An anatomical study of the intradural space.

We have previously postulated that it is possible to accidentally insert an epidural needle or catheter into the substance of the dura during attempted epidural block, creating an intradural space. It appears that injection of local anaesthetic into an intradural space leads to an initially inadequate neuraxial block but further doses may produce an extensive life-threatening block. In the laboratory, 54 samples of human thoraco-lumbar dura were obtained from six cadavers and prepared for scanning electron microscopy. Images from these dehydrated specimens were assessed for the presence of spaces within the dura, and attempts were made to insert an epidural catheter, under optical microscopy, into the substance of the dura in 32 cases. Electron microscopy revealed the concentric laminae that compose the dura and the presence of artefactual spaces between some of these. It was possible to insert an epidural catheter into the substance of the dura in eight specimens, creating intradural spaces which remained following catheter removal. If this represents the clinical situation, it may help to explain previously reported cases of atypical neuraxial block and their associated radiological findings.

Three-dimensional magnetic resonance image of structures enclosed in the spinal canal relevant to anesthetists and estimation of the lumbosacral CSF volume.

Three-dimensional (3D) image-reconstruction of structures inside the spinal canal certainly produces relevant data of interest in regional anesthesia. Nowadays, all hospital MRI equipment is designed mainly for clinical diagnostic purposes. In order to overcome the limitations we have produced more accurate images of structures contained inside the spinal canal using different software, validating our quantitative results with those obtained with standard hospital MRI equipment. Neuroanatomical 3D reconstruction using Amira software, including detailed manual edition was compared with semi-automatic 3D segmentation for CSF volume calculations by commonly available software linked to the MR equipment (MR hospital). Axial sections from seven patients were grouped in two aligned blocks (T1 Fast Field Eco 3D and T2 Balance Fast Field Eco 3D-resolution 0,65 x 0,65 x 0,65 mm, 130 mm length, 400 sections per case). T2 weighted was used for CSF volume estimations. The selected program allowed us to reconstruct 3D images of human vertebrae, dural sac, epidural fat, CSF and nerve roots. The CSF volume, including the amount contained inside nerve roots, was calculated. Different segmentation thresholds were used, but the CSF volume estimations showed high correlation between both teams (Pearson coefficient = 0.98, p = 0.003 for lower blocks; Pearson 0.89, p = 0.042 for upper blocks). The mean estimated value of CSF volume in lower blocks (L3-S1) was 15.8 + 2.9 ml (Amira software) and 13.1 +/- 1.9 ml (software linked to the MR equipment) and in upper blocks (T11-L2) was 21 +/- 4.47 ml and 18.9 +/- 3.5 ml, respectively. A high variability was detected among cases, without correlation with either weight, height or body mass index. Aspects concerning the partial volume effect are also discussed. Quick semi-automatic hospital 3D reconstructions give results close to detailed neuroanatomical 3D reconstruction and could be used in the future for individual quantification of lumbosacral CSF volumes and other structures for anesthetic purposes.

[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.

Posibilidad de lesiones nerviosas relacionadas con los bloqueos nerviosos periféricos. Un estudio en nervio ciático humano con diferentes agujas / Possibility of nervous injuries related to the nervous peripheral blockades. A study in human sciatic nerve with different needles

OBJETIVO: El estímulo mecánico de una aguja sobre los axones de un nervio produce parestesias. Nosotros estudiamos la interacción de los biseles de las agujas y de los fascículos del nervio ciático durante una hipotética parestesia. MATERIAL Y MÉTODO: Se estudiaron muestras de nervio ciático de tres pacientes de 68, 74 y 76 años. Las muestras se fijaron, deshidrataron y trataron con oro para poder ser observadas por microscopia electrónica de barrido. Con la misma técnica microscópica y con iguales aumentos se estudiaron diez agujas de bisel largo y 10 agujas de bisel corto. Se superpusieron las imágenes del nervio ciático y de las agujas en diferentes posiciones para evaluar su posible interacción.RESULTADOS: Los fascículos se localizaban a 0,1 a 0,2 mm de profundidad. Se aportaron medidas de la longitud y ángulo de los biseles de las agujas. Las parestesias pueden aparecer cuando la aguja se introduce a partir de 0,3 a 0,4 mm de profundidad cuando su punta rompe el perineuro y penetra dentro de un fascículo. A 1 mm de profundidad la lesión será mayor con las agujas de bisel corto que con las agujas de bisel largo. Las agujas de bisel corto y largo originan diferentes lesiones epineurales. CONCLUSIONES: Las parestesias pueden desencadenarse por compresión fascicular con lesión superficial que afectará sólo al epineuro y sin alteraciones futuras, o con rotura del perineuro que se asociará a una alteración de la barrera hemato-nerviosa. Las parestesias no son inocuas para el nervio y su frecuencia puede disminuirse usando técnicas de neuroestimulación para su localización (AU)

[The blood-nerve barrier in peripheral nerves]. / La barrera hemato-nerviosa en los nervios periféricos.

AIM: To study ultrastructural details of perineurium and endothelium samples from the endoneural vessels that form part of the blood-nerve barrier of peripheral nerves, with the intention of furthering our understanding of how these natural structures protect axons against foreign substances. METHODS: We obtained samples from the sciatic nerve at the superior angle of the popliteal fossa. The samples were first fixed in glutaraldehyde and then in osmium tetroxide; later they were dehydrated with acetone and soaked in resin epoxy (Epon 812). Ultra-thin sections were treated with uranyl acetate and lead citrate in solution. The slides were observed under a transmission electron microscope. RESULTS: The perineurium has a thickness of 10 to 25 microns and is composed of 8 to 15 continuous cell layers lying concentrically around each nerve fascicle. Each perineurial cell layer consists of a single layer of flat cells joined together by specialized junctions to provide a barrier against diffusion. Most of the endoneural vessels found near the axons were capillaries measuring 6 to 10 microns in diameter and composed of 6 to 8 endothelial cells with specialized junctions without fenestrations. CONCLUSIONS: The blood-nerve barrier is a cylindrical structure formed partly by membranes composed of tightly joined perineurial cell layers whose union is reinforced by specialized junctions that tend to isolate each fascicle. In addition, there is a cylindrical structure made up of endoneural endothelial cells also united by specialized junctures. These tend to keep blood away from axons and to impede the passage of circulating substances into the endoneural environment. Systemic diseases that alter and diminish the efficacy of the barrier in peripheral nerves may have implications for the creation of peripheral nerve blocks.

La barrera hemato-nerviosa en los nervios periféricos / The blood-nerve barrier in peripheral nerves

OBJETIVO: Estudiar la morfología del perineuro y del endotelio de los vasos endoneurales que forman la barrera hemato-nerviosa en nervios periféricos, para ayudar a deducir por qué estas estructuras de forma natural protegen a las fibras nerviosas de los agentes exógenos. MATERIAL Y MÉTODO: Muestras de nervio ciático humano a nivel del ángulo superior de la fosa poplítea. Las muestras se fijaron en glutaral de hido y después en tetróxido de osmio, se deshidrataron en acetona y embebieron en resina epoxi Epon 812. Los cortes ultrafinos se trataron con acetato de uranilo y citrato de plomo y después fueron estudiados en un microscopio electrónico de transmisión. RESULTADOS: El perineuro ocupaba un espesor de 10 a 25 micrómetros y estaba formado por 8 a 15 láminas celulares continuas y concéntricas a cada fascículo. Cada lámina está formada por un solo plano de células aplanadas unidas entre sí por uniones especializadas formando una barrera a la difusión. La mayoría de los vasos ubicados dentro del endoneuro y próximos a los axones eran capilares de 6 a 10 micrómetros de diámetro, formados por 6 a 8 células endoteliales que tenían uniones especializadas y no presentaban fenestraciones. CONCLUSIONES: La barrera hemato-nerviosa está formada por una estructura cilíndrica que resulta de la suma de las membranas celulares de las células perineurales adosadas entre sí y reforzadas por uniones especializadas que tiende a aislar a cada fascículo; y por otra estructura cilíndrica formada por las células endoteliales de los vasos endoneurales unidas entre sí por uniones especializadas, que tiende a aislar al contenido hemático de los axones y a dificultar el pasaje de sustancias disueltas en el torrente circulatorio hacia el medio endoneural. Las patologías sistémicas que afecten y disminuyan el efecto barrera en los nervios periféricos pueden tener implicaciones en los bloqueos nerviosos periféricos (AU)