Depth relationships and measures of tissue thickness in dorsal midbrain.

Dorsal human midbrain contains two nuclei with clear laminar organization, the superior and inferior colliculi. These nuclei extend in depth between the superficial dorsal surface of midbrain and a deep midbrain nucleus, the periaqueductal gray matter (PAG). The PAG, in turn, surrounds the cerebral aqueduct (CA). This study examined the use of two depth metrics to characterize depth and thickness relationships within dorsal midbrain using the superficial surface of midbrain and CA as references. The first utilized nearest-neighbor Euclidean distance from one reference surface, while the second used a level-set approach that combines signed distances from both reference surfaces. Both depth methods provided similar functional depth profiles generated by saccadic eye movements in a functional MRI task, confirming their efficacy for delineating depth for superficial functional activity. Next, the boundaries of the PAG were estimated using Euclidean distance together with elliptical fitting, indicating that the PAG can be readily characterized by a smooth surface surrounding PAG. Finally, we used the level-set approach to measure tissue depth between the superficial surface and the PAG, thus characterizing the variable thickness of the colliculi. Overall, this study demonstrates depth-mapping schemes for human midbrain that enables accurate segmentation of the PAG and consistent depth and thickness estimates of the superior and inferior colliculi.

Visualization of the cavum septi pellucidi, cavum Vergae, and cavum veli interpositi using magnetic resonance imaging.

PURPOSE: The morphology of the cavum septi pellucidi (CSP), cavum Vergae (CV), and cavum veli interpositi (CVI) has been infrequently explored with neuroimaging. The aim of the present study was to delineate these cavities using magnetic resonance (MR) imaging. METHODS: A total of 71 patients were enrolled in the present study. Following initial examinations with conventional MR sequences, constructive interference in steady-state (CISS) sequence was performed in the coronal and sagittal sections for 60 and 11 patients, respectively. RESULTS: The coronal CISS images at the level of the aqueduct showed two distinct morphologies of the CV roof, one formed by the fornices with varying degrees of conjugation and the other formed by the corpus callosum with completely separated fornices. Appearance of the CSP was classified into four distinct types. Furthermore, the CVI presented two distinct appearances. CONCLUSIONS: Typically, the CSP, CV, and CVI present with asymptomatic conditions with morphological variabilities. Visualization of the CSP, CV, and CVI using the CISS sequences may be useful when managing lesions affecting these cavities.

Franciscus Sylvius on Clinical Teaching, Iatrochemistry and Brain Anatomy.

Born in Hanau, Germany, in 1614, Franciscus (Dele Boë) Sylvius received his medical doctor diploma from Basel University in 1637 and became Professor of Practical Medicine at Leiden University in 1658. One of the founders of medical biochemistry, Sylvius was also an outstanding anatomopathologist, with contributions ranging from the first description of the pulmonary tubercles to that of the lateral fissure of the brain. Thanks to Sylvius, a gifted teacher and one of the greatest physicians of his time, Leiden became a major European medical training center. He died in 1772 after having served as Rector Magnificus at Leiden University.

Physical phantom of craniospinal hydrodynamics.

INTRODUCTION: Inside the craniospinal system, blood, and cerebrospinal fluid (CSF) interactions occurring through volume exchanges are still not well understood. We built a physical model of this global hydrodynamic system. The main objective was to study, in controlled conditions, CSF-blood interactions to better understand the phenomenon underlying pathogenesis of hydrocephalus. MATERIALS AND METHODS: A structure representing the cranium is connected to the spinal channel. The cranium is divided into compartments mimicking anatomical regions such as ventricles or aqueduct cerebri. Resistive and compliant characteristics of blood and CSF compartments can be assessed or measured using pressure and flow sensors incorporated in the model. An arterial blood flow input is generated by a programmable pump. Flows and pressures inside the system are simultaneously recorded. RESULTS: Preliminary results show that the model can mimic venous and CSF flows in response to arterial pressure input. Pulse waveforms and volume flows were measured and confirmed that they partially replicated the data previously obtained with phase-contrast magnetic resonance imaging. The phantom shows that CSF oscillations directly result from arteriovenous flow, and intracranial pressure measurements show that the model obeys an exponential relationship between pressure and intracranial volume expansion. CONCLUSION: The phantom will be useful to investigate the hydrodynamic hypotheses underlying development of hydrocephalus.

Sylvian fissure splitting revisited: Applied arachnoidal anatomy and proposition of a live practice model.

Opening the Sylvian fissure is an important technique in neurosurgery. Despite providing excellent anatomic fidelity, cadaveric and synthetic models lack real-time hemodynamics and coagulation physiology. We introduce a live rat aortoiliac model to practice the basic skills of Sylvian fissure splitting based on its arachnoidal microanatomy. Cadaveric dissections were carried out to assess the microanatomical relationships between the Sylvian fissure arachnoid and its contents, namely arteries (A), veins (V), and brain (B). Rat surgeries were performed to assess the similarities between separating aortoiliac arteries from adjacent veins and the various technical aspects of dissecting the Sylvian fissure. The Sylvian fissure could be divided into 3 compartments regarding the progressive steps of its dissection: (1) superficial opercular, (2) deep opercular, and (3) cisternal. The major arachnoidal connections that required division during dissection of each Sylvian compartment were as follows: B-V and V-V types in the superficial opercular; B-B and A-B types in the deep opercular; and A-B and A-A types in the cisternal compartments. Dissection techniques in the rat aortoiliac model correlated with key techniques in Sylvian fissure dissection. Despite lacking brain tissue, the rat aortoiliac arteries offer a model in which the arteries and veins with their investing connective tissues mimic the arachnoid-vessel interconnections in the Sylvian fissure. Therefore, using this model simulates the essential sub-techniques of splitting the Sylvian fissure. The rat model may be used to provide trainees with an opportunity to practice under the duress of the real-time hemodynamics and coagulation physiology.

Extracranial outflow of particles solved in cerebrospinal fluid: Fluorescein injection study.

Cerebrospinal fluid is thought to be mainly absorbed into arachnoid granules in the subarachnoid space and drained into the sagittal sinus. However, some observations such as late outbreak of arachnoid granules in fetus brain and recent cerebrospinal fluid movements study by magnetic resonance images, conflict with this hypothesis. In this study, we investigated the movement of cerebrospinal fluid in fetuses. Several kinds of fluorescent probes with different molecular weights were injected into the lateral ventricle or subarachnoid space in mouse fetuses at a gestational age of 13 days. The movements of the probes were monitored by live imaging under fluorescent microscope. Following intraventricular injection, the probes dispersed into the 3rd ventricle and aqueduct immediately, but did not move into the 4th ventricle and spinal canal. After injection of low and high molecular weight conjugated probes, both probes dispersed into the brain but only the low molecular weight probe dispersed into the whole body. Following intra-subarachnoid injection, both probes diffused into the spinal canal gradually. Neither probe dispersed into the brain and body. The probe injected into the lateral ventricle moved into the spinal central canal by the fetus head compression, and returned into the aqueduct by its release. We conclude this study as follows: (i) The movement of metabolites in cerebrospinal fluid in the ventricles will be restricted by molecular weight; (ii) Cerebrospinal fluid in the ventricle and in the subarachnoid space move differently; and (iii) Cerebrospinal fluid may not appear to circulate. In the event of high intracranial pressure, the fluid may move into the spinal canal.

Topographic Surgical Anatomy of the Parasylvian Anterior Temporal Artery for Intracranial-Intracranial Bypass.

BACKGROUND: The anterior temporal artery (ATA) is an appealing donor artery for intracranial-intracranial bypass procedures. However, its identification may be difficult. Current literature lacks useful landmarks to help identify the ATA at the surface of the sylvian fissure. The objective of this study was to define the topographic anatomy of the cortical segment of the ATA relative to constant landmarks exposed during the pterional approach. METHODS: The temporopolar artery (TPA), ATA, and middle temporal artery (MTA) were examined in 16 cadaveric specimens. The topographic anatomy and key landmarks of the arteries at the sylvian fissure were recorded. The distance between the point of emergence from the sylvian fissure to the lesser sphenoid wing and anterior tip of the temporal lobe was measured. The features of the inferior frontal gyrus relative to each of the arteries at the sylvian fissure were also recorded. RESULTS: The average distances from the lesser sphenoid wing to the TPA, ATA, and MTA were 3.7 mm, 21.2 mm, and 37 mm. The mean distances from the temporal pole were TPA, 14.7 mm; ATA, 32.0 mm; and MTA, 45.4 mm. The differences between the average distances were statistically significant (P < 0.0001). The ATA most frequently faced pars triangularis, whereas the TPA always faced pars orbitalis. The MTA was always found posterior to the junction of pars triangularis and pars opercularis. CONCLUSIONS: This article provides topographic evidence for efficient identification of the ATA in the parasylvian space. The key relationship and landmarks identified in this study may increase efficiency and safety when harvesting the ATA for intracranial-intracranial bypass.

Endoscopic navigation of the fourth ventricle. Technical note and preliminary experience.

Transaqueductal navigation of the fourth ventricle has long been considered dangerous and of no clinical relevance. After the refinement of the endoscopic technique and supported by the extensive experience gained at the authors' institution since 1994, endoscopic exploration of the fourth ventricle has been performed by the same surgeon in 54 patients. In all cases reviewed, endoscopic navigation of the fourth ventricle was successfully performed with no related neurological deficit. This preliminary experience shows the feasibility of transaqueductal navigation of the fourth ventricle, which is made possible by the use of small, flexible endoscopes in expert hands.

The synaptic terminations of certain midbrain-olivary fibers in the opossum.

The nuclear origin and distribution of midbrain-olivary fibers has been described in a previous study utilizing axonal transport techniques (Linauts and Martin, '78a). The present report extends their results to the electron microscopic level and details the postsynaptic distribution of such fibers. Lesions within the ventral periaqueductal grey and adjacent tegmentum, the red nucleus or the nucleus subparafascicularis result in electron dense axon terminals within the olive at survival times of 48, 72 and 96 hours. At 72 hours, many degenerating presynaptic profiles shrink, become irregular in shape and are totally or partially surrounded by glial processes. The principal olivary nucleus contains the majority of these profiles. However, the subparafascicular terminals are more abundant in the rostral and intermediate parts of the medial accessory nucleus and the rubral terminals are concentrated within the dorsal lamella of the principal nucleus. The nuclear location of the degenerating terminals was determined by examination of 1 micrometer plastic sections cut in the transverse plane from each block face prior to thin sectioning. Degenerating terminals were counted in three cases, one from each of the three lesion sites described above. When taken together these cases show that just over 50% of the degenerating terminals are presynaptic to spiny appendages and are located within the synaptic clusters (glomeruli) described previously (King, '76). The percentage of degenerating terminals in the glomeruli increases to 70% when the lesion is in the ventral periaqueductal grey and adjacent tegmentum. The remaining degenerating terminals contact dendritic shafts outside the astrocytic boundaries of the synaptic clusters. The synpatic vesicle populations within the degenerating terminals vary with the location of the lesion. Lesions in the ventral periaqueductal grey and the adjacent tegmentum result in the degeneration of terminals with either clear spherical vesicles or endings with both clear spherical vesicles and a variable number of large dense core vesicles. In contrast, the primary degenerative changes that occur after destruction of the red nucleus or the nucleus subparafascicularis are in terminals with clear spherical vesicles. When the synaptic complex was present in the plane of section, regardless of the site of the lesion, the degenerating terminals could be classified as Gray's type I. Thus, we have demonstrated that afferents from the mesencephalon terminate within synpatic clusters located in the principal and medial accessory (part A) subnuclei of the inferior olive. Although the mesencephalic afferents have multiple origins (Linauts and Martin, '78a), many of their synaptic terminals contact spiny appendages within the synaptic clusters. This postsynaptic site also receives cerebellar terminals (King et al., '76). The origin of presynaptic profiles within the synaptic clusters that contain clear pleomorphlic vesicles is yet to be determined.

Reissner's fiber in the sacral cord and filum terminale of the possum Trichosurus vulpecula: a light, scanning, and electron microscopic study.

The ending of Reissner's fiber (RF) and structural features associated with gaps or fissures in the rostral part of the filum were investigated using light, scanning, and transmission microscopic techniques in young and mature possums of both sexes. To the best of the author's knowledge the report contains results of the first successful application of the SEM for a study of RF in the spinal cord. Some new observations suggest that while the bulk of RF is formed by the subcommissural organ and moved caudally, additional secretory products may be added by ependymal cells in the sacral and possibly other regions of the spinal cord. Evidence is provided in support of the view that RF may pass through gaps in the ependymal lining in the rostral part of the dorsal wall of the filum terminale and caudal end of the sacral cord to reach the periependymal loose tissue and possibly the subarachnoid space. The region of the gap shows the surface of the ependyma facing the lumen of the filum to be covered with microvilli and cilia, and to be in direct continuity with the external surface of the ependyma covered with basement membrane with glial processes and collagen fibers in close proximity. The present results confirm and extend observations reported by Wislocki et al. ('56).

The midbrain periaqueductal gray in the rat, cat, and monkey: a Nissl, Weil, and Golgi analysis.

Anatomical staining methods including Nissl, Weil, Golgi, and horseradish peroxidase stain have been used to elucidate the cyto- and myeloarchitectural organization of the periaqueductal gray in monkey, cat, and rat. From these various staining methods it appears that the periaqueductal gray is composed of a tightly packed group of cells, which show a slight increase in soma size, dendritic diameter, and degree of myelinization from central to peripheral borders. This central gray region contains a wide variety of cell types including multipolar, fusiform, stellate, and pyramidal neurons. Clearly delineated subnuclei, distinguished on the basis of soma size, dendritic arborizations, pigmentation, or evidence of cytological individuality could not be discerned in this study. Together with the immunohistochemical and connectivity studies the present data suggest that the neuronal organization of the PAG could be described as a mosaic of clusters of functional related neurons rather than as three distinct subnuclei, each with its own unique cytoarchitecture and connectivity.

A light and electron microscopic study of the interstitial nucleus of Cajal in rat.

The morphology of the interstitial nucleus of Cajal (INC) in the rat was studied with the light and electron microscope. The INC was mapped throughout its rostrocaudal extent from cresyl violet-stained frozen sections cut transversely through the midbrain in the stereotaxic plane. Caudally, the INC consisted of a small number of scattered cells lying ventrolateral to the periaqueductal grey. In three of four cases studied, the caudal tip of the nucleus was located between 40 and 120 micrometers rostral to the rostral tip of the somatic cell columns of the oculomotor nucleus. Proceeding rostrally, the INC increased in size, reaching its maximal development just caudal to its most rostral extent. The INC was limited rostrally by the fibers of the fasciculus retroflexus. The mean rostrocaudal length of the INC was 1.12 mm. On the basis of light microscopic observations of cresyl violet-stained paraffin sections, two groups of neurons could be distinguished in the INC. One group consisted of large, oval to multipolar cells with mean dimensions of 33 X 23 micrometers. The second group, which included by far the greatest number of cells, consisted of small to medium neurons, round, triangular, polygonal or fusiform in shape, with mean dimensions of 19 X 14 micrometers. Injection of horseradish peroxidase into lesions in the cervical spinal cord resulted in retrograde labeling of neurons of all sizes and shapes throughout the length of the INC. Labeled neurons were also found in the red nucleus, the mesencephalic reticular formation, and the nucleus of the posterior commissure. All the morphological varieties of neurons described with the light microscope could be identified in the electron microscope. Large neurons, and some cells of the small to medium group, contained well developed Nissl bodies together with numerous cytoplasmic organelles. Many neurons in the small to medium group, however, did not contain conspicuous Nissl bodies, and had a poorly developed rough endoplasmic reticulum. Axon terminals containing either round or pleomorphic vesicles were seen in the INC. Axosomatic synapses were formed by both types of terminals. Such synapses were usually symmetrical, regardless of the shape of the vesicles within the terminal. In a number of neurons, the percentage of the surface of the neuronal somata in direct apposition to axon terminals was measured. The results of such measurements suggest that a greater percentage (more than 50%) of the surface of larger neurons is apposed by axon terminals than is the case with smaller neurons, which, on the average, were invested by axon terminals over 15% of their total surface in any given single plane of section. Axon terminals investing the surfaces of proximal dendrites were morphologically similar to those in apposition to neuronal somata.

Changes in size and magnetic resonance signal intensity of the cerebral CSF spaces during the cardiac cycle as studied by gated, high-resolution magnetic resonance imaging.

In 1966, du Boulay demonstrated the pulsatile nature of CSF flow in the cerebral aqueduct by using air cineventriculography, which disturbs normal CSF dynamics by replacing part of the incompressible CSF with air. To investigate this phenomenon noninvasively, 35 normal volunteers were studied using high-resolution, cardiac-gated MR imaging. Specifically, we wished to document changes in size and configuration of the CSF spaces and the incidence and magnitude of signal loss (an indication of CSF motion) in these spaces as they related to time in the cardiac cycle. Changes in size and configuration were measurable in the third ventricle only (size increased during systole in seven of the 35 volunteers). Except for the lateral ventricles, some loss in signal intensity was seen in all CSF spaces at least during systole in all 35 volunteers--findings consistent with those of du Boulay. However, contrary to du Boulay's observations, asymmetric loss of signal, consistent with pulsatile CSF flow, was demonstrated at the level of the foramen of Monro in 15 of the 35 volunteers. Based on the pattern of flow void at the level of the foramen of Monro and on the expansion of the third ventricle during systole, we propose a theory of synchronous CSF flow at the foramen of Monro and aqueduct, which unifies our MR findings with du Boulay's cineventriculographic observations.

Mesencephalic and diencephalic afferents to the superior colliculus and periaqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat.

The mesencephalic and diencephalic afferent connections to the superior colliculus and the central gray substance in the cat were examined by means of the retrograde transport of horseradish peroxidase (HRP). After deep collicular injections numerous labeled cells were consistently found in the parabigeminal nucleus, the mesencephalic reticular formation, substantia nigra pars reticulata, the nucleus of posterior commissure, the pretectal area, zona incerta, and the ventral nucleus of the lateral geniculate body. A smaller number of cells was found in the inferior colluculus, the nucleus of the lateral lemniscus, the central gray substance, nucleus reticularis thalami, the anterior hypothalamic area, and, in some cases, in the contralateral superior colliculus, Forel's field, and the ventromedial hypothalamic nucleus. Only the parabigeminal nucleus and the pretectal area showed labeled cells following injections in the superficial layers of the superior colliculus. In the cats submitted to injections in the central gray substance, labeled cells were consistently found in the contralateral superior colliculus, the mesencephalic reticular formation, substantia nigra parts reticulata, zona incerta and various hypothalamic areas, especially the ventromedial nucleus. In some cases, HRP-positive cells were seen in the nucleus of posterior commissure, the pretectal area, Forel's field, and nucleus reticularis thalami. A large injection in the mediodorsal part of the caudal mesencephalic reticular formation, which included the superior colliculus and the central gray substance, resulted in numerous labeled cells in nucleus reticularis thalami. The findings are discussed with respect to the suggested functional division of the superior colliculus into deep and superficial layers. Furthermore, the possible implications of labeled cells in zona incerta and the reticular thalamic nucleus are briefly discussed.

Ascending projections to nucleus parafascicularis of the cat.

Experiments utilizing the retrograde transport of horseradish peroxidase (HRP) were performed in order to locate the cells of origin of ascending projections to the parafascicular nucleus (Pf) of the cat. HRP-labelled cells were identified in several regions of the brain stem including: trigeminal nuclei, vestibular nuclei, nucleus coeruleus, tegmental field, deep layers of the superior colliculus, substantia nigra, dorsal median nucleus of Raphe and periaqueductal grey substance. Of these, the periaqueductal grey contained approximately 40% of labelled neurones. A weak spinal cord projection to Pf originated bilaterally from laminae VI and VII-VIII at C1 and C2 and some neurones were also found contralaterally at C7 and L7.

Corticopontine projections of the lateral suprasylvian cortex: de-emphasis of the central visual field.

Layer V pyramidal cells of the cat lateral suprasylvian visual areas project to the pontine nuclei. Although all 6 of the suprasylvian visual areas project to the pons, the densest projections are from 3 areas: anterior medial lateral suprasylvian (AMLS), posterior medial lateral suprasylvian (PMSL) and ventral lateral suprasylvian (VLS). The organization of the corticopontine pathway from one of these areas (PMLS) suggests a disproportionate representation of the peripheral visual fields. This pattern of projection would serve to de-emphasize the central visual field.

Afferent and efferent connections of the parabigeminal nucleus in cat revealed by retrograde axonal transport of horseradish peroxidase.

Afferent and efferent connections of the parabigeminal nucleus (PBG) of the cat have been demonstrated by means of horseradish peroxidase (HRP) tracing technique. Following HRP injection in the PBG, labelled cells were observed mainly in the deep layers of the ipsilateral superior colliculus (SC). The other labelled structures were the prepositus hypoglossi complex (PH), the ventral nucleus of the lateral geniculate body (LGV), the locus coeruleus, the cuneiform nucleus, the periaqueductal gray and the dorsomedial hypothalamic area. Efferent projections of the PBG were investigated by HRP injection in SC, LGV, PH, hypothalamus and in some acoustic relays, i.e. medial geniculate body and inferior colliculus. Only the PBG-SC projection appeared to be well systematized. The positive labelling of the PBG following injection of LGV and hypothalamus is discussed in terms of the specificity of the injection. The absence of afferent and efferent connections of the PGB with any acoustic relay tends to exclude this nucleus from the auditory system in contrast to previous suggestions. On the basis of the close reciprocal PBG-SC connections a possible role of the PBG within visuomotor tectal function is proposed.

Origin of descending afferents to the rostral part of dorsal cap of inferior olive which transfers contralateral optic activities to the flocculus. A horseradish peroxidase study.

Neurons in the ventromedial tegmental area that project to the rostral part of the dorsal cap of the ipsilateral inferior olive were labeled by the technique of retrograde transport of horseradish peroxidase (HRP). Following iontophoresis of HRP into the rostral part of the dorsal cap a cluster of labeled cells are found ipsilaterally in the area ventromedial to the red nucleus as well as in the area between the substantia nigra and the medial lemniscus. Following HRP injections into the medial accessory olive just beneath the dorsal cap, labeled cells are found exclusively contralaterally in the deep layers of the superior colliculus and in the adjacent reticular formation. These findings clearly show that neuronal groups in the ventromedial tegmental area are involved in the pathway which from the contralateral eye via the rostral half of the dorsal cap conveys impulses to the flocculus, recorded as climbing fiber activation.

Edinger-Westphal nucleus: cholecystokinin immunocytochemistry and projections to spinal cord and trigeminal nucleus in the cat.

Immunocytochemical methods were used to determine the distribution of cells with cholecystokinin-like immunoreactivity (CCK-LI) in the cat Edinger-Westphal complex (EW). Numerous cells with CCK-LI are found throughout the length of EW. The distribution and frequency of such cells are similar to the pattern of EW neurons that show substance P-like immunoreactivity (SP-LI). Companion retrograde transport experiments reveal that EW neurons which project to spinal cord or the region of the caudal trigeminal nucleus are found throughout the length of EW, and that some EW neurons which project to spinal cord also show CCK-LI.