Anatomical Analysis of the Eustachian Tube in the Temporal Bone Through the Middle Fossa Window.

PURPOSE: This cadaveric anatomical study aimed to explore precise morphometric measurements of the eustachian tube (ET) and adjacent structures in the middle cranial fossa, focusing on identifying reliable surgical landmarks when traditional markers are compromised due to tumors or trauma. METHODS: Twenty-two temporal bones from 11 adult cadavers (mean age: 75.70 ± 13.75 yr, range: 40-90 yr; sex: 5 females and 6 males) were dissected bilaterally. Surgical tools, including an operation microscope, endoscope, and digital caliper, were used for meticulous measurements. Parameters such as ET dimensions, distances between key points, and relevant angles were quantified, ensuring precise anatomical data. RESULTS: ET width at the foramen spinosum (FS) level, the midline level, and the eustachian orifice level were measured as 2.18 ± 0.68, 2.42 ± 0.70, and 2.30 ± 0.74 mm, respectively. The distances from the zygomatic root (ZR) to FS, ET, superior semicircular canal (SSC), and internal carotid artery (ICA) were 29.61 ± 2.56, 23.28 ± 2.61, 26.53 ± 2.56, and 32.61 ± 3.69 mm, respectively. The angles between SSC-ZR-ICA and FS-ZR-ICA were measured as 36.57 ± 10.32 and 13.63 ± 3.72 degrees, respectively. No statistical difference was found between right-left or male-female measurements ( p > 0.05). CONCLUSION: The present study offers invaluable insights for neurotological surgeons performing middle fossa approaches. ET and ZR may serve as crucial reference points, enhancing surgical orientation and minimizing risks during complex procedures. These precise anatomical data may empower surgeons, ensuring safer and more confident middle cranial fossa operations, even in challenging clinical scenarios.

[Microanatomical Investigation of the Subtemporal Transtentorial Approach]. / é¢žä¸‹ç»å°è„‘å¹•å ¥è·¯çš„æ˜¾å¾®è§£å‰–å­¦ç ”ç©¶.

Objective: To study the microanatomic structure of the subtemporal transtentorial approach to the lateral side of the brainstem, and to provide anatomical information that will assist clinicians to perform surgeries on the lateral, circumferential, and petroclival regions of the brainstem. Methods: Anatomical investigations were conducted on 8 cadaveric head specimens (16 sides) using the infratemporal transtentorial approach. The heads were tilted to one side, with the zygomatic arch at its highest point. Then, a horseshoe incision was made above the auricle. The incision extended from the midpoint of the zygomatic arch to one third of the mesolateral length of the transverse sinus, with the flap turned towards the temporal part. After removing the bone, the arachnoid and the soft meninges were carefully stripped under the microscope. The exposure range of the surgical approach was observed and the positional relationships of relevant nerves and blood vessels in the approach were clarified. Important structures were photographed and the relevant parameters were measured. Results: The upper edge of the zygomatic arch root could be used to accurately locate the base of the middle cranial fossa. The average distances of the star point to the apex of mastoid, the star point to the superior ridge of external auditory canal, the anterior angle of parietomastoid suture to the superior ridge of external auditory canal, and the anterior angle of parietomastoid suture to the star point of the 10 adult skull specimens were 47.23 mm, 45.27 mm, 26.16 mm, and 23.08 mm, respectively. The subtemporal approach could fully expose the area from as high as the posterior clinoid process to as low as the petrous ridge and the arcuate protuberance after cutting through the cerebellar tentorium. The approach makes it possible to handle lesions on the ventral or lateral sides of the middle clivus, the cistern ambiens, the midbrain, midbrain, and pons. In addition, the approach can significantly expand the exposure area of the upper part of the tentorium cerebelli through cheekbone excision and expand the exposure range of the lower part of the tentorium cerebelli through rock bone grinding technology. The total length of the trochlear nerve, distance of the trochlear nerve to the tentorial edge of cerebellum, length of its shape in the tentorial mezzanine, and its lower part of entering into the tentorium cerebelli to the petrosal ridge were (16.95±4.74) mm, (1.27±0.73) mm, (5.72±1.37) mm, and (4.51±0.39) mm, respectively. The cerebellar tentorium could be safely opened through the posterior clinoid process or arcuate protrusion for localization. The oculomotor nerve could serve as an anatomical landmark to locate the posterior cerebral artery and superior cerebellar artery. Conclusion: Through microanatomic investigation, the exposure range and intraoperative difficulties of the infratemporal transtentorial approach can be clarified, which facilitates clinicians to accurately and safely plan surgical methods and reduce surgical complications.

Optimizing the Endoscopic Transorbital Approach: MacCarty Keyhole for Enhanced Surgical Exposure in the Opticocarotid Region.

BACKGROUND: In recent years, the endoscopic transorbital (TO) approach has gained increasing interest for the treatment of middle cranial fossa lesions. We propose a technical refinement to the conventional superior eyelid TO approach, which improves the surgical exposure and augments the working angles when targeting the opticocarotid region. METHODS: Four embalmed adult cadaveric specimens (8 sides) were dissected at the Laboratory of Surgical Neuroanatomy of our institution. A TO approach was performed, with removal of the anterior clinoid process and the lateral orbital rim. Subsequently, the MacCarty keyhole was drilled in the superolateral orbital wall. Given that the lesser sphenoid wing was already drilled in the conventional TO craniectomy, the opening of the keyhole was essentially a lateral extension of the craniectomy. RESULTS: The procedure was successfully conducted in all 4 orbits. Clinoidectomy was performed either before or after extending the craniectomy to the MacCarty point. Extending the craniectomy made anterior clinoidectomy easier, by increasing the surgical exposure, and allowing a more lateral entrance for the endoscope. The extension also facilitated frontal lobe retraction, and it facilitated the optic nerve and carotid artery manipulation. Postoperative computed tomography scans showed a minimal 10-mm craniectomy extension, which remained covered by the temporal muscle after reconstruction. CONCLUSIONS: The modified endoscopic TO approach with the extension of the craniectomy to MacCarty point improves surgical access and visualization of the opticocarotid region. This facilitates anterior clinoidectomy and optic nerve decompression. Although it implies judicious instrument manipulation and a larger incision size, further studies can define its potential benefits.

The M-Point A Novel Landmark in Middle Fossa Surgery: A Cadaveric Morphometric Study.

BACKGROUND: The arcuate eminence (AE) is an anatomically consistent bony protrusion located on the upper surface of the petrous bone that has been previously studied as a reference for lateral skull base approaches. There is a paucity of information in the neurosurgical literature seeking to improve the safety of the extended middle cranial fossa (MCF) approach using detailed morphometric analysis of the AE. OBJECTIVE: To evaluate the use of the AE as an anatomical landmark to help with early identification of the internal acoustic canal (IAC) in MCF approaches by means of a cadaveric study, using a new morphometric reference termed the "M-point." METHODS: A total of 40 dry temporal bones and 2 formalin-preserved, latex-injected cadaveric heads were used. The M-point was established as a new anatomic reference by identifying the intersection of a line perpendicular to the alignment of the petrous ridge (PR), originating from the midpoint of the AE, with the PR itself. Subsequent anatomical measurements were performed to measure the distance between M-point and IAC. Additional distances, including PR length and the anteroposterior and lateral AE surfaces, were also measured. RESULTS: The mean distance between the M-point and the center of the IAC was 14.9 mm (SD ± 2.09), offering a safe drilling area during an MCF approach. CONCLUSIONS: This study provides novel information on identification of a new anatomic reference point known as the M-point that that can be used to improve early surgical identification of the IAC.

A Three-Dimensional Anterior and Middle Cranial Fossa Model for Skull Base Surgical Training with Two Layers of the Colored Dura Mater.

BACKGROUND: Adequate epidural procedures and anatomical knowledge are essential for the technical success of skull base surgery. We evaluated the usefulness of our three-dimensional (3D) model of the anterior and middle cranial fossa as a learning tool in improving knowledge of anatomy and surgical approaches, including skull base drilling and dura matter peeling techniques. METHODS: Using a 3D printer, a bone model of the anterior and middle cranial fossa was created based on multi-detector row computed tomography data, incorporating artificial cranial nerves, blood vessels, and dura mater. The artificial dura mater was painted using different colors, with 2 pieces glued together to allow for the simulation of peeling the temporal dura propria from the lateral wall of the cavernous sinus. Two experts in skull base surgery and 1 trainee surgeon operated on this model and 12 expert skull base surgeons watched the operation video to evaluate this model subtlety on a scale of 1 to 5. RESULTS: A total of 15 neurosurgeons, 14 of whom were skull base surgery expert, evaluated, scoring 4 or higher on most of the items. The experience of dural dissection and 3D positioning of important structures, including cranial nerves and blood vessels, was similar to that in actual surgery. CONCLUSIONS: This model was designed to facilitate teaching anatomical knowledge and essential epidural procedure-related skills. It was shown to be useful for teaching essential elements of skull-base surgery.

The "Crista Ovale": A Reliable Anatomical Landmark in Transorbital Endoscopic Approaches to the Middle Cranial Fossa.

BACKGROUND: Transorbital endoscopic approaches (TOEAs) have emerged as adjunct and alternatives for accessing the middle cranial fossa (MCF). Nuances of the skull base anatomy from a ventral transorbital endoscopic viewpoint remain to be fully described. OBJECTIVE: To assess the anatomy of the "crista ovale" (COv), described transcranially as the midsubtemporal ridge (MSR), from a ventral transorbital perspective and evaluate its role as a landmark in TOEA to the MCF. METHODS: Lateral TOEAs to the MCF were performed in 20 adult cadaveric heads (40 sides). The presence of the COv/MSR was evaluated under endoscopic visualization. Anatomic relationships between COv/MSR and surrounding structures were assessed. The presence of COv/MSR was also examined in 30 cadaveric head computed tomography (CT) scans (60 sides). RESULTS: The COv/MSR was identified in 98% (39/40) of sides at the MCF, as 1 of 4 major configurations. The COv/MSR was found anterolateral to the foramen ovale and foramen spinosum (mean distance: 9.2 ± SD 2.4 mm and 12.3 ± SD 2.6 mm, respectively) directly anterior or anteromedial to the petrous apex (mean distance: 26.2 ± SD 2.6 mm) and at a mean 47.6 ± SD 4.7 mm from the approach's surgical portal. It was recognized in 95% (57/60) of CT scans. CONCLUSION: The COv/MSR can be readily identified during TOEA to the MCF and on CT. It serves as a reliable landmark to localize the foramen ovale, foramen spinosum, and petrous apex. Further studies may confirm its surgical significance in transorbital endoscopic procedures.

High-Fidelity Virtual Reality Simulation for the Middle Cranial Fossa Approach-Modules for Surgical Rehearsal and Education.

BACKGROUND: Virtual reality simulation has gained prominence as a valuable surgical rehearsal and education tool in neurosurgery. Approaches to the internal auditory canal, cerebellopontine angle, and ventral brainstem region using the middle cranial fossa are not well explored by simulation. OBJECTIVE: We hope to contribute to this paucity in simulation tools devoted to the lateral skull base, specifically the middle cranial fossa approach. METHODS: Eight high-resolution microcomputed tomography scans of human cadavers were used as volumetric data sets to construct a high-fidelity visual and haptic rendering of the middle cranial fossa using CardinalSim software. Critical neurovascular structures related to this region of the skull base were segmented and incorporated into the modules. RESULTS: The virtual models illustrate the 3-dimensional anatomic relationships of neurovascular structures in the middle cranial fossa and allow a realistic interactive drilling environment. This is facilitated by the ability to render bone opaque or transparent to reveal the proximity to critical anatomy allowing for practice of the virtual dissection in a graduated fashion. CONCLUSION: We have developed a virtual library of middle cranial fossa approach models, which integrate relevant neurovascular structures with aims to improve surgical training and education. A ready extension is the potential for patient-specific application and pathology.

Endoscopic Transorbital Approach to the Middle Fossa: Qualitative and Quantitative Anatomic Study.

BACKGROUND: The endoscopic superior eyelid transorbital route to the skull base is gaining progressive popularity in the neurosurgical community. OBJECTIVE: To evaluate the anatomy of the middle cranial fossa from this novel ventral perspective to reach the skull base through the transorbital route and to show limits for possible safe middle fossa drilling from the transorbital route. METHODS: Anatomic study was performed; 5 cadaveric specimens (ie, 10 sides) and 2 dry skulls (ie, 4 sides) were dissected. RESULTS: To obtain a functional result, there are boundaries that correspond to neurovascular structures that traverse, enter, or leave the middle fossa that must be respected: inferiorly, the lateral pterygoid muscle; medially, the Gasserian ganglion and the lateral border of the foramen rotundum; laterally, the foramen spinosum with the middle meningeal artery; superiorly, the lesser sphenoid wing; posteriorly, the anterior border of the foramen ovale. Average bone resected was 6.49 ± 0.80 cm3 which is the 63% of total middle fossa floor. The mean axial surgical length calculated was 3.85 cm (3.18-5.19 cm) while the mean sagittal surgical length was 5.23 cm (4.87-6.55 cm). The mean horizontal angle of approach was 38.14° (32.87°-45.63°), while the mean vertical angle of approach was 18.56° (10.81°-26.76°). CONCLUSION: Detailed anatomy of the middle cranial fossa is presented, and herewith we demonstrated that from the endoscopic superior eyelid transorbital approach removal of middle cranial fossa floor is possible when anatomic landmarks are respected.

A Frontal Route to Middle and Posterior Cranial Fossa: Quantitative Study for the Lateral Transorbital Endoscopic Approach and Comparison with the Subtemporal Approach.

BACKGROUND: Skull base lesions within the middle cranial fossa (MCF) remain challenging. Recent reports suggest that transorbital endoscopic approaches (TOEAs) might be particularly suitable to access the MCF and expose the lateral wall of the cavernous sinus and the Meckel's cave. METHODS: The present study was developed to compare the nuances of the subtemporal approach (STA) with those of the lateral TOEA (LTOEA) to the MCF and posterior cranial fossa (PCF) in cadaveric specimens. After orbital craniectomy, interdural opening of the cavernous sinus lateral wall (CSlw), exposure of the Gasserian ganglion, and extradural elevation of the temporal lobe was performed. Next, anterior endoscopic petrosectomy was performed and the PCF was accessed. We quantitatively analyzed and compared the angles of attack and distances between LTOEA and STA to different structures at the CSlw, petrous apex (PA), and PCF. RESULTS: Cadaveric dissection through the LTOEA completely exposed the CSlw and PA. LTOA exhibited larger distances than the STA to all targets. Importantly, these differences were greater at the PA and its surrounding key anatomic landmarks. The horizontal and vertical angles of attack allowed by the LTOA were smaller both for the CSlw and PA. However, these differences were not significant for the vertical angle of attack at the CSlw. CONCLUSIONS: LTOEA provides a direct ventral route to the medial aspect of MCF, PA, and PCF. Although TOEAs are versatile approaches, the unfamiliar surgical anatomy and limited instrument maneuverability demand extensive cadaveric dissection before moving to the clinical setting.

Decompression of the geniculate ganglion and labyrinthine segments of the facial nerve through a middle cranial fossa approach using an ultrasonic surgical system: an anatomic study.

PURPOSE: The aim of this study is to evaluate the feasibility and the safety of a novel, alternative method for bone tissue management in facial nerve decompression by a middle cranial fossa approach. Several applications of Piezosurgery technology have been described, and the technique has recently been extended to otologic surgery. The piezoelectric device is a bone dissector which, using micro-vibration, preserves the anatomic integrity of soft tissue thanks to a selective action on mineralized tissue. METHODS: An anatomic dissection study was conducted on fresh-frozen adult cadaveric heads. Facial nerve decompression was performed by a middle cranial fossa approach in all specimens using the piezoelectric device under a surgical 3D exoscope visualization. After the procedures, the temporal bones were examined for evidence of any injury to the facial nerve or the cochleovestibular organs. RESULTS: In all cases, it was possible to perform a safe dissection of the greater petrosal superficial nerve, the geniculate ganglion, and the labyrinthine tract of the facial nerve. No cases of semicircular canal, cochlea, or nerve damage were observed. All of the dissections were carried out with the ultrasonic device without the necessity to replace it with an otological drill. CONCLUSION: From this preliminary study, surgical decompression of the facial nerve via the middle cranial fossa approach using Piezosurgery seems to be a safe and feasible procedure. Further cadaveric training is recommended before intraoperative use, and a wider case series is required to make a comparison with conventional devices.

Transosseous Veins of the Temporal Bone: Connection Between Middle and Posterior Cranial Fossa Venous Structures.

BACKGROUND: The veins and dural venous sinuses of the skull base are important to understand in terms of imaging findings, diagnoses, and surgery. However, to date and to the best of our knowledge, the transosseous veins of the petrous part of the temporal bone have not been studied. METHODS: Ten latex-injected adult cadaveric specimens (20 sides) were dissected to identify the intraosseous and transosseous veins. The petrous part of the temporal bone was drilled away, and the petrous part of the internal carotid artery and the veins of the middle and posterior cranial fossa adjacent to the petrous part of the temporal bone were exposed. RESULTS: Transosseous veins traveling through the petrous part of the temporal bone were identified on all 20 sides. In general, these were most concentrated near the anterior and posterior parts of the petrous part of the temporal bone. Most traveled more or less vertically from the petrous ridge and related superior petrosal sinus internally through the petrous part of the temporal bone toward the inferior petrosal sinus or horizontally, uniting the veins of the floor of the middle cranial fossa with the veins of the posterior cranial fossa. These transosseous veins connected the veins in the middle cranial fossa with the veins of the posterior cranial fossa. Most (70%) of these transosseous veins were also found to have small connections to the internal carotid venous plexus. CONCLUSIONS: To the best of our knowledge, previous studies have not reported on transosseous veins of the temporal bone or described their anatomy of connecting the veins of the middle and posterior cranial fossae.

Meckel Cave: An Anatomical Study Using Magnetic Resonance Imaging.

OBJECTIVE: To our knowledge, few studies have investigated anatomy of the Meckel cave with neuroimaging modalities. The present study aimed to characterize it using magnetic resonance imaging (MRI). PATIENTS AND METHODS: Following conventional MRI examination, a total of 101 patients underwent T2-weighted imaging in thin-sliced coronal and sagittal sections, and 11 patients underwent constructive interference steady-state sequences in thin-sliced sagittal sections. Moreover, 3 injected cadaver heads were dissected. RESULTS: In the cadaver specimens, the size and extent of the cerebrospinal fluid-filled space between the Gasserian ganglion and surrounding arachnoids were difficult to define. On the T2-weighted imaging, the Meckel cave was delineated with variable morphologies and left-right asymmetry. On the sagittal images, the shape of the Meckel cave could be classified into 3 different types, bulbous, oval, and flat, with the oval being the most frequent that comprised 60%. Furthermore, on the sagittal constructive interference steady-state images, parts of the trigeminal nerve distributed in the Meckel cave were delineated in all patients. The ophthalmic, maxillary, and mandibular divisions were clearly distinguished on both sides. CONCLUSIONS: The Meckel cave is a structure characterized by diverse morphologies and left-right asymmetry. Thin-sliced T2-weighted imaging is useful for exploring the anatomy of the Meckel cave.

Endoscopic Transorbital Approaches to Anterior and Middle Cranial Fossa: Exploring the Potentialities of a Modified Lateral Retrocanthal Approach.

BACKGROUND: Among the new perspectives to revolutionize skull base surgery, there are the transorbital neuroendoscopic (TONES) approaches to reach the anterior and middle cranial fossa (ACF and MCF). We conceived to explore the potentialities of a modified superiorly and medially extended lateral retrocanthal (LRC) approach. METHODS: Six head specimens were dissected. Applying the established conic model and the key surgical landmark of sphenofrontal suture, we tested the feasibility of a modified LRC to reach ACF and MCF; computed tomography (CT) scans were performed before and after dissection to obtain a morphometric analysis of the surgical corridors using a polygonal surfaces model. RESULTS: Through our anatomical study, we were able to identify and explore 3 different surgical corridors to reach the ACF and MCF: the superomedial, the superolateral, and the inferolateral. The superomedial corridor appeared most suitable to reach the medial part of the ACF and the optic-carotid region, whereas through the superolateral and inferolateral corridors it was possible to reach and explore the lateral part of ACF and MCF. The mean volumes of the 3 surgical corridors calculated on post-dissection CT scans were: 12.72 ± 1.99, 5.69 ± 0.34, and 6.24 ± 0.47 cm3, respectively. CONCLUSIONS: The development of TONES approaches has not replaced the traditional open or endoscopic approach; nonetheless, identification of surgical corridors and the possibility to combine them represent a major breakthrough. Clinical studies are necessary to demonstrate their validity and test the effectiveness, safety, and reproducibility of TONES approaches in managing lesions harboring in the ACF and MCF.

Surgical anatomy of basal turn in relation to middle cranial fossa and round window as pertaining to middle fossa cochlear implant technique.

PURPOSE: The purpose of this investigation was to evaluate the relation of the basal turn of cochlea with middle cranial fossa and round window as pertaining to middle cranial fossa cochlear implant technique. METHODS: Fifty-four formalin preserved temporal bones were micro-dissected to expose the basal turn. The point (f) was marked on the basal turn of cochlea where there was minimum distance of basal turn of cochlea from the floor of middle cranial fossa (f1). The f-f1 distance, the angle (∠smf) and distance of point "f" from the round window (s-f) was measured. RESULTS: The mean minimum distance between basal turn of cochlea and floor of middle cranial fossa (f-f1) was 2.0 ± 0.7 mm.The point f was at mean distance (s-f) and angle (∠smf) of 14.7 ± 1.6 mm and 217° ± 13.7° from round window, respectively. CONCLUSIONS: The information may be helpful for designing appropriate electrode array for middle fossa technique especially for deciding the length of electrode array towards round window, as otherwise electrode may extend into vestibule of inner ear. In the cases where bone thickness between superior part of basal turn of cochlea and middle cranial fossa is < 1.5 mm, surgeon should be extra cautious.

Anatomic Study Quantifying the Relationship Between the Arcuate Eminence and the Root of the Zygoma: Application to Skull Base Surgery.

OBJECTIVE: The aim of this study was to define the structural relationship between the arcuate eminence (AE) and a known fixed external bony landmark, the root of the zygoma (ZR), and to determine its reliability as a consistent guide for guiding surgical approaches. To our knowledge, this is the only anatomic study to quantify the relationship between the AE and ZR. METHODS: Twenty-one dry temporal bones were measured using digital calipers. The distance from the posterior aspect of the ZR to the midpoint of the AE was measured. Additionally, the anteroposterior distance between the ZR and AE and vertical distance between the 2 structures were measured. Student's t-test was used to compare the left and right sides. RESULTS: An AE was found in every specimen. The mean ZR to AE distance was 30.9 mm. On most sides (91%), the ZR was located more inferiorly than the AE with a mean distance of 3 mm between the 2 structures. The mean distance between the AE and ZR was 17 mm. On all sides, the AE was located posterior to the ZR. No significant differences were found between sides. No anatomic variations or pathologic conditions were noted in any of the specimens. CONCLUSIONS: The ZR is an easily identifiable and consistent bony landmark often used by skull base surgeons. In this investigation, we measured the anatomic relationships between the ZR and AE. Such data might assist in planning surgical trajectories and minimizing complications when skull base pathologies are approached.

The Anterolateral Triangle: Implications for a Transnasal Prelacrimal Approach to the Floor of the Middle Cranial Fossa.

BACKGROUND: The anterolateral triangle enclosed by the foramen rotundum and foramen ovale constitutes part of the floor of the middle cranial fossa (MCF). OBJECTIVE: To assess the feasibility of a transnasal prelacrimal approach for accessing the floor of MCF via an anterolateral triangle corridor and to determine the extent of maximal exposure while safeguarding neurovascular structures. METHODS: A transnasal prelacrimal approach was performed in 5 cadaveric specimens (10 sides). Following the identification of foramen rotundum and foramen ovale, the bony ridge between 2 was drilled to expose the MCF. The temporal lobe dura was then elevated laterally, and the distances from foramen ovale to the respective borders of the area of the MCF window were measured using a surgical navigation device. RESULTS: The MCF was exposed with a 0° scope in all specimens also exposing significant landmarks including the middle meningeal artery, greater superficial petrosal nerve, superior petrous sinus, and arcuate eminence. Average distances from foramen ovale to the anterior, posterior, and lateral exposed borders were 22.86 ± 1.87 mm, 27.24 ± 0.94 mm, and 24.23 ± 1.61 mm, respectively. The average area of exposed MCF window was 554.12 ± 60.22 mm2. Preservation of vidian nerve, greater palatine nerve, lateral nasal wall, and nasolacrimal duct was possible in all 10 sides. CONCLUSION: It is feasible to access the floor of MCF via an endoscopic transnasal prelacrimal approach with seemingly low risk.

Is the middle cranial fossa a reliable predictor of temporal lobe volume in extant and fossil anthropoids?

OBJECTIVES: We investigate the suitability of middle cranial fossa (MCF) size as a proxy for temporal lobe volume (TLV), examining the strength of the association between TLV and MCF metrics and assess the reliability predicting TLV in fossil anthropoids. The temporal lobe of the primate brain is a multimodal association cortex involved in long-term memory, auditory, and visual processing with unique specializations in modern humans for language comprehension. The MCF is the bony counterpart for the temporal lobe providing inferences for fossil hominin temporal lobe evolution. We now investigate whether the MCF is a suitable proxy for the temporal lobe. METHODS: A sample of 23 anthropoid species (n = 232, including 13 fossil species) from computed tomography (CT) scans of ex vivo crania and magnetic resonance imaging (MRI) of the in vivo brain were generated into three-dimensional (3D) virtual models. Seven linear metrics were digitally measured on the right MCF with right TLV calculated from in vivo MRI. RESULTS: Regression analyses produced statistically significant correlations between TLV and all MCF metrics (r ≥ 0.85; p ≤ 0.0009) with TLV predictions within ±1 standard error and three MCF metrics (posterior-width, mid-length, and mid-width) the most reliable predictors of TLV with only one metric weakly associated with TLV. DISCUSSION: These findings indicate a strong association between the MCF and TLV, provide reliable predictors of fossil TLV that were previously unattainable, allow the inclusion of fragmentary fossil material, and enable inferences into the emergence of modern human temporal lobe morphology.

Comparative anatomical analysis between the minipterional and supraorbital approaches.

OBJECTIVE: Keyhole approaches, namely the minipterional approach (MPTa) and the supraorbital approach (SOa), are alternatives to the standard pterional approach to treat lesions located in the anterior and middle cranial fossae. Despite their increasing popularity and acceptance, the indications and limitations of these approaches require further assessment. The purpose of the present study was to determine the differences in the area of surgical exposure and surgical maneuverability provided by the MPTa and SOa. METHODS: The areas of surgical exposure afforded by the MPTa and SOa were analyzed in 12 sides of cadaver heads by using a microscope and a neuronavigation system. The area of exposure of the region of interest and surgical freedom (maneuverability) of each approach were calculated. RESULTS: The area of exposure was significantly larger in the MPTa than in the SOa (1250 ± 223 mm2 vs 939 ± 139 mm2, p = 0.002). The MPTa provided larger areas of exposure in the ipsilateral and midline compartments, whereas there was no significant difference in the area of exposure in the contralateral compartment. All targets in the anterior circulation had significantly larger areas of surgical freedom when treated via the MPTa versus the SOa. CONCLUSIONS: The MPTa provides greater surgical exposure and better maneuverability than that offered by the SOa. The SOa may be advantageous as a direct corridor for treating lesions located in the contralateral side or in the anterior cranial fossa, but the surgical exposure provided in the midline region is inferior to that exposed by the MPTa.

Endoscopic transnasal transmaxillary approach to the upper parapharyngeal space and the skull base.

PURPOSE: Treatment of tumors arising in the upper parapharyngeal space (PPS) or the floor of the middle cranial fossa is challenging. This study aims to present anatomical landmarks for a combined endoscopic transnasal and anterior transmaxillary approach to the upper PPS and the floor of the middle cranial fossa and to further evaluate their clinical application. METHODS: Dissection of the upper PPS using a combined endoscopic endonasal transpterygoid and anterior transmaxillary approach was performed in six cadaveric heads. Surgical landmarks associated with the approach were defined. The defined approach was applied in patients with tumors involving the upper PPS. RESULTS: The medial pterygoid muscle, tensor veli palatini muscle and levator veli palatini muscle were key landmarks of the approach into the upper PPS. The lateral pterygoid plate, foramen ovale and mandibular nerve were important anatomical landmarks for exposing the parapharyngeal segment of the internal carotid artery through a combined endoscopic transnasal and anterior transmaxillary approach. The combined approach provided a better view of the upper PPS and middle skull base, allowing for effective bimanual techniques and bleeding control. Application of the anterior transmaxillary approach also provided a better view of the inferior limits of the upper PPS and facilitated control of the internal carotid artery. CONCLUSIONS: Improving the knowledge of the endoscopic anatomy of the upper PPS allowed us to achieve an optimal approach to tumors arising in the upper PPS. The combined endoscopic transnasal and anterior transmaxillary approach is a minimally invasive alternative approach to the upper PPS.

Quantitative Anatomical Comparison of Anterior, Anterolateral and Lateral, Microsurgical and Endoscopic Approaches to the Middle Cranial Fossa.

OBJECTIVE: To quantitatively compare different microsurgical and endoscopic approaches to the middle cranial fossa in a preclinical setting with a novel, computer-based research method. METHODS: Different approaches were performed bilaterally in 5 head and neck specimens that underwent high-resolution computed tomography scans: 5 transcranial anterolateral (supraorbital, mini-pterional, pterional, pterional-transzygomatic, fronto-temporal-orbito-zygomatic) without and with anterior clinoidectomy; 2 transcranial lateral (subtemporal and subtemporal-transzygomatic); 2 endoscopic transnasal (transpterygoid, transpterygoid to infratemporal fossa); 2 endoscopic transorbital (superior eyelid and inferolateral), and endoscopic transmaxillary. A dedicated navigation system was used to quantify surgical working volumes and exposure of different areas of the middle cranial fossa (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada). Statistical analysis was performed using a mixed linear model with bootstrap resampling. RESULTS: Endoscopic transnasal and fronto-temporal-orbito-zygomatic approaches with anterior clinoidectomy showed the largest surgical volumes. Endoscopic approaches allowed a wider exposure of medial anatomical surfaces (e.g., the petrous apex) compared with transcranial ones. Transcranial approaches with larger craniotomies allowed the widest exposure of superomedial anatomical structures (e.g., roof of cavernous sinus). The resection of the zygomatic arch allowed exposure of more medial surfaces with an inferior to superior trajectory. CONCLUSIONS: This study implemented a novel neuronavigation-based research method to quantitatively compare different approaches to the middle cranial fossa; its results might guide, after consideration of clinical implications, the choice of the neurosurgical approach to different areas of this complex skull base region.