Identification of direct connections between the dura and the brain

The arachnoid barrier delineates the border between the central nervous system and dura mater. Although the arachnoid barrier creates a partition, communication between the central nervous system and the dura mater is crucial for waste clearance and immune surveillance1,2. How the arachnoid barrier balances separation and communication is poorly understood. Here, using transcriptomic data, we developed transgenic mice to examine specific anatomical structures that function as routes across the arachnoid barrier. Bridging veins create discontinuities where they cross the arachnoid barrier, forming structures that we termed arachnoid cuff exit (ACE) points. The openings that ACE points create allow the exchange of fluids and molecules between the subarachnoid space and the dura, enabling the drainage of cerebrospinal fluid and limited entry of molecules from the dura to the subarachnoid space. In healthy human volunteers, magnetic resonance imaging tracers transit along bridging veins in a similar manner to access the subarachnoid space. Notably, in neuroinflammatory conditions such as experimental autoimmune encephalomyelitis, ACE points also enable cellular trafficking, representing a route for immune cells to directly enter the subarachnoid space from the dura mater. Collectively, our results indicate that ACE points are a critical part of the anatomy of neuroimmune communication in both mice and humans that link the central nervous system with the dura and its immunological diversity and waste clearance systems.

Choroid plexus of the fourth ventricle: Review and anatomic study highlighting anatomical variations

Relatively few studies have been performed that analyze the morphology of the choroid plexus of the fourth ventricle. Due to the importance of this tissue as a landmark on imaging and during surgical intervention of the fourth ventricle, the authors performed a cadaveric study to better characterize this important structure. The choroid plexus of the fourth ventricle of 60 formalin fixed adult human brains was examined and measured. The horizontal distance from the midline to the lateral most point of the protruding tip of the horizontal limbs was measured. In the majority of the 60 brain specimens, right and left horizontal limbs of the choroid plexus were seen extending from the midline and protruding out of their respective lateral apertures of the fourth ventricle and into the subarachnoid space. However, on 3.3% of sides, there was absence of an extension into the foramen of Luschka and in one specimen, this lack of extension into the foramen of Luschka was bilateral. On two sides, there was discontinuity between the midline choroid plexus and the tuft of choroid just outside the foramen of Luschka. For specimens in which the choroid plexus did protrude through the foramen of Luschka (96.7%), these tufts were located anterior to the flocculus and inferolateral to the facial/vestibulocochlear nerve complex and posterosuperior to the glossopharyngeal/vagal/accessory complex. A thorough understanding of the normal and variant anatomy of the fourth ventricular choroid plexus is necessary for those who operate in, or interpret imaging of, this region.

Does a small posterior fossa increase nerve vascular conflict in trigeminal neuralgia?

BACKGROUND

Magnetic resonance imaging (MRI) can be helpful in visualizing neurovascular conflict (NVC) of the trigeminal nerve in patients with trigeminal neuralgia (TN), but the relationship between these two events is controversial.

PURPOSE

To investigate whether posterior fossa volume is a predisposing factor for NVC in TN.

MATERIAL AND METHODS

We conducted a case-control study of clinically diagnosed idiopathic TN of 30 patients aged 30-79 years and 30 age- and sex-matched controls. We compared the volume of the posterior fossa and subarachnoid space using fast-imaging employing steady-state acquisition MRI and the iPlan® programme of BrainLab.

RESULTS

The posterior fossa volumes in controls and patients with TN were 168.97 cm(3) and 167.63 cm(3), respectively. A small pontomesencephalic cistern volume was more frequent in TN. However, neither the cisternal nor parenchymal portions of the posterior fossa were different between patients with TN and controls, and no significant volume difference was observed in this study.

CONCLUSION

Although the hypothesis that small posterior fossa volume influences TN was feasible, we did not find any volumetric differences (including the cisternal and parenchymal volumes).However, small pontomesencephalic cistern volumes were more frequent in patients with TN.

Evaluation of a new training device to simulate the epidural and subarachnoid spaces for neuraxial anesthesia techniques

BACKGROUND

We are introducing a new epidural/spinal simulation unit to be used either as a part-task trainer to teach and learn regional anesthesia techniques or to be inserted in the manikin's back to allow reliable advanced simulation scenarios. The aim of this study was to determine if it may be a useful tool for training novice anesthesiologists in these procedures according to the evaluation performed by experienced anesthetists.

METHODS

Experienced anesthetists performed an epidural followed by a lumbar puncture procedure on the simulator model. Various aspects of both epidural and lumbar puncture insertions were scored for likeness to a real patient using a Likert scale.

RESULTS

Experienced anesthetists found the simulator to be life-like for almost all the aspects of epidural or spinal insertion and that the overall impression was that the simulator could provide a useful tool for training of epidural and spinal techniques. Almost all the examiners appreciated that this device contained layers representing the anatomical boundaries of each compartment, and the module can be added blood or sponge to the epidural compartment or water to the spinal compartment to challenge the trainee with more difficult procedure such as inadvertent dural or vascular puncture or difficult catheter insertion.

CONCLUSION

This device to be inserted in a full scale manikin may be a promising tool for training of neuraxial procedures. It could be also an essential component of more complex high fidelity scenarios when neuraxial anesthesia is one of the major learning goals.

Subarachnoid space: new tricks by an old dog

PURPOSE

The purpose of the study was to: (1) evaluate the subarachnoid space (SAS) width and pial artery pulsation in both hemispheres, and (2) directly compare magnetic resonance imaging (MRI) to near-infrared transillumination/backscattering sounding (NIR-T/BSS) measurements of SAS width changes in healthy volunteers.

METHODS

The study was performed on three separate groups of volunteers, consisting in total of 62 subjects (33 women and 29 men) aged from 16 to 39 years. SAS width was assessed by MRI and NIR-T/BSS, and pial artery pulsation by NIR-T/BSS.

RESULTS

In NIR-T/BSS, the right frontal SAS was 9.1% wider than the left (p<0.01). The SAS was wider in men (p<0.01), while the pial artery pulsation was higher in women (p<0.01). Correlation and regression analysis of SAS width changes between the back- and abdominal-lying positions measured with MRI and NIRT-B/SS demonstrated high interdependence between both methods (r = 0.81, p<0.001).

CONCLUSIONS

NIR-T/BSS and MRI were comparable and gave equivalent modalities for the SAS width change measurements. The SAS width and pial artery pulsation results obtained with NIR-T/BSS are consistent with the MRI data in the literature related to sexual dimorphism and morphological asymmetries between the hemispheres. NIR-T/BSS is a potentially cheap and easy-to-use method for early screening in patients with brain tumours, increased intracranial pressures and other abnormalities. Further studies in patients with intracranial pathologies are warranted.

The presence of arachnoiditis affects the characteristics of CSF flow in the spinal subarachnoid space: a modelling study

Syringomyelia is a neurological disorder characterised by high pressure fluid-filled cysts within the spinal cord. As syringomyelia is associated with abnormalities of the central nervous system that obstruct cerebrospinal fluid (CSF) flow, it is thought that changes in CSF dynamics play an important role in its pathogenesis. Using three-dimensional computational models of the spinal subarachnoid space (SAS), this study aims to determine SAS obstructions, such as arachnoiditis, change in CSF dynamics in the SAS. The geometry of the SAS was reconstructed from a series of MRI images. CSF is modelled as an incompressible Newtonian fluid with a dynamic viscosity of 1 mPa s. Three computational models simulated CSF flow in either the unobstructed SAS, or with the SAS obstructed by a porous region simulating dorsal or circumferential arachnoiditis. The permeability of this porous obstruction was varied for the model with dorsal arachnoiditis. The results show that arachnoiditis increases flow resistance in the SAS and this is accompanied by a modest increase in magnitude and/or shift in timing (with respect to the cardiac cycle) of the CSF pressure drop across the region of arachnoiditis. This study suggests that syrinx formation may be related to a change in temporal CSF pulse pressure dynamics.

The use of nicardipine prolonged release implants (NPRI) in microsurgical clipping after aneurysmal subarachnoid haemorrhage: comparison with endovascular treatment

BACKGROUND

Nicardipine prolonged release implants (NPRI) have been shown to decrease the incidence of cerebral vasospasm and infarcts significantly in patients after aneurysmal subarachnoid haemorrhage (SAH) following microsurgical clipping. Yet, the comparison with results after endovascular coiling is lacking. This study was conducted to determine the differences in the incidence of cerebral vasospasm and infarctions between those two treatment modalities

METHODS

The design of this investigation reflects a case-control study; 27 patients suffering from acute SAH were treated by microsurgical clipping and received an intracisternal implantation of NPRI. Twenty-seven matching consecutive patients after microsurgical treatment without implantation of NPRI or endovascular treatment, respectively, served as controls. The incidence of angiographic vasospasm and cerebral infarctions were documented.

RESULTS

All groups were comparable concerning demographics and severity of SAH. Twenty-four of 81 patients developed angiographic vasospasm (>33% constriction). The incidence of vasospasm was 48%, 44% and 11% for patients after endovascular treatment, microsurgical clipping without NPRI and microsurgical clipping with NPRI, respectively. New cerebral infarctions occurred in 28%, 22% and 7% of the treated patients, respectively. A good clinical recovery 1 year after the initial bleeding (modified Rankin scale 0-2) was seen in 48%, 50% and 77% of the treated patients, respectively.

CONCLUSION

The use of NPRI during microsurgical clipping was confirmed to be safe and effective. Patients who received intracisternally implanted NPRI during clipping after aneurysmal SAH yielded significantly lower vasospasm and infarction rates, and showed a better clinical outcome when compared with clipping without NPRI and also when compared with endovascular coiling.

Microsurgical and endoscopic anatomy of Liliequist's membrane and the prepontine membranes: cadaveric study and clinical implications

BACKGROUND

Liliequist's membrane is mostly described as having a diencephalic leaf, mesencephalic leaf, and diencephalic-mesencephalic leaves in the literature. Also different descriptions of the prepontine membranes were reported. In this study, we visualized the regular structural forms of membranes without disturbing any attachments and defined infrachiasmatic and prepontine safety zones. We discussed the clinical significance of these structures.

MATERIALS AND METHODS

The study was carried out on 24 adult human cadavers at the Morgue Specialization Department of the Forensic Medicine Institution following the initial autopsy examination. Liliequist's membrane and the prepontine membranes were explored after retraction of the frontal lobes. Dissections were performed under the operative microscope. A 0- and 30-degree, 2.7-mm angled rigid endoscope (Aesculap, Tuttlingen, Germany) was advanced through the prepontine cistern from the natural holes of membranes, or small holes were opened without damaging the surrounding structures.

RESULTS

The basal arachnoid membrane (BAM) continued as Liliequist's membrane (LM) without any distinct separation in all specimens. The LM coursed over the posterior clinoids and split into two leaves as the diencephalic leaf (DL) and mesencephalic leaf (ML) in 18 specimens; the medial pontomesencephalic membrane (MPMM) coursed anterolaterally as a continuation of the ML and attached to the medial surfaces of the fifth and sixth nerves, joining with the lateral pontomesencephalic membrane (LPMM), which was also a posterolateral continuation of the ML in all specimens. The medial pontomedullar membrane (MPMdM) and lateral pontomedullar membrane (LPMdM) were observed in 21 specimens. The MPMdM membrane was a continuation of the MPMM, and the LPMdM was a continuation of the LPMM in all 21 specimens.

CONCLUSION

We observed that the LM is a borderless continuation of the BAM. The MPMM and LPMM split from the ML without any interruptions. The MPMdM and LPMdM were a single membrane continuing from the MPMM and LPMM. We determined infrachiasmatic and prepontine areas that can be important for inferior surgical approaches.

Median aperture of the fourth ventricle revisited

BACKGROUND

The median aperture of Magendie is the largest of three openings of the fourth ventricle and thus it forms the main path for the outflow of the cerebrospinal fluid from the ventricle. The Magendie aperture connects the fourth ventricle with the cisterna magna and makes a natural corridor for neurosurgical approach and inspection of the ventricle and its floor. The purpose of this study was to give a contemporary anatomical view of this structure in the context of historical data.

MATERIAL AND METHODS

The Magendie foramen was studied in 30 fixed specimens of human brainstems with cerebella. The microdissection technique was used. Measurements were taken with a microscope ocular ruler.

RESULTS

The aperture is limited by the following structures: obex and gracile tubercles inferiorly, and tela choroidea with choroid plexus superolaterally. Obex tubercles usually have the form of a piece of neural tissue bridging two halves of the brainstem above the entrance to the central canal. Gracile tubercles together are 8.15 mm wide and the maximal width of the foramen is 6.53 mm. Tela choroidea attaches laterally at both sides to the inferior medullary velum. In most cases the right and left choroid plexus are connected to each other with a triangular membrane of tela choroidea, which protrudes through the median foramen and attaches to the vermis at a highly variable level.

CONCLUSIONS

We hope that the presented description of anatomical relations around the Magendie aperture, with its new measurements, will be helpful for those operating in the area and will explain some of the inaccuracies found in literature.

The distance from the skin to the epidural and subarachnoid spaces in parturients scheduled for caesarean section

BACKGROUND

The purpose of this study was to measure the skin to epidural space distance (SED), the skin to subarachnoid space distance (SSD) and the epidural to subarachnoid space distance (ESD) at the L3-4 interspace in parturients scheduled for caesarean section (CS) and to investigate whether any correlations exist between these distances and various physical and anthropometric parameters.

METHODS

This study consisted of 332 parturients scheduled for CS. The epidural space was identified by noting the loss of resistance to air at the L3-4 intervertebral space with a Tuohy needle, thus permitting measurement of the SED. The spinal needle was introduced through the Tuohy needle and, after identification of the subarachnoid space, was locked in the epidural needle. The distance between the tip of the Tuohy needle and tip of spinal needle (ESD) was recorded. This number was added to the SED to obtain the SSD value.

RESULTS

Mean values ± standard deviations for SED, SSD and ESD were 5.6 ± 1.6 cm, 6.5 ± 1.2 cm and 0.9 ± 0.5 cm, respectively. Statistically significant correlations were observed between SED, SSD and ESD with body mass index and body weight of the parturients, as well as between the SED and the parturient's height. Furthermore, a significant negative correlation was observed between the ESD and gestational age. Finally, a significant correlation existed between the SSD and ESD.

CONCLUSION

Measurements of SED, SSD and ESD in parturients and the correlations between these distances to various physical and anthropometric parameters may be of potential value for combined spinal-epidural anesthesia (CSEA) in parturients scheduled for CS.

Radiological anatomy of the ambient cistern in children

Ambient cistern (AC) is a thin extension of the subarachnoid space surrounding the brainstem at the level of the mesencephalon and pons. Despite various definitions, it constitutes an important landmark in clinical assessment of intracranial volume reserve. Although it is indisputably useful, there exists no defined standard for radiological examination for the dimensions and ranges in specific age groups. This paper aims to describe the ambient cistern anatomically and give the ranges of dimensions for proper radiological interpretation. The study was performed on 160 axial computed tomography (CT) examinations of Polish children of both sexes, aged 1-18 years, admitted to the hospital because of mild brain concussion. Pictures were made using a Siemens 8-row CT scanner, without contrast administration. We estimated distances at the level of the pons and midbrain, based on axial cross-sections, according to standard radiological protocol. The parameters included the width of the AC in its anterior and posterior part, the width of the tentorial notch, and the distance from the pons and sella. All measurements were analyzed statistically with StatSoft Statistica 8.0 software. The average width of the AC differs between age groups. It is greatest at 1-3 years (2.8 +/- 0.6 mm) and lowest at 4-10 years (2.4 +/- 0.6 mm). AC is more likely to be greater in its anterior part in boys. The distance from the sella to the pons is greatest in 1-3-year-old girls (6.9 +/- 1.3 mm), and the tentorial notch is widest in the 15-18-year-old group (24.6 +/- 2.4 mm). Dimensions of the AC correlate with intracranial reserve volume. This is particularly visible in the youngest children. Thin and narrow AC is not always a sign of raised intracranial pressure. It may be specific for the child's age.

Intrathecal catheter-syringe adaptor for short-term intrathecal analgesia with an externalized pump: a case report

BACKGROUND

In most patients, cancer pain is effectively treated with conservative medical management consisting of oral and/or transdermal analgesics. Cancer patients tend to fail conservative medical management near the end of their life expectancy, thus requiring alternative routes of analgesia such as intravenous, epidural, or intrathecal. The intrathecal route provides the most effective analgesia due to the close proximity of the opioid receptors in the spinal cord. Though there are many techniques that exist for intrathecal drug delivery, complications can limit effectiveness such as infection, bleeding, cerebrospinal fluid (CSF) leaks, post-dural puncture headaches (PDPH), pump and/or catheter malfunctions, or limitations of technical expertise. Therefore, an important goal in palliative cancer pain therapy is to use equipment that is going to have the fewest number of complications and will be the most familiar to the health care providers. We describe the combination of the Medtronic Indura 1P catheter, which has the least catheter-related complications and can be used with any external drug infusion pump. These are regular infusion pumps that the health care workers are familiar with so they can provide excellent and efficient service to the patient.

METHODS

In an operating room, the intrathecal catheter was placed using sterile technique under fluoroscopic guidance. The epidural space was identified with loss of resistance technique. Then the introducer needle (supplied in the Indura 1P catheter kit) was advanced until free-flowing CSF was obtained. The spinal catheter was advanced into the intrathecal space through the introducer needle to lumbar 2-3 level. The catheter was tunneled subcutaneously 10 cm lateral to the catheter exit site. A syringe filling device was inserted into the catheter opening and was secured with silk suture. A luer lock syringe was attached to the syringe filling device and CSF was aspirated. The syringe filling device was capped and later attached to an external drug infusion pump.

RESULTS

We report the successful use of the Medtronic Indura 1P, one piece intrathecal catheter, connected to the external drug pump for a 3 week period in a patient with metastatic cervical cancer for palliative pain control.

LIMITATIONS

Case report only.

CONCLUSION

This technique is simple to perform by pain specialists. The catheter modification allows the use of the Medtronic intrathecal catheter with standard external drug infusion pumps. This facilitates the patient's care in the hospice setting.

Outcome correlates with blood distribution in subarachnoid hemorrhage of unknown origin

PURPOSE

Between 15 and 30 % of patients with subarachnoid hemorrhage (SAH) have no bleeding source and usually have a benign clinical course and outcome. The objectives of this study were to classify the pattern of blood distribution on initial computed tomography (CT) and to correlate it with clinical outcome in aneurysmal (ASAH) and SAH of unknown origin (SAHuO).

METHODS

We reviewed 112 CTs of SAHuO and 104 CTs of ASAH patients. Blood distribution was classified according to a new grading system (type 0-4) and correlated to Hunt and Hess (H&H) grade and modified Rankin scores (MRS) at short- and long-term follow-up.

RESULTS

Fifty percent of 112 SAHuO patients were classified as type 0 (no visible blood on CT) or 1 (blood restricted to prepontine cisterns). Most ASAH patients presented with bleeding into the lateral Sylvian fissure (66%; type 3) or with intracerebral hemorrhage (27%; type 4) whereas types 0 and 1 were not observed. SAHuO patients were in better clinical condition on admission than ASAH patients (p < 0.0001). H&H grades of SAHuO patients correlated with the amount of subarachnoid blood according to the new classification (p = 0.004). Short-term outcome was obtained from 100% and long-term outcome from 95% patients (follow-up 29 +/- 31 months). Short- and long-term MRS correlated with blood distribution in SAHuO patients (p = 0.012) and was significantly better than in ASAH patients (p < 0.0001). No correlation was observed between blood distribution, H&H grade, and short- and long-term outcome in aneurysmal patients.

CONCLUSIONS

In SAH of unknown origin, a new classification allows to predict outcome based on the extent of blood on CT.

Five-level one-piece laminoplasty for extensive tumors of the lumbar spine

The authors describe the surgical method and results of nonexpansive one-piece multivel laminoplasty of the whole lumbar spine, for microsurgical resection of extensive spinal tumors. This technique allows a very comfortable approach to the dura and intradural content, as well as a perfect replacement of the posterior spinal arch with supporting elements and an optimal reconstruction of the spinal anatomy. A nonexpansive whole lumbar one-piece laminoplasty was performed for resection of extensive multilevel lumbar tumors. The authors report an illustrative case of a patient who initially presented with a three-year history of numbness on both legs and progressive difficulty in walking. Two months before admission, he complained of bilateral sciatica and rectourinary dysfunction. A spinal magnetic resonance imaging (MRI) documented an intradural tumor extending from L2 to S1. The patient underwent a nonexpansive whole lumbar one-piece laminoplasty and microsurgical removal of the intradural lesion. The postoperative course was uneventful, the sensory disturbances and bilateral sciatica early recovered while rectourinary disturbance gradually improved up to a complete resolution at one year follow-up. The authors believe that multilevel laminoplasty rather than laminectomy is the technique of choice as a posterior procedure for extensive lumbar spinal tumors. With this technique, it is possible to obtain a very confortable approach to the dura and intradural content, as well as a perfect replacement of the posterior spinal arch with supporting elements and an optimal reconstruction of the normal spine. Moreover, this method prevents postoperative instability and deformity and avoids the so called post-laminectomy epidural membrane.

Bacterial toxins and Multiple Sclerosis

The primary pathogenetic mechanism responsible for the distinctive demyelinating lesions in the Central Nervous System (CNS) in Multiple Sclerosis (MS), first described in remarkable detail by Charcot more than 170 years ago, remains one of the most baffling conundrums in medicine. A possible role for bacterial cell molecules and transportable proteins in the pathogenesis of MS is reviewed. The ability of bacterial toxins to distort immunity and to cause distinctive toxic damage in the nervous system is discussed in the light of largely forgotten data linking bacterial nasopharyngeal infections with optic neuritis, optochiasmatic arachnoiditis and MS. While the blood-brain barrier substantially protects the CNS from hematogenous toxins, there is a route by which the barrier may be by-passed. Data is reviewed which shows that the CSF and extra-cellular fluid circulation is bi-directionally linked to the lymphatic drainage channels of the nasopharyngeal mucosa. While this provides a facility by which the CNS may mount immunological responses to antigenic challenges from within, it is also a route by which products of nasopharyngeal infection may drain into the CNS and be processed by the immune cells of the meninges and Virchow-Robin perivascular spaces. If potentially toxic bacterial products are identified in early MS tissues at these sites, this would provide an entirely new insight into the pathogenetic mechanisms of this frustratingly enigmatic disease.

EEG and MEG coherence: measures of functional connectivity at distinct spatial scales of neocortical dynamics

We contrasted coherence estimates obtained with EEG, Laplacian, and MEG measures of synaptic activity using simulations with head models and simultaneous recordings of EEG and MEG. EEG coherence is often used to assess functional connectivity in human cortex. However, moderate to large EEG coherence can also arise simply by the volume conduction of current through the tissues of the head. We estimated this effect using simulated brain sources and a model of head tissues (cerebrospinal fluid (CSF), skull, and scalp) derived from MRI. We found that volume conduction can elevate EEG coherence at all frequencies for moderately separated (<10 cm) electrodes; a smaller levation is observed with widely separated (>20 cm) electrodes. This volume conduction effect was readily observed in experimental EEG at high frequencies (40-50 Hz). Cortical sources generating spontaneous EEG in this band are apparently uncorrelated. In contrast, lower frequency EEG coherence appears to result from a mixture of volume conduction effects and genuine source coherence. Surface Laplacian EEG methods minimize the effect of volume conduction on coherence estimates by emphasizing sources at smaller spatial scales than unprocessed potentials (EEG). MEG coherence estimates are inflated at all frequencies by the field spread across the large distance between sources and sensors. This effect is most apparent at sensors separated by less than 15 cm in tangential directions along a surface passing through the sensors. In comparison to long-range (>20 cm) volume conduction effects in EEG, widely spaced MEG sensors show smaller field-spread effects, which is a potentially significant advantage. However, MEG coherence estimates reflect fewer sources at a smaller scale than EEG coherence and may only partially overlap EEG coherence. EEG, Laplacian, and MEG coherence emphasize different spatial scales and orientations of sources.

When is enlargement of the subarachnoid spaces not benign? A genetic perspective

Enlargement of the subarachnoid spaces is occasionally encountered during neuroimaging of children. This enlargement is generally regarded as a nonpathologic process that resolves uneventfully. However, there are several genetic disorders in which enlargement of the subarachnoid spaces can be an early sign, or the feature of an associated syndrome, that may aid in the underlying diagnosis. Recognizing subarachnoid space enlargement in these circumstances requires an understanding of the normal physiology of the subarachnoid space at different time points in a child's neurodevelopment. This article reviews the events shaping the subarachnoid space, both during normal physiologic maturation and in specific genetic disorders.

MRI findings of the normal and diseased trigeminal nerve ganglion and branches: a pictorial review

The trigeminal nerve is the largest cranial nerve with both a sensory and motor function. MRI is an excellent technique to evaluate the trigeminal nerve. We report the MRI findings and illustrate the normal and diseased trigeminal nerve at Meckel's cave, the cavernous sinus, the skull base foramina, the pterygopalatine fossa and the peripheral branches.

Endoscopic anatomy of the thecal sac using a flexible steerable endoscope

In this study the ability for upward-orientated endoscopic visualization of thecal subarachnoid space using a flexible steerable endoscope was evaluated in order to compare endoscopic anatomical findings with the already known macroscopic ones of the incontained structures and to test the approach for clinical employment. For this purpose, four adult phenol-formalin embalmed cadavers were used and the approach selected was through a laminectomy window at the S1-S2 level. The dura mater was opened and a flexible steerable endoscope (Storz, of 2.8 mm external diameter with one working channel) was inserted subarachnoidally for upward-orientated observation of the content of thecal sac. By using this approach filum terminale, lower lumbar, sacral and coccygeal nerve rootlets were identified and observed in detail. By moving the endoscope even more upwards, inspection of the upper part of the thecal subarachnoid space and conus medullaris was also possible. The findings collected from the study indicate that this approach for upward-orientated intradural subarachnoid endoscopy gives an appropriate working and inspecting window to the lower, as well as to the upper part of the thecal subarachnoid space and even of the conus medullaris. Furthermore, inspection and identification of lower lumbar, sacral and coccygeal nerve rootlets is possible and efficient and the endoscopic anatomical observations coincide with the already known gross-anatomical ones.

Optimizing the transplant dose of a human neuronal cell line graft to treat SCI pain in the rat

Neuropathic pain is a prevalent and difficult problem in the setting of spinal cord injury (SCI). The use of cellular transplant therapy to treat this pain has been successful with the use of a human neuronal cell line, hNT2.17 [M.J. Eaton, S.Q. Wolfe, M.A. Martinez, M. Hernandez, C. Furst, J. Huang, B.R. Frydel, O. Gomez-Marin, Subarachnoid transplant of a human neuronal cell line attenuates chronic allodynia and hyperalgesia after excitotoxic SCI in the rat, J. Pain 8 (2007) 33-50]. Intrathecal transplant of these cells potently reverses behavioral hypersensitivity after excitotoxic spinal cord injury in the rat model. This study focuses on delineating the optimal dose of these cell grafts in the same model. Two weeks after intraspinal injection of quisqualic acid (QUIS) with subsequent behavioral hypersensitivity, terminally differentiated hNT2.17 cells were transplanted into 300 g Wistar-Furth rats in a logarithmic variation of doses: 10(6), 10(5) and 10(3) cells. Behavioral hypersensitivity testing was performed weekly for 6 weeks following transplant. The dose of 10(6) cells (or approximately 3 million/kg) potently and permanently reversed both cutaneous allodynia (CA) and thermal hyperalgesia (TH). Reduced transplant doses of the hNT2.17 cell line did not permanently reverse behavioral hypersensitivity, suggesting that there is an optimal dose that can be used as a clinical tool to treat SCI-associated neuropathic pain.

Novel application of computer-assisted cisternal endoscopy for the biopsy of pineal region tumors: cadaveric study

BACKGROUND

Long-standing debate continues about the management and biopsy of pineal tumors because of their complex microsurgical anatomy and deep location. Inspired by the concept of biopsy under direct visualization in the absence of hydrocephalus, we explored the effectiveness of neuroendoscope outside of its traditional territory using a new minimally invasive technique, computer-assisted cisternal endoscopy (CACE), for the biopsy of pineal tumors.

METHOD

Five cadaver heads were dissected to expose the pineal region through the posterior fossa. In the other 5 heads, a rigid endoscope-wand combination was introduced in the supracerebellar space lateral to the arachnoid of the superior cerebellar cistern in midline. Endoscopic exposure of the pineal gland was correlated with the real-time image of the localizing wand. After the wand was removed, arachnoid was further dissected from the deep veins and the pineal gland, and a four-quadrant biopsy was obtained.

FINDINGS

The combination of technologies of frameless guided stereotaxy and neuroendoscopy enhanced our ability to navigate the ventriculoscope in narrow spaces (e.g., posterior fossa cisterns). Compared with transventricular and conventional stereotactic trajectories, application of CACE in supracerebellar infratentorial trajectory offered the shortest route to the pineal region, anatomical orientation, no violation of eloquent neurovascular structures, and adequate visibility to deep veins and arteries.

CONCLUSIONS

CACE may be used to approach pineal lesions outside the cerebral ventricular system for biopsy or debulking. Continuous computer updates on the endoscope position allows its safe navigation in narrow spaces (e.g., cerebrospinal fluid cistern). Its success will await future surgical trials.

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.