Window anatomy for neurosurgical approaches. Laboratory investigation

Anatomic evaluation of the posterior temporal approach via the Heschl's gyrus to the thalamus, internal capsule, and atrium

OBJECTIVE

Posterior temporal craniotomy allows for the exposure of the superior surface of the planum temporale. Heschl's gyrus is the most prominent structure of the planum temporale and can be an anatomical landmark to approach deep brain structures such as the internal capsule, lateral thalamus, and ventricular atrium.

METHODS

Ten human cadavers' heads underwent a posterior bilateral temporal craniotomy and the microsurgical dissection of Heschl's gyrus was performed and variables were measured with a neuronavigation system and statistically analyzed.

RESULTS

The mean distance between the keyhole and Heschl's gyrus was 61.7 ± 7.3 mm, the mean distance between the stephanion to Heschl's gyrus was 40.8 ± 6.0 mm, and the mean distance between the temporal lobe and Heschl's gyrus was 54.9 ± 6.9 mm. The length of Heschl's gyrus was 24 ± 7.5 mm, and the inclination angle in the axial plane was 20.0 ± 3.7° having the vertex as its deepest point as the base on the surface of the temporal plane. From Heschl's gyrus, the distance from the surface to the internal capsule was 29.1 ± 5.6 mm, the distance to the lateral thalamus was 34.8 ± 7.3 mm, and the distance to the ventricular atrium was 39.6 ± 7.2 mm. No statistical difference was found between the right and left sides.

CONCLUSIONS

Through a posterior temporal craniotomy, the temporal planum is exposed by opening the Sylvian fissure, where Heschl's gyrus can be identified and used as a natural corridor to approach the internal capsule, the ventricular atrium, and the lateral thalamus.

Cortical and white matter anatomy relevant for the lateral and superior approaches to resect intraaxial lesions within the frontal lobe

Despite being associated with high-order neurocognitive functions, the frontal lobe plays an important role in core neurological functions, such as motor and language functions. The aim of this study was to present a neurosurgical perspective of the cortical and subcortical anatomy of the frontal lobe in terms of surgical treatment of intraaxial frontal lobe lesions. We also discuss the results of direct brain mapping when awake craniotomy is performed. Ten adult cerebral hemispheres were prepared for white matter dissection according to the Klingler technique. Intraaxial frontal lobe lesions are approached with a superior or lateral trajectory during awake conditions. The highly eloquent cortex within the frontal lobe is identified within the inferior frontal gyrus (IFG) and precentral gyrus. The trajectory of the approach is mainly related to the position of the lesion in relation to the arcuate fascicle/superior longitudinal fascicle complex and ventricular system. Knowledge of the cortical and subcortical anatomy and its function within the frontal lobe is essential for preoperative planning and predicting the risk of immediate and long-term postoperative deficits. This allows surgeons to properly set the extent of the resection and type of approach during preoperative planning.

Rolandic Cortex Morphology: Magnetic Resonance Imaging-Based Three-Dimensional Cerebral Reconstruction Study and Intraoperative Usefulness

Background  During brain surgery, the neurosurgeon must be able to identify and avoid injury to the Rolandic cortex. However, when only a small part of the cortex is exposed, it may be difficult to identify the Rolandic cortex with certainty. Despite various advanced methods to identify it, visual recognition remains an important backup for neurosurgeons. The aim of the study was to find any specific morphology pattern that may help to identify the Rolandic cortex intraoperatively.

Materials and Methods  Magnetic resonance imaging of the brain from patients with various conditions was used to create the three-dimensional cerebral reconstruction images. A total of 216 patients with 371 intact hemispheres were included. Each image was inspected to note the morphology of the Rolandic cortex and the suprasylvian cortex. Additionally, other two evaluators exclusively inspected the morphology of the suprasylvian cortex. Their observation results were compared to find the agreements.

Results  Several distinctive morphology patterns have been identified at the Rolandic cortex and the suprasylvian cortex including a genu, or a knob at the upper precentral gyrus, an angulation of the lower postcentral gyrus, a strip for pars opercularis, a rectangle for the lower precentral gyrus, and a triangle for the lower postcentral gyrus. Combined total and partial agreement of the suprasylvian cortex morphology pattern ranged from 60.4 to 85.2%.

Conclusion  The authors have demonstrated the distinctive morphology of the Rolandic cortex and the suprasylvian cortex. This information can provide visual guidance to identify the Rolandic cortex particularly during surgery with limited exposure.

Cortical and Subcortical Anatomy of the Parietal Lobe From the Neurosurgical Perspective

Introduction: The anatomical structures of the parietal lobe at the cortical and subcortical levels are related mainly to sensory, visuospatial, visual and language function. The aim of this study was to present an intraoperative perspective of these critical structures in terms of the surgical treatment of intra-axial lesions. The study also discusses the results of the technique and the results of direct brain stimulation under awake conditions.

Materials and Methods: Five adult brains were prepared according to the Klingler technique. Cortical assessments and all measurements were performed with the naked eye, while white matter dissection was performed with microscopic magnification.

Results: Intra-axial lesions within the parietal lobe can be approached through a lateral or superior trajectory. This decision is based on the location of the lesions in relation to the arcuate fascicle/superior longitudinal fascicle (AF/SLF) complex and ventricular system. Regardless of the approach, the functional borders of the resection are defined by the postcentral gyrus anteriorly and Wernicke's speech area inferiorly. On the subcortical level, active identification of the AF/SLF complex and of the optic radiation within the sagittal stratum should be performed. The intraparietal sulcus (IPS) is a reliable landmark for the AF/SLF complex in ~60% of cases.

Conclusion: Knowledge of the cortical and subcortical anatomical and functional borders of the resection is crucial in preoperative planning, prediction of the risk of postoperative deficits, and intraoperative decision making.

Development and validation of a rapidly deployable CT-guided stereotactic system for external ventricular drainage: preclinical study

External ventricular drainage (EVD) is an emergency neurosurgical procedure to decrease intracranial pressure through a catheter mediated drainage of cerebrospinal fluid. Most EVD catheters are placed using free hands without direct visualization of the target and catheter trajectory, leading to a high rate of complications- hemorrhage, brain injury and suboptimal catheter placement. Use of stereotactic systems can prevent these complications. However, they have found limited application for this procedure due to their long set-up time and expensive hardware. Therefore, we have developed and pre-clinically validated a novel 3D printed stereotactic system for rapid and accurate implantation of EVD catheters. Its mechanical and imaging accuracies were found to be at par with clinical stereotactic systems. Preclinical trial in human cadaver specimens revealed improved targeting accuracy achieved within an acceptable time frame compared to the free hand technique. CT angiography emulated using cadaver specimen with radio-opaque vascular contrast showed vessel free catheter trajectory. This could potentially translate to reduced hemorrhage rate. Thus, our 3D printed stereotactic system offers the potential to improve the accuracy and safety of EVD catheter placement for patients without significantly increasing the procedure time.

Anatomical aspects of the insula, opercula and peri-insular white matter for a transcortical approach to insular glioma resection

The insula is a lobe located deep in each hemisphere of the brain and is surrounded by eloquent cortical, white matter, and basal ganglia structures. The aim of this study was to provide an anatomical description of the insula and white matter tracts related to surgical treatment of gliomas through a transcortical approach. The study also discusses surgical implications in terms of intraoperative brain mapping. Five adult brains were prepared according to the Klingler technique. Cortical anatomy was evaluated with the naked eye, whereas white matter dissection was performed with the use of a microscope. The widest exposure of the insular surface was noted through the temporal operculum, mainly in zones III and IV according to the Berger-Sanai classification. By going through the pars triangularis in all cases, the anterior insular point and most of zone I were exposed. The narrowest and deepest operating field was observed by going through the parietal operculum. This method provided a suitable approach to zone II, where the corticospinal tract is not covered by the basal ganglia and is exposed just under the superior limiting sulcus. At the subcortical level, the identification of the inferior frontoocipital fasciculus at the level of the limen insulae is critical in terms of preserving the lenticulostriate arteries. Detailed knowledge of the anatomy of the insula and subcortical white matter that is exposed through each operculum is essential in preoperative planning as well as in the intraoperative decision-making process in terms of intraoperative brain mapping.

Anatomical Predictors of Transcranial Surgical Access to the Suprasellar Space

Objective  The suprasellar space is a common location for intracranial lesions. The position of the optic chiasm (prefixed vs. postfixed) results in variable sizes of operative corridors and is thus important to identify when choosing a surgical approach to this region. In this study, we aim to identify relationships between suprasellar anatomy and external cranial metrics to guide in preoperative planning. Methods  T2-weighted magnetic resonance images (MRIs) from 50 patients (25 males and 25 females) were analyzed. Various intracranial and extracranial metrics were measured. Statistical analysis was performed to determine any associations between metrics. Results  Interoptic space (IOS) size correlated with interpupillary distance (IPD; a  = 7.3, 95% confidence interval [CI] = 4.5-10.0, R ²  = 0.3708, p  = 0.0009). IOS size also correlated with fixation of the optic chiasm, for prefixed chiasms ( n  = 7), the mean IOS is 205.14 mm ² , for normal chiasm position ( n  = 33) the mean IOS is 216.94 mm ² and for postfixed chiasms ( n  = 10) the mean IOS is 236.20 mm ² ( p  = 0.002). IPD correlates with optic nerve distance (OND; p  = 0.1534). Cranial index does not predict OND, IPD, or IOS. Conclusion  This study provides insight into relationships between intracranial structures and extracranial metrics. This is the first study to describe a statistically significant correlation between IPD and IOS. Surgical approach can be guided in part by the size of the IOS and its correlates. Particularly small intraoptic space may guide the surgeon away from a subfrontal approach.

Immersive Surgical Anatomy of the Craniometric Points

Craniometric points (CPs) have been used in neurosciences since the 1800s. Localization of the CPs allows for the identification of crucial intracranial structures. Despite the contribution of advanced technology to surgery, the knowledge of these points remains crucial for surgical planning and intraoperative orientation. The understanding of these crucial points can be facilitated with the use of three-dimensional technology combined with anatomical dissections. The present study is part of a stereoscopic collection of volumetric models (VMs) obtained from cadaveric dissections that depict the relevant anatomy of the CPs. Five embalmed heads and two dry skulls have been used to depict these points. After the anatomical dissection, stereoscopic images and VMs were generated to show the correlation between external and internal landmarks. The CPs identified were divided into sutures, suture junctions, prominences and depressions, and cortical surface landmarks. The VMs represent an interactive way to define these points easily and their correlation with different intracranial structures (vascular structure, ventricle cavity, and Brodmann’s areas).

Evaluation of Dimensions of Kambin's Triangle to Calculate Maximum Permissible Cannula Diameter for Percutaneous Endoscopic Lumbar Discectomy : A 3-Dimensional Magnetic Resonance Imaging Based Study

Objective

To evaluate 3-dimensional magnetic resonance imaging (MRI) of Kambin’s safe zone to calculate maximum cannula diameter permissible for safe percutaneous endoscopic lumbar discectomy.

Methods

Fifty 3D MRIs of 19 males and 31 females (mean, 47 years) were analysed. Oblique, axial and sagittal views were used for image analysis. Three authors calculated the inscribed circle (cannula diameter) individually, within the neural (original) and bony Kambin’s triangle in oblique views, disc heights on sagittal views and root to facet distances at upper and lower end plate levels on axial views and their averages were taken.

Results

The mean root to facet distances at upper end plate level measured on axial sections increased from 3.42±3.01 mm at L12 level to 4.57±2.49 mm at L5S1 level. The mean root to facet distances at lower end plate level measured on axial sections also increased from 6.07±1.13 mm at L12 level to 12.9±2.83 mm at L5S1 level. Mean maximum cannula diameter permissible through the neural Kambin’s triangle increased from 5.67±1.38 mm at L12 level to 9.7±3.82 mm at L5S1 level. The mean maximum cannula diameter permissible through the bony Kambin’s triangle also increased from 4.03±1.08 mm at L12 level to 6.11±1 mm at L5S1 level. Only 2% of the 427 bony Kambin’s triangles could accommodate a cannula diameter of 8mm. The base of the bony Kambin’s triangle taken in oblique view (3D MRI) was significantly higher than the root to facet distance at lower end plate level taken in axial view.

Conclusion

The largest mean diameter of endoscopic cannula passable through “bony” Kambin’s triangle was distinctively smaller than the largest mean diameter of endoscopic cannula passable through “neural” Kambin’s triangle at all levels. Although proximity of exiting root to the facet joint is always taken into consideration before PELD procedure, our 3D MRI based anatomical study is the first to provide actual maximum cannula dimensions permissible in this region.

Microsurgical anatomy of the central lobe

OBJECT

Central Lobe consists of the pre- and postcentral gyri on the lateral surface and the Paracentral Lobule on the medial surface and corresponds to the sensorimotor cortex. The objective of the present study was to define the neural features, craniometric relationships, arterial supply, and venous drainage of the central lobe.

METHODS

Cadaveric hemispheres dissected using microsurgical techniques provided the material for this study.

RESULTS

The coronal suture is closer to the precentral gyrus and central sulcus at its lower rather than at its upper end, but they are closest at a point near where the superior temporal line crosses the coronal suture. The arterial supply of the lower two-thirds of the lateral surface of the central lobe was from the central, precentral, and anterior parietal branches that arose predominantly from the superior trunk of the middle cerebral artery. The medial surface and the superior third of the lateral surface were supplied by the posterior interior frontal, paracentral, and superior parietal branches of the pericallosal and callosomarginal arteries. The venous drainage of the superior two-thirds of the lateral surface and the central lobe on the medial surface was predominantly through the superior sagittal sinus, and the inferior third of the lateral surface was predominantly through the superficial sylvian veins to the sphenoparietal sinus or the vein of Labbé to the transverse sinus.

CONCLUSIONS

The pre- and postcentral gyri and paracentral lobule have a morphological and functional anatomy that differentiates them from the remainder of their respective lobes and are considered by many as a single lobe. An understanding of the anatomical relationships of the central lobe can be useful in preoperative planning and in establishing reliable intraoperative landmarks.

Morphometry, asymmetry and variations of cerebral sulci on superolateral surface of cerebrum in autopsy cases

BACKGROUND

The cerebral sulci are known as main microanatomical borders that serve as a gateway and surgical passage to reach the ventricles or to the deeper lesions. It is a matter of curiosity that whether there is a convergence between the morphological asymmetry and the functional asymmetry, and also its significance in surgery. The aim of this study is make morphometric measurements and evaluate asymmetry of several sulci on the lateral aspects of the cerebrum in regard to main sulci and related reference key points.

METHODS

A total of 100 cerebral hemispheres from 50 autopsy cadavers were examined. The lengths of several sulci on the superolateral aspect of the hemispheres and the distances between the sulci and nearby sulci and the reference key points were measured. Encountered variations were examined and photographed.

RESULTS

Evaluation of the variations: superior frontal sulcus (SFS), inferior frontal sulcus, superior temporal sulcus (STS), precentral sulcus and postcentral sulcus were found to be discontinuous in 60, 46, 41, 84 and 70 % of the hemispheres, respectively. Evaluation of the asymmetry: the distances between SFS posterior end and longitudinal fissure, STS posterior end and lateral sulcus posterior end, as well as lengths of external occipital fissure (EOF), and discontinuous course of STS were significantly different between left and right hemispheres.

CONCLUSIONS

There is usually a morphological partial asymmetry between the right and left hemispheres for any individual. Also, some of our measurements were found to be compatible with the ones in the literature, while others were incompatible.

Neurovascular structures adjacent to the lumbar intervertebral discs: an anatomical study of their morphometry and relationships

Object

Although infrequent, injury to adjacent neurovascular structures during posterior approaches to lumbar intervertebral discs can occur. A detailed anatomical knowledge of relationships may decrease surgical complications.

Methods

Ten formalin-fixed male cadavers were used for this study. Posterior exposure of the lumbar thecal sac, nerve roots, pedicles, and intervertebral discs was performed. To identify retroperitoneal structures at risk during posterior lumbar discectomy, a transabdominal retroperitoneal approach was performed, and observations were made. The distances between the posterior and anterior edges of the lumbar intervertebral discs were measured, and the relationships between the disc space, pedicle, and nerve root were evaluated.

Results

For right and left sides, the mean distance from the inferior pedicle to the disc gradually increased from L1–2 to L4–5 (range 2.7–3.8 mm and 2.9–4.5 mm for right and left side, respectively) and slightly decreased at L5–S1. For right and left sides, the mean distance from the superior pedicle to the disc was more or less the same for all disc spaces (range 9.3–11.6 mm and 8.2–10.5 mm for right and left, respectively). The right and left mean disc-to-root distance for the L3–4 to L5–S1 levels ranged from 8.3 to 22.1 mm and 7.2 to 20.6 mm, respectively. The root origin gradually increased from L-1 to L-5. The right and left nerve root–to-disc angle gradually decreased from L-3 to S-1 (range 105°–110.6° and 99°–108°). Disc heights gradually increased from L1–2 to L5–S1 (range 11.3–17.4 mm). The mean distance between the anterior and posterior borders of the intervertebral discs ranged from 39 to 46 mm for all levels.

Conclusions

To avoid neighboring neurovascular structures, instrumentation should not be inserted into the lumbar disc spaces more than 3 cm from their posterior edge. Accurate anatomical knowledge of the relationships of intervertebral discs to nerve roots is needed for spine surgeons.