Studies on the permeability of potassium ions across the dura and arachnoid mater of the rat spinal cord

A combined impounder-surface K+ electrode was developed to measure change in K+ ion concentration of the cerebrospinal fluid (CSF) across the dura and arachnoid maters. To determine whether K+ permeability of the rat dura and arachnoid maters is due to an intrinsic permeability, a study was conducted using an atraumatic laminectomy model. Dorsal laminectomy was performed at T7-8, T12, and L1. Artificial CSF containing 4.2 mM, 24.2 mM, or 54.2 mM of K+ was administered by anterograde subdural infusion into the subarachnoid space from the proximal laminectomy site (T7-8), with effluent overflow at the distal laminectomy site (L1). K+ concentration on the dorsal aspect of the central laminectomy site (T12) was measured. It was found that changes in K+ concentrations of the infused solution were detected by the epidural surface electrode. This suggests that the intact rat spinal cord dura and arachnoid maters may be permeable to K+ in this laminectomy model. This study supports the use of the combined impounder-K+ electrode for measuring changes in K+ ion concentration of the CSF that can result from spinal cord trauma and ischemia.

Subarachnoid injection--a potential complication of retrobulbar block

This study was undertaken to illustrate the potential for subarachnoid injection during retrobulbar block as a cause of respiratory arrest. Cadaver orbits were used to document the connection between the optic nerve sheath and the subarachnoid space. Following dissections of the orbits on one side of 24 cadavers, the optic nerve sheaths were identified and injected with 0.5 ml of water for measurement of pressure generated during injection. This was followed by intrasheath injection of equal volume of methylene blue for demonstrating the subarachnoid space surrounding the optic nerves. All injections were performed with a 1-ml syringe with a one-and-one-half-inch 22-G needle over a period of 10 s. The blue dye was found to track along the subarachnoid space of the optic nerve sheath to the chiasmatic cistern in the middle cranial fossa. Retrobulbar injections were performed on the contralateral undissected orbits and intrascleral injections were performed on undissected eyes. The size of the syringes, the gauge of the needles, and the speed of injection were uniform for all injections. The pressure generated by injection into the optic nerve sheath or intrascleral injection (approximately 138 mmHg) was three- to fourfold that produced by injection into the retrobulbar adipose tissue (approximately 35 mmHg) (P less than 0.05). The authors conclude that any resistance encountered during retrobulbar block should serve as a warning signal, mandating redirection of the needle, in order to prevent subarachnoid injection.

Ultrasound measurement of the subarachnoid space in infants

An original non-invasive method for easy and reproducible measurement of the subarachnoid space width in infants is described. Preliminary results of normal values during the neonatal period are presented as well as of the validity of the ultrasound method for abnormal values obtained by available computed tomography scanning.

Technical aspects on magnetic resonance imaging of the spine at 1.5 tesla

Technical aspects on surface coil magnetic resonance imaging of the spine using a superconducting system with a field strength of 1.5 tesla are described. By using a flat surface coil instead of the body coil the image quality was markedly improved and the signal-to-noise ratio (S/N) was increased approximately 2.6 times. Small voxels resulted in low S/N. The best image quality was achieved with a slice thickness of 5 mm, a field of view of 20 to 24 cm and a matrix of 256 X 256. Interleaved slices provided superior image quality compared with contiguous slices at the expense of acquisition time. For sagittal images the phase encoding gradient should be in the cranio-caudal direction to minimize motion artifacts. To obtain T1 and T2 images of high quality, spin echo pulse sequences with TR 600/TE 20 ms and TR 2000/TE 40 to 80 ms are useful.

[CT-cisternography of the basal cisterns. A roentgen anatomic study]

Air cisternograms at post mortem and positive contrast cisternograms on patients were performed in order to study intracisternal structures, particularly cranial nerves, as seen on CT. Air and contrast CT cisternograms showed excellent demonstration of the second, third, fifth, sixth, seventh and eighth cranial nerves. The ninth and tenth cranial nerves could not always be separated from each other and demonstration of the first, fourth, eleventh and twelfth cranial nerves was often not possible or was unsatisfactory. With a knowledge of the normal anatomy and of important surrounding structures, the individual cranial nerves are easily identified. The anthropologic baseline appears highly suitable for CT examination of the basal cisterns. The complementary coronal projection is also very valuable.

Appearance of Pantopaque on MR images

Pantopaque was shown to be both a radiographic and magnetic resonance (MR) contrast agent in two patients with suspected cord abnormalities who underwent MR examination following myelography. The Pantopaque appeared as a linear band of high signal intensity along the dependent portion of the spinal canal on MR images obtained with a repetition time of 500 msec and an echo time of 30 msec. MR images of two dogs--one injected with Pantopaque in the cervical subarachnoid space and the other with Amipaque--confirmed that the high signal arose from the Pantopaque. This high signal intensity is due to Pantopaque's short T1 relaxation time. Although Pantopaque will probably not be used as an MR contrast agent, it is important to recognize this property so that its high signal is not mistaken for fat or hemorrhage in the subarachnoid space on MR images.

Radiology of the ambient cistern. Part I: Normal

The angiographic and high-resolution, thin-section CT appearance of the normal ambient cistern is correlated with anatomic dissections and sections of normal, formalin-fixed cadaver brains. Each of three separate anatomic segments of the ambient cistern--the supratentorial segment, the tentorial edge and the subtentorial segment--has a characteristic CT appearance that can be correlated with specific vascular structures on routine angiography.

Intraorbital cerebrospinal fluid outflow and the posterior uveal compartment of the hamster eye

An ultrastructural and tracer study was undertaken to determine normal outflow pathways of cerebrospinal fluid (CSF) at the terminal subarachnoid space (SAS) of the optic nerve. In the morphological studies, the optic nerve dura and arachnoid were found to be continuous with the sclera of the eye beyond the optic nerve SAS. The pia mater is continuous with the inner sclera and the lamina fusca of the eye. Montages and serial sections demonstrated that the distal SAS is divided into numerous tortuous channels to form an "arachnoidal trabecular meshwork". Spaces of this meshwork continue into "microcanals" which bypass the outer arachnoid barrier layers of the optic nerve meninges to reach the sclera and posterior intraorbital connective tissue. Ferritin infused into the cisterna magna entered the optic nerve SAS within 1 min and reached arachnoidal trabecular meshwork channels and the microcanals within 8 min. It then passed into intraorbital connective tissue spaces at the posterior pole of the eye. Ferritin appeared to be blocked by the lamina fusca and a newly discovered "posterior compact zone" which together prevented its entrance into the choroidal interstitium. These observations suggest that a "subarachnoidal-scleral-orbital outflow pathway" provides a route for CSF drainage from the optic nerve SAS to intraorbital connective tissue. The previously described "posterior uveal compartment" in the hamster eye (Kelly et al. 1983) appears to be relatively isolated from this subarachnoidal-scleral-orbital CSF outflow.

Microsurgical anatomy of spinal subarachnoid space

The anatomy of the spinal subarachnoid space is reviewed with special reference to the work of Key and Retzius, the authors' own cadaver dissections, and experience from operative cases. It appears that despite some variations in the spinal arachnoid anatomy, there are many consistent features that can serve to guide the operating neurosurgeon.

Morphology and dimensions of the thoracic cord by computer-assisted metrizamide myelography

Computed tomographic (CT) measurements of the thoracic spine and its contents were obtained in 33 patients undergoing metrizamide myelography for various spinal disorders. Twenty-eight of these patients had symptoms referable to the cervical or lumbar region and form the basis of this study. Five patients had symptoms referable to the thoracic spine. Sagittal and coronal CT measurements of the thoracic cord and subarachnoid space were obtained in all cases. In addition, macroscopic measurements of the thoracic cord were obtained from 10 autopsies for correlation with the CT findings. The technical aspects of the measurements are discussed; the normal morphology of the thoracic cord and thecal sac is presented; and the metrizamide CT pattern associated with pathologic lesions involving the thoracic cord is analyzed.

[M. A. Baron's concept of subarachnoid communications of the pia mater of the cerebral hemispheres]

In the pia mater of the human cerebral hemisphere certain specific structures named subarachnoid alveoli have been revealed. The best method for their revealing is the method of volumetric microscopy--tracheoscopy--but they can be detected in histological sections, as well. The subarachnoid alveoli are situated in the subarachnoid space between liquor canals. By their form they resemble honeycombs. Their walls have a carcass consisting of argyrophile and collagenous fibres to give the alveoli a definite form. The carcass is lined with arachnoid-endothelial cells. The alveoli are connected with the liquor canals by means of holes in the walls of the canals. The subarachnoid alveoli are connected with each other by means of holes in their walls. The arachnoid-endothelial cells of the subarachnoid alveoli are capable to accumulate colloid substances from the spinal liquor. The walls of the subarachnoid alveoli discharge macrophages into the lumen of the latter. Protective function of the subarachnoid alveoli system contributes to normalization of the spinal liquor composition both under normal and pathological conditions.

Size of the subarachnoid space in stenosis of the lumbar canal

Measurements of the subarachnoid space at myelography were carried out in three groups of patients, one group with stenosis of the lumbar spinal canal, one group without stenosis, and one intermediate group. Although spinal canal stenosis is most prominent at disc levels, the results demonstrate decreased sagittal diameter at mid-vertebral body level as well. The mean transverse diameters did not differ in three groups. This points towards congenital or developmental factors as the basic abnormality in the majority of patients with stenosis of the lumbar spinal canal.

[Anatomical structures, physiology and pathophysiology of cerebrospinal fluid metabolism; a review for an understanding of cerebrospinal fluid findings]

The very different macroscopic and microscopic details of the structures involved in production and reabsorption of cerebrospinal fluid in the different parts of the central nervous system are causing confusing laboratory findings in cerebrospinal fluids, the ingredients of which change even under normal condition in these different parts. Moreover the chemical ingredients of cerebrospinal fluid differ especially from the normal situation during some diseases of the central nervous system. Although we can be sure that there is much more diagnostic information in cerebrospinal fluid, we mainly prefer certain standard methods today, as there are cell counts and measuring of the protein concentration, as diagnostic parameters. Their unspecific changes during several pathologic states do not yet allow to point out the exact localization of the disease, nor can they contribute in every case in finding the cause of the disease. Therefore other and more specific diagnostic laboratory methods are to be developed, which will make possible more precise statements about the nature and the localization of central nervous system diseases.

Developmental changes in normal cranial measurements by computed tomography

Computed tomography (CT) scans were examined for 89 selected patients in an attempt to establish normal values at various ages for longitudinal and transverse diameters of the brain, the greatest distance between the right and left sides of the anterior horn of the lateral ventricle, the width of the lateral ventricles in the region of the caudate nuclei, and the greatest width of the third ventricle. The patients' ages ranged from less than one year to over 40 years. These measurements and their ratios to one another are reported. The cerebral longitudinal fissure, Sylvian fissure and subarachnoid space were evident to some degree below the age of two years, especially below the age of one year, and again above the age of 40 years. The cortical sulcus was occasionally found to have a width of less than 1.9mm below the age of one year and above the age of 40 years.

Measurement of the normal ventricular system and supratentorial subarachnoid space in children with computed tomography

The normal ventricular system and subarachnoid space were evaluated on the CT scans of 155 children chosen from 1,400 pediatric CT examinations, and linear measurements were made. The left septum-caudate distance was greater than the right, and the width of the left anterior horn and size of the skull were larger in boys. The interhemispheric and sylvian fissures, the third ventricle and Evans' ratio were larger in the younger group (less than 3 years) than in the older (greater than or equal to 3 years), while the opposite was found for the cella media index and size of the skull. The size of the lateral ventricles (expressed by anterior horn width, septum-caudate distance and width of cella media) was not different in the two age groups of children. Normal limits for the linear measurements and indices are given in Table 2.

Subarachnoid space of the CNS, nasal mucosa, and lymphatic system

We have briefly reviewed the literature pertaining to the movement of tracer molecules and infectious organisms within the olfactory nerve. There is a body of evidence indicating that tracers placed in the CSF will quickly move via the olfactory nerve to the nasal mucosa and then to the cervical lymph nodes. Organic and inorganic tracer materials and organisms as diverse as viruses, a bacillus, and an amoeba, when placed in the nasal cavity, have been shown to move from the nasal mucosa via the olfactory nerve to the olfactory bulb and the CSF. We think that a portion of the data on tracer movement is due to incorporation of tracer materials and organisms into the axoplasm of the olfactory neurons with subsequent anterograde or retrograde axoplasmic transport. However, some of the movement of tracers may occur within the olfactory perineural space. This space may be continuous with a subarachnoid extension that surrounds the olfactory nerve as it penetrates the cribriform plate. To our knowledge, no one has yet followed the perineural space to determine if it is continuous from olfactory receptor to olfactory bulb. The consideration of this space and its role is the main reason for this review.

Electron microscopic studies on the lamprey meninges

Lamprey meninges were revealed to consist of four layers. The I (outermost) layer was made up of densely packed collagen fibrils and microfibrils with fibrocytes interposed between them. It contained a vascular network (epidural vascular plexus). The II layer was a cellular layer, consisting of two parts: the outer, membranous and the inner, spongy part. The membranous part was composed of two sheets of type 1 cells which were held together by desmosomes, gap junctions and tight junctions. Continuous basal laminae were found on both the outer and the inner surface of the membranous part. The spongy part consisted of type 2 cells, collagen fibrils and microfibrils, which were loosely arranged. Type 2 cells were joined together with each other, or with type 1 cells, by gap junctions. These cells lacked a basal lamina covering. The III layer was a peculiar thick layer, being mostly occupied by fine filamentous matrix substance with scattered round cells, fibroblasts and microfibrils. The IV (innermost) layer was a thick fibrous one, consisting of two parts: the outer, vascular and the inner, loose part. The former consisted of a vascular network (perineural vascular plexus) and thick bundles of microfibrils which frequently contained a dense filamentous core. The latter was composed of loosely arranged collagen fibrils. The inner part of the I layer (inside the epidural vascular plexus) was considered to correspond to the true dura, and the II and IV layer to the arachnoid and pia in the meninges of higher animals, respectively. Characteristically the subarachnoid space was absent in lamprey meninges, and instead a peuliar "gelatinous" layer, III layer, was present between the II and IV layer.

Continuity between the ventricular and subarachnoid cerebrospinal fluid in an amphibian, Rana pipiens

Continuity between the ventricular and subarachnoid cerebrospinal fluid has been investigated in Rana pipiens. The structure of the posterior tela, a deficient membrane situated at the extreme caudal end of the roof of the fourth ventricle, has been studied using whole membrane mounts and by light microscopy of resin embedded tissue. The ependymal component consists of columnar and rounded cells which form a regular 'syncytium' enclosing round and oval fenestrations. Small fenestrations are covered on the subarachnoid side by elongated pial cells and thus do not give total continuity between the fourth ventricle and the subarachnoid space. Large fenestrations, on the other hand, are accompanied by equivalent pial fenestrations giving direct access between the fluid compartments. Towards the caudal end the fenestrations break up and the numbers of ependymal and pial cells decrease, the caudal end itself being characterised by a small remaining clump of ependyma and pia or of pia alone. Flow through the tela has been studied using fluorescein-labelled dextran placed in the intraventricular space. Infusion into the lateral ventricle and subsequent localisation by fluorescence microscopy shows the marker to be in the fourth ventricle, in the fenestrations of the posterior tela and in the subarachnoid space overlying the tela. Infusion of the marker followed by freezing and examination of the cut heads on a freezing microtome, shows fluorescence throughout the ventricular system, in the subarachnoid space adjacent to the posterior tela and also along the dorsal subarachnoid space of the spinal cord.

Normal computed tomography anatomy of the suprasellar subarachnoid space

To assess normal variants of the suprasellar subarachnoid space, 680 CT scans were reviewed. Three main configurations with subgroups of the suprasellar cistern could be found: a large hexagon (60.7%), a small hexagon (17.6%) and a small tetragon (21.7%). In about a third of the scans, the region of interest was not visualized sufficiently. The large variety of CT appearance of the normal suprasellar space could be attributed to anatomical and technical reasons. To exclude a suprasellar mass lesion it is necessary to be aware of the anatomical variations, investigate the suprasellar region with additional intermediate cuts or contrast enhancement and define the cut level and osseous structures by a lateral skull radiograph.

The calculation of CSF spaces in CT

Objective digital determination of CSF spaces is discussed, with ventricular and subarachnoid spaces handled separately. This method avoids the difficulty of visual definition of ventricular borders in planimetric measurements. The principle is to count automatically all pixels corresponding to CSF in a given region with a Hounsfield unit and to multiply this number by the pixel size. This will give the total surface area of CSF spaces in square millimeters. The calculation of pixel values for CSF spaces and brain tissue is experimentally formulated taking the intersection of the Gaussian curves for ventricular content and brain tissue. In practice, the determination of CSF spaces is done by first calculating a histogram of the total brain in a given slice defining all CSF spaces. Next a histogram of a region including ventricles with adjoining tissue is calculated and the ventricular size is calculated. By subtraction of the ventricle value from the total CSF space value, the subarachnoid space size is obtained. The advantages of this method will be discussed.

Chronic catheterization of the spinal subarachnoid space

To administer drugs into the spinal subarachnoid space of unanesthetized and intact rats and rabbits, a procedure is described whereby a polyethylene catheter (PE-10) may be inserted through a puncture of the atlanto-occipital membrane and secured to the skull. Calibration experiments carried out with bromophenol blue dye, 3H-naloxone and 14C-urea revealed first, that there was little rostro-caudal diffusion of the injectate along the spinal axis and secondly, that even for compounds such as naloxone which can rapidly permeate neural tissues, the levels which do appear in the brain are small following the spinal subarachnoid administration of the drug. Control injections, administered either acutely or repeatedly over a prolonged period of time, had no detectable effect on the animal's behavior. These observations, as well as the lack of pathology in the spinal cords of rats having such catheters for periods of up to 4 months suggests that the implant is well tolerated.