Neurosurgery Blog

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Daily bibliographic review of the Neurosurgery Department. La Fe University Hospital. Valencia, Spain

Perpetuation of errors in illustrations of cranial nerve anatomy

J Neurosurg 127:192–198, 2017

For more than 230 years, anatomical illustrations have faithfully reproduced the German medical student Thomas Soemmerring’s cranial nerve (CN) arrangement. Virtually all contemporary atlases show the abducens, facial, and vestibulocochlear nerves (CNs VI–VIII) all emerging from the pontomedullary groove, as originally depicted by Soemmerring in 1778.

Direct observation at microsurgery of the cerebellopontine angle reveals that CN VII emerges caudal to the CN VIII root from the lower lateral pons rather than the pontomedullary groove. Additionally, the CN VI root lies in the pontomedullary groove caudal to both CN VII and VIII in the vast majority of cases.

In this high-resolution 3D MRI study, the exit location of CN VI was caudal to the CN VII/VIII complex in 93% of the cases. Clearly, Soemmerring’s rostrocaudal numbering system of CN VI-VII-VIII (abducens-facial-vestibulocochlear CNs) should instead be VIII-VII-VI (vestibulocochlear- facial-abducens CNs). While the inaccuracy of the CN numbering system is of note, what is remarkable is that generations of authors have almost universally chosen to perpetuate this ancient error. No doubt some did this through faithful copying of their predecessors. Others, it could be speculated, chose to depict the CN relationships incorrectly rather than run contrary to long-established dogma.

This study is not advocating that a universally recognized numbering scheme be revised, as this would certainly create confusion. The authors do advocate that future depictions of the anatomical arrangements of the brainstem roots of CNs VI, VII, and VIII ought to reflect actual anatomy, rather than be contorted to conform with the classical CN numbering system.

 

A method for safely resecting anterior butterfly gliomas

J Neurosurg 126:1795–1811, 2017

Gliomas invading the anterior corpus callosum are commonly deemed unresectable due to an unacceptable risk/benefit ratio, including the risk of abulia. In this study, the authors investigated the anatomy of the cingulum and its connectivity within the default mode network (DMN). A technique is described involving awake subcortical mapping with higher attention tasks to preserve the cingulum and reduce the incidence of postoperative abulia for patients with so-called butterfly gliomas.

METHODS The authors reviewed clinical data on all patients undergoing glioma surgery performed by the senior author during a 4-year period at the University of Oklahoma Health Sciences Center. Forty patients were identified who underwent surgery for butterfly gliomas. Each patient was designated as having undergone surgery either with or without the use of awake subcortical mapping and preservation of the cingulum. Data recorded on these patients included the incidence of abulia/akinetic mutism. In the context of the study findings, the authors conducted a detailed anatomical study of the cingulum and its role within the DMN using postmortem fiber tract dissections of 10 cerebral hemispheres and in vivo diffusion tractography of 10 healthy subjects.

RESULTS Forty patients with butterfly gliomas were treated, 25 (62%) with standard surgical methods and 15 (38%) with awake subcortical mapping and preservation of the cingulum. One patient (1/15, 7%) experienced postoperative abulia following surgery with the cingulum-sparing technique. Greater than 90% resection was achieved in 13/15 (87%) of these patients.

CONCLUSIONS This study presents evidence that anterior butterfly gliomas can be safely removed using a novel, attention-task based, awake brain surgery technique that focuses on preserving the anatomical connectivity of the cingulum and relevant aspects of the cingulate gyrus.

 

Contralateral supraorbital keyhole approach to medial optic nerve

J Neurosurg 126:940–944, 2017

The authors describe the supraorbital keyhole approach to the contralateral medial optic nerve and tract, both in a series of cadaveric dissections and in 2 patients. They also discuss the indications and contraindications for this procedure.

METHODS In 3 cadaver heads, bilateral supraorbital keyhole minicraniotomies were performed to expose the ipsilateral and contralateral optic nerves. The extent of exposure of the medial optic nerve was assessed. In 2 patients, a contralateral supraorbital keyhole approach was used to remove pathology of the contralateral medial optic nerve and tract.

RESULTS The supraorbital keyhole craniotomy provided better exposure of the contralateral superomedial nerve than it did of the same portion of the ipsilateral nerve. In both patients gross-total resections of the pathology was achieved.

CONCLUSIONS The authors demonstrate the suitability of the contralateral supraorbital keyhole approach for lesions involving the superomedial optic nerve.

 

Craniotomy for perisellar meningiomas: comparison of simple (appropriate for endoscopic approach) versus complex anatomy and surgical outcomes

J Neurosurg 126:1191–1200, 2017

Microsurgical resection of perisellar meningiomas has remained the gold standard for treatment, with extended endoscopic endonasal surgery emerging as a viable alternative. Historical microsurgical series do not distinguish based on tumor anatomy, but are being used as a comparison against endonasal surgery. In this study, the authors retrospectively reviewed and compared the anatomy of perisellar meningiomas seen at their institution. The tumors were separated into 2 groups based on whether they would be appropriate for endoscopic resection, and the authors compared the surgical outcomes.

METHODS Between 2001 and 2013, 53 patients (73.6% women) with perisellar meningiomas underwent open microsurgical resection at Vancouver General Hospital performed by the senior author (R.A.). These tumors were separated into 2 groups based on their anatomy, and the authors analyzed the resection rates, surgical results, patient quality of life, and complications.

RESULTS Among the 53 patients who presented with perisellar meningiomas, the authors were able to identify 18 lesions with “simple” anatomy suitable for endoscopic resection and 35 lesions with “complex” anatomy suitable for craniotomy resection. The mean age of patients in the study cohort was 57.4 years (range 33–91 years), and most patients presented with visual loss (68.0%) and visual field restriction (64.2%). There were no major differences in patient demographic data between the 2 groups. Patients with simple anatomy had smaller lesions (2.1 vs 3.5 cm; p = 0.004), no optic canal invasion (89% vs 26%; p < 0.0001), minimal vascular encasement (cortical cuff 83% vs 9%; p < 0.0001), and a rounded tumor shape (100% vs 31.8%; p = 0.0001) when compared with those with complex anatomy. The majority of lesions originated from the tuberculum sellae and planum sphenoidale. A greater degree of resection was achieved in the favorable anatomy group (99% vs 87.1%; p < 0.0001). Vision was improved or normalized in 96.6% of patients. Patients in the cohort with complex anatomy had more transient complications; there were no incidents of surgical-site infection, meningitis, or death in this series. One patient who underwent removal of a recurrent lesion experienced a CSF leak that required endoscopic repair. The overall persisting complications rate was higher in the group with complex anatomy (11.1% vs 37.1%; p = 0.0498); overall, 28.3% of patients experienced disabling complications. Patient-perceived quality of life improved in the simple anatomy group following surgery (DSF-36 +16.6 vs -8.4; p = 0.0045).

CONCLUSIONS Extended endoscopic surgery is emerging as a viable alternative to microsurgical resection of perisellar meningiomas. The authors identified 2 patient groups based on tumor anatomy, with distinctly separate surgical outcomes. In the future, patients considered for endoscopic resection should be compared against the surgical group with simple anatomy that includes smaller tumors, no vascular encasement, and limited optic canal invasion.

 

 

Transtentorial transcollateral sulcus approach to the ventricular atrium

J Neurosurg 126:1246–1252, 2017

Conventional approaches to the atrium of the lateral ventricle may be associated with complications related to direct cortical injury or brain retraction. The authors describe a novel approach to the atrium through a retrosigmoid transtentorial transcollateral sulcus corridor.

METHODS: Bilateral retrosigmoid craniotomies were performed on 4 formalin-fixed, colored latex–injected human cadaver heads (a total of 8 approaches). Microsurgical dissections were performed under 3× to 24× magnification, and endoscopic visualization was provided by 0° and 30° rigid endoscope lens systems. Image guidance was provided by coupling an electromagnetic tracking system with an open source software platform. Objective measurements on cortical thickness traversed and total depth of exposure were recorded. Additionally, the basal occipitotemporal surfaces of 10 separate cerebral hemisphere specimens were examined to define the surface topography of sulci and gyri, with attention to the appearance and anatomical patterns and variations of the collateral sulcus and the surrounding gyri.

RESULTS: The retrosigmoid approach allowed for clear visualization of the basal occipitotemporal surface. The collateral sulcus was identified and permitted easy endoscopic access to the ventricular atrium. The conical corridor thus obtained provided an average base working area of 3.9 cm2 at an average depth of 4.5 cm. The mean cortical thickness traversed to enter the ventricle was 1.4 cm. The intraventricular anatomy of the ipsilateral ventricle was defined clearly in all 8 exposures in this manner. The anatomy of the basal occipitotemporal surface, observed in a total of 18 hemispheres, showed a consistent pattern, with the collateral sulcus abutted by the parahippocampal gyrus medially, and the fusiform and lingual gyrus laterally. The collateral sulcus was found to be caudally bifurcated in 14 of the 18 specimens.

CONCLUSIONS: The retrosigmoid supracerebellar transtentorial transcollateral sulcus approach is technically feasible. This approach has the potential advantage of providing a short and direct path to the atrium, hence avoiding violation of deep neurovascular structures and preserving eloquent areas. Although this approach appears unconventional, it may provide a minimally invasive option for the surgical management of selected lesions within the atrium of the lateral ventricle.

 

The paramedian supracerebellar transtentorial approach to the posterior fusiform gyrus

the-paramedian-supracerebellar-transtentorial-approach-to-the-posterior-fusiform-gyrus

Acta Neurochir (2016) 158:2149–2154

The posterior fusiform gyrus lies in a surgically challenging region. Several approaches have been described to access this anatomical area. The paramedian supracerebellar transtentorial (SCTT) approach benefits from minimal disruption of normal neurovascular tissue. The aim of this study was to demonstrate its application to access the posterior fusiform gyrus.

Methods Three brains and six cadaveric heads were examined. A stepwise dissection of the SCTT approach to the posterior fusiform gyrus was performed. Local cortical anatomy was studied. The operability score was applied for comparative analysis on surgical anatomy.

Results The major posterior landmark used to identify the fusiform gyrus with respect to the medial occipitotemporal gyrus was the collateral sulcus, which commonly bifurcated at its caudal extent. Compared with other surgical approaches addressed to access the region, SCTT demonstrated the best operability in terms of maneuverability arc. Favorable tentorial anatomy is the only limiting factor.

Conclusions The supracerebellar transtentorial approach is able to provide access to the posterior fusiform gyrus via a minimally disruptive, anatomic, microsurgical corridor.

Virtual and stereoscopic anatomy: when virtual reality meets medical education

virtual-and-stereoscopic-anatomy-when-virtual-reality-meets-medical-education

J Neurosurg 125:1105–1111, 2016

The authors sought to construct, implement, and evaluate an interactive and stereoscopic resource for teaching neuroanatomy, accessible from personal computers.

Methods Forty fresh brains (80 hemispheres) were dissected. Images of areas of interest were captured using a manual turntable and processed and stored in a 5337-image database. Pedagogic evaluation was performed in 84 graduate medical students, divided into 3 groups: 1 (conventional method), 2 (interactive nonstereoscopic), and 3 (interactive and stereoscopic). The method was evaluated through a written theory test and a lab practicum.

Results Groups 2 and 3 showed the highest mean scores in pedagogic evaluations and differed significantly from Group 1 (p < 0.05). Group 2 did not differ statistically from Group 3 (p > 0.05). Size effects, measured as differences in scores before and after lectures, indicate the effectiveness of the method. ANOVA results showed significant difference (p < 0.05) between groups, and the Tukey test showed statistical differences between Group 1 and the other 2 groups (p < 0.05). No statistical differences between Groups 2 and 3 were found in the practicum. However, there were significant differences when Groups 2 and 3 were compared with Group 1 (p < 0.05).

Conclusions The authors conclude that this method promoted further improvement in knowledge for students and fostered significantly higher learning when compared with traditional teaching resources.

The nondecussating pathway of the dentatorubrothalamic tract in humans

The nondecussating pathway of the dentatorubrothalamic tract in humans

J Neurosurg 124:1406–1412, 2016

The dentatorubrothalamic tract (DRTT) is the major efferent cerebellar pathway arising from the dentate nucleus (DN) and decussating to the contralateral red nucleus (RN) and thalamus. Surprisingly, hemispheric cerebellar output influences bilateral limb movements. In animals, uncrossed projections from the DN to the ipsilateral RN and thalamus may explain this phenomenon. The aim of this study was to clarify the anatomy of the dentatorubrothalamic connections in humans.

Methods The authors applied advanced deterministic fiber tractography to a template of 488 subjects from the Human Connectome Project (Q1–Q3 release, WU-Minn HCP consortium) and validated the results with microsurgical dissection of cadaveric brains prepared according to Klingler’s method.

Results The authors identified the “classic” decussating DRTT and a corresponding nondecussating path (the nondecussating DRTT, nd-DRTT). Within each of these 2 tracts some fibers stop at the level of the RN, forming the dentatorubro tract and the nondecussating dentatorubro tract. The left nd-DRTT encompasses 21.7% of the tracts and 24.9% of the volume of the left superior cerebellar peduncle, and the right nd-DRTT encompasses 20.2% of the tracts and 28.4% of the volume of the right superior cerebellar peduncle.

Conclusions The connections of the DN with the RN and thalamus are bilateral, not ipsilateral only. This affords a potential anatomical substrate for bilateral limb motor effects originating in a single cerebellar hemisphere under physiological conditions, and for bilateral limb motor impairment in hemispheric cerebellar lesions such as ischemic stroke and hemorrhage, and after resection of hemispheric tumors and arteriovenous malformations. Furthermore, when a lesion is located on the course of the dentatorubrothalamic system, a careful preoperative tractographic analysis of the relationship of the DRTT, nd-DRTT, and the lesion should be performed in order to tailor the surgical approach properly and spare all bundles.

Fiber tracts of the dorsal language stream in the human brain

Fiber tracts of the dorsal language stream in the human brain

J Neurosurg 124:1396–1405, 2016

The aim of this study was to examine the arcuate (AF) and superior longitudinal fasciculi (SLF), which together form the dorsal language stream, using fiber dissection and diffusion imaging techniques in the human brain.

Methods Twenty-five formalin-fixed brains (50 hemispheres) and 3 adult cadaveric heads, prepared according to the Klingler method, were examined by the fiber dissection technique. The authors’ findings were supported with MR tractography provided by the Human Connectome Project, WU-Minn Consortium. The frequencies of gyral distributions were calculated in segments of the AF and SLF in the cadaveric specimens.

Results The AF has ventral and dorsal segments, and the SLF has 3 segments: SLF I (dorsal pathway), II (middle pathway), and III (ventral pathway). The AF ventral segment connects the middle (88%; all percentages represent the area of the named structure that is connected to the tract) and posterior (100%) parts of the superior temporal gyri and the middle part (92%) of the middle temporal gyrus to the posterior part of the inferior frontal gyrus (96% in pars opercularis, 40% in pars triangularis) and the ventral premotor cortex (84%) by passing deep to the lower part of the supramarginal gyrus (100%). The AF dorsal segment connects the posterior part of the middle (100%) and inferior temporal gyri (76%) to the posterior part of the inferior frontal gyrus (96% in pars opercularis), ventral premotor cortex (72%), and posterior part of the middle frontal gyrus (56%) by passing deep to the lower part of the angular gyrus (100%).

Conclusions This study depicts the distinct subdivision of the AF and SLF, based on cadaveric fiber dissection and diffusion imaging techniques, to clarify the complicated language processing pathways.

Endoscopic endonasal clip ligation of cerebral aneurysms

Endoscopic endonasal clip ligation of cerebral aneurysms

J Neurosurg 124:463–468, 2016

The expansion of endovascular procedures for obliteration of cerebral aneurysms highlights one of the drawbacks of clip ligation through the transcranial route, namely brain retraction or brain transgression. Sporadic case reports have emerged over the past 10 years describing endonasal endoscopic clip ligation of cerebral aneurysms. The authors present a detailed anatomical study to evaluate the feasibility of an endoscopic endonasal approach for application of aneurysm clips.

Methods Nine human cadaveric head specimens were used to evaluate operative exposures for clip ligation of aneurysms in feasible anterior and posterior circulation locations. Measurements of trajectories were completed using a navigation system to calculate skull base craniectomy size, corridor space, and the surgeon’s ability to gain proximal and distal control of parent vessels.

Results In each of the 9 cadaveric heads, excellent exposure of the target vessels was achieved. The transplanum, transtuberculum, and transcavernous approaches were used to explore the feasibility of anterior circulation access. Application of aneurysm clips was readily possible to the ophthalmic artery, A1 and A2 segments of the anterior cerebral artery, anterior communicating artery complex, and the paraclinoid and paraclival internal carotid artery. The transclival approach was explored, and clips were successfully deployed along the proximal branches of the vertebrobasilar system and basilar trunk and bifurcation. The median sizes of skull base craniectomy necessary for exposure of the anterior communicating artery complex and basilar tip were 3.24 cm2 and 4.62 cm2, respectively. The mean angles of surgical corridors to the anterior communicating artery complex and basilar tip were 11.4° and 14°, respectively. Although clip placement was feasible on the basilar artery and its branches, the associated perforating arteries were difficult to visualize, posing unexpected difficulty for safe clip application, with the exception of ventrolateral-pointing aneurysms.

Conclusions The authors characterize the feasibility of endonasal endoscopic clip ligation of aneurysms involving the paraclinoid, anterior communicating, and basilar arteries and proximal control of the paraclival internal carotid artery. The endoscopic approach should be initially considered for nonruptured aneurysms involving the paraclinoid and anterior communicating arteries, as well as ventrolateral basilar trunk aneurysms. Clinical experience will be mandatory to determine the applicability of this approach in practice.

Venous preservation in the anterior transpetrosal approach

Venous preservation in the anterior transpetrosal approach

J Neurosurg 124:432–439, 2016

The drainage of the superficial middle cerebral vein (SMCV) has previously been classified into 4 subtypes. Extradural procedures and dural incisions during the anterior transpetrosal approach (ATPA) may interrupt the route of drainage from the SMCV. In this study, the authors examined the relationship between anatomical variations in the SMCV and the corresponding surgical modifications to the ATPA that are necessary for venous preservation.

Methods This study included 48 patients treated via the ATPA in whom the SMCV was examined using 3D CT venography. The drainage patterns of the SMCV were classified into 3 types: cavernous or absent (Type 1), sphenobasal (Type 2), and sphenopetrosal (Type 3). Type 2 was subdivided into medial (Type 2a) and lateral (Type 2b), and Type 3 was subdivided into vein (Type 3a), vein and sinus (Type 3b), and sinus (Type 3c). The authors performed 3 ATPA modifications to preserve the SMCV: epidural anterior petrosectomy with subdural visualization of the sphenobasal vein (SBV), modification of the dural incision, and subdural anterior petrosectomy. Standard ATPA can be performed with Type 1, Type 2a, and Type 3a drainage. With Type 2b drainage, an epidural anterior petrosectomy with subdural SBV visualization is appropriate. The dural incision should be modified in Type 3b. With Type 3c, a subdural anterior petrosectomy is required.

Results The frequency of each type was 68.7% (33/48) in Type 1, 8.3% (4/48) in Type 2a, 4.2% (2/48) in Type 2b, 14.6% (7/48) in Type 3a, 2.1% (1/48) in Type 3b, and 2.1% (1/48) in Type 3c. No venous complications were found.

Conclusions The authors propose an SMCV modified classification based on ATPA modifications required for venous preservation.

Microvascular anatomy of the cerebellar parafloccular perforating space

Microvascular anatomy of parafloccular perforating space

J Neurosurg 124:440–449, 2016

The cerebellopontine angle is a common site for tumor growth and vascular pathologies requiring surgical manipulations that jeopardize cranial nerve integrity and cerebellar and brainstem perfusion. To date, a detailed study of vessels perforating the cisternal surface of the middle cerebellar peduncle—namely, the paraflocculus or parafloccular perforating space—has yet to be published. In this report, the perforating vessels of the anterior inferior cerebellar artery (AICA) in the parafloccular space, or on the cisternal surface of the middle cerebellar peduncle, are described to elucidate their relevance pertaining to microsurgery and the different pathologies that occur at the cerebellopontine angle.

Methods Fourteen cadaveric cerebellopontine cisterns (CPCs) were studied. Anatomical dissections and analysis of the perforating arteries of the AICA and posterior inferior cerebellar artery at the parafloccular space were recorded using direct visualization by surgical microscope, optical histology, and scanning electron microscope. A comprehensive review of the English-language and Spanish-language literature was also performed, and findings related to anatomy, histology, physiology, neurology, neuroradiology, microsurgery, and endovascular surgery pertaining to the cerebellar flocculus or parafloccular spaces are summarized.

Results A total of 298 perforating arteries were found in the dissected specimens, with a minimum of 15 to a maximum of 26 vessels per parafloccular perforating space. The average outer diameter of the cisternal portion of the perforating arteries was 0.11 ± 0.042 mm (mean ± SD) and the average length was 2.84 ± 1.2 mm. Detailed schematics and the surgical anatomy of the perforating vessels at the CPC and their clinical relevance are reported.

Conclusions The parafloccular space is a key entry point for many perforating vessels toward the middle cerebellar peduncle and lateral brainstem, and it must be respected and protected during surgical approaches to the cerebellopontine angle.

Subcortical anatomy as an anatomical and functional landmark in insulo-opercular gliomas

Subcortical anatomy as an anatomical and functional landmark in insulo-opercular gliomas

J Neurosurg 123:1081–1092, 2015

Little attention has been given to the functional challenges of the insular approach to the resection of gliomas, despite the potential damage of essential neural networks that underlie the insula. The object of this study is to analyze the subcortical anatomy of the insular region when infiltrated by gliomas, and compare it with the normal anatomy in nontumoral hemispheres.

Methods Ten postmortem human hemispheres were dissected, with isolation of the inferior fronto-occipital fasciculus (IFOF) and the uncinate fasciculus. Probabilistic diffusion tensor imaging (DTI) tractography was used to analyze the subcortical anatomy of the insular region in 10 healthy volunteers and in 22 patients with insular Grade II and Grade III gliomas. The subcortical anatomy of the insular region in these 22 insular gliomas was compared with the normal anatomy in 20 nontumoral hemispheres.

Results In tumoral hemispheres, the distances between the peri-insular sulci and the lateral surface of the IFOF and uncinate fasciculus were enlarged (p < 0.05). Also in tumoral hemispheres, the IFOF was identified in 10 (90.9%) of 11 patients with an extent of resection less than 80%, and in 4 (36.4%) of 11 patients with an extent of resection equal to or greater than 80% (multivariate analysis: p = 0.03).

Conclusions Insular gliomas grow in the space between the lateral surface of the IFOF and uncinate fasciculus and the insular surface, displacing and compressing the tracts medially. Moreover, these tracts may be completely infiltrated by the tumor, with a total disruption of the bundles. In the current study, the identification of the IFOF with DTI tractography was significantly associated with the extent of tumor resection. If the IFOF is not identified preoperatively, there is a high probability of achieving a resection greater than 80%.

Venous organization in the transverse foramen

Venous organization in the transverse foramen

J Neurosurg 123:118–125, 2015

The anatomical arrangement of the venous system within the transverse foramen is controversial; there is disagreement whether the anatomy consists of a single vertebral vein or a confluence of venous plexus. Precise knowledge of this arrangement is necessary in imaging when vertebral artery dissection is suspected, as well as in surgical approaches for the cervical spine. This study aimed to better explain anatomical organization of the venous system within the transverse foramen according to the Trolard hypothesis of a transverse vertebral sinus.

Methods This was an anatomical and radiological study. For the anatomical study, 10 specimens were analyzed after vascular injection. After dissection, histological cuts were prepared. For the radiological study, a high-resolution MRI study with 2D time-of-flight segment MR venography sequences was performed on 10 healthy volunteers.

Results Vertebral veins are arranged in a plexiform manner within the transverse canal. This arrangement begins at the upper part of the transverse canal before the vertebral vein turns into a single vein along with the vertebral artery running from the transverse foramen of the C-6. This venous system runs somewhat ventrolaterally to the vertebral artery. In most cases, this arrangement is symmetrical and facilitates radiological readings. The anastomoses between vertebral veins and ventral longitudinal veins are uniform and arranged segmentally at each vertebra.

Conclusions These findings confirm recent or previous anatomical descriptions and invalidate others. It is hard to come up with a common description of the arrangement of vertebral veins. The authors suggest providing clinicians as well as anatomists with a well-detailed description of components essential to the understanding of this organization.

The endoscopic endonasal approach to the odontoid and its impact on early extubation and feeding

The endoscopic endonasal approach to the odontoid and its impact on early extubation and feeding-1

J Neurosurg 122:511–518, 2015

The gold-standard surgical approach to the odontoid is via the transoral route. This approach necessitates opening of the oropharynx and is associated with risks of infection, and swallowing and breathing complications. The endoscopic endonasal approach has the potential to reduce these complications as the oral cavity is avoided. There are fewer than 25 such cases reported to date. The authors present a consecutive, single-institution series of 9 patients who underwent the endonasal endoscopic approach to the odontoid.

Methods The charts of 9 patients who underwent endonasal endoscopic surgery to the odontoid between January 2005 and August 2013 were reviewed. The clinical presentation, radiographic findings, surgical management, complications, and outcome, particularly with respect to time to extubation and feeding, were analyzed. Radiographic measurements of the distance between the back of the odontoid and the front of the cervicomedullary junction (CMJ) were calculated, as well as the location of any residual bone fragments.

Results There were 7 adult and 2 pediatric patients in this series. The mean age of the adults was 54.8 years; the pediatric patients were 7 and 14 years. There were 5 females and 4 males. The mean follow-up was 42.9 months. Symptoms were resolved or improved in all but 1 patient, who had concurrent polyneuropathy. The distance between the odontoid and CMJ increased by 2.34 ± 0.43 mm (p = 0.03). A small, clinically insignificant fragment remained after surgery, always on the left side, in 57% of patients. Mean times to extubation and oral feeding were on postoperative Days 0.3 and 1, respectively. There was one posterior cervical wound infection; there were 2 cases of epistaxis requiring repacking of the nose and no instances of breathing or swallowing complications or velopharyngeal insufficiency.

Conclusions This series of 9 cases of endonasal endoscopic odontoidectomy highlights the advantages of the approach in permitting early extubation and early feeding and minimizing complications compared with transoral surgery. Special attention must be given to bone on the left side of the odontoid if the surgeon is standing on the right side.

The 1-piece transbasal approach

The 1-piece transbasal approach

J Neurosurg 121:1446–1452, 2014

The transbasal approach (TBA) is an anterior skull base approach, which provides access to the anterior skull base, sellar-suprasellar region, and clivus. The TBA typically involves a bifrontal craniotomy with orbital bar and/or nasal bone osteotomies performed in 2 separate steps. The authors explored the feasibility of routinely performing this approach in 1 piece with a quantitative cadaveric anatomical study, and present an operative case example of their approach.

Methods. Seven latex-injected cadaveric heads underwent a 1-piece TBA, followed by additional bone removal typical for a traditional 2-piece approach. Six surgical angles relative to the pituitary stalk, as well as the surface area of the orbital roof osteotomy, were measured before and after additional bone removal. The vertical angle from the frontonasal suture to the foramen cecum was measured in all specimens. In addition to an anatomical study, the authors have used this technique in the operating room, and present an illustrative case of resection of an anterior skull base meningioma.

Results. Morphometric results were as follows: the vertical angle from the frontonasal suture to the foramen cecum ranged from 17.4° to 29.7° (mean 23.8° ± 4.8°) superiorly. Of the 6 surgical angle measures, only the middle horizontal angle was increased in the 2-piece versus the 1-piece approach (mean 43.4° ± 4.6° vs 43.0° ± 4.3°, respectively; p = 0.049), with a mean increase of 0.4°. The surface area of the orbital osteotomy was increased in the 2-piece versus the 1-piece approach (mean 2467 mm2 ± 360 mm2 vs 2045 mm2 ± 352 mm2, respectively; p < 0.001). The patient in the illustrative clinical case had a good outcome, both clinically and cosmetically.

Conclusions. The 1-piece TBA provides an alternative to the traditional 2-piece approach. It allows easier reconstruction, potentially decreased operative time, and improved cosmesis. While more of the orbital roof can be removed with the 2-piece approach, this additional bone removal offers only a small increase in 1 of 6 surgical angles that were measured.

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The direct anterior approach to the thoracolumbar junction

The direct anterior approach to the thoracolumbar junction

Eur Spine J (2014) 23:2265–2271

The thoracolumbar junction (TJ) is traditionally exposed by lateral or posterior approaches. This usually requires splitting of the diaphragm, or extensile removal of the posterior elements. A circumferential exposure (i.e. simultaneous anterior and bilateral exposure) of the vertebral body is not possible. Direct anterior access would allow circumferential exposure of the vertebral body, with adjacent disc levels, and would avoid splitting the diaphragm or extensive removal of the posterior bony structures.

Materials and methods Twelve Thiel cadavers (8 f/4 m) were dissected to access T12 or L1 via a midline laparotomy. Supra- and infragastric laparatomy techniques were investigated. Six cadavers were used to reach T12 through the lesser omentum, six to reach L1 through the greater omentum.

Results T12 after bluntly dissecting the lesser omentum, the lesser gastric curvature and the caudate lobe of the liver were utilised as landmarks. A small retroperitoneal incision was performed to mobilise the aorta allowing exposure of the T12 vertebra and its adjacent discs. Discectomy, corpectomy and insertion of an anterior column support were possible. The L1 level can be reached through the greater omentum by mobilising the pancreas as a single retroperitoneal structure, leaving the aorta and celiac trunk as landmarks. Retraction of the great vessels is necessary to expose L1 with its adjacent discs. Implantation of an anterior column support was possible utilising this approach.

Conclusion Direct anterior access to the TJ is feasible in a reproducible manner. This approach would avoid splitting the diaphragm, or dissection of the erector spinae muscles, and is likely to be less invasive than standard lateral or posterior approaches. This technique may offer a significant time reduction to surgery, especially in exposing the spine. Anterior column support can easily be performed, offering a better avoidance of kyphotic deformities.

Novel embalming solution for neurosurgical simulation in cadavers

Novel embalming solution for surgical simulation

J Neurosurg 120:1229–1237, 2014

Surgical simulation using postmortem human heads is one of the most valid strategies for neurosurgical research and training. The authors customized an embalming formula that provides an optimal retraction profile and lifelike physical properties while preventing microorganism growth and brain decay for neurosurgical simulations in cadavers. They studied the properties of the customized formula and compared its use with the standard postmortem processing techniques: cryopreservation and formaldehyde-based embalming.

Methods. Eighteen specimens were prepared for neurosurgical simulation: 6 formaldehyde embalmed, 6 cryopreserved, and 6 custom embalmed. The customized formula is a mixture of ethanol 62.4%, glycerol 17%, phenol 10.2%, formaldehyde 2.3%, and water 8.1%. After a standard pterional craniotomy, retraction profiles and brain stiffness were studied using an intracranial pressure transducer and monitor. Preservation time—that is, time that tissue remained in optimal condition—between specimen groups was also compared through periodical reports during a 48-hour simulation.

Results. The mean (± standard deviation) retraction pressures were highest in the formaldehyde group and lowest in the cryopreserved group. The customized formula provided a mean retraction pressure almost 3 times lower than formaldehyde (36 ± 3 vs 103 ± 14 mm Hg, p < 0.01) and very similar to cryopreservation (24 ± 6 mm Hg, p < 0.01). For research purposes, preservation time in the cryopreserved group was limited to 4 hours and was unlimited for the customized and formaldehyde groups for the duration of the experiment.

Conclusions. The customized embalming solution described herein is optimal for allowing retraction and surgical maneuverability while preventing decay. The authors were able to significantly lower the formaldehyde content as compared with that in standard formulas. The custom embalming solution has the benefits from both cryopreservation (for example, biological brain tissue properties) and formaldehyde embalming (for example, preservation time and microorganism growth prevention) and minimizes their drawbacks, that is, rapid decay in the former and stiffness in the latter. The presented embalming formula provides an important advance for neurosurgical simulations in research and teaching.

Anatomy and morphology of giant aneurysms

Giant aneurysms

Acta Neurochir (2014) 156:1–10

Giant intracranial aneurysms are rare and heterogeneous lesions with complex vascular anatomy. The aim of this retrospective study was to provide a comprehensive description of the anatomical features of giant aneurysms.

Methods We identified 125 patients with 129 giant aneurysms (≥25 mm) who were treated between 1987 and 2007 at the Department of Neurosurgery of Helsinki University Central Hospital (HUCH). All the imaging studies and medical records were reviewed for relevant information.

Results The distribution of the giant aneurysms among regions was as follows: internal carotid artery (ICA) 39 %, middle cerebral artery (MCA) 32 %, vertebrobasilar and posterior cerebral artery (VB-PCA) region 25 %, and anterior cerebral artery (ACA) including the anterior communicating artery 5%. The cavernous ICA segment (n =21, 16 %) and the MCA bifurcation (n =25, 19 %) were the most frequent specific locations. Half (n =11) of all fusiform aneurysms were found in the VB-PCA region. As many as 41 % of the giant MCA aneurysms were ruptured. Major anatomic variations were found in three (2 %) and multiple giant aneurysms in three (2 %) patients.Wall calcification was noted in 24 % and intraluminal thrombosis in 33 % of ruptured giant aneurysms (n =42).

Conclusions The majority of giant aneurysms are located in the ICA and MCA regions, while the ACA region is an exceptional site. The MCA region is the most common site for ruptured giant aneurysms. Associated anatomic variations and the multiplicity of giant aneurysms are a rare finding.

The Aqueduct of Sylvius: Applied 3-T Magnetic Resonance Imaging Anatomy and Morphometry With Neuroendoscopic Relevance

Aqueduct of Sylvius MRI morphometry

Neurosurgery 73[ONS Suppl 2]:ons132–ons140, 2013

The aqueduct of Sylvius (AqSylv) is a structure of increasing importance in neuroendoscopic procedures. However, there is currently no clear and adequate description of the normal anatomy of the AqSylv.

OBJECTIVE: To study in detail hitherto unavailable normal magnetic resonance imaging morphometry and anatomic variants of the AqSylv.

METHODS: We retrospectively studied normal midsagittal T1-weighted 3-T magnetic resonance images in 100 patients. We measured widths of the AqSylv pars anterior, ampulla, and pars posterior; its narrowest point; and its length. We recorded angulation of the AqSylv relative to the third ventricle as multiple deviations of the long axis of the AqSylv from the Talairach bicommissural line. We statistically determined age- and sexrelated changes in AqSylv morphometry using the Pearson correlation coefficient. We measured angulation of the AqSylv relative to the fourth ventricle and correlated this to the cervicomedullary angle (a surrogate for head position).

RESULTS: Patients were 13 to 83 years of age (45% male, 55% female). Mean morphometrics were as follows: pars anterior width, 1.1 mm; ampulla width, 1.2 mm; pars posterior width, 1.4 mm; length, 14.1 mm; narrowest point, 0.9 mm; and angulation in relation to the third and fourth ventricles, 26 and 18, respectively. Age correlated positively with width and negatively with length of the AqSylv. There was no correlation between AqSylv alignment relative to the foramen magnum and the cervicomedullary angle.

CONCLUSION: Normative dimensions of the AqSylv in vivo are at variance with published cadaveric morphometrics. The AqSylv widens and shortens with cerebral involution. Awareness of these normal morphometrics is highly useful when stent placement is an option during aqueductoplasty. Reported data are valuable in guiding neuroendoscopic management of hydrocephalus and aqueductal stenosis.

Neurosurgery Department. “La Fe” University Hospital. Valencia, Spain

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