical feasibility. Anatomical dissections were performed in five human cadaveric heads (10 sides) using 0-degree and 30-degree endoscopes. A stepwise description of eTOA to anterolateral skull base through IOF was documented. The anterosuperior corner of the maxillary sinus in the horizontal plane of the upper edge of zygomatic arch was defined as reference point (RP). The distances between the RP to the foramen rotundum (FR), foramen ovale (FO), and Gasserian ganglion (GG) were measured. The exposed area of anterolateral skull base in the coronal plane of the posterior wall of the maxillary sinus was quantified. The surgical procedure consisted of six steps: (1) lateral canthotomy with cantholysis and preseptal lower eyelid approach with periorbita dissection; (2) drilling of the ocular surface of greater sphenoid wing and lateral orbital rim osteotomy; (3) entry into the maxillary sinus and exposure of PPF and ITF; (4) mobilization of infraorbital nerve with drilling of the infratemporal surface of the greater sphenoid wing and pterygoid process; (5) exposure of middle cranial fossa, Meckel's cave, and lateral wall of cavernous sinus; and (6) reconstruction of orbital floor and lateral orbital rim. The distances measured were as follows: RP-FR = 45.0 ± 1.9mm, RP-FO = 55.7 ± 0.5mm, and RP-GG = 61.0 ± 1.6mm. In comparison with the horizontal portion of greater sphenoid wing, the superior and inferior axes of the exposed area were 22.3 ± 2.1mm and 20.5 ± 1.8mm, respectively. With reference to the FR, the medial and lateral axes of the exposed area were 11.6 ± 1.1mm and 15.8 ± 1.6mm, respectively. The eTOA through IOF can be used as a minimally invasive surgery to access whole anterolateral skull base. It provides a possible resolution to target lesion involving multiple compartments of anterolateral skull base.

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

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. 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. 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. 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.

Microscope and micro-camera assessment of Schneiderian membrane perforation via transcrestal sinus floor elevation: A randomized ex vivo study.

We sought to assess the effectiveness of using a microscope and non-invasive camera for assessing sinus membrane perforations during transcrestal sinus floor elevation (TSFE). Five fresh human cadaver heads corresponding to eight maxillary sinuses (six bilateral and two unilateral) underwent 4 TSFEs per sinus (a total of 32 single site elevations). Each elevation was randomly assigned to receive a three or sixmm membrane elevation height (MEH). A microscope and micro-camera were used to assess the sinus membrane perforation. Afterwards, radiological and clinical membrane perforation assessments were performed. The statistical analysis results are expressed using the means, standard deviations, range values of the residual ridge height (RRH), residual ridge width (RRW), sinus membrane thickness (SMT) and incidence of perforation (IoP). Generalized linear methods were used to test for the correlation of RRH and MEH to the microscope and micro-camera perforation assessments and the correlation of microscope and micro-camera assessments with the post-operative CBCT and crestal liquid evaluation. The cumulative percentage of IoP was 40.62%, (23.07% with 3mm MEH, and 76.92% with 6mm MEH, p<0.05). The perforation assessed using either the microscope or micro-camera coincided with the post-operative CBCT and crestal liquid assessment in 87.55% sites. No significant correlation was found between the microscope or micro-camera assessments with RRH or MEH. Application of a microscope and micro-camera during transcrestal sinus floor elevation may allow the detection of the integrity of the Schneiderian membrane with greater than 85% accuracy in this ex vivo model.

Imaging re-evaluation of the tympanic segment of the facial nerve canal using cone-beam computed tomography compared with multi-slice computed tomography.

This study aims to evaluate the imaging findings of cone-beam computed tomography (CBCT) in displaying subtle structures of the tympanic segment of the facial nerve canal in human cadaver heads compared with multi-slice computed tomography (MSCT). Between January 2017 and July 2017, images of the tympanic segment of the facial nerve canal acquired from 73 human cadaver ears by both CBCT and MSCT were prospectively studied. Then, images of the lateral and inferior walls of the tympanic segment were scored using standard imaging slices through a four-point rating scale. Subsequently, the detailed findings of these two imaging modalities were recorded and compared, including interruptions of the bony walls, thread-like bony tubes connected with the walls, and separations in the cavity. The Wilcoxon signed-rank test was used to investigate the differences between scores derived by CBCT and MSCT. The mean score in the inferior and lateral walls by CBCT were significantly higher than that by MSCT (P = 0.000-0.005), which ranged from 2.0 (1.5, 2.5) to 3.5 (3.0, 4.0), and from 1.5 (1.0, 2.0) to 3.5 (2.5, 4.0), respectively. The interruption of the walls was most common at the anterior part of the inferior wall (38/73 cases). Furthermore, thread-like bony tubes were evident in 18 ears, which connected with the anterior part of the inferior wall (18/73 cases). Moreover, separation was found in 22 ears in the posterior part (22/73 cases). CBCT can readily demonstrate subtle imaging findings of the tympanic segment of the facial nerve canal.

Temporomandibular Joint Condyle–Disc Morphometric Sexual Dimorphisms Independent of Skull Scaling

Approximately 2 to 4% of the US population have been estimated to seek treatment for temporomandibular symptoms, predominately women. The study purpose was to determine whether sex-specific differences in temporomandibular morphometry result from scaling with sex differences in skull size and shape or intrinsic sex-specific differences. A total of 22 (11 male [aged 74.5±9.1years]; 11 female [aged 73.6±12.8years]) human cadaveric heads with no history of temporomandibular disc derangement underwent cone beam computed tomography and high-resolution magnetic resonance imaging scanning to determine 3-dimensional cephalometric parameters and temporomandibular morphometric outcomes. Regression models between morphometric outcomes and cephalometric parameters were developed, and intrinsic sex-specific differences in temporomandibular morphometry normalized by cephalometric parameters were determined. Subject-specific finite element (FE) models of the extreme male and extreme female conditions were developed to predict variations in articular disc stress-strain under the same joint loading. In some cases, sex differences in temporomandibular morphometric parameters could be explained by linear scaling with skull size and shape; however, scaling alone could not fully account for some differences between sexes, indicating intrinsic sex-specific differences. The intrinsic sex-specific differences in temporomandibular morphometry included an increased condylar medial length and mediolateral disc lengths in men and a longer anteroposterior disc length in women. Considering the extreme male and female temporomandibular morphometry observed in the present study, subject-specific FE models resulted in sex differences, with the extreme male joint having a broadly distributed stress field and peak stress of 5.28MPa. The extreme female joint had a concentrated stress field and peak stress of 7.37MPa. Intrinsic sex-specific differences independent of scaling with donor skull size were identified in temporomandibular morphometry. Understanding intrinsic sex-specific morphometric differences is critical to determining the temporomandibular biomechanics given the effect of anatomy on joint contact mechanics and stress-strain distributions and requires further study as one potential factor for the increased predisposition of women to temporomandibular disc derangement.

Experimental investigation of cranial fracture initiation in blunt human head impacts

The relationship between the point of blunt impact and the location of cranial fracture initiation continues to be poorly understood. The current study used high-speed video to capture cranial fracture initiation and propagation in impact experiments on twelve unembalmed, intact human cadaver heads. Video footage provided direct evidence that blunt cranial impacts can produce linear fractures initiating peripheral to the impact site. Four tests produced only remote peripheral linear fractures with no damage at the known point of impact, demonstrating that the pattern of linear fractures does not necessarily indicate impact site. The range of variation observed in these experiments suggests that cranial fracture formation is more complex than it is typically described in the current literature. Differences in biomechanical and fracture results obtained with three different shaped implements provided evidence that impact surface is one important factor influencing the outcomes of blunt cranial impacts.

Meningeal Architecture of the Jugular Foramen: An Anatomic Study Using Plastinated Histologic Sections

This 3-dimensional histologic study aimed to provide a precise description of the meningeal structures in the jugular foramen. 22 posterior skull base tissue blocks containing the jugular foramen region were obtained from 11 human cadaveric heads. These blocks were plastinated and cut into serial sections. After staining, these sections were examined under an optical microscope and used to reconstruct a 3-dimensional visualization model. At the intracranial orifice of the jugular foramen, the meningeal dura formed 2 separate dural perforations: the glossopharyngeal meatus and the vagal meatus. The arachnoid extended into 2 dural meatuses and terminated at the inferior ganglion of the glossopharyngeal nerve in the glossopharyngeal meatus and the superior ganglion of the vagus nerve in the vagal meatus. At the intraforaminal part of the jugular foramen, the meningeal dura encased the glossopharyngeal nerve to form a dural sheath while encasing the vagus and accessory nerves to form a dural network. At the extracranial orifice of the jugular foramen, the dural wall of the jugular bulb extended downward to form a dense connective tissue sheath. The initial end of the internal jugular vein invaginated into this sheath and fused with the jugular bulb. Knowledge of the anatomy of the meningeal architecture of the jugular foramen can be helpful in avoiding surgical complications of the lower cranial nerves when this complex area is approached.

Endoscopic transorbital transtentorial approach to middle incisural space: preclinical cadaveric study.

Endoscopic transorbital approach is a novel development of minimally invasive skull base surgery. Recently, anatomical studies have started to discuss the expanded utilization of endoscopic transorbital route for intracranial intradural lesions. The goal of this cadaveric study is to assess the feasibility of endoscopic transorbital transtentorial approach for exposure of middle incisural space. Anatomical dissections were performed in four human cadaveric heads (8 sides) using 0- and 30-degree endoscopes. A stepwise description of endoscopic transorbital transtentorial approach to middle incisural space and related anatomy was provided. Orbital manipulation following superior eyelid crease incision with lateral canthotomy and cantholysis established space for bone drilling. Extradural stage consisted of extensive drilling of orbital roof of frontal bone, lessor, and greater wings of sphenoid bone. Intradural stage was composed of dissection of sphenoidal compartment of Sylvian fissure, lateral mobilization of mesial temporal lobe, and penetration of tentorium. A cross-shaped incision of tentorium provided direct visualization of crural cistern with anterolateral aspect of cerebral peduncle and upper pons. Interpeduncular cistern, prepontine cistern, and anterior portions of ambient and cerebellopontine cisterns were exposed by 30-degree endoscope. The endoscopic transorbital transtentorial approach can be used as a minimally invasive surgery for exposure of middle incisural space. Extensive drilling of sphenoid wing and lateral mobilization of mesial temporal lobe are the main determinants of successful dissection. Further studies are needed to confirm the clinical feasibility of this novel approach.

Evaluation of cranial base repair techniques utilizing a novel cadaveric CPAP model.

Although recent guidelines for obstructive sleep apnea recommend early postoperative use of continuous positive airway pressure (CPAP) after endonasal skull base surgery, the time of initiation of CPAP is unclear. In this study we used a novel, previously validated cadaveric model to analyze the pressures delivered to the cranial base and evaluate the effectiveness of various repair techniques to withstand positive pressure. Skull base defects were surgically created in 3 fresh human cadaver heads and repaired using 3 commonly used repair techniques: (1) Surgicel™ onlay; (2) dural substitute underlay with dural sealant onlay; and (3) dural substitute underlay with nasoseptal flap onlay with dural sealant. Pressure microsensors were placed in the sphenoid sinus and sella, both proximal and distal to the repair, respectively. The effectiveness of each repair technique against various CPAP pressure settings (5-20 cm H2 O) was analyzed. Approximately 79%-95% of positive pressure administered reached the sphenoid sinus. Sellar pressure levels varied significantly across the 3 repair techniques and were lowest after the third technique. "Breach" points (CPAP settings at which sellar repair was violated) were lowest for the first group. All 3 specimens showed a breach after the first repair technique. For the second repair technique, only a single breach was created in 1 specimen at 20 cm H2 O. No breaches were created in the third group. Different skull base repair techniques have varying ability to withstand CPAP. Both second and third repair techniques performed in a nearly similar fashion with regard to their ability to withstand positive pressure ventilation.

Degree of Frontal Bone Exposure via Upper Blepharoplasty Incision: Considerations for Frontal Sinus Fracture.

The upper eyelid blepharoplasty incision affords direct access to the frontal bone for skull base surgery and trauma reconstruction with a well-hidden scar. The goal of this study is to quantify frontal bone exposure that can be achieved with an upper eyelid blepharoplasty incision. Anatomic study with human cadaver heads. UC Davis Medical Center. Fourteen human cadaver heads were used to perform 26 upper blepharoplasty approaches. Exposure was measured with virtual planning software to create virtual reference points at the midline of the superior orbital rim. Surgical navigation was used with a 3-dimensionally printed drill model to measure the maximum exposure achievable relative to the virtual reference point at 5 standardized angles. Mean ± SD exposures at medial 60°, medial 30°, 0°, lateral 30°, and lateral 60° were 16.1 ± 1.3 mm, 17.8 ± 1.3, 18.3 ± 1.4, 19.3 ± 1.9, and 20.9 ± 1.9, respectively. Significant differences were detected between exposures at 60° laterally and 60° medially and between exposures 60° laterally and 30° medially ( P < .05). The upper eyelid blepharoplasty incision provides direct surgical access to the inferior frontal bone. Access was greatest with far lateral extension (mean, 20.9 mm) and most limited with far medial extension (mean, 16.1 mm). Treatment of injuries above this level could be achieved with additional percutaneous incisions for screw placement.

Analysis of anterior and posterior maneuvers to enhance intraconal exposure.

The medial and inferior recti encompass the ideal surgical corridor to approach the intraconal space endonasally. Here, we describe 3 different maneuvers to achieve greater access to orbital contents through an expanded endonasal approach (EEA). Four human cadaver heads were dissected bilaterally (n = 8). EEA to the medial intraconal orbit was executed. The following 3 maneuvers were performed: (1) anterior: extraocular muscles control (EOM); (2) posterior: annulus of Zinn (AZ) release; and (3) anterior/posterior combined. Measurements of the inferior and medial rectus corridor at the level of anterior ethmoidal artery (AEA) and posterior ethmoidal artery (PEA) and extent of optic nerve and medial rectus visualization was performed before and after each maneuver. Medial rectus length (MRL) and optic nerve length (ONL) achieved were 1.72 ± 0.28 cm and 0.85 ± 0.2 cm, respectively. Mean caudal-rostral distances between the rectus muscles at the level of the AEA and PEA were 3.45 ± 0.7 mm and 1.30 ± 0.3 mm, respectively. After EOM control, mean caudal-rostral distances at the same level were as follows: AEA 4.90 ± 1.15 mm (p = 0.009) and PEA 1.70 ± 0.20 mm (p = 0.016). With AZ release, MRL was 2.20 ± 0.7 cm (p = 0.002) and ONL was 1.30 ± 0.2 cm (p = 0.003), with mean rostral-caudal distance at the level of AEA at 4.03 ± 0.8 mm (p = 0.16) and PEA at 1.71 ± 0.36 mm (p = 0.039). Mean caudal-rostral distances achieved with AZ release and EOM control were as follows: AEA 5.6 ± 1.2 mm (p = 0.001) and PEA 2.15 ± 0.4 mm (p = 0.001). Progressive access to the orbital contents is afforded with the 3 delineated maneuvers. The magnitude of access is optimized with the combined maneuver. The actual anterior/posterior location of the target will determine which maneuvers are required.

The Rhomboid Lip: Anatomy, Pathology, and Clinical Consideration in Neurosurgery

To describe microsurgical anatomy of the rhomboid lip (RL) and to consider its role by presenting histology and clinical cases. We examined 10 (20 sides) formalin-fixed adult human cadaveric heads injected with colored silicone. A total of 20 RLs were examined posteriorly. We examined the expansion of the RL in the cerebellopontine cistern. We assessed the relationship between the RL and choroid plexus and the RL and cranial nerve IX and classified the RL. We also observed these relationships in clinical cases during surgeries and examined histologic assessments of the RL. The RL was divided into 3 types, non-extension type, lateral extension type, and jugular foramen type, according to the relationship between the RL and choroid plexus. There were many variations of the extension of the RL. The jugular foramen type was rare. Histologically, the RL is the remnant of the fourth ventricle covered with ependymal cells. Knowledge of the detailed anatomy and proper dissection of the RL may help surgeons to obtain good visualization of structures around the foramen of Luschka.

Expanded Endoscopic Endonasal Approach to the Inframeatal Area: Anatomic Nuances with Surgical Implications

The inframeatal area represents a challenging region for skull base surgeons. Various surgical corridors have been described to access this area and frequently are used in combination. Recent studies describe the expanded endoscopic endonasal approach (EEA) as an established route for midline regions, particularly medial to the internal carotid arteries (ICA). We sought to evaluate the accessibility, maneuverability, and freedom of movement of the expanded endoscopic endonasal approach to the inframeatal region. An EEA combining a middle and an inferior transclival corridor with an infrapetrous and a supracondylar lateral expansion was performed in 5 embalmed human cadaveric heads. The area of exposure and the surgical freedom to access the inframeatal area were calculated. The angle of attack and distances from the lacerum segment of the ICA to several anatomical targets also were measured. Our database was searched to select clinical case examples. The EEA provided an exposure area of 101.26 ± 16.66 mm2 and an area of surgical freedom of 1208.50 ± 507.01 mm2. The angles of attack in both the sagittal and axial planes were wider at the lacerum segment of the ICA and narrower at the dural entrance zone of cranial nerves VII/VIII. Three chondrosarcomas are presented as case illustrations. The EEA is a feasible route to the inframeatal area. This approach provides a safe working corridor for lesions in this region, as shown by the anatomical and clinical findings presented here. Comparative studies and large case series are warranted to further establish its clinical value.

Technique for Latex Injection and Reuse of Human Heads Preserved in Formaldehyde.

Background Understanding the anatomy of the skull base is paramount for every skull base surgeon, particularly in light of the expanded endoscopic endonasal approaches, and of the refined surgical technique used in both medial and lateral approaches. A comprehensive knowledge of anatomy is the cornerstone for a safe surgery, maximizing resection and minimizing complications. The best study method is the careful dissection of fresh human cadaveric heads in a well-equipped anatomy laboratory. In this study, we describe our protocol for preparing cadaveric specimens without vascular injection, which had been preserved in a formaldehyde solution after treating them with a dimethyldioctadecylammonium chloride/distearyl dimethyl ammonium chloride solution (commercial fabric softener) and injecting the vascular system with latex. Method Six cadaveric specimens underwent our treatment and subsequent injection of the vascular system and dissection. Results All specimens showed a good penetration of the latex and a clear improvement of the malleability of the tissues was noticed. The authors agree that this technique improved the quality of the head and facilitated studying. Conclusion We consider this an effective treatment with latex, reaching small caliber vessels, and a greater malleability and flexibility of tissues, allowing better dissections, and greater anatomical exposure, making them suitable for skull base training, study, and research.