Rhoton

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Daniel Dutra Cavalcanti, Bárbara Albuquerque Morais, Eberval Gadelha Figueiredo, Robert F. Spetzler and Mark C. Preul

OBJECTIVE

The brainstem is a compact, delicate structure. The surgeon must have good anatomical knowledge of the safe entry points to safely resect intrinsic lesions. Lesions located at the lateral midbrain surface are better approached through the lateral mesencephalic sulcus (LMS). The goal of this study was to compare the surgical exposure to the LMS provided by the subtemporal (ST) approach and the paramedian and extreme-lateral variants of the supracerebellar infratentorial (SCIT) approach.

METHODS

These 3 approaches were used in 10 cadaveric heads. The authors performed measurements of predetermined points by using a neuronavigation system. Areas of microsurgical exposure and angles of the approaches were determined. Statistical analysis was performed to identify significant differences in the respective exposures.

RESULTS

The surgical exposure was similar for the different approaches—369.8 ± 70.1 mm2 for the ST; 341.2 ± 71.2 mm2 for the SCIT paramedian variant; and 312.0 ± 79.3 mm2 for the SCIT extreme-lateral variant (p = 0.13). However, the vertical angular exposure was 16.3° ± 3.6° for the ST, 19.4° ± 3.4° for the SCIT paramedian variant, and 25.1° ± 3.3° for the SCIT extreme-lateral variant craniotomy (p < 0.001). The horizontal angular exposure was 45.2° ± 6.3° for the ST, 35.6° ± 2.9° for the SCIT paramedian variant, and 45.5° ± 6.6° for the SCIT extreme-lateral variant opening, presenting no difference between the ST and extreme-lateral variant (p = 0.92), but both were superior to the paramedian variant (p < 0.001). Data are expressed as the mean ± SD.

CONCLUSIONS

The extreme-lateral SCIT approach had the smaller area of surgical exposure; however, these differences were not statistically significant. The extreme-lateral SCIT approach presented a wider vertical and horizontal angle to the LMS compared to the other craniotomies. Also, it provides a 90° trajectory to the sulcus that facilitates the intraoperative microsurgical technique.

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Spyridon Komaitis, Georgios P. Skandalakis, Aristotelis V. Kalyvas, Evangelos Drosos, Evgenia Lani, John Emelifeonwu, Faidon Liakos, Maria Piagkou, Theodosis Kalamatianos, George Stranjalis and Christos Koutsarnakis

OBJECTIVE

The aim of this study was to investigate the anatomical consistency, morphology, axonal connectivity, and correlative topography of the dorsal component of the superior longitudinal fasciculus (SLF-I) since the current literature is limited and ambiguous.

METHODS

Fifteen normal, adult, formalin-fixed cerebral hemispheres were studied through a medial to lateral fiber microdissection technique. In 5 specimens, the authors performed stepwise focused dissections of the lateral cerebral aspect to delineate the correlative anatomy between the SLF-I and the other two SLF subcomponents, namely the SLF-II and SLF-III.

RESULTS

The SLF-I was readily identified as a distinct fiber tract running within the cingulate or paracingulate gyrus and connecting the anterior cingulate cortex, the medial aspect of the superior frontal gyrus, the pre–supplementary motor area (pre-SMA), the SMA proper, the paracentral lobule, and the precuneus. With regard to the morphology of the SLF-I, two discrete segments were consistently recorded: an anterior and a posterior segment. A clear cleavage plane could be developed between the SLF-I and the cingulum, thus proving their structural integrity. Interestingly, no anatomical connection was revealed between the SLF-I and the SLF-II/SLF-III complex.

CONCLUSIONS

Study results provide novel and robust anatomical evidence on the topography, morphology, and subcortical architecture of the SLF-I. This fiber tract was consistently recorded as a distinct anatomical entity of the medial cerebral aspect, participating in the axonal connectivity of high-order paralimbic areas.

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Wei-Hsin Wang, Stefan Lieber, Roger Neves Mathias, Xicai Sun, Paul A. Gardner, Carl H. Snyderman, Eric W. Wang and Juan C. Fernandez-Miranda

OBJECTIVE

The foramen lacerum is a relevant skull base structure that has been neglected for many years. From the endoscopic endonasal perspective, the foramen lacerum is a key structure due to its location at the crossroad between the sagittal and coronal planes. The objective of this study was to provide a detailed investigation of the surgical anatomy of the foramen lacerum and its adjacent structures based on anatomical dissections and imaging studies, propose several relevant key surgical landmarks, and demonstrate the surgical technique for its full exposure with several illustrative cases.

METHODS

Ten colored silicone-injected anatomical specimens were dissected using a transpterygoid approach to the foramen lacerum region in a stepwise manner. Five similar specimens were used for a comparative transcranial approach. The osseous anatomy was examined in 32 high-resolution multislice CT studies and 1 disarticulated skull. Representative cases were selected to illustrate the application of the findings.

RESULTS

The pterygosphenoidal fissure is the synchondrosis between the lacerum process of the pterygoid bone and the floor of the sphenoid bone. It constantly converges with the posterior end of the vidian canal at a 45° angle, and its posterolateral end points directly to the lacerum foramen. The pterygoid tubercle separates the vidian canal from the pterygosphenoidal fissure, and forms the anterior wall of the lower part of the foramen lacerum. The lingual process, which forms the lateral wall of the foramen lacerum, was identified in 53 of 64 sides and featured an average height of 5 mm. The mandibular strut separates the foramen lacerum from the foramen ovale and had an average width of 5 mm.

CONCLUSIONS

This study provides relevant surgical landmarks and a systematic approach to the foramen lacerum by defining anterior, medial, lateral, and inferior walls that may facilitate its safe exposure for effective removal of lesions while minimizing the risk of injury to the internal carotid artery.

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Maria Peris-Celda, Avital Perry, Lucas P. Carlstrom, Christopher S. Graffeo, Colin L. W. Driscoll and Michael J. Link

OBJECTIVE

Middle fossa surgery is challenging, and reliable surgical landmarks are essential to perform accurate and safe surgery. Although many descriptions of the middle fossa components have been published, a clinically practical description of this very complex anatomical region is lacking. Small structure arrangements in this area are often not well visualized or accurately demarcated with neuronavigation systems. The objective is to describe a “roadmap” of key surgical reference points and landmarks during middle fossa surgery to help the surgeon predict where critical structures will be located.

METHODS

The authors studied 40 dry skulls (80 sides) obtained from the anatomical board at their institution. Measurements of anatomical structures in the middle fossa were made with a digital caliper and a protractor, taking as reference the middle point of the external auditory canal (MEAC). The results were statistically analyzed.

RESULTS

The petrous part of the temporal bone was found at a mean of 16 mm anterior and 24 mm posterior to the MEAC. In 87% and 99% of the sides, the foramen ovale and foramen spinosum, respectively, were encountered deep to the zygomatic root. The posterior aspect of the greater superficial petrosal nerve (GSPN) groove was a mean of 6 mm anterior and 25 mm medial to the MEAC, nearly parallel to the petrous ridge. The main axis of the IAC projected to the root of the zygoma in all cases. The internal auditory canal (IAC) porus was found 5.5 mm lateral and 4.5 mm deep to the lateral aspect of the trigeminal impression along the petrous ridge (mean measurement values). A projection from this point to the middle aspect of the root of the zygoma, being posterior to the GSPN groove, could estimate the orientation of the IAC.

CONCLUSIONS

In middle fossa approaches, the external acoustic canal is a reliable reference before skin incision, whereas the zygomatic root becomes important after the skin incision. Deep structures can be related to these 2 anatomical structures. An easy method to predict the location of the IAC in surgery is described. Careful study of the preoperative imaging is essential to adapt this knowledge to the individual anatomy of the patient.

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Ariel Kaen, Eugenio Cárdenas Ruiz-Valdepeñas, Alberto Di Somma, Francisco Esteban, Javier Márquez Rivas and Jesús Ambrosiani Fernandez

OBJECTIVE

The endoscopic endonasal transpterygoid route has been widely evaluated in cadavers, and it is currently used during surgery for specific diseases involving the lateral skull base. Identification of the petrous segment of the internal carotid artery (ICA) is a key step during this approach, and the vidian nerve (VN) has been described as a principal landmark for safe endonasal localization of the petrous ICA at the level of the foramen lacerum. However, the relationship of the VN to the ICA at this level is complex as well as variable and has not been described in the pertinent literature. Accordingly, the authors undertook this purely anatomical study to detail and quantify the peri-lacerum anatomy as seen via an endoscopic endonasal transpterygoid pathway.

METHODS

Eight human anatomical specimens (16 sides) were dissected endonasally under direct endoscopic visualization. Anatomical landmarks of the VN and the posterior end of the vidian canal (VC) during the endoscopic endonasal transpterygoid approach were described, quantitative anatomical data were compiled, and a schematic classification of the most relevant structures encountered was proposed.

RESULTS

The endoscopic endonasal transpterygoid approach was used to describe the different anatomical structures surrounding the anterior genu of the petrous ICA. Five key anatomical structures were identified and described: the VN, the eustachian tube, the foramen lacerum, the petroclival fissure, and the pharyngobasilar fascia. These structures were specifically quantified and summarized in a schematic acronym—VELPPHA—to describe the area. The VELPPHA area is a dense fibrocartilaginous space around the inferior compartment of the foramen lacerum that can be reached by following the VC posteriorly; this area represents the posterior limits of the transpterygoid approach and, of utmost importance, no neurovascular structures were observed through the VELPPHA area in this study, indicating that it should be a safe zone for surgery in the posterior end of the endoscopic endonasal transpterygoid approach.

CONCLUSIONS

The VELPPHA area represents the posterior limits of the endoscopic endonasal transpterygoid approach. Early identification of this area can enhance the safety of the endoscopic endonasal transpterygoid approach expanded to the lateral aspect of the skull base, especially when treating patients with poorly pneumatized sphenoid sinuses.

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Raywat Noiphithak, Juan C. Yanez-Siller, Juan Manuel Revuelta Barbero, Bradley A. Otto, Ricardo L. Carrau and Daniel M. Prevedello

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.

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Huy Q. Truong, Edinson Najera, Robert Zanabria-Ortiz, Emrah Celtikci, Xicai Sun, Hamid Borghei-Razavi, Paul A. Gardner and Juan C. Fernandez-Miranda

OBJECTIVE

The endoscopic endonasal approach has become a routine corridor to the suprasellar region. The superior hypophyseal arteries (SHAs) are intimately related to lesions in the suprasellar space, such as craniopharyngiomas and meningiomas. Here the authors investigate the surgical anatomy and variations of the SHA from the endoscopic endonasal perspective.

METHODS

Thirty anatomical specimens with vascular injection were used for endoscopic endonasal dissection. The number of SHAs and their origin, course, branching, anastomoses, and areas of supply were collected and analyzed.

RESULTS

A total of 110 SHAs arising from 60 internal carotid arteries (ICAs), or 1.83 SHAs per ICA (range 0–3), were found. The most proximal SHA always ran in the preinfundibular space and provided the major blood supply to the infundibulum, optic chiasm, and proximal optic nerve; it was defined as the primary SHA (pSHA). The more distal SHA(s), present in 78.3% of sides, ran in the retroinfundibular space and supplied the stalk and may also supply the tuber cinereum and optic tracts. In the two sides (3.3%) in which no SHA was present, the territory was covered by a pair of infundibular arteries originating from the posterior communicating artery. Two-thirds of the pSHAs originated proximal to the distal dural ring; half of these arose from the carotid cave portion of the ICA, whereas the other half originated proximal to the cave. Four branching patterns of the pSHA were recognized, with the most common pattern (41.7%) consisting of three or more branches with a tree-like pattern. Descending branches were absent in 25% of cases. Preinfundibular anastomoses between pSHAs were found in all specimens. Anastomoses between the pSHA and the secondary SHA (sSHA) or the infundibular arteries were found in 75% cases.

CONCLUSIONS

The first SHA almost always supplies the infundibulum, optic chiasm, and proximal optic nerve and represents the pSHA. Compromising this artery can cause a visual deficit. Unilateral injury to the pSHA is less likely to cause an endocrine deficit given the artery’s abundant anastomoses. A detailed understanding of the surgical anatomy of the SHA and its many variations may help surgeons when approaching challenging lesions in the suprasellar region.

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Ali Tayebi Meybodi, Andrew S. Little, Vera Vigo, Arnau Benet, Sofia Kakaizada and Michael T. Lawton

OBJECTIVE

The transpterygoid extension of the endoscopic endonasal approach provides exposure of the petrous apex, Meckel’s cave, paraclival area, and the infratemporal fossa. Safe and efficient localization of the lacerum segment of the internal carotid artery (ICA) is a crucial part of such exposure. The aim of this study is to introduce a novel landmark for localization of the lacerum ICA.

METHODS

Ten cadaveric heads were prepared for transnasal endoscopic dissection. The floor of the sphenoid sinus was drilled to expose an extension of the pharyngobasilar fascia between the sphenoid floor and the pterygoid process (the pterygoclival ligament). Several features of the pterygoclival ligament were assessed. In addition, 31 dry skulls were studied to assess features of the bony groove harboring the pterygoclival ligament.

RESULTS

The pterygoclival ligament was identified bilaterally during drilling of the sphenoid floor in all specimens. The ligament started a few millimeters posterior to the posterior end of the vomer alae and invariably extended posterolaterally and superiorly to blend into the fibrous tissue around the lacerum ICA. The mean length of the ligament was 10.5 ± 1.7 mm. The mean distance between the anterior end of the ligament and midline was 5.2 ± 1.2 mm. The mean distance between the posterior end of the ligament and midline was 12.3 ± 1.4 mm. The bony pterygoclival groove was identified at the confluence of the vomer, pterygoid process of the sphenoid, and basilar part of the occipital bone, running from posterolateral to anteromedial. The mean length of the groove was 7.7 ± 1.8 mm. Its posterolateral end faced the anteromedial aspect of the foramen lacerum medial to the posterior end of the vidian canal. A clinical case illustration is also provided.

CONCLUSIONS

The pterygoclival ligament is a consistent landmark for localization of the lacerum ICA. It may be used as an adjunct or alternative to the vidian nerve to localize the ICA during endoscopic endonasal surgery.

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Christos Koutsarnakis, Aristotelis V. Kalyvas, Spyridon Komaitis, Faidon Liakos, Georgios P. Skandalakis, Christos Anagnostopoulos and George Stranjalis

OBJECTIVE

The authors investigated the specific topographic relationship of the optic radiation fibers to the roof and floor of the ventricular atrium because the current literature is ambiguous.

METHODS

Thirty-five normal, adult, formalin-fixed cerebral hemispheres and 30 focused MRI slices at the level of the atrium were included in the study. The correlative anatomy of the optic radiation with regard to the atrial roof and floor was investigated in 15 specimens, each through focused fiber microdissections. The remaining 5 hemispheres were explored with particular emphasis on the trajectory of the collateral sulcus in relation to the floor of the atrium. In addition, the trajectory of the collateral sulcus was evaluated in 30 MRI scans.

RESULTS

The atrial roof was observed to be devoid of optic radiations in all studied hemispheres, whereas the atrial floor was seen to harbor optic fibers on its lateral part. Moreover, the trajectory of the intraparietal sulcus, when followed, was always seen to correspond to the roof of the atrium, thus avoiding the optic pathway, whereas that of the collateral sulcus was found to lead to either the lateral atrial floor or outside the ventricle in 88% of the cases, therefore hitting the visual pathway.

CONCLUSIONS

Operative corridors accessing the ventricular atrium should be carefully tailored through detailed preoperative planning and effective use of intraoperative navigation to increase patient safety and enhance the surgeon’s maneuverability. The authors strongly emphasize the significance of accurate anatomical knowledge.

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Abuzer Güngör, Şevki Serhat Baydın, Vanessa M. Holanda, Erik H. Middlebrooks, Cihan Isler, Bekir Tugcu, Kelly Foote and Necmettin Tanriover

OBJECTIVE

Despite the extensive use of the subthalamic nucleus (STN) as a deep brain stimulation (DBS) target, unveiling the extensive functional connectivity of the nucleus, relating its structural connectivity to the stimulation-induced adverse effects, and thus optimizing the STN targeting still remain challenging. Mastering the 3D anatomy of the STN region should be the fundamental goal to achieve ideal surgical results, due to the deep-seated and obscure position of the nucleus, variable shape and relatively small size, oblique orientation, and extensive structural connectivity. In the present study, the authors aimed to delineate the 3D anatomy of the STN and unveil the complex relationship between the anatomical structures within the STN region using fiber dissection technique, 3D reconstructions of high-resolution MRI, and fiber tracking using diffusion tractography utilizing a generalized q-sampling imaging (GQI) model.

METHODS

Fiber dissection was performed in 20 hemispheres and 3 cadaveric heads using the Klingler method. Fiber dissections of the brain were performed from all orientations in a stepwise manner to reveal the 3D anatomy of the STN. In addition, 3 brains were cut into 5-mm coronal, axial, and sagittal slices to show the sectional anatomy. GQI data were also used to elucidate the connections among hubs within the STN region.

RESULTS

The study correlated the results of STN fiber dissection with those of 3D MRI reconstruction and tractography using neuronavigation. A 3D terrain model of the subthalamic area encircling the STN was built to clarify its anatomical relations with the putamen, globus pallidus internus, globus pallidus externus, internal capsule, caudate nucleus laterally, substantia nigra inferiorly, zona incerta superiorly, and red nucleus medially. The authors also describe the relationship of the medial lemniscus, oculomotor nerve fibers, and the medial forebrain bundle with the STN using tractography with a 3D STN model.

CONCLUSIONS

This study examines the complex 3D anatomy of the STN and peri-subthalamic area. In comparison with previous clinical data on STN targeting, the results of this study promise further understanding of the structural connections of the STN, the exact location of the fiber compositions within the region, and clinical applications such as stimulation-induced adverse effects during DBS targeting.