[Structure of the arachnoid layer of the human spinal meninges: a barrier that regulates dural sac permeability]. / Morfología de la lámina aracnoidea espinal humana. Barrera que limita la permeabilidad del saco dural.

OBJECTIVES: Drugs injected into the epidural space are known to penetrate the subarachnoid space by simple diffusion through the dural sac. We aimed to study the cellular ultrastructure of the arachnoid membrane and the type of intercellular junctions responsible for creating the barrier that regulates the passage of drugs through the dural sac in humans. MATERIAL AND METHODS: Fourteen tissue samples of arachnoid membrane were taken from 2 patients during procedures that required opening the lumbar dural sac. The samples were treated with glutaraldehyde, osmium tetroxide, ferrocyanide and acetone, and then embedded in resin. Ultrathin sections were stained with lead citrate for examination by transmission electron microscopy. RESULTS: The arachnoid membrane was 35 to 40 microm thick. The outer surface contained neurothelial cells (dural border cells) along the subdural compartment, while the internal portion was made up of a plane 5 to 8 microm thick with 4 to 5 arachnoid cells overlapping to form a barrier layer. The intercellular spaces on this plane were 0.02 to 0.03 microm wide; the arachnoid cells were bridged by specialized junctions (desmosomes and other tight junctions). CONCLUSIONS: Structural features of the arachnoid cells provide a barrier within the human dural sac. They occupy only the internal portion of the arachnoid membrane. Specialized intercellular junctions explain the selective permeability of this membrane.

Clinical implications of epidural fat in the spinal canal. A scanning electron microscopic study.

BACKGROUND AND OBJECTIVES: This review of articles summarizes recent developments in relation to fat located in the epidural space and also in dural sleeves of spinal nerve roots in order to improve our understanding of the clinical effects of the epidural blockade. METHOD: Medline search was carried cross-matching of the following words: "epidural fat", "epidural space", "adipose tissue" and "fat cells" from 1966 to 2008 in which articles referring to different pathologies that alter the epidural fat were also reviewed. Techniques used by different authors included the use of samples from dissections, cryomicrotome sections, as well as light and electron microscopy. RESULTS: Fat in the epidural space has a metameric distribution along the spinal canal that can be altered in some pathological conditions. Epidural fat is not evenly distributed. At cervical level fat is absent while in the lumbar region, fat in the anterior and posterior aspects of the epidural space forms two unconnected structures. Fat cells are found also in the thickness of dural sleeves enveloping spinal nerve roots but not in the region of the dural sac. Epidural lipomatosis is characterized by an increase in epidural fat content. When a patient has a combination of kyphosis and scoliosis of the spine, the epidural fat distributes asymmetrically. Spinal stenosis is frequently accompanied by a reduction in the amount of epidural fat around the stenotic area. CONCLUSIONS: The epidural space contains abundant epidural fat that distributes along the spinal canal in a predictable pattern. Fat cells are also abundant in the dura that forms the sleeves around spinal nerve roots but they are not embedded within the laminas that form the dura mater of the dural sac. Drugs stored in fat, inside dural sleeves, could have a greater impact on nerve roots than drugs stored in epidural fat, given that the concentration of fat is proportionally higher inside nerve root sleeves than in the epidural space, and that the distance between nerves and fat is shorter. Similarly, changes in fat content and distribution caused by different pathologies may alter the absorption and distribution of drugs injected in the epidural space.

[Discrepancy between clinical and radiologic manifestations of an epidural hematoma after catheterization]. / Discordancia clínico-radiológica y resolución espontánea de un hematoma postcateterización epidural.

Neuraxial techniques are considered safe if certain guidelines are followed, but they are not risk free. We report the case of an 81-year-old woman with an invasive bladder tumor who underwent radical cystectomy with a Bricker-type procedure. General anesthesia was used and epidural analgesia was also provided for surgical and postoperative pain management. Late in the postoperative recovery period a large epidural hematoma was diagnosed based on radiologic signs of spinal cord compression, in the absence of symptoms other than mild and progressive back pain that developed after extubation. The surgeon decided against emergency surgery to reduce compression. Symptoms resolved gradually, and a magnetic resonance image 45 days after discharge confirmed that the hematoma was smaller. In addition to the usual safety recommendations for epidural anesthesia with regard to drugs that alter hemostasis, it is important to bear in mind circumstances that have pharmacokinetic repercussions and that increase risk. Lower back pain can be a warning sign. Some cases may resolve spontaneously.

[Ziconotide: an innovative alternative for intense chronic neuropathic pain]. / Ziconotide: una alternativa innovadora en el dolor crónico neuropático intenso.

INTRODUCTION: Intense chronic pain is a very important health problem, as it has a high prevalence (5-10%), a multifactorial aetiology and its management is very often a very complex affair. Treatment of severe cases sometimes requires interventional approaches, such as continuous intrathecal infusion of opioids. CASE REPORT: We report the case of a 38-year-old female with intense neuropathic pain in the lower back and the lower limbs secondary to three operations on the L5-S1 lumbar segment. After implementing several different pharmacological regimes involving both oral and implanted systems (spinal cord stimulation and subarachnoid infusion pump with different pharmacological combinations) with no clinical improvement, intrathecal infusion with ziconotide was included in the protocol. CONCLUSIONS: Ziconotide is the first specific neuronal blocker that acts on the calcium channel by blocking the N-type voltage-dependent calcium channels. It is a new non-opioid analgesic with approved indication in the treatment of intense chronic pain, in patients who require intrathecal analgesics and are refractory to other analgesic treatments. Therefore, we shall have to consider this drug as a therapeutic alternative in patients do not experience sufficient relief with the pharmacological agents and means currently available to treat them.

[Fat inside the dural sheath of lumbar nerve roots in humans]. / Grasa dentro de los manguitos durales de las raíces nerviosas de la columna lumbar humana.

OBJECTIVES: Epidural fat deposition, which varies at different levels of the vertebral column, generates a reservoir from which retained lipophilic substances could be redistributed. The aim of the study was to determine whether fat is deposited within or underneath the dural sheath or whether it is only found within the epidural space, outside the sheath. MATERIAL AND METHODS: Samples of dural sheath from the lumbar spine of human cadavers aged 65 to 72 years were analyzed by scanning electron microscopy. RESULTS: The dural sheaths were made up of an arachnoid layer and a dura mater with a thickness of 100 to 150 microm. A large number of adipocytes were observed between the layers of the dura mater as well as beneath it. CONCLUSIONS: Fat similar to that found in the peripheral nerves is present within and underneath the dural sheaths. The fat found in the dural sheaths would be in close contact with the axons of the nerve roots, unlike the fat contained in the epidural space. The release of lipophilic substances from the fat in the dural sheath could have a greater effect on the nerve roots due to the limited distance that separates the fat from the axons as well as to the poor vascular clearance.

[Epidural fat in various diseases: contribution of magnetic resonance imaging and potential implications for neuro axial anesthesia]. / La grasa epidural en diferentes patologías. Aportaciones de la resonancia magnética y posibles implicaciones en la anestesia neuroaxial.

Epidural fat is a reservoir of lipophilic substances that cushions the pulsatile movements of the dural sac, protects nerve structures, and facilitates the movement of the dural sac over the periosteum of the spinal canal during flexion and extension. Excessive epidural fat can compress the underlying structures, however, and affect the placement of catheters and the distribution of injected solutions. This review discusses changes in epidural fat related to various diseases and events: lipomatosis, epidural lymphoma, arachnoid cysts, epidural hematoma, meningiomas, angiolipomas, spondylolysis, scoliosis, spinal stenosis, and liposarcoma. Also discussed are the sequencing and protocols for magnetic resonance imaging that enable epidural fat to be observed and distinguished from neighboring structures. The relevance of epidural fat in spinal surgery is considered. Finally, we discuss the possible anesthetic implications of the abnormal deposition of epidural fat, to explain the unexpected complications that can arise during performance of epidural anesthesia.

[Bilateral axillary brachial plexus block guided by multiple nerve stimulation and ultrasound in a multiple trauma patient]. / Bloqueo axilar bilateral del plexo braquial guiado por neuroestimulación múltiple y ultrasonidos en una paciente con politraumatismo.

We present the case of a woman with multiple wounds and injuries after attempted suicide by jumping from a high place. She had multiple craniofacial injuries and fractures of both forearms requiring emergency osteosynthesis. The neurosurgeons requested that a level of consciousness be maintained for frequent assessment; therefore it was decided to provide a bilateral axillary brachial plexus block. The procedure was carried out with the aid of a nerve stimulator to locate a triple response in the left arm (radial, medial and musculocutaneous nerves) and with both ultrasound and double nerve stimulation in the right arm (medial and radial nerves). Surgery proceeded without adverse events. The location of nerves or nerve roots with both ultrasound and stimulators was highly useful in this patient in need of bilateral brachial plexus blockade. This combination, and ultrasound in particular, might be the technique of choice because it offers an image in real time and assessment of the least amount of anesthetic that seems to be needed for achieving a block.

[Possibility of cauda equina nerve root damage from lumbar punctures performed with 25-gauge Quincke and Whitacre needles]. / Posibilidad de lesión en las raíces nerviosas de la cola de caballo en relación con las punciones lumbares realizadas con agujas 25-G Quincke y Whitacre.

OBJECTIVE: To assess the possibility of puncturing nerve roots in the cauda equina with spinal needles with different point designs and to quantify the number of axons affected. MATERIAL AND METHODS: We performed in vitro punctures of human nerve roots taken from 3 fresh cadavers. Twenty punctures were performed with 25-gauge Whitacre needles and 40 with 25-gauge Quincke needles; half the Quincke needle punctures were carried out with the point perpendicular to the root and the other half with the point parallel to it. The samples were studied by optical and scanning electron microscopy. The possibility of finding the needle orifece inserted inside the nerve was assessed. On a photographic montage, we counted the number of axons during a hypothetical nerve puncture. RESULTS: Nerve roots used in this study were between 1 and 2.3 mm thick, allowing the needle to penetrate the root in the 52 samples studied. The needle orifice was never fully located inside the nerve in any of the samples. The numbers of myelinized axons affected during nerve punctures 0.2 mm deep were 95, 154, and 81 for Whitacre needles, Quincke needles with the point held perpendicular, or the same needle type held parallel, respectively. During punctures 0.5 mm deep, 472, 602, and 279 were affected for each puncture group, respectively. The differences in all cases were statistically significant. CONCLUSIONS: It is possible to achieve intraneural puncture with 25-gauge needles. However, full intraneural placement of the orifice of the needle is unlikely. In case of nerve trauma, the damage could be greater if puncture is carried out with a Quincke needle with the point inserted perpendicular to the nerve root.

[Origin of spinal subdural hematomas: a postmortem anatomical study]. / Origen de los hematomas subdurales espinales. Estudio anatómico en cadáveres.

OBJECTIVE: Although the mechanism by which cranial subdural hematomas form is known, the formation of spinal subdural hematomas is less clearly defined. The aim of this study was to identify vessels that can be found in the dural sac and whose rupture might lead to the formation of spinal subdural hematomas. MATERIAL AND METHOD: The dura mater, subdural space, and the arachnoid mater were studied in samples of dural sac taken from the eleventh thoracic vertebra to the fifth lumbar vertebra. The samples were taken from 3 fresh cadavers. Some were fixed in glutaraldehyde, dehydrated, and metallized with gold for scanning electron microscopy. Others were fixed in glutaraldehyde, treated with osmium tetroxide, and embedded in an epoxy resin for observation under a transmission electron microscope. RESULTS: Small hematomas--some on the internal surface of the dura mater and others surrounding nerve roots--were found within a thin, translucent arachnoid mater. Vessels measuring up to 100 microm were found within the dura mater, between its inner and outer laminae. Venules and capillaries were observed in the subdural space and in the arachnoid mater. CONCLUSIONS: Vessels are present between the laminae of the dura mater, in the subdural space, the arachnoid mater, and in spinal nerve roots. The rupture of these vessels could account for the formation of spinal subdural hematomas.

[Hypothesis concerning the anatomical basis of cauda equina syndrome and transient nerve root irritation after spinal anesthesia]. / Hipótesis sobre las bases anatómicas del síndrome de cauda equina e irritación radicular transitoria postanestesia espinal.

OBJECTIVE: Cauda equine syndrome is a rare neurological complication associated with subarachnoid anesthesia, and particularly with the use of 5% hyperbaric lidocaine and small gauge catheters. Our aim was to study a possible anatomical factor that might impede adequate dilution of local anesthetic and explain the development of cauda equine syndrome and transitory radicular irritation. MATERIAL AND METHOD: The spinal dura matters and their contents from two male human cadavers were examined after organs had been extracted for transplantation. Both men had recently died at ages 56 and 65 years of age. Samples were fixed in a glutaraldehyde phosphate buffer and dehydrated in acetone, which was then removed by critical point elimination. The samples were then metallized with gold and observed under a scanning electron microscope. RESULTS: We found that one portion of the arachnoids was more compact and another was lax. The compact portion had a laminar structure formed by the fusion of fibers and cell components lining the inner surface of the dural mater. The lax portion was comprised of a weblike network of filaments and few cells bodies. This portion extended from the compact inner arachnoid lamina to the cell plane of the pia mater, where it dispersed, sending out compact arachnoid projections that wrapped around structures in the subarachnoid space. We termed these wrappings "arachnoid sheaths".

[Anatomical description of a natural perforation present in the human lumbar pia mater]. / Descripción anatómica de la presencia de perforaciones naturales en la piamadre humana en la médula lumbar.

OBJECTIVE: The pia mater has always been considered more permeable than other meningeal membranes. Natural pia mater perforations found in some animals at-test to this membrane's permeability. Such perforations, however, have never been demonstrated in human tissue. Our objective was to study human pia mater from the dorsal lumbar region, looking for perforations that facilitate the diffusion of substances to the spinal cord following subarachnoid administration. MATERIAL AND METHOD: The specimens were removed from four human cadavers aged 70, 72, 77 and 78 years between 8 and 12 hours after death. The specimens were fixed in a phosphate glutaraldehyde buffer solution, followed by desiccation in acetone and critical point elimination of acetone, treatment with carbon and metallization with gold. RESULTS: The pia mater was composed of a smooth surfaced, thin layer of cells and underlying connective tissue formed mainly of collagen fibers and fundamental amorphous matter. The collagen fibers were oriented in various directions. Throughout the surface of the pia mater, natural circular, elliptical and ovoid perforations were distributed irregularly. Size varied. Most measured over 10 to 15 micrometers in diameter or less than 5 to 8 micrometers. Inside the openings, fibers similar to collagen fibers could be seen at the point where they would normally be found beneath the cell layer. CONCLUSION: The total thickness of the pia mater varies in different zones of the spine, as a result of variations in the thickness of the cell layer and in the underlying extracellular layer. The existence of natural fenestrations in all the analyzed specimens of human dorsal lumbar pia mater accounts for the high permeability of this membrane, which permits substances administered in spinal fluid to reach the spinal cord. These natural fenestrations are areas where the cell surface in absent, with underlying collagen fibers usually visible. The pia mater is generally believed to be composed of a complete cell layer that forms a barrier between the central nervous system and the subarachnoid space; however, the presence of fenestrations would indicate that such a barrier does not exist, the base membrane being placed under the connective fibers, the only intact structure prior to medullary glial cells.

[Importance of the needle in regional anesthesia]. / Importancia de la aguja en anestesia regional.

The safety of regional anesthesia lies on a set of factors, namely, selection of the adequate technique, skill and proper training from the part of anesthesiologists and use of right equipment. The needle, as a prolongation of the hand of the anesthesiologist, must provide references in technique either by itself or joined to an objective method of nerve localization; this will result in a high percentage of success without iatrogenesis. We have reviewed 1,132 cases of regional anesthesia and grouped them into: intradural anesthesia, epidural anesthesia, and plexus anesthesia. We have evaluated the equipment used according to the success and iatrogenesis directly produced by the needle. Results were analyzed by Fisher's exact test and were statistically significant in the three groups, a fact that would indicate some specificity of the characteristics of the needle in each group of techniques. It would seem reasonable to adopt those techniques appearing to be the most efficacious after analysis in order to increase percentage of success and achieve the greatest safety in the clinical practice of anesthesiologists.

[Possibility of nerve lesions related to peripheral nerve blocks. A study of the human sciatic nerve using different needles]. / Posibilidad de lesiones nerviosas relacionadas con los bloqueos nerviosos periféricos. Un estudio en nervio ciático humano con diferentes agujas.

UNLABELLED: When a needle tip comes too close to a nerve axon, the mechanical effect over the nerve membrane produces paresthesia. We examined the hypothetical mechanical damage of short bevel and long bevel needles over sciatic nerve bundles under scanning electron microscopy. METHODS: We obtained samples of sciatic nerve from three patients of 68, 74 and 76 years old. These samples were fixed, dehydrated and coated with gold microfilm for their observation under scanning electron microscopy. Ten short bevel needles and ten long bevel needles were studied under the same microscopic technique. We interpolated microscopic images from sciatic nerve samples and different needle bevels at various angles to study the mechanical damage of these needles to nerve axons. RESULTS: Sciatic nerve bundles were found 0.1 to 0.2 mm deep in the samples; information was given about the bevel length and angle of needles. The damage is perceptible under scanning electron microscopy, when the needle bevel is introduced 0.3-0.4 mm deep into the nerve bundle; here, the needle tip cuts through the perineurum, piercing the nerve bundle. At a depth of 1 mm, the lesion caused by short bevel needles is greater than that caused by long bevel needles. The type of epineural lesions caused by short bevel needles is also different from the ones caused by long bevel needles. CONCLUSIONS: Lesions that affect superficially the epineurum can cause paresthesia by compression of nerve fascicles without damaging the axons. If the perineurm is damaged, the lession will also affect the blood-nerve barrier, leading probably to posterior sequels.

[Comparative study of detection methods in epidural anesthesia: Episensor and loss of resistance]. / Estudio comparativo del método de detección en anestesia epidural: Episensor y pérdida de resistencia.

The aim of the present study is to evaluate an electronic detector of negative pressure (Episensor, Palex, Spain) designed for the identification of epidural space. Ninety patients were randomly assigned to two groups: group 1 (n = 47) received epidural anesthesia as perioperative analgesic technique with Episensor method and group 2 (n = 43) received epidural anesthesia with the classic method of loss of resistance with gas mandrin. The following parameters were studied: a) demographic features, b) characteristics of epidural anesthesia, and c) complications occurring during space detection. There were no statistical differences in the analysis of demographic variables neither in the quality of the epidural anesthesia achieved in both groups. With respect to complications, group I presented the highest number of complications although only the lack of detection of epidural space achieved statistical significance (8.5%, p less than 0.05); the incidence was lower than that reported in the literature as physiologically possible in the lumbar epidural segment. We conclude that progressive knowledge of Episensor may decrease the initial incidence of complications with a success rate similar to that of classic techniques of identification of epidural space.

[Continuous block of the brachial plexus with nerve stimulation. Intra and postoperative control in orthopedic surgery of the arm]. / Bloqueo continuo del plexo braquial con neuroestimulación. Control intra y postoperatorio en la cirugía ortopédica del miembro superior.

A perivascular axillary plexus block was performed to 87 patients scheduled for orthopedic surgery of hand or arm using an electric nerve stimulator. A catheter was inserted for the postoperative pain control. The success rate was of 90.8% (79 cases); 65 patients (74.7%) presented a complete motor block. Complications were: arterial puncture (3), difficulty in inserting catheter (3), injection out of the sheath (1), pain at the electric stimulation (3). No allergic reactions nor neurologic complications were founded during a year of posterior control.

[Adipose tissue within peripheral nerves. Study of the human sciatic nerve]. / Tejido adiposo dentro de los nervios periféricos. Un estudio en nervio ciático humano.

AIM: To describe the distribution of intraneural adipose cells in relation to nerve fascicles in a portion of peripheral nerve usually involved in accomplishing an anesthetic blockade of a lower extremity. METHOD: Using a scanning electron microscope, we studied sciatic nerve samples from the point of amputation of a lower limb of three patients. The samples were obtained at the upper angle of the popliteal fossa, 10-15 cm cephalad to the knee joint line. RESULTS: During dissection of the sciatic nerve samples, we observed a solitary trunk, but examination of the cross-sections under the microscope revealed the components of two clearly separated branches joined by supporting tissue. The sciatic nerve had an oval form in the portion under study, measuring 6.5 to 7.5 mm by 3.6 to 3.9 mm. Between the fascicles, the adipose tissue varied in thickness from 0.5 mm in the central zones to 0.2 mm in the peripheral zones. The adipocytes, which were all similar in the size with diameters of 40 microns, were empty, as a result of elimination of the lipid vacuoles during fixation. The adipose tissue was distributed inside the epineurium to surround isolated fascicles or groups of fascicles. CONCLUSIONS: The adipose tissue inside a nerve surrounded the fascicles to form adipose sheaths that separated the fascicles from one another. The thicknesses of these adipose sheaths varied from one fascicle to another. Cells join to make it possible to create a compact adipose sheet that can delay the diffusion of local anesthetic injected near a nerve and that can therefore interfere with the characteristics of an anesthetic blockade.

[Morphology of peripheral nerves, their sheaths, and their vascularization]. / Morfología de los nervios periféricos, de sus cubiertas y de su vascularización.

This review aims to update our understanding of peripheral nerves, including the nature and function of their sheaths and, finally, their vascularization. The peripheral nervous system is made up of nerves whose function is to gather stimuli from the periphery as well as to transport the motor, secretory or vegetative responses that are triggered to the periphery. The connective tissue surrounding peripheral nerves all along their extension is made up of endoneurial, perineurial and epineurial. The endoneurium surrounds individual axons, which are grouped in fasciculi, each of which is surrounded by the perineurium and finally, the group of fasciculi that comprise all the axons present in this nerve are surrounded by the epineurium. Axons form an intraneural plexus such that they occupy positions in the various fasciculi along the trajectory of the plexus. The number and size of fasciculi vary along the trajectory of a nerve as a result of the plexus positioning of the axons. Peripheral nerves are richly vascularized throughout their length, with multiple anastomoses forming the intraneural vascular network, which is made up mainly of arterioles, capillaries, postcapillary venules and venules. Regarding the blood-nerve barrier and the existence of capillary permeability: endoneural capillaries have junctions that are stronger than those of the endothelial cells of vessels in the epineurium and perineurium. Two distinct lymph channels networks are present in the peripheral nerve stems and are separated by the perineural barrier. The nervi-nervorum are special nerves of a sympathetic and sensory nature that arise from the nerve itself and the perivascular plexuses.

[Continuous intradural anesthesia in geriatric patients undergoing orthopedic and traumatologic surgery]. / Anestesia intradural continua en pacientes geriátricos sometidos a cirugía ortopédica y traumatológica.

OBJECTIVES: The aim of the study was to prospectively evaluate the results of continuous intradural anesthesia with 18G Tuohy needle and 20G catheter in geriatric patients. MATERIAL AND METHODS: We studied 70 patients with a mean age of 75.9 +/- 10.8 years who were subjected to orthopedic or traumatologic surgery of the lower extremities with a duration of 104.6 +/- 53.6 min. RESULTS: Success index was 95.7%. The initial dose of 1% tetracaine was 10.36 +/- 3.96 mg, the second dose in 29 patients was 7.2 +/- 2.7 mg, the third in 7 cases was 7.40 +/- 2.47 mg, and the total dose was 14.56 +/- 5.6 mg. The metameric level was between T8 and T11 in 80.32% of patients. Peroperative complications were limited to paresthesia in 5 cases (7.14%) during insertion of the catheter, difficulties in catheter placement in one case (1.42%), and accidental catheter extraction during withdrawal of the needle in 2 cases (2.85%). Ten patients (14.28%) presented arterial hypotension (pressure decrease greater than 30% of baseline systolic arterial pressure). During the postoperative phase there were 3 cases of slight headache after dural puncture (4.28%) that recovered with conservative treatment, and one case of lumbalgia at the puncture zone (1.42%). CONCLUSIONS: Continuous intradural anesthesia with the material used in this study is technically easy. It allows to accurately reach the desired metameric level, avoiding massive sympathetic blockade, and providing a steady hemodynamic condition. All these effects are essential for anesthesia in geriatric patients.