The tentorial notch and complications produced by herniations of the brain through that aperture

Kernohan-Woltman notch phenomenon: an exceptional neurological picture?

INTRODUCTION

Ipsilateral hemiparesis (IH) can be defined as a paradoxical dysfunction of the first motor neuron involving the extremities on the opposite side to that expected, given the location of the triggering intracranial pathology. Compression of the corticospinal tract (CSt) along its course through the contralateral cerebral peduncle against the free edge of the tentorium, known as the Kernohan-Woltman notch phenomenon (KWNP), represents the main cause of IH.

METHODS

This retrospective study analyses a series of 12 patients diagnosed with IH secondary to KWNP treated at our institution, including a descriptive study of epidemiological, clinical, radiological, neurophysiological, and prognostic variables.

RESULTS

In 75% of the cases, symptoms had an acute or subacute onset. Initial imaging studies showed signs of significant mass effect in half of the patients, whereas magnetic resonance imaging (MRI) identified a structural lesion in the contralateral cerebral peduncle in two thirds of them. Impairment of the motor evoked potentials (MEP) was verified in 4 patients. During follow-up 7 patients experienced improvement in motor activity, and near half of the cases were classified in the first three categories of the modified Rankin scale.

CONCLUSIONS

In contrast to prior historical series, most of our patients developed a KWNP secondary to a traumatic mechanism. MRI represents the optimal method to identify both the classic cerebral peduncle notch and the underlying structural lesion of the CSt. The use of MEP can help to establish the diagnosis, especially in those cases lacking definite radiological findings.

Anisocoria and mydriasis after scalp nerve block: a case report

Strategies for the assessment of abnormal neurological findings during general anesthesia are limited. However, pupil abnormalities may represent serious neurological complications. We herein present a case of new-onset anisocoria and mydriasis that developed after scalp nerve block. The patient's signs were possibly related to increased intracranial pressure with resulting brain shift that ultimately affected the oculomotor nerves. A 45-year-old man was scheduled for left cerebellar tumor resection and ventricular drainage surgery; however, anisocoria and left pupillary mydriasis were observed after induction of general anesthesia and performance of scalp nerve block. After reducing the intracranial pressure, the right pupil showed constriction (1 mm) but the left pupil was dilated (5 mm). The pupils were of similar size postoperatively. Although pupillary dilation during general anesthesia has been previously described, this is the first case in which the mydriasis was considered to have been caused by brain shift due to increased intracranial pressure after scalp nerve block. Thus, we propose this phenomenon as a new possible cause of pupillary changes. Actively monitoring this presentation intraoperatively could enable early detection of and intervention for complications, therefore improving the prognosis.

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

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.

Surface reconstruction from routine CT-scan shows large anatomical variations of falx cerebri and tentorium cerebelli

BACKGROUND

Finite element modeling of the human head offers an alternative to experimental methods in understanding the biomechanical response of the head in trauma brain injuries. Falx, tentorium, and their notches are important structures surrounding the brain, and data about their anatomical variations are sparse.

OBJECTIVE

To describe and quantify anatomical variations of falx cerebri, tentorium cerebelli, and their notches.

METHODS

3D reconstruction of falx and tentorium was performed by points identification on 40 brain CT-scans in a tailored Matlab program. A scatter plot was obtained for each subject, and 8 anatomical landmarks were selected. A reference frame was defined to determine the coordinates of landmarks. Segments and areas were computed. A reproducibility study was done.

RESULTS

The height of falx was 34.9 ± 3.9 mm and its surface area 56.5 ± 7.7 cm². The width of tentorium was 99.64 ± 4.79 mm and its surface area 57.6 ± 5.8 cm². The mean length, height, and surface area of falx notch were respectively 96.9 ± 8 mm, 41.8 ± 5.9 mm, and 28.8 ± 5.8 cm² (range 15.8-40.5 cm²). The anterior and maximal widths of tentorial notch were 25.5 ± 3.5 mm and 30.9 ± 2.5 mm; its length 54.9 ± 5.2 mm and its surface area 13.26 ± 1.6 cm². The length of falx notch correlated with the length of tentorial notch (r = 0.62, P < 0.05).

CONCLUSION

We observe large anatomical variations of falx, tentorium, and notches, crucial to better understand the biomechanics of brain injury, in personalized finite element models.

Contralateral pupillary dilatation and hemiparesis: Kernohan’s notch revisited

Intracranial mass lesions can lead to transtentorial uncal herniation, and pupillary asymmetry is a well-recognized sign of impending cerebral herniation. Impending uncal herniation can lead to ipsilateral, bilateral, or uncommonly the contralateral pupillary dilatation. We report a case of a 22-year old, who had contralateral pupillary dilatation due to expanding intracranial mass lesion and recovered well after neurosurgical intervention. This case illustrates contralateral pupillary dilatation (“false-localizing” sign) in a sub-group of patients, and if untreated and ICP continues to rise, this is followed by ipsilateral pupil dilatation.

Kernohan-Woltman Notch Phenomenon Caused by Acute Traumatic Subdural Haematoma

A 27-year-old man suffered from right hemiparesis after a closed head injury. Computed tomography (CT) revealed a right hemisphere subdural haematoma with midline structure shifted to the left. The CT finding was believed to be mislabeled because the site of haematoma did not correlate with an ipsilateral hemiparesis. Magnetic resonance imaging revealed a right transtentorial uncal herniation and a small lesion within left cerebral peduncle, suggesting Kernohan-Woltman notch phenomenon (KWNP). KWNP has been rarely seen in patients with acute traumatic subdural haemorrhage. Anatomical small maximum tentorial notch width is the possible anatomical factor predisposing our patient to this phenomenon. (Hong Kong j.emerg.med. 2014;21:116-119)

Brainstem Monitoring in the Neurocritical Care Unit: A Rationale for Real-Time, Automated Neurophysiological Monitoring

Patients with severe traumatic brain injury or large intracranial space-occupying lesions (spontaneous cerebral hemorrhage, infarction, or tumor) commonly present to the neurocritical care unit with an altered mental status. Many experience progressive stupor and coma from mass effects and transtentorial brain herniation compromising the ascending arousal (reticular activating) system. Yet, little progress has been made in the practicality of bedside, noninvasive, real-time, automated, neurophysiological brainstem, or cerebral hemispheric monitoring. In this critical review, we discuss the ascending arousal system, brain herniation, and shortcomings of our current management including the neurological exam, intracranial pressure monitoring, and neuroimaging. We present a rationale for the development of nurse-friendly-continuous, automated, and alarmed-evoked potential monitoring, based upon the clinical and experimental literature, advances in the prognostication of cerebral anoxia, and intraoperative neurophysiological monitoring.

Reconsidering the logic of World Federation of Neurosurgical Societies grading in patients with severe subarachnoid hemorrhage

OBJECT

Current data show a favorable outcome in up to 50% of patients with World Federation of Neurosurgical Societies (WFNS) Grade V subarachnoid hemorrhage (SAH) and a rather poor prediction of worst cases. Thus, the usefulness of the current WFNS grading system for identifying the worst scenarios for clinical studies and for making treatment decisions is limited. One reason for this lack of differentiation is the use of “negative” or “silent” diagnostic signs as part of the WFNS Grade V definition. The authors therefore reevaluated the WFNS scale by using “positive” clinical signs and the logic of the Glasgow Coma Scale as a progressive herniation score.

METHODS

The authors performed a retrospective analysis of 182 patients with SAH who had poor grades on the WFNS scale. Patients were graded according to the original WFNS scale and additionally according to a modified classification, the WFNS herniation (hWFNS) scale (Grade IV, no clinical signs of herniation; Grade V, clinical signs of herniation). The prediction of poor outcome was compared between these two grading systems.

RESULTS

The positive predictive values of Grade V for poor outcome were 74.3% (OR 3.79, 95% CI 1.94–7.54) for WFNS Grade V and 85.7% (OR 8.27, 95% CI 3.78–19.47) for hWFNS Grade V. With respect to mortality, the positive predictive values were 68.3% (OR 3.9, 95% CI 2.01–7.69) for WFNS Grade V and 77.9% (OR 6.22, 95% CI 3.07–13.14) for hWFNS Grade V.

CONCLUSIONS

Limiting WFNS Grade V to the positive clinical signs of the Glasgow Coma Scale such as flexion, extension, and pupillary abnormalities instead of including “no motor response” increases the prediction of mortality and poor outcome in patients with severe SAH.

From the notch to a glioma grading system: the neurological contributions of James Watson Kernohan

During his lifetime and a career spanning 42 years, James Watson Kernohan made numerous contributions to neuropathology, neurology, and neurosurgery. One of these, the phenomenon of ipsilateral, false localizing signs caused by compression of the contralateral cerebral peduncle against the tentorial edge, has widely become known as "Kernohan's notch" and continues to bear his name. The other is a grading system for gliomas from a neurosurgical viewpoint that continues to be relevant for grading of glial tumors 60 years after its introduction. In this paper, the authors analyze these two major contributions in detail within the context of Kernohan's career and explore how they contributed to the development of neurosurgical procedures.

Anatomy of the pineal region applied to its surgical approach

INTRODUCTION

The pineal region is situated in the posterior part of the incisural space. This region includes the pineal body inside the quadrigeminal arachnoidal cistern. This article reviews the anatomic features of this region, with particular emphasis on those aspects of importance for surgical access to the pineal region.

MATERIAL & METHODS

Five cadaver heads fixed in 10% formalin and injected with colored latex were used for anatomic dissection (five other specimens were also prepared and dissected to illustrate the articles on surgical techniques and approaches presented elsewhere in this issue).

RESULTS

The pineal body is surrounded by several important structures such as: posterior part of the third ventricle, tectum, the complex of the great cerebral vein of Galen, pulvinar nuclei of the thalamus and splenium of corpus callosum.

CONCLUSION

The surgical approach of the pineal body, whatever the route or the technique used (microsurgical, endoscopic or stereotactic), creates a great challenge for the neurosurgeons due to its location in the deep part of the brain and its close relationships with complex surrounded vascular structures.

Kernohan-Woltman notch phenomenon caused by an acute subdural hematoma

Uncal herniation through the tentorial notch is occasionally associated with false localizing ipsilateral hemiparesis, known as the Kernohan-Woltman notch phenomenon (KWNP). We report an 81-year-old female who presented with a decreased level of consciousness, a right mydriasis and an ipsilateral motor deficit caused by a large right hemispheric subdural hematoma that was immediately evacuated. The patient recovered well, although her right hemiplegia persisted. A follow-up MRI showed a residual lesion in the left cerebral peduncle, corresponding to KWNP. The presence of such a structural lesion suggests a poor prognosis for recovery from the initial motor deficit.

Paradoxical fixed dilatation of the contralateral pupil as a false-localizing sign in intraparenchymal frontal hemorrhage

Unilateral fixed pupillary dilatation represents an important clinical sign of transtentorial herniation of an ipsilateral mass lesion. Rarely the contralateral pupil is affected to produce a false-localizing sign. Two cases of this paradoxical contralateral fixed pupillary dilatation involving intra-axial lesions have been reported. We report a case of a 33-year-old man with a left frontal intraparenchymal hemorrhage who developed a false localizing fixed dilatation of his right pupil, which resolved after craniotomy and evacuation of the clot. The possible mechanisms of contralateral third nerve palsy are discussed.

Isolated hypoplasia of the tentorium

Developmental defects of the tentorium represent a spectrum of disease with small defects and apertures that have little clinical significance on one end and hypoplasia or aplasia on the other. The latter is associated with serious central nervous system malformations, it is seldom isolated, and aside from the 3 cases described below, there have only been 2 case reports published on isolated hypoplasia. This condition is important to recognize so as to avoid unnecessary investigations and interventions.

Microsurgical anatomy of the great cerebral vein of Galen and its tributaries

Object. The deep cerebral veins may pose a major obstacle in operative approaches to deep-seated lesions, especially in the pineal region where multiple veins converge on the great cerebral vein of Galen. Because undesirable sequelae may occur from such surgery, the number of veins and branches to be sacrificed during these approaches should kept to a minimum. The purpose of this study was to examine venous drainage into the vein of Galen with a view to surgical approaches. If a vein hampering surgical access must be sacrificed, it can therefore be selected according to the smallest draining territory.

Methods. The deep cerebral veins and their surrounding neural structures were examined in 50 cerebral hemispheres from 25 adult cadavers in which the arteries and veins had been perfused with red and blue silicone, respectively. Special consideration was given to the size and location of drainage of the vein of Galen and its tributaries.

Conclusions. When a surgeon approaches the pineal region, several veins may hamper the access route. From posterior to anterior, these include the following: the superior vermian and the precentral or superior cerebellar veins, which drain into the posteroinferior aspect of the vein of Galen; and the tectal and pineal veins, which drain into its anterosuperior aspect. The internal occipital vein is the main vessel draining into the lateral aspect of the vein of Galen. It may be joined by the posterior pericallosal vein, and in that case has an extensive territory. To avoid intraoperative venous infarction, it is important to use angiography to determine the venous organization before surgery and to estimate the permeability and size of the branches of the deep venous system.

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 degrees). 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.

Imaging of acquired cerebral herniations

The consequences of cerebral herniation are compression of the brain, cranial nerves, and blood vessels that may result in serious neurologic morbidity, coma, and even death. A thorough understanding of the various patterns of cerebral herniation is essential, and it is important to remember that many of these patterns of herniation overlap. CT and MR imaging are effective at establishing the diagnosis of cerebral herniation, which will guide important decisions regarding therapeutic options and prognosis.

Unilateral fixed dilation of the pupil as a false-localizing sign with intracranial hemorrhage: case report and literature review

OBJECTIVE AND IMPORTANCE

Although other focal signs may prove "false localizing," it is a neurosurgical axiom that unilateral fixed dilation of the pupil occurs ipsilateral to a supratentorial mass.

CLINICAL PRESENTATION

A 25-year-old man collapsed with a dense right hemiplegia and a Glasgow Coma Scale score of 6 (eye opening, 1; motor, 4; verbal, 1) after rupture of a left middle cerebral artery aneurysm associated with an intrasylvian hematoma. Initially, both pupils had remained equal-sized and reactive: however, within hours, the right (contralateral) pupil became fixed and dilated (i.e., false localizing). For some time, the left (ipsilateral) pupil remained small and reactive; at emergency craniotomy, this also became fixed and equally dilated.

INTERVENTION

After evacuation of the clot and wrapping of the aneurysm, both pupils rapidly became equal-sized and reactive. Twenty-four hours later, concurrent with massive left hemispheric swelling and a midline shift, the left (ipsilateral) pupil became unilaterally fixed and dilated (i.e., false localizing). Eventually, the right (contralateral) pupil also became fixed and dilated, concurrent with cardiovascular collapse. Death occurred within 10 hours.

CONCLUSION

Unilateral fixed dilation of the pupil in patients with hemispheric mass lesions may be false localizing. Furthermore, disparate "herniating mechanisms" can arise despite mass effect emanating from the same side. Because such mechanisms cannot be witnessed, their nature remains speculative. An extensive review is contained in this article.

New frontiers in diagnostic imaging in concussive head injury

Concussed athletes may have documented incapacitating postconcussive symptoms, neuropsychological deficits, and consequent important changes in their lives and sport, yet the majority of neuroimaging attempts reveal few findings to account for these signs and symptoms. In this paper, we explore new techniques in the neuroimaging of concussion including diffusion-weighted magnetic resonance imaging and functional brain imaging technology.

Brain herniation: a revision of classical concepts

This paper is an update on evolving ideas about brain herniations. Following observations on cerebellar pressure coning that raised doubts about its reputed lethal connotations, herniation at the tentorium was re-examined for its role in critically damaging the brain stem. Combining clinical, pathologic, computed tomography and magnetic resonance imaging data, it is concluded that temporal lobe herniation is not the means by which the midbrain sustains irreversible damage in acute cases, but rather lateral displacement of the brain at the tentorium is the prime mover and herniation a harmless accompaniment. Transtentorial herniation has been investigated with computed tomography using the three calcification relationship and descent through the tentorial opening could not be documented. Bilateral brain stem compression in acute bilateral cases must be distinguished from herniation. Upward cerebellar herniation is only the sign of an overfull posterior fossa. Subfalcial herniation is tolerated unless lateral displacement is excessive.

Initial enlargement of the opposite pupil as a false localising sign in intraparenchymal frontal haemorrhage

Ipsilateral third nerve palsy with early pupillary enlargement is an important sign of transtentorial herniation from a supratentorial mass lesion. A case of frontal, intraparenchymal haemorrhage is reported in which the first ocular manifestation of transtentorial herniation was enlargement of the contralateral pupil. The ipsilateral pupil dilated only after complete oculomotor palsy of the contralateral eye. After partial frontal lobectomy and removal of blood clot, the ipsilateral third nerve recovered before the contralateral third nerve. Clinical findings localised the contralateral third nerve lesion to an extra-axial site. The possible mechanisms of contralateral third nerve compression are discussed. This seems to be the first example of pupillary enlargement as a false localising sign from a contralateral, supratentorial, intraparenchymal mass lesion.

Magnetic resonance imaging assessment of brainstem distortion associated with a supratentorial mass

Quantitative measurements of brainstem distortion and neural dysfunction were obtained in 25 cases of chronic subdural haematoma. The horizontal and rotational brainstem displacements were measured on axial and coronal MRI in all patients pre-operatively, and brainstem auditory evoked responses (BAERs) were obtained in 11 cases. Logarithmic relationships were noted on both horizontal and rotational displacements of the brainstem and cerebrum. The type of shift changed in the rostro-caudal direction. In the axial plane, the cerebral hemisphere shifts and rotates, the midbrain shifts laterally with no rotation, and the pons shifts minimally but rotates moderately. In the coronal plane, the marked rotation of the cerebral hemisphere and moderate rotation of the brainstem result in midbrain kinking, suggesting a downward displacement of the midbrain. The prolongation of BAER latencies and central conduction times correlated with septum shift. The results of peak-V latency indicated that brainstem rotation in the coronal plane reflects upper brainstem dysfunction most closely. This study presents objective measurements of brainstem displacement shown on MRI, and clarifies the relationships between anatomical and physiological changes in the brainstem that are associated with supratentorial lesions.

Measurement of local directional pressures in the brain with mass

In order to understand the effects and the direction of pressure transmitted from a mass lesion through various brain structures, miniature strain gauges were inserted in different brain locations in eight anesthetized monkeys. Mass lesions were created by inflating a balloon in either of two locations--subcortical in four animals (Group I) and deep (lateral to the caudate nucleus) in the other four animals (Group II). Anterior-posterior directed pressures were thus measured from a gauge placed in the parietal lobe, and lateromedially directed pressures (LM-dPs) were measured from gauges in the temporal lobe and midbrain. Intracranial pressure, systemic mean arterial pressure, and cerebral blood flow were also monitored. After balloon inflation was begun, temporal changes in pressure were recorded from gauges as percentage increase or decrease from baseline measurements. In both groups, balloon inflation caused a gradual increase in the parietal lobe anterior-posterior directed pressure with a concomitant increase in intracranial pressure and a decrease in cerebral blood flow. The temporal lobe gauge in Group I recorded an initial negative followed by a positive LM-dP with further balloon inflation. In Group II, this gauge recorded a positive LM-dP throughout. The midbrain gauges in both groups recorded an initial positive followed by a negative LM-dP. This reversal in the direction of pressure in the midbrain occurred just before the supratentorial pressure reached a peak and was noted to be concurrent with a sudden rise in mean arterial pressure and a decline in cerebral blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Topographic anatomy of preformed intracranial spaces

This article gives descriptions and measurements of the cerebral ventricles, especially our measurements of the interventricular foramen and the third ventricle. Included are measurements of previous and recent research. The results of endoscopic reviews of the lateral, third and fourth ventricles are also discussed. The subarachnoid spaces are described and illustrated by our corrosion casts. During endoscopic inspection of the subarachnoid spaces, the transcisternal veins are extremely vulnerable. Therefore, these veins in the anterior, middle and posterior cranial fossae are described.

Cortical blindness caused by acute general cerebral swelling

A 7-year-old girl who suffered from acute general cerebral swelling as a result of a traffic accident showed cortical blindness. Computed tomography (CT) scan on admission revealed marked slitlike ventricles and narrowing of the perimesencephalic cisterns, which indicated general cerebral swelling. While hospitalized, the patient developed transtentorial herniation twice on day 3, and CT scans at herniation episodes showed disappearance of the perimesencephalic cisterns. After recovery of consciousness, the patient showed cortical blindness, and during gradual recovery she showed pure alexia without agraphia. The visual evoked potentials at 8 weeks, 16 weeks, and 3 years 4 months after trauma showed normalization of the pattern, but revealed left occipital inactivity.

Transient blindness following intracranial pressure changes in a hydrocephalic child with a V-P shunt

A hydrocephalic child with a V-P shunt developed transient blindness following shunt revision. A year later, visual function deteriorated when shunt malfunction occurred. Following shunt revision, the child regained sight. The effects of intracranial hypertension and hypotension on the visual pathways are discussed.

Lateral displacement of the brain and level of consciousness in patients with an acute hemispheral mass

Brain-tissue shifts associated with drowsiness, stupor, and coma were studied by clinical examination and CT scanning in 24 patients with acute unilateral cerebral masses. Studies were performed soon after the appearance of the mass to detect the earliest CT changes associated with depression of consciousness. Contrary to traditional concepts, early depression of the level of alertness corresponded to distortion of the brain by horizontal displacement rather than transtentorial herniation with brain-stem compression. Horizontal displacement of the pineal body of 0 to 3 mm from the midline was associated with alertness, 3 to 4 mm with drowsiness, 6 to 8.5 mm with stupor, and 8 to 13 mm with coma. Moreover, drowsy or stuporous patients and some comatose patients had widened cisterns between the tentorial edge and the midbrain on the side of the mass, suggesting that the space was not filled by herniated medial temporal lobe. Downward displacement of the pineal body, indicating central transtentorial herniation, did not occur. Compression of one hemisphere by the other anteriorly (transfalcial herniation) was inconsistently related to alertness, though very large anterior displacements may have caused stupor in some patients. Current concepts of the pathoanatomical nature of depressed consciousness, based on pathological material obtained well after clinical examinations, may require revision, because they do not reflect early brain-tissue distortions.

Symmetrical thalamic low densities in descending transtentorial herniation

In a case with descending transtentorial herniation due to an acute subdural hematoma, symmetrical round low densities located bilaterally in the anterior thalamus are reported in addition to a diffuse low density in the territory of one posterior cerebral artery. The possible mechanism involved is discussed.

Microsurgical anatomy of the region of the tentorial incisura

The microsurgical anatomy of the tentorial incisura was evaluated in 25 adult cadavers using X 3 to X 40 magnification. The area surrounding the incisura is divided into the anterior, middle, and posterior incisural spaces. The anterior incisural space is located anterior to the brain stem and extends upward around the optic chiasm to the subcallosal area; the middle incisural space is located lateral to the brain stem and is intimately related to the hippocampal formation in the medial part of the temporal lobe; and the posterior incisural space is located posterior to the midbrain and corresponds to the region of the pineal gland and vein of Galen. The neural, cisternal, ventricular, and vascular relationships of each space were examined. The arterial relationships in the anterior incisural space and the venous relationships in the posterior incisural space are extremely complex, since the anterior incisural space contains all the components of the circle of Willis and the bifurcation of the internal carotid and basilar arteries, and the posterior incisural space contains the convergence of the internal cerebral and basal veins and many of their tributaries on the vein of Galen. The discussion reviews tentorial herniation and operative approaches to the incisura.

Secondary brain stem hemorrhage in stroke

The occurrence of secondary brain stem hemorrhage was studied in 435 autopsies from patients with recent cerebral hemorrhage, infarction or ruptured cerebral aneurysms. The frequency of secondary brain stem hemorrhage was found to be 45% in cerebral hemorrhage, 15% in cerebral infarction, and 36% in ruptured aneurysms. In the majority of cases the secondary brain stem hemorrhage occurred a few days after the onset of cerebral hemorrhage or infarction. Ruptured aneurysms showed a more widespread temporal distribution of secondary brain stem hemorrhage. The median survival time was 2 days in cases of cerebral hemorrhage, 4 days in ruptured aneurysm and 4 days in cerebral infarction. The frequency of secondary brain stem hemorrhage was significantly lower in patients younger than 20 years. No significant difference was found in its distribution between the sexes. Secondary occipital lobe infarction was present in 3.5% of the patients. It is concluded that secondary brain stem hemorrhage is a common major contribution to the cause of death in stroke.

Developmental defects of the tentorium cerebelli

✓ Congenital defects of the tentorium cerebelli were observed in 16 of 90 cadaver cranial cavities examined. These consisted of tentorial dural bands in two, a hole in one case, transverse ridges in eight cases, and an aperture in five cases. In one specimen, the trochlear nerve made a spiral turn around the tentorial band before pursuing its forward course.