Cranial arachnoid membranes: Some aspects of microsurgical anatomy

Although the arachnoid membranes have been known for more than 300 years, the anatomy of the arachnoid membranes has not been studied in detail. This study was performed to explore the microanatomical features of the cranial arachnoid membranes. The arachnoid membranes and cisterns were observed in eight Han Chinese adult human cadaveric brains with an operating microscope, without staining of intracranial structures or injection of colored material into blood vessels. Twenty seven arachnoid membranes and 21 subarachnoid cisterns were identified. The topographical features of each arachnoid membrane were described. On the basis of the arachnoid membranes we identified, the arachnoidal limits of the cisterns were discussed. The microsurgical anatomical research on the arachnoid membranes is a supplement to the anatomical study of the subarachnoid cisterns. The understanding of the topographical features of the arachnoid membranes is valuable to the reasonable dissection of the cisterns and the minimally invasive manipulations during microsurgical procedures.

[The topographic anatomy of the interpeduncular cistern and endoscopic ventriculocisternostomy in the region of the bottom of the third ventricle]

The interpeduncular cistern was microanatomically studied on 14 anatomic specimens of the brain. It was divided into 2 parts: superficial (free) and deep (vascular). The upper interpeduncular cistern wall was divided into hypothalamic and mesencephalic parts. The interpeduncular cistern is connected with the ambient, pretontine, carotid, cerebellopontine, oculomotor, and peduncular cisterns. It is a composite space-occupying, structural formation. Liliequist's membrane is the basic membranous component of a cistern. The proposed division makes it possible to study different parts of the interpeduncular cistern qualitatively and quantitatively and to define clear topographic and anatomic criteria as a guideline in this field.

The endoscopic extended transsphenoidal approach for craniopharyngiomas

OBJECTIVE

The endoscope has recently been applied to the supradiaphragmatic transsphenoidal approach, but only case reports dealing with different pathological features have been described. The authors present their experience with this technique in 10 patients with craniopharyngiomas.

METHODS

A pure endoscopic endonasal technique was used. From November 1998 through May 2005, four males and six females with a craniopharyngioma, either purely supradiaphragmatic (six patients) or with a significant suprasellar component (four patients), were treated. The tumors had a mean diameter of 2.9 cm (range, 1-4 cm); four patients had a major prechiasmatic component and six had a retrochiasmatic one.

RESULTS

Seven total, one subtotal, and two partial resections were obtained. Vision symptoms improved significantly in six out of eight patients. Endocrine function did not improve after surgery, and diabetes insipidus was the most frequent deficit, although it was transient in five out of eight patients. Cerebrospinal fluid leak was the most frequent complication and required reoperation in two patients. Postoperative obesity occurred in two patients. No recurrence has yet been documented in the total resection group. The mean follow-up period is 37 months (range, 3-75 mo).

CONCLUSION

The endoscopic technique allows results comparable with the best microscopic series. We think that this technique increases the safety of the procedure because of improved vision. Further studies are required to better define the exact location of the tumor with respect to the arachnoidal plane, the extra-arachnoidal craniopharyngioma being the most suitable for a radical removal using a transsphenoidal supradiaphragmatic approach.

Morphological Study of the Spinal Canal Content for Subarachnoid Endoscopy

STUDY DESIGN AND OBJECTIVE

This study was designed to examine the morphology of the spinal dural sac and contents, using magnetic resonance imaging in order to define the inner geometrical dimensions that confine the manoeuvre of an endoscope inserted in the lumbar region and along the thoracic and cervical spine.

BACKGROUND

The morphology of the spine has been studied since the development of myelography. However, most studies have measured the diameters of the spinal cord only, not the size of the subarachnoid space. In addition, the few studies available on the subarachnoid space have focused on the cervical spine, leaving a near-complete dearth of data on the subarachnoid space dimensions along the thoracic spine.

METHODS

Based on MRI images of the spine from 42 patients, the dimensions of the spinal cord, dural sac, and subarachnoid space were measured at mid-vertebral and inter-vertebral disc levels.

RESULTS

It was found that at each selected transverse level, the subarachnoid space tends to be symmetrical on the right and left sides of the cord, and measures 2.5 mm on average. However, the posterior and anterior segments, measured on the mid-sagittal plane, are generally asymmetrical and vary widely in size, ranging from 1 to 5 mm. These measurements match those found in previous studies, where these are available. The coefficient of variance for the dimensions of the subarachnoid space is as high as 42.4%, while that for the dimensions of the spinal cord is 10-15%.

CONCLUSIONS

The findings presented here expand our knowledge of the spinal canal's morphology, and show that an endoscope designed to travel within the subarachnoid space must be smaller than 2.5 mm in diameter.

Eyebrow Surgery: The Supraciliary Craniotomy: Technical Note

OBJECTIVE:

Many approaches have been recommended for the surgical treatment of anterior and middle cranial fossa lesions. The frontobasal approach and its many modifications have been proposed and developed for such situated lesions. An alternative approach is the frontolateral craniotomy through a supraciliary skin incision.

METHODS:

This minimally invasive technique, a 2.5 × 3.0 cm craniotomy, just above the eyebrow through a supraciliary incision, is a simple but elegant modification of the traditional approach to the anterior cranial fossa.

RESULTS:

A step-by-step description of the approach is offered in this report to facilitate a clear understanding of the lesions treatable with this minimally invasive technique.

CONCLUSION:

The supraciliary frontolateral keyhole craniotomy is a minimally invasive cosmetic approach that provides excellent exposure to a variety of intracranial lesions. This approach cannot be used for all intracranial pathologies, but is recommended for many anterior and middle cranial fossa lesions.

Development of cerebrospinal fluid absorption sites in the pig and rat: connections between the subarachnoid space and lymphatic vessels in the olfactory turbinates

The textbook view that cerebrospinal fluid (CSF) absorption occurs mainly through the arachnoid granulations and villi is being challenged by quantitative and qualitative studies that support a major role for the lymphatic circulation in CSF transport. There are many potential sites at which lymphatics may gain access to CSF but the primary pathway involves the movement of CSF through the cribriform plate foramina in association with the olfactory nerves. Lymphatics encircle the nerve trunks on the extracranial surface of the cribriform plate and absorb CSF. However, the time during development in which the CSF compartment and extracranial lymphatic vessels connect anatomically is unclear. In this report, CSF-lymphatic connections were investigated using the silastic material Microfil and a soluble Evan's blue-protein complex in two species; one in which significant CSF synthesis by the choroid plexus begins before birth (pigs) and one in which CSF secretion is markedly up regulated within the first weeks after birth (rats). We examined a total of 46 pig fetuses at embryonic (E) day E80-81, E92, E101, E110 (birth at 114 days). In rats, we investigated a total of 115 animals at E21 (birth at 21 days), postnatal (P) day P1-P9, P12, P13, P15, P22, and adults. In pigs, CSF-lymphatic connections were observed in the prenatal period as early as E92. Before this time (E80-81 fetuses) CSF-lymphatic connections did not appear to exist. In rats, these associations were not obvious until about a week after birth. These data suggest that the ability of extracranial lymphatic vessels to absorb CSF develops around the time that significant volumes of CSF are being produced by the choroid plexus and further support an important role for lymphatic vessels in CSF transport.

Establishing intercrestal line by posture:--a radiographic evaluation

In this study, we examined the position of intercrestal line that is called Jacoby's line at heights of the vertebral body and spinous process in different positions of the lumbar spine using radiographs of 100 subjects. At the height of the spinous process, Jacoby's line was most often observed in the extension position in L4 spinous process middle 1/3 region in males and in L4-5 interspinous region in females. In the neutral position, it was in L4 spinous process middle 1/3 region in males and in L4-5 interspinous region in females. And that in the flexion position, it was in L4-5 interspinous region in both males and females. At the height of the vertebral body, Jacoby's line was most often observed in the extension position in L4-5 intervertebral region in males and in L5 vertebral body upper 1/3 region in females. In the neutral position, it was in L4 vertebral body lower 1/3 region in males and in L5 vertebral body upper 1/3 region in females. In the flexion position, it was in L5 vertebral body upper 1/3 region in males and in L5 vertebral body upper 1/3 region or L4 vertebral body lower 1/3 region in females. There was no gender difference in the most often observed position of Jacoby's line at the height of the spinous process in the flexion position. The position of Jacoby's line was found to vary in different positions of the lumbar spine. Positioning Jacoby's line in the neutral lumbar spine from the body surface, as conventionally proposed, was not always accurate, and it was considered practical to establish Jacoby's line using the spinous process in the flexion of the lumbar spine as the standard. When Jacoby's line is established by this method, it is considered to be positioned between L4-5 spinous processes middle 1/3 regions. In subarachnoid puncture in elderly patients, the puncture may be performed at a higher position in relation to the spinal cord because of spinal degeneration. Therefore, it is important to perform subarachnoid puncture in elderly patients at a site lower than the established Jacoby's line.

What is the true location of Jacoby's line?

We investigated 60 cadavers to examine the accurate location of conus medullaris, lower end of dura mater, and intercrestal line (Jacoby's line). Jacoby's line was established using the method described by Jacoby GW (1899). Then the intersection of this line and vertical line through the spinous processes was marked by a fine nail. After a laminectomy was performed to expose the spinal cord, spinal level of the conus medullaris, the lower end of dura mater, and Jacoby's line were examined, and marked and recorded these locations of nailing. In 2 of 48 cases (2.1%), Jacoby's line passed through the level superior to 3rd lumber vertebra (L3). The Conus medullaris was at the level beneath L3 in 2 of 57 cases (3.5%). And lower end of dura mater was located beneath the superior margin of S3 in 1 of 28 cases (3.6%). When Jacoby's line is used as a guide-point, the site for subarachnoid puncture is established in the L3-4 interspinous space. But when we consider the risk of spinal cord injury cannot be completely excluded, in case that conus medullaris is located inferior to L3 in 3.5% of cases. Conseqently, it should be important to avoid performing subarachnoid puncture at L2-3 or higher lumbar vertebral level especially in the elderly.

Thecaloscopy through sacral bone approaches, cadaver study: further anatomic landmarks

Endoscopy of the spinal canal, for interventional studies, diagnosis and therapy, is a scientific topic that has attracted the interest of neurosurgeons, anesthesiologists and orthopedic surgeons for the past twenty years. Endoscopy of the thecal sac was assumed to be less important than endoscopy of the ventricular system by neurosurgeons. Nevertheless, during the last years it has attained increasing scientific interest, firstly because of the introduction of small diameter flexible endoscopes and secondly due to the growing interest for minimal invasive diagnostic and therapeutic procedures in modern neurosurgery. Until now thecaloscopy was performed by the ISGT (International Study Group for Thecaloscopy) using co-axial downward orientated approaches. We have examined transsacral approaches to facilitate the navigation of flexible scopes in the lumbosacral subarachnoid space, and thus we now introduce further recognizable endoscopic anatomic landmarks.

Subarachnoid injection of Microfil reveals connections between cerebrospinal fluid and nasal lymphatics in the non-human primate

Based on quantitative and qualitative studies in a variety of mammalian species, it would appear that a significant portion of cerebrospinal fluid (CSF) drainage is associated with transport along cranial and spinal nerves with absorption taking place into lymphatic vessels external to the central nervous system. CSF appears to convect primarily through the cribriform plate into lymphatics associated with the submucosa of the olfactory and respiratory epithelium. However, the significance of this pathway for CSF absorption in primates has never been established unequivocally. In past studies, we infused Microfil into the subarachnoid compartment of numerous species to visualize CSF transport pathways. The success of this method encouraged us to use a similar approach in the non-human primate. Yellow Microfil was injected post mortem into the cisterna magna of 6 years old Barbados green monkeys (Cercopithecus aethiops sabeus, n = 6). Macroscopic and microscopic examination revealed that Microfil was (1) distributed throughout the subarachnoid compartment, (2) located in the perineurial spaces associated with the fila olfactoria, (3) present within the olfactory submucosa, and (4) situated within an extensive network of lymphatic vessels in the nasal submucosa, nasal septum and turbinate tissues. We conclude that the Microfil distribution patterns in the monkey were very similar to those observed in many other species suggesting that significant nasal lymphatic uptake of CSF occurs in the non-human primate.

Ultrasonographic measurement of subarachnoid space in normal term newborns

This study was conducted in order to assess the normal range of subarachnoid space width in healthy term newborns. A total of 230 healthy newborns were evaluated within the first 28 days of life. Measurements were correlated with body weight, height and head circumference. Mean measurements for falx-cortex and craniocortical widths and the correlations are given in tables. Subarachnoid space widths increased as weight, height and head circumference increased and the correlation was statistically significant.

Microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes

OBJECT

The goal of this study was to investigate the microsurgical anatomy of the interpeduncular cistern and related arachnoid membranes.

METHODS

The interpeduncular cistern and related arachnoid membranes were studied in eight Han Chinese adult human cadaveric brains with the aid of an operating microscope. The interpeduncular cistern is one area in the cranial cavity in which the arachnoid membranes and trabeculae are extremely luxuriant and complicated. The Liliequist membrane, the medial pontomesencephalic membrane, and the lateral pontomesencephalic membranes form the walls of the interpeduncular cisterns. The basilar artery (BA) bifurcation membrane, posterior perforated membrane, and arachnoid trabeculae fill the cistern. These arachnoid membranes and trabeculae adhere to the hypothalamus, brainstem, and oculomotor nerves, and bind the bifurcation of the BA, posterior cerebral arteries, superior cerebellar arteries, posterior communicating arteries, and their perforating branches.

CONCLUSIONS

Arachnoid membranes and trabeculae complicate the exposure and dissection of lesions within the interpeduncular cistern. All arachnoid membranes and trabeculae should be dissected and incised sharply during surgical procedures. The BA bifurcation membrane and the posterior perforated membrane must be incised after opening the Liliequist membrane for sufficient exposure of deep structures within the interpeduncular cistern.

Anatomy and physiology of the leptomeninges and CSF space

The arachnoid membrane and pia mater are the two membranous layers that comprise the leptomeninges. Cerebrospinal fluid is made within the ventricular system by cells of the choroid plexus and ependyma. This chapter describes in detail the normal anatomic structure and physiologic interactions of the cerebrospinal fluid and leptomeningeal space that are critical to our understanding and treatment of leptomeningeal metastases.

Characteristics of distribution and configuration of intracranial arachnoid membranes

An understanding of the microsurgical anatomy of the arachnoid membranes and the subarachnoid cisterns is important in minimally invasive neurosurgery. But the topography of the arachnoid membranes has not been completely elucidated. The description of the distribution and the configuration of the intracranial arachnoid membranes is still a subject of controversy. In order to clarify this we examined eight Han Chinese adult human cadavers under an operating microscope. The dissections were performed with microsurgical instruments and techniques without staining of the intracranial structures nor injection of colored material into blood vessels. Twenty seven arachnoid membranes were identified. They were named according to their locations and attachment. They were divided into three groups: basal, convex and trabecular arachnoid membranes. They varied greatly in appearances and configurations. They were single-leaf structured except Liliequist's membrane, the chiasmatic membrane and the cerebellar precentral membrane. They were distributed extensively and unevenly and crisscrossed in the cranial cavity. The more complexly and intricately the blood vessels or the nerves converged or branched within the subarachnoid space, the more luxuriant and complex the arachnoid membranes and trabeculae were. The areas where the arachnoid membranes crowded most thickly in the subarachnoid space included the regions around the bifurcation of the internal carotid artery, the area around the hypothalamus, the interpeduncular cistern, the arachnoidal sheaths of the oculomotor nerve, the quadrigeminal cistern and the cisterna magna. Almost all the cranial nerves were encased by their own arachnoidal sheaths when they crossed the cisterns. The arachnoid membranes and trabeculae must be dissected or incised sharply during the operations. Thorough knowledge of the anatomy of the intracranial arachnoid membranes is valuable to take full advantage of the natural anatomic landmarks and interfaces formed by them during surgery.

A novel method for subarachnoid drug delivery in the medullary region of rats

This study describes a novel method for direct subarachnoid drug delivery to the medullary dorsal horn region of rats, without introducing a catheter. The reliability of the method was demonstrated by a pharmacological validation; that is, morphine administration to the medullary region blocked the nociceptive response to formalin injected in the temporomandibular joint (TMJ) region, an effect that was prevented by co-administration of naloxone. The method proposed offers many advantages over the existing methods for medullary drug delivery with catheter implantation. It is easy to be employed, it does not induce any sign of motor impairment, and it does not require the neck surgery performed to implant a catheter in the medullary dorsal horn region. Therefore, it is a useful method for subarachnoid drug delivery in behavioral trigeminal pain studies, particularly when nociceptive behavioral measures that require normal neck muscle activity to occur, such as head withdraw or head flinch, are evaluated.

Percutaneous intraspinal navigation for access to the subarachnoid space: use of another natural conduit for neurosurgical procedures

OBJECT

The purpose of this paper was to demonstrate the usefulness of various fiberoptic endoscopes for percutaneous intraspinal navigation of the spinal canal, posterior fossa, and ventricular system.

METHODS

Fresh, unembalmed cadavers were used, in which lumbar punctures were made for access to the subarachnoid space (in the case of larger [3.8- and 5-mm-diameter] endoscopes, small laminotomies were performed). Static and video images of pertinent structures were acquired for comparison among devices. Endoscopes were compared for their maneuverability, durability, field of view, and image quality. Seven sizes and types of endoscopes were considered. Overall, the devices offering a tip-deflecting mechanism were superior in maneuverability. Endoscopes in which a charged couple display chip was used at the tip of the scope for image acquisition offered improved image quality and field of view. Larger scopes, although more durable, were more rigid and may be limited in application. Multiple images from multiple devices are presented.

CONCLUSIONS

Percutaneous intraspinal navigation offers a promising neurosurgical approach to the spinal canal, the posterior fossa, and the ventricular system. Concerns regarding safety, management of complications, and the lack of adjunctive tools for intervention through the endoscopes or for use under fluoroscopic guidance represent areas that warrant further investigation and development.

[Observation of the ventricular system and subarachnoid space in the skull base by flexible neuroendoscopy: normal structures]

Worldwide in the last two decades, in Latin America in the last decade, and Mexico in particular cerebral endoscopy as part of the minimally invasive neurological surgery, has constituted a significant advance for the treatment of neurological diseases such as congenital or acquired hydrocephalus, Chiari malformation, neurocysticercosis, stroke, ventricular and paraventricular tumors and cysts, arachnoidal cyst and hydrocephalus secondary to shunt malfunction. The lateral ventricles, the third ventricle, the cerebral aqueduct, the fourth ventricle, and the subarachnoid basal cisterns are among the most non-accessible regions of the central nervous system. Due to light-rand fiber optic-systems in combination with the experiences of nine consecutive year's and more than 600 endoscopies, most of them flexible neuroendoscopies, we present the neuroendoscopic approach with flexible cerebral endoscope to the anatomy and its normal variants of the whole ventricle system and the subarachnoid basal cisterns including the subarachnoid space of the cervical spine. We also describe their site related structures including veins, arteries, cranial nerves, pituitary gland, choroidal plexus and their normal anatomic variants.

The cisternal segment of the abducens nerve in man: three-dimensional MR imaging

PURPOSE

The goal of this study was to identify the abducens nerve in its cisternal segment by using three-dimensional turbo spin echo T2-weighted image (3DT2-TSE). The abducens nerve may arise from the medullopontine sulcus by one singular or two separated rootlets.

MATERIAL AND METHODS

We studied 285 patients (150 males, 135 females, age range: 9-72 years, mean age: 33.3 +/- 14.4) referred to MR imaging of the inner ear, internal auditory canal and brainstem. All 3D T2-TSE studies were performed with a 1.5 T MR system. Imaging parameters used for 3DT2-TSE sequence were TR:4000, TE:150, and 0.70 mm slice thickness. A field of view of 160 mm and 256 x 256 matrix were used. The double rootlets of the abducens nerve and contralateral abducens nerves and their relationships with anatomical structures were searched in the subarachnoid space.

RESULTS

We identified 540 of 570 abducens nerves (94.7%) in its complete cisternal course with certainty. Seventy-two cases (25.2%) in the present study had double rootlets of the abducens nerve. In 59 of these cases (34 on the right side and 25 on the left) presented with unilateral double rootlets of the abducens. Thirteen cases presented with bilateral double rootlets of the abducens (4.5%).

CONCLUSION

An abducens nerve arising by two separate rootlets is not a rare variation. The detection of this anatomical variation by preoperative MR imaging is important to avoid partial damage of the nerve during surgical procedures. The 3DT2-TSE as a noninvasive technique makes it possible to obtain extremely high-quality images of microstructures as cranial nerves and surrounding vessels in the cerebellopontine cistern. Therefore, preoperative MR imaging should be performed to detect anatomical variations of abducens nerve and to reduce the chance of operative injuries.

Detailed MR imaging anatomy of the abducent nerve: evagination of CSF into Dorello canal

BACKGROUND AND PURPOSE

The abducent nerve is difficult to identify reliably and consistently with conventional radiologic techniques. In this study, a 3D fast asymmetrical spin-echo MR imaging technique was used to obtain detailed images of the abducent nerve in normal volunteers.

METHODS

The 3D fast asymmetrical spin-echo MR protocol was used to image the abducent nerves in 24 normal volunteers by using a 1-mm section thickness in the tilted axial and parasagittal planes. The microanatomy of the abducent nerve within Dorello's canal was also demonstrated in a cadaver study.

RESULTS

In 24 normal volunteers, the anatomy of 47 abducent nerves was clearly depicted on MR images. The length of the cisternal segment of the abducent nerve, extending from the brain stem to its dural foramina, ranged from 6.7 to 19.6 mm (mean, 13.1 mm). The abducent nerves were at an angle of 5 to 90 degrees (mean, 24.5 degrees) to the clivus. CSF evagination was detected in the region of Dorello's canal in 36 (77%) of 47 abducent nerves. The length of CSF evagination varied: 0.9 mm in five nerves, 1.0 to 1.9 mm in 18 nerves, 2.0 to 2.9 mm in eight nerves, and 3.0 mm or more in five nerves. Histologic examination of serial sections of the abducent nerve revealed that the petroclival segment of the nerve was covered by an envelope composed of an arachnoid cell layer.

CONCLUSION

The course of the abducent nerve was reliably identified using the 3D fast asymmetrical spin-echo MR protocol and a histologically proven arachnoid envelope around the petroclival segment of the nerve was shown as CSF evagination into Dorello's canal by MR imaging.

The distance from the skin to the subarachnoid space can be predicted in premature and formerpremature infants

PURPOSE

Spinal anesthesia can be technically challenging in young infants. We studied whether the distance between the skin and the lumbar subarachnoid space in premature and former-premature young infants could be predicted prior to lumbar puncture.

METHODS

The distance from skin entry point to tip of the spinal needle was measured using a caliper after lumbar spinal anesthesia at the L4-5 interspace. This distance was correlated to the patient's weight, postconceptual age and lumbar ultrasonographic measurement of the skin-to-subarachnoid space and predictive statistical models were sought.

RESULTS

Thirty-five premature or former-premature infants were studied. Three models were examined: all three independent variables, weight and postconceptual age only, and weight only. The model selected contained the weight and postconceptual age, because it had the highest value for adjusted R squared, as well as the lowest value for the mean squared error. Adding the ultrasonic measurement to the model worsened the results. The statistical model that described the depth of the subarachnoid space at the L4-5 level was Y = 13.19 + 0.0026 x W - 0.12 x PCA, where Y is the distance (mm) from the skin to the subarachnoid space, W is the patient's weight (g) and PCA is the postconceptual age (weeks). Adjusted R squared was 0.72, mean square error was 2.63 and P < 10(-9).

CONCLUSION

The distance between the skin and the subarachnoid space at the level of L4-5 interspace can be predicted using a statistical model based on the infant's weight and postconceptual age. Spinal ultrasound has no value in L4-5 subarachnoid space depth prediction.

Relationship between the concentration of supplemental oxygen and signal intensity of CSF depicted by fluid-attenuated inversion recovery imaging

BACKGROUND AND PURPOSE

Prior reports have described increased signal intensity (SI) of CSF on fluid-attenuated inversion recovery (FLAIR) images of anesthetized patients receiving 100% O(2). This appearance can simulate that of diseases. We evaluated the relationship between the concentration of inhaled O(2) and the development of increased SI of CSF on FLAIR images.

METHODS

FLAIR was performed in 25 healthy volunteers breathing room air and 100% O(2) through a face mask for 5, 10, and 15 minutes. MR imaging, including FLAIR imaging, was performed in 52 patients with no potential meningeal abnormalities under general anesthesia: 21 received an equal mixture of N(2)O and O(2), and 31 received 100% O(2). The SI of CSF in volunteers and patients was graded in several locations by using a three-point scale.

RESULTS

SI of CSF significantly increased (P <.05) in various locations, in both volunteers and patients breathing 100% O(2), when compared with SI in the same volunteers breathing room air. Hyperintensity of CSF was not significantly different in volunteers receiving 100% O(2) through a face mask compared with anesthetized patients receiving 100% O(2) through a laryngeal airway or an endotracheal tube. No significant increase in SI occurred in patients receiving 50% O(2), when compared with the SI of volunteers breathing room air.

CONCLUSION

Supplemental oxygen at 100% is a main cause of artifactual CSF hyperintensity on FLAIR images, regardless of the anesthetic drug used. This artifact does not develop when 50% O(2) is administered.

Architecture of arachnoid trabeculae, pillars, and septa in the subarachnoid space of the human optic nerve: anatomy and clinical considerations

AIMS

To describe the anatomy and the arrangement of the arachnoid trabeculae, pillars, and septa in the subarachnoid space of the human optic nerve and to consider their possible clinical relevance for cerebrospinal fluid dynamics and fluid pressure in the subarachnoid space of the human optic nerve.

METHODS

Postmortem study with a total of 12 optic nerves harvested from nine subjects without ocular disease. All optic nerves used in this study were obtained no later than 7 hours after death, following qualified consent for necropsy. The study was performed with transmission (TEM) and scanning electron microscopy (SEM).

RESULTS

The subarachnoid space of the human optic nerve contains a variety of trabeculae, septa, and stout pillars that are arranged between the arachnoid and the pia layers of the meninges of the nerve. They display a considerable numeric and structural variability depending on their location within the different portions of the optic nerve. In the bulbar segment (ampulla), adjacent to the globe, a dense and highly ramified meshwork of delicate trabeculae is arranged in a reticular fashion. Between the arachnoid trabeculae, interconnecting velum-like processes are observed. In the mid-orbital segment of the orbital portion, the subarachnoid space is subdivided, and can appear even loosely chambered by broad trabeculae and velum-like septa at some locations. In the intracanalicular segment additionally, few stout pillars and single round trabeculae are observed.

CONCLUSION

The subarachnoid space of the human optic nerve is not a homogeneous and anatomically empty chamber filled with cerebrospinal fluid, but it contains a complex system of arachnoid trabeculae and septa that divide the subarachnoid space. The trabeculae, septa, and pillars, as well as their arrangement described in this study, may have a role in the cerebrospinal fluid dynamics between the subarachnoid space of the optic nerve and the chiasmal cistern and may contribute to the understanding of the pathophysiology of asymmetric and unilateral papilloedema. All the structures described are of such delicate character that they can not even be visualised with high resolution magnetic resonance imaging (MRI).

Could ultrasonography be used by an anaesthetist to identify a specified lumbar interspace before spinal anaesthesia?

BACKGROUND

Insertion of a needle into the lumbar subarachnoid space may cause damage to the spinal cord. Current techniques to identify a safe interspace have limitations. Ultrasound was investigated as a means to improve anatomical accuracy.

METHODS

Seventeen patients attending for elective magnetic resonance imaging (MRI) of the spine were studied. Ultrasonic identification of the L3-4 interspace was attempted by an anaesthetist and a marker was placed. A radiologist identified the anatomical location of the marker on the MRI scan.

RESULTS

Thirteen out of 17 markers were at the L3-4 interspace; four were at the L2-3 interspace.

CONCLUSIONS

These results suggest that ultrasonography may be a useful adjunct to safe subarachnoid anaesthesia.

[Gradient-index (GRIN) endoscopic examinations from the inner structures of the optic nerve meninges]

BACKGROUND

Due to the excellent image quality and the small outer diameter of the GRIN-(gradient index) endoscope tips we were able to examine the subdural and the subarachnoidal space of the optic nerve meninges by endoscopy. This examination was performed to obtain more information about the inner structure of the optic nerve meninges.

MATERIAL AND METHODS

In this post-mortem study 7 optic nerves were examined from the chiasm to the globe by GRIN endoscopy (Volpi, Schlieren, Switzerland), with an outer diameter of 0.89 mm, integrated optic of 0.5 mm diameter and an integrated fluid channel of 0.2 mm diameter.

RESULTS

In all cases the endoscopic examination of the optic nerve meninges was technically easy to perform. It was possible to study the inner surface of the nerve sheaths and the nerve sheath spaces in close-up. We found horizontal and vertical cords on the inner surface of the dura mater, which could tighten by movements of the optic nerve.

CONCLUSIONS

With a gradient-index (GRIN) endoscope we obtained new information about the inner structure of the optic nerve meninges. New theories about the changes of the optic nerve meninges during movements of the optic nerve may evolve from this study. Further studies with this new method should be encouraged.