Individual variation of tentorial notch morphometry in a series of neurocritical patients

ABSTRACT Background: Cadaveric studies on humans have shown anatomical variabilities in the morphometric characteristics of the tentorial notch. These anatomical variations could influence the worsening of neurocritical patients. Objectives: 1) To investigate the morphometric characteristics of the tentorial notch in neurocritical patients using computed tomography (CT); 2) To investigate the correlation between tentorial notch measurements by CT and by magnetic resonance imaging (MRI); and 3) To analyze the individual variability of the tentorial notch anatomy seen in neurocritical patients. Methods: Prospective series of neurocritical patients was examined. An imaging protocol for measurements was designed for CT and MRI. The level of the agreement of the measurements from CT and MR images was established. According to the measurements found, patients were divided into different types of tentorial notch. Results: We studied 34 neurocritical patients by CT and MRI. Measurements of the tentorial notch via CT and MRI showed significant agreement: concordance correlation coefficient of 0.96 for notch length and 0.85 for maximum width of tentorial notch. Classification of tentorial notch measurements according to the criteria established by Adler and Milhorat, we found the following: 15 patients (58%) corresponded to a "short" subtype; 7 (21%) to "small"; 3 (9%) to "narrow"; 2 (6%) to "wide"; 2 (6%) to “large”; 1 (3%) to “long”; and 4 (12%) to "typical". Conclusions: The anatomical variability of the tentorial notch could be detected in vivo by means of CT scan and MRI. Good agreement between the measurements made using these two imaging methods was found.

Surgical Management of Tentorial Notch Meningioma Guided by Further Classification: A Consecutive Study of 53 Clinical Cases

BackgroundManagement of tentorial notch meningiomas (TNM) remains a challenge for neurosurgeons. We demonstrate the clinical characteristics and surgical experiences of TNM based on our cases according to a proposed further classification.MethodsWe retrospectively analyzed clinical and follow-up data in a consecutive series of 53 TNM patients who underwent microsurgical operation from 2011 to 2019 in our institution. The operations were performed using various approaches. Clinical history, preoperative and postoperative neurofunction, imaging results, and surgical outcomes were collected for further classification of TNM.ResultsAll TNM cases were divided into anterior (T1), middle (T2), and posterior notch (T3). According to the direction of tumor extension and correlation with the neurovascular structures, detailed subtypes of anterior TNMs were identified as the central (T1a), posterior (T1b), and medial type (T1c). The middle TNMs were divided into the infratentorial (T2a), supratentorial (T2b), and supra-infratentorial type (T2c). The posterior TNMs were divided into superior (T3a), inferior (T3b), lateral (T3c), and straight sinus type (T3d) in reference to Bassiouni’s classification. Total removal of the tumor was achieved in 46 cases, with five cases of subtotal and two cases of partial removal without any recorded deaths in our series. In total, five subtotal resected cases underwent gamma-knife treatment and achieved stable disease. Postoperative aggravation or new onset cranial nerve dysfunction occurred in some individual cases, with incidences ranging from 3.77 to 15.10% and improved preoperative neurological deficits ranging from 0 to 100%.ConclusionFurther, TNM classification based on the intracranial location, extension direction, relationship with brainstem, and neurovascular structures guides preoperative evaluation, rational surgical approach selection, and surgical strategy formulation. Taking microsurgery as the main body, a satisfactory outcome of TNM treatment can be achieved for complicated tumors by combining stereotactic radiotherapy. This study demonstrates the surgical outcomes and complications in detail. Further classification might be helpful for treatment decisions in the future.

The Tentorial Notch: Morphometric Analysis and its Clinical Relevance to Neurosurgery

Introduction: The tentorial aperture is a complex space that varies considerably in size and shape. Although this space is defined by the free edges of the tentorium cerebelli, it has remained anatomically elusive. Modern neuroimaging methods routinely provide images of the tentorial notch but the literature so far available is remarkably devoid of extensive observations on the different types of tentorial notches. Dimensions of tentorial notch may determine the clinical sequelae and prognosis of many neurological conditions. Aim: To analyse the anatomical variations of tentorial notch, elucidating its clinical relevance in neurosurgery. Materials and Methods: A descriptive cross-sectional study was performed from August 2010-January2012. The midbrain was sectioned in an axial plane following the contour of the tentorial edge during medico-legal autopsies in 40 adult human cadavers, age ranging from 20 to 65 years. The parameters measured were: 1) Anterior Notch Width (ANW), the width of tentorial notch through the posterior aspect of the dorsum sellae; 2) Maximum Notch Width (MNW), the maximum width of the tentorial notch in axial plane; 3) Notch Length (NL), the distance between posterosuperior edge of the dorsum sellae in the mid-plane and the apex of notch; 4) Interpedunculoclival (IC) distance, the distance from the interpeduncular fossa to the posterosuperior edge of the dorsum sellae; 5) Apicotectal (AT) distance, the distance between the tectum of midbrain in the mid-plane and the apex of tentorial notch. The data obtained was analysed using Statistical Package for the Social Sciences (SPSS) version 21.0. Results: The quartile groups defined by MNW (mean 29.77±2.26 mm) were labeled as narrow, midrange and wide. Quartile groups defined by NL (mean 57.98±4.52 mm) were labeled as short, midrange and long. By combining these six groups into matrix formation, tentorial notches were classified into eight types. Applying quartile distribution technique to IC (mean 21.21±3.72 mm), brainstem positions within the tentorial notch were labeled as prefixed, midposition and postfixed. Conclusion: Variations in the dimensions of tentorial aperture may be implicated in the different clinical presentations related to transtentorial herniation, concussion and acceleration-deceleration injuries. The results of the present study provide a baseline data about tentorial notch which may facilitate neurosurgical decision making.

A Study to Analyze the Tentorial Incisura in Indian Population, for Racial Differences and Its Impact in the Outcome of Patients with Head Injury

Aim To measure the size of tentorial notch in Indian population, compare it with the western population from the literature available, and analyze the relation between size of tentorial notch and the outcome in patients with head injury. Materials and Methods The study was done using 10 cadavers and 15 autopsy specimens. In all the specimens, tentorial incisura was measured using vernier caliper after opening the skull and cutting the midbrain at the level of tentorial edge carefully without damaging the tentorium. All measurements were done in millimeters. Results Mean values, age-dependent mean values, and percentile values were calculated for various parameters in the tentorial incisura. Majority of the tentorial incisura are of typical type. Cases of tentorial incisura are significantly smaller in the age group of 20 to 25 years. Rate of deterioration of Glasgow coma scale (GCS) is rapid when the tentorial incisura is large. Conclusion There were no significant variations in measurements of tentorial incisura in Indian population compared with the western population. Rate of deterioration of GCS is higher in patients who had large tentorial incisura compared with other groups, which is statistically significance. However, this is to be confirmed by further study using large groups of patients to be used for clinical applications.

Subtemporal approach for distal basilar occlusion for giant aneurysm. Nuances and advantages of the subtemporal approach

We described the subtemporal approach, which was used for distal basilar artery occlusion in a patient with a symptomatic giant unclippable aneurysm. We discuss issues related to positioning and lumbar drainage. We illustrate the basic steps: identification of the tentorial notch; sharp opening of the arachnoid behind the third nerve; placement of a fixed mechanical retractor to “hold” the brain; identification of the third nerve and mobilization from arachnoid attachments; identification of the course and insertion of the fourth nerve; division and retraction of the tentorial edge to enhance exposure; preparation of the “perforator-free zone”; and final clip application followed by ICG fluorescein angiography. We show some of the areas exposed with this approach.The video can be found here: http://youtu.be/S_NLIjKQL_o.

Microsurgical anatomy of the mesencephalic veins

Object The mesencephalic veins drain crucial brainstem areas. Due to the narrowness of the tentorial notch, these veins can become obstructed as a result of herniation or surgery, leading to hemorrhage and severe consequences for the patient. There is little in the literature about the mesencephalic veins. The aim of this study was to perform an exact analysis of their microanatomy. Methods Fifty-two cadaveric hemispheres were examined under an operating microscope, and measurements were made with a digital caliper. The authors focused on the basal vein (BV), pontomesencephalic vein (PMV), peduncular vein (PV), lateral mesencephalic vein (LMV), and other smaller veins. The PMV was identified in 84.6% of specimens (mean diameter 0.54 mm); the PV, in 86.5% (mean diameter 0.86 mm); and the LMV, in 100% (mean diameter 1.07 mm). Four types of LMV were identified on the basis of the vein's course. Other smaller veins were also differentiated according to whether they drained mainly the cerebral peduncle, the lemniscal trigone, or the tectum. These veins and their junctions with other veins were depicted. Conclusions A thorough understanding of the microanatomy of the mesencephalic veins is crucial in brainstem surgery in order to avoid brain damage due to venous infarction and subsequent edema. Because knowledge of the course, variations, and outflow system of these veins could improve surgical outcome, they warrant special attention during surgery.

Subtemporal Approach To The Tentorial Incisura: Normative Morphometric Data Based On Magnetic Resonance Imaging Scans

OBJECTIVE: The tentorial notch can be contained within a transversal line made in front of the cerebral peduncles and another line through the posterior border of the quadrigeminal plate into the anterior, middle and posterior parts. Different approaches to the tentorial incisura have been established. The subtemporal approach represents one of those options. Since morphometrical analyses of this approach in this region have not yet been performed, the aim of the present study was to measure the surgical corridor along these borders. METHODS: Fifty-three magnetization prepared rapid acquisition gradient echo-sequences of individual brains without pathological lesions were analyzed. For this study, an axial section along the pontomesencephalic sulcus and two coronal sections along the above-described borders were measured using a program specially written by one of the coauthors to obtain various parameters. A triangle circumscribing the surgical corridor was delimited by exactly defined anatomic landmarks for the coronal section, and the depths of the temporal lobe at the incisural borders were measured for the axial section. RESULTS: Various data are given concerning the surgical corridor of a subtemporal approach to the tentorial incisura. The different shapes of this corridor to the incisural region were recorded. According to our measurements, four different types of the temporal lobe could be differentiated. CONCLUSION: Knowledge of these distances and various contours of the path is crucial to avoid brain damage during retraction or manipulation. The curvature of the floor of the middle cranial fossa is highly variable and thus determines the surgical path chosen.

The tentorial notch: anatomical variation, morphometric analysis, and classification in 100 human autopsy cases

Object. Variations in the structure of the tentorial notch may influence the degree of brainstem distortion in transtentorial herniation, concussion, and acceleration—deceleration injuries. The authors examined the anatomical relationships of the mesencephalon, cerebellum, and oculomotor nerves to the dimensions of the tentorial aperture. On the basis of numerical data collected from this study, the authors have developed the first classification system of the tentorial notch and present new neuroanatomical observations pertaining to the subarachnoid third cranial nerve and the brainstem. Methods. The mesencephalon was sectioned at the level of the tentorial edge in 100 human autopsy cases (specimens from 23 female and 77 male cadavers with a mean age at time of death of 42.5 years [range 18–80 years]). The following measurements were determined: 1) anterior notch width, the width of the tentorial notch in the axial plane through the posterior aspect of the dorsum sellae; 2) maximum notch width (MNW), the maximum width of the notch in the axial plane; 3) notch length (NL), the length of the tentorial notch from the superoposterior edge of the dorsum sellae to the apex of the notch; 4) posterior tentorial length, the shortest distance between the apex of the notch and the most anterior part of the confluence of the sinuses; 5) interpedunculoclival (IC) distance, the distance from the interpeduncular fossa to the superoposterior edge of the dorsum sellae; 6) apicotectal (AT) distance, the distance from the tectum in the median plane to a perpendicular line dropped from the apex of the tentorial notch to the cerebellum; 7) cisternal third nerve distance, the distance covered by the cisternal portion of the third cranial nerve; and 8) inter—third nerve angle, the angle between the two third cranial nerves. The quartile distribution technique was applied to all measurements. Mean values are presented as the means ± standard deviations. Quartile groups defined by NL (mean 57.7 ± 5.6 mm) were labeled long, short, and midrange, and those defined by MNW (mean 29.6 ± 3 mm) were labeled wide, narrow, and midrange. Combining these groups into a matrix formation resulted in the classification of the tentorial notch into the following eight types: 1) narrow (15% of specimens); 2) wide (12% of specimens); 3) short (8% of specimens); 4) long (15% of specimens); 5) typical (24% of specimens); 6) large (9% of specimens); 7) small (10% of specimens); and 8) mixed (7% of specimens). The IC distance (mean 20.4 ± 3.2 mm) was used to characterize brainstem position as prefixed (28% of specimens), postfixed (36% of specimens), or midposition (36% of specimens). The IC distance was correlated with the left and right cisternal third nerve distances (means 26.7 ± 2.9 mm and 26.1 ± 3.2 mm, respectively) and the inter—third nerve angle (mean 57.3 ± 7.3°). The exposed cerebellar parenchyma within the notch, the relationship between the brainstem and tentorial edge, and the brainstem position varied considerably among individuals. The cisternal third nerve distance, its trajectory, and its anatomical relation to the skull base also varied widely. Two anatomically distinct segments of the subarachnoid third cranial nerves were characterized with respect to the skull base as suspended and supported segments. Conclusions. The authors present a new classification system for the tentorial aperture to help explain variations in herniation syndromes in patients with otherwise similar intracranial pathological conditions, and responses to concussive and acceleration—deceleration injuries. The authors present observations not previously described regarding the position of the brainstem within the tentorial aperture and the cisternal portion of the third cranial nerves. A significant statistical correlation was discovered among specific morphometric parameters of the tentorial notch, brainstem, and oculomotor nerves. These findings may have neurosurgical implications in clinical situations that cause brainstem distortion. Additionally, this analysis provides baseline data for interpreting magnetic resonance and computerized tomography images of the tentorial notch and its regional anatomy.

Meningiomas of the tentorial notch: surgical anatomy and management

✓ Twenty-five meningiomas located at the tentorial notch were surgically treated between 1978 and 1993 at the Neurosurgical Department of Nordstadt Hospital in Hannover, Germany. Nineteen meningiomas were classified as originating from the lateral tentorial incisura (Group I) and six were from the posteromedial tentorial incisura (Group II). Clinically, the most common symptom was trigeminal neuralgia, followed by headache. Neuroradiologically, 64% of the meningiomas were larger than 30 × 30 mm. Further evaluation revealed signs of brainstem compression in 88% of the patients. Radical surgical removal (Simpson I and II) was achieved in 88% of the cases. There was no mortality. Follow up revealed that 80% of patients were able to return to their premorbid activity. Surgical approaches to the tentorial notch included the suboccipital retrosigmoidal or the combined subtemporal—presigmoidal approach for Group I tentorial notch meningiomas; and the supracerebellar—infratentorial or the suboccipital—transtentorial approaches for Group II meningiomas. Because the best surgical approach to the tentorial incisura is still a matter of debate, the anatomy of the tentorial incisura, the clinical presentation of the patients, diagnostic indications, surgical findings, and follow up are discussed, with reference to the literature.

Removal of the roof of the external auditory meatus in approaching the tentorial notch through a low temporal craniotomy

✓ Improved access to the tentorial notch can be obtained by removal of the roof of the external auditory meatus in association with a low temporal craniotomy. This approach decreases temporal lobe retraction and the risk of venous infarction. This method was perfected in the surgical laboratory on five cadavers and was successfully performed in a patient with a giant aneurysm of the posterior cerebral artery.