Dislodgment of continuous suprascapular nerve block catheters after physiotherapy: A cadaver study

BACKGROUND

Continuous peripheral nerve blocks are commonly used for pain management. However, the incidence of catheter dislodgement or migration is unclear, and may be underestimated and underreported. Our objective was to assess suprascapular catheter tip positioning before and after routine simulated shoulder physiotherapy manipulation in an anatomical cadaver model.

METHOD

Eight ultrasound-guided continuous suprascapular nerve block catheters were placed in cryopreserved fresh cadavers. Computed tomography (CT) confirmed the location of the catheter tip after injection of 1 ml of contrast medium. We performed a series of standardized shoulder movements during a simulated shoulder physiotherapy session in cadavers. Following this, we administered 1 ml of methylene blue through the catheters, and then performed anatomical dissections to accurately identify the location of the catheter tips and compare them to their placement prior to the 'physiotherapy'.

RESULT

CT imaging confirmed the location of the catheter tips at the suprascapular notch in all cases. However, following physiotherapy, 2 catheters (25%) were found to have migrated - specifically, 1 was located in the supraspinatus muscle, and the other was located in the trapezius muscle.

CONCLUSION

Our findings suggest that catheter dislodgement may occur in approximately 25% of cases following simulated physiotherapy manipulation. However, further research is needed to determine the read incidence of catheter dislodgement in clinical practice.

Electron microscopy of human peripheral nerves of clinical relevance to the practice of nerve blocks. A structural and ultrastructural review based on original experimental and laboratory data

AIM

The goal is to describe the ultrastructure of normal human peripheral nerves, and to highlight key aspects that are relevant to the practice of peripheral nerve block anaesthesia.

METHOD

Using samples of sciatic nerve obtained from patients, and dural sac, nerve root cuff and brachial plexus dissected from fresh human cadavers, an analysis of the structure of peripheral nerve axons and distribution of fascicles and topographic composition of the layers that cover the nerve is presented. Myelinated and unmyelinated axons, fascicles, epineurium, perineurium and endoneurium obtained from patients and fresh cadavers were studied by light microscopy using immunohistochemical techniques, and transmission and scanning electron microscopy. Structure of perineurium and intrafascicular capillaries, and its implications in blood-nerve barrier were revised.

RESULTS

Each of the anatomical elements is analyzed individually with regard to its relevance to clinical practice to regional anaesthesia.

CONCLUSIONS

Routine practice of regional anaesthetic techniques and ultrasound identification of nerve structures has led to conceptions, which repercussions may be relevant in future applications of these techniques. In this regard, the ultrastructural and histological perspective accomplished through findings of this study aims at enlightening arising questions within the field of regional anaesthesia.

Cerebrospinal Fluid Volume and Nerve Root Vulnerability during Lumbar Puncture or Spinal Anaesthesia at Different Vertebral Levels

Cerebrospinal fluid (CSF) and nerve root volumes within the lumbosacral dural sac were estimated at various vertebral levels, in an attempt to determine any possible relevance to the incidence of nerve root trauma during lumbar puncture or spinal anaesthesia. Magnetic resonance images from seven patients were studied. Volumes were calculated by semi-automatic threshold segmentation combined with manual editing of each slice. The mean dural sac volume from S1 to T12 was 42.8±5.8 ml and the mean CSF volume 34.3±5.1 ml with the mean root volume being 10.4±2.2 cm3. The mean CSF volume per vertebral segment ranged from 4.3±0.7 ml at L5, to 5.8±2.5 ml at L1, with high inter-individual variability. The mean root volume ranged from 0.6±0.1 cm3 at L5 to 2.4±0.5 cm3 at T12.

The conus medullaris was located at L1 in four of the five patients scanned at upper lumbar levels, and at the lower border of L2 in the other. Vulnerability to nerve root damage was expressed as the Vulnerability Index (%), being defined as the ratio of root volume to dural sac volume (CSF volume + root volume). The value ranged between 7 and 14% at L5, increasing rostrally to 30 to 43% at T12. Caution is obviously required in high punctures to avoid contact with the conus medullaris, but the cauda equina is also vulnerable to contact with more caudal punctures and had a Vulnerability Index of about 25% at L4, that increased rostrally.

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.

[Structure of the arachnoid layer of the human spinal meninges: a barrier that regulates dural sac permeability]

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.

[Reversal of acenocoumarol anticoagulation with activated factor VII in massive hemorrhage following rupture of a splenic artery pseudoaneurysm]

A 66-year-old man with a metallic valve and under treatment with acenocoumarol developed hypovolemic shock after rupture of a splenic artery pseudoaneurysm. We managed to reverse anticoagulation within 60 minutes by administering 20 mg of vitamin K and 4.8 mg of activated recombinant factor VII. No thromboembolic adverse events were observed. We discuss the pharmacologic effects of coumarin derivatives and their antagonists, as well as the use of activated factor VII in the reversal of anticoagulation by these drugs.

[Paresthesia and spinal anesthesia for cesarean section: comparison of patient positioning]

OBJECTIVE

To determine the incidence of paresthesia during lumbar puncture performed with the patient in different positions.

MATERIAL AND METHODS

A single-blind prospective study of patients scheduled for elective cesarean section, randomized to 3 groups. In group 1 patients were seated in the direction of the long axis of the table, with heels resting on the table. In group 2 they were seated perpendicular to the long axis of the table, with legs hanging from the table. In group 3 they were in left lateral decubitus position. Lumbar punctures were performed with a 27-gauge Whitacre needle.

RESULTS

One hundred sixty-eight patients (56 per group) were enrolled. Paresthesia occurred most often in group 3 (P = .009). We observed no differences in blood pressure after patients moved from decubitus position to the assigned position. Nor did we observe between-group differences in blood pressure according to position taken during puncture.

CONCLUSION

Puncture undertaken with the patient seated, heels on the table and knees slightly bent, is associated with a lower incidence of paresthesia than puncture performed with the patient seated, legs hanging from the table. Placing the patient's heels on the table requires hip flexion and leads to anterior displacement of nerve roots in the dural sac. Such displacement would increase the nerve-free zone on the posterior side of the sac, thereby decreasing the likelihood of paresthesia during lumbar puncture. A left lateral decubitus position would increase the likelihood of paresthesia, possibly because the anesthetist may inadvertently not follow the medial line when inserting the needle.

[Trapped epidural catheter: reconstruction of computed tomography images]

A trapped epidural catheter without a knot is a rare complication. During placement of an epidural catheter for analgesia during labor, resistance made it impossible to position the catheter within the epidural space. A second catheter was inserted to provide the required analgesia. When the second catheter was removed, computed tomography (CT) revealed that the tip of the first catheter was close to the the right facet joint space. A second attempt to extract the catheter failed. In light of this situation, the patient was seated with the spine slightly bent to one side, a guidewire was inserted through the catheter lumen, and the catheter and guidewire were gently pulled; the catheter was extracted without causing the tip to break up. Three-dimensional CT reconstruction allowed the catheter tip and characteristics of the joint surfaces to be observed. We discuss protcols and alternative strategies that can be followed when an epidural catheter is difficult to remove, including the most appropriate images to use for guidance.

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.

[Continuous subarachnoid analgesia and anesthesia for labor and cesarean section in a patient who had previously undergone surgery for ependymoma]

We report the case of a 38-year-old primipara who had undergone surgery 2 years earlier for an intradural ependymoma at L2-L3 and who was currently asymptomatic. A combined epidural-subarachnoid block was performed for analgesia during labor but this technique was only effective for the first 2 hours. When analgesia via epidural cannula was no longer adequate, it was decided to perform a continuous subarachnoid block. Later, the fetus's head was seen to be too large to fit through the pelvis; for cesarean section, the mother was administered fractionated doses of local anesthetic via the subarachnoid cannula until analgesia reached T4. The patient did not develop postdural puncture headache. Continuous subarachnoid anesthesia may be considered the technique of choice where the patient has a history of spinal surgery.

[Paresthesia in various spinal anesthesia techniques for cesarean section]

OBJECTIVE

To determine the incidence of paresthesia with different spinal puncture techniques using a 27-gauge Whitacre needle.

MATERIAL AND METHODS

Spinal puncture was performed in 224 elective cesarean sections using different techniques in this single-blind, prospective trial. Patients were randomized to 4 groups: group 1, combined epidural and subarachnoid puncture using an introducer needle; group 2, combined epidural and subarachnoid puncture without an introducer; group 3, subarachnoid puncture with an introducer; and group 4, subarachnoid puncture with an introducer to within a few millimeters of the dural sac, at which point the introducer was withdrawn.

RESULTS

Paresthesia developed in 23, 11, 16 and 5 patients in groups 1, 2, 3 and 4, respectively. Various nerve roots were affected. In 2 and 11 cases the fourth and fifth lumbar nerve roots were affected; in 29 and 13 cases, the first and second sacral nerve roots were involved. In comparison with group 4, the risk of paresthesia was 7, 2.5 and 4 times greater in groups 1, 2 and 3, respectively.

CONCLUSIONS

Combined epidural-subarachnoid puncture leads to a higher incidence of paresthesia in comparison with simple spinal puncture, probably because the lumbar puncture is performed on a dural sac that has been previously deformed due to the "tent effect" caused by the epidural needle. Fewer cases of paresthesia occur when the subarachnoid puncture is slow and steady and the introducer needle is withdrawn millimeters before it reaches the dural sac.

[Fat inside the dural sheath of lumbar nerve roots in humans]

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.

[Horner's syndrome secondary to epidural anesthesia]

INTRODUCTION

The Horner's syndrome in association with the anesthetic techniques is produced by a blockade of the stellate ganglion sympathetic fibers. This complication is produced by the local anesthetic non-expected migration when it is administered either in the epidural space while performing an epidural block or inside the aponeurosis vascular elements during the performance of a brachial plexus block. Its evolution is quick, with benign incident that disappears in a few hours, without leaving any sequels. It can occur in patients without any previous clinical condition.

CLINICAL CASE

We described the case of 28 years old pregnant woman, with a body mass index of 40.6, without any previous neurological background, who was admitted into hospital for labour. She had epidural analgesia and needed a caesarean section 2 hours later. Twenty minutes after the administration of an epidural dose of local anesthetic, the patient developed a completed left side Horner's Syndrome, as well as ipsi-lateral brachial paresis, that lasted for three hours, with complete recovery.

CONCLUSIONS

Several etiopathologenic options were considered at the time, such as a possible subdural or paravertebral migration of the local anesthetic, the influence of the patient's position (decubitus) and the possible existence of fibrotic compartments in the epidurals space.

[Epidural fat in various diseases: contribution of magnetic resonance imaging and potential implications for neuro axial anesthesia]

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.

[Characteristics and distribution of normal human epidural fat]

Epidural fat provides sufficient cushion for the pulsatile movements of the dural sac, protects nerve structures, facilitates the movement of the dural sac over the periosteum of the spinal column during flexion and extension, and forms a pharmacologic reservoir of lipophilic substances. We review epidural fat and related structures, including their development during the fetal period when the epidural space is filled by undifferentiated loose, areolar mesenchymal tissue that surrounds the dural sac. In the adult, epidural fat has a continuous distribution and follows a certain metameric pattern. It is located mainly on the dorsal side of the epidural space, where it is organized in triangular capsules joined to the midline of the ligamentum flavum by a vascular pedicle. We consider the distribution of epidural fat in the axial and sagittal planes; its presence in the anterior, lateral and posterior epidural space; its presence in the cervical, thoracic and lumbar portions of the spinal column; and its characteristics and variations according to differing body habits and sex. Finally, we speculate on the possible anesthetic implications of epidural fat in terms of the pharmacokinetics of drugs injected into the epidural space and the tasks of locating the epidural space and inserting an epidural catheter during anesthetic procedures.

[Possibility of cauda equina nerve root damage from lumbar punctures performed with 25-gauge Quincke and Whitacre needles]

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.

Dura-arachnoid lesions produced by 22 gauge Quincke spinal needles during a lumbar puncture

AIMS

The dural and arachnoid hole caused by lumbar puncture needles is a determining factor in triggering headaches. The aim of this study is to assess the dimensions and morphological features of the dura mater and arachnoids when they are punctured by a 22 gauge Quincke needle having its bevel either in the parallel or in the transverse position.

METHODS

Fifty punctures were made with 22 gauge Quincke needles in the dural sac of four fresh cadavers using an "in vitro" model especially designed for this purpose. The punctures were performed by needles with bevels parallel or perpendicular to the spinal axis and studied under scanning electron microscopy.

RESULTS

Thirty five of the 50 punctures done by Quincke needles (19 in the external surface and 16 in the internal) were used for evaluation. When the needle was inserted with its bevel parallel to the axis of the dural sac (17 of 35), the size of the dura-arachnoid lesion was 0.032 mm(2) in the epidural surface and 0.037 mm(2) in the subarachnoid surface of the dural sac. When the needle's bevel was perpendicular to the axis (18 of 35) the measurement of the lesion size was 0.042 mm(2) for the external surface and 0.033 mm(2) for the internal. There were no statistical significant differences between these results.

CONCLUSIONS

It is believed that the reported lower frequency of postdural puncture headache when the needle is inserted parallel to the cord axis should be explained by some other factors besides the size of the dura-arachnoid injury.

[Origin of spinal subdural hematomas: a postmortem anatomical study]

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.

[Intracranial and spinal subdural hematoma: a rare complication of epidural and subarachnoid anesthesia]

Subdural and epidural hematomas complicating central blocks are rare but serious complications that can lead to permanent neurological deficits. This review discusses cranial and spinal subdural hematomas, including the history of this complication in the literature. Theories to explain the mechanisms by which hematomas are formed are presented and risk factors are analyzed. The associations between such hematomas and the design of the various needles used for lumbar puncture are evaluated and the most common cranial and spinal locations are discussed. The anatomy of tissues that envelop and contain chronic subdural hematomas are described and the various neurological alterations that can develop are mentioned. Finally, diagnostic imaging options and corrective surgical techniques are reviewed.

[Possibility of nerve lesions related to peripheral nerve blocks. A study of the human sciatic nerve using different needles]

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.

[The blood-nerve barrier in peripheral nerves]

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.

[Adipose tissue within peripheral nerves. Study of the human sciatic nerve]

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.

[Magnetic resonance in dural post-puncture headache in patient with cerebrospinal fluid hypotension]

Magnetic resonance imaging (MRI) has allowed us to establish a set of radiologic signs associated with intracranial hypotension syndrome. Findings are partly influenced by cerebral displacement. Intracranial hypotension syndrome is characterized by a decrease in cerebrospinal fluid (CSF) pressure to less than 60 mm H2O associated with occipital headache radiating to the frontal and temporal zones. For diagnostic purposes, the most common cause is anesthetic or therapeutic dural puncture, although spontaneous CSF leakage can occur. CSF protein and lymphocyte counts may be high, while the cranial meninges biopsy is normal. MRI images may show a descended brain, taking the start of the sylvian aqueduct and the location of the cerebellar amygdalae as points of reference; diminished size of the subarachnoidal cisterns and occasionally of the cerebral ventricles; meningeal enhancement from increased uptake of the contrast solution; subdural hygromas and hematomas; and pituitary enlargement. Paraspinal fluid and dilated epidural veins may be observed. Radiologic images and clinical signs are related. When CSF pressure is very low, there is greater meningeal enhancement, subdural collection and cerebral displacement. Findings gradually disappear as symptoms diminish. The signs and symptoms that might develop during intracranial hypotension syndrome vary according to the brain structure that might be affected during descent, repositioning and the traction of anchoring structures. MRI allows the degree of cerebral and spinal involvement to be ascertained, to predict whether resolution of the clinical picture will be early or late and to visualize the effect of approaches to reducing CSF leakage.

[Intracranial hypotension syndrome]

Intracranial hypotension syndrome is an essential or, more frequently, secondary entity. This is characterized by orthostatic headaches and diffuse dural gadolinium enhancement on magnetic resonance imaging with or without subdural fluid collections or evidence of descent of the brain. What determines the various clinical and imaging features of intracranial hypotension syndrome is the cerebrospinal fluid volume depletion. In this article, we review the clinical and neuroimaging findings, pathophysiology, and treatment of this syndrome.

[Morphology of peripheral nerves, their sheaths, and their vascularization]

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.

An in vitro study of dural lesions produced by 25-gauge Quincke and Whitacre needles evaluated by scanning electron microscopy

BACKGROUND AND OBJECTIVES

A study using scanning electron microscopy showed that although the laminas forming the dura mater are concentric and parallel to the surface of the medulla, the fiber layers' orientations are different in each sub-lamina, dispelling the conventional knowledge that all the fibers of the dura are arranged in a parallel direction. Thus, this study evaluated the dural lesions produced by Whitacre and Quincke spinal needles in the external and internal surface of the dura mater of the lower spine area in an attempt to gain more insight into the pathophysiology of postdural puncture headaches (PDPH).

METHODS

The T11-L4 dural membranes from 5 fresh (immediately after extraction of organs for transplantation), male patients declared brain dead, ages 23, 46, 48, 55, and 60 years, were excised by anterior laminectomy. Morphologic orientation of the membrane and normal pH were maintained with an apparatus designed for this purpose. One hundred punctures (20 on each sample) at 90-degree angles were done with a new needle each time, 50 with 25-gauge Whitacre and 50 with 25-gauge Quincke needles. Half of the punctures with the Quincke needles were done with the bevel in parallel direction to the axis of the spinal cord, and the rest with the bevel perpendicular to it. Fixation in solutions of 2.5% glutaraldehyde phosphate buffer, followed by dehydration with acetone, was done 15 minutes after the punctures. After acetone was removed at ideal conditions of temperature and pressure, the specimens were then metallized with carbon followed by gold and inspected under a scanning electron microscope.

RESULTS

Twenty-five of the Whitacre and 23 of the Quincke punctures were found for evaluation. There were no differences in the cross-sectional area of the punctures produced by the Whitacre or Quincke needles on the dura. The area of the dural lesions produced by 25-gauge Quincke needles, 15 minutes after they have been withdrawn, was 0.023 mm2 (confidence interval [CI] 95%, 0.015 to 0.027) in the external aspect (epidural surface) and 0.034 mm2 (CI 95%, 0.018 to 0.051) in the internal aspect (arachnoid surface) of the dural sac. The area of the lesions produced by the 25-gauge Whitacre needles was 0.026 mm2 (CI 95%, 0.019 to 0.032) and 0.030 mm2 (CI 95%, 0.025 to 0.036) in the external and internal surfaces of the dural sac, respectively. There were no significant differences in the cross-sectional areas of the punctures produced by the 25-gauge Whitacre or 25-gauge Quincke needles. Moreover, with Quincke needles the dural lesions closed in an 88.3% (CI 95%, 86.3 to 92.4) and 82.7% (CI 95%, 74.1 to 90.9) of their original sizes in the epidural and arachnoid surfaces, respectively. With Whitacre needles, the closure occurred in an 86.8% (CI 95%, 83.8 to 90.3) and 84.8% (CI 95% 81.7 to 87.3) in the dural and arachnoid surfaces, respectively. However, there were differences in the morphology of the lesions. The Whitacre needles produced coarse lesions with significant destruction in the dura's fibers while the Quincke needles produced a 'U'-shaped lesion (flap) that mimics the opened lid of a tin can, regardless of the tip's direction.

CONCLUSIONS

The needles produced lesions in the dura with different morphology and characteristics. Lesions with the Quincke needles resulted in a clean-cut opening in the dural membrane while the Whitacre needle produced a more traumatic opening with tearing and severe disruption of the collagen fibers. Thus, we hypothesized that the lower incidence of PDPH seen with the Whitacre needles may be explained, in part, by the inflammatory reaction produced by the tearing of the collagen fibers after dural penetration. This inflammatory reaction may result in a significant edema which may act as a plug limiting the leakage of cerebrospinal fluid.

[Thickness variation of the dural sac]

OBJECTIVE

To measure carefully the thickness of the dural sac and evaluate possible variation in recently removed human specimens that had not yet undergone postmortem change. The thickness of the dural membrane is of interest because of its function as a barrier during diffusion processes and during closure of spinal lesions.

MATERIAL AND METHODS

After receiving the consent of our hospital's ethics committee and the family of the deceased, and immediately after extraction of organs for transplantation, we removed the dural sac and nerves contained therein from the cadaver of 56-year-old patient diagnosed of brain death. The membrane was dissected and 240 measurements of thickness were made over the entire surface of the sample. A micrometer was used, controlled through a surgical microscope. To analyze variations in thickness, the specimen was divided into 48 zones.

RESULTS

The dural sac open on its anterior side was treated as a rectangular membrane measuring 130 x 54 mm. Mean thickness of the sample was 0.322 mm. Mean thickness of anterior zones was 0.353 mm, with no significant differences among them. Posterior zones measured a mean 0.295 mm with significant differences among them (p < 0.001). Up to the second lumbar root, anterior and posterior zone thicknesses presented no significant differences. However, after the space between the second and third lumbar roots, the posterior side was significantly thinner. Where the first, second and third lumbar roots emerged, we measured thicknesses of 0.315, 0.361 and 0.322 mm, with no significant differences among anterior, posterior and side zones on any level. At the fourth lumbar root and in the spaces of the dura mater between the emergence of the first and second, the second and third, the third and fourth and fourth and fifth lumbar roots, we observed significant differences. The measurements were 0.298 mm (p < 0.01); 0.348 mm (p < 0.01); 0.337 mm (p < 0.001), 0.306 mm (p < 0.01); 0.289 mm (p < 0.001), respectively.

CONCLUSION

Possible inter- or intra-individual variation in dural sac thickness is an unpredictable variable affecting the management of dural lesions. The data we report on thickness allow for future objective assessment of the maximum sizes recommended for the lateral orifices of bevelled, pencil-point needles in order to avoid straddling the membrane when subarachnoid anesthesia is given. The data also contributes to the study of substance diffusion through this membrane.

[Hypothesis concerning the anatomical basis of cauda equina syndrome and transient nerve root irritation after spinal anesthesia]

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".

[Electron microscopic analysis of particles from surgical gloves and their possible introduction into the epidural space during epidural anesthesia]

OBJECTIVE

Many publications have linked surgical glove powder to inflammatory reactions of the peritoneum, pleura, pericardium and meninges. Accidental contamination may also increase the likelihood of complications after spinal and epidural anesthesia. We aimed to analyze the morphological characteristics of microscopic particles adhering to surgical gloves and to analyze how likely such particles are to enter the epidural space during catheterization.

MATERIAL AND METHOD

One hundred epidural catheters were studied in two groups (A and B) of 50. Group A catheters contained stylettes and the distal ends were open (Vygon). Group B catheters contained no stylettes and had closed distal ends and three side openings (Becton Dickinson). Continuous epidural anesthesia was simulated with half the catheters in each group (25) by touching the distal end of each line with the gloves and later inserting the catheter through a Tuohy needle. All catheters--those used in the simulation as well as the untouched ones--were then examined under a scanning electron microscope. The particles on the internal and external surfaces of the gloves had previously been identified under a microscope and analyzed by X-ray diffraction.

RESULTS

Gloves: external glove surfaces carried particles measuring between 3 and 4 mu; their morphology was consistent with calcium carbonate. On internal surfaces we found larger particles, between 11 and 14 mu in diameter, shaped differently and of smooth appearance. Analysis of the latter showed them to contain traces of magnesium and to have characteristics consistent with organic molecules. The particles of one surface were never observed on the other. Catheters: the non-manipulated catheters in both groups contained no free particles matching those described above, whereas the outside surfaces of the catheters in contact with gloves contained particles consistent with those of external glove surfaces. The number of particles per square millimeter of surface was 2,598 (95% CI 2,200 to 2,900) in group A catheters and 2,340 (95% CI 2,000 to 2,600) in the group B catheters (p = NS). The differences in the number of particles adhering to catheters touched by gloves and those that had not been manipulated were statistically significant (p < 0.001).

CONCLUSIONS

Particles adhering to gloves can be drawn into the epidural space during continuous epidural anesthesia. All unnecessary manipulation should therefore be avoided, and the portion of the catheter to be inserted into the epidural space should not be touched in order to prevent possible nonspecific meningeal inflammatory responses.

[Does the subdural space exist?]

A potential space between the dura mater and the arachnoides is thought to exist, occupied by a serous fluid and called the subdural space. Recent studies may change this classical concept, however. The dura-arachnoid complex from the epidural to the arachnoid space is formed by morphologically distinct layers: the dura mater, the subdural compartment and the arachnoid mater, which are made up of different cell types. The dura mater consists of greater and lesser laminae formed mainly of collagen fibers aligned differently. The subdural compartment is formed by a number of so-called "neurothelial cells", which are in close contact with the inner dural layers. These cells are flat and have long interlaced branches. The arachnoides are made of cells grouped in three different layers. The outer layer is the "barrier arachnoid layer". Located just inside the anterior cell plane, this layer is made of less flattened cells that form an epithelial-type tissue, with complex cell-cell junctures surrounded by collagen fibers. The middle layer is the reticular arachnoid, composed of irregularly interlaced cells alternating with collagen fibers and intercellular gaps of varying sizes. The innermost layer, the trabecular arachnoid, is in direct contact with the subarachnoid space. The cells of this layer form strands that contribute to the weblike pattern found in the subarachnoid space. Recently, special techniques for fixing and preparing samples, preserving in situ the anatomical relations between the arachnoides and the dura mater, have allowed us to examine the normal configuration of the subdural space. All samples examined revealed the presence of a cellular plane between the dura mater and the arachnoides, with no evidence of the classically described space. The zone of least resistance in the dura-arachnoid complex was the subdural compartment, which could be torn mainly along intercellular spaces, though cell rupture was also observed, affecting the cytoplasmic membranes of adjacent cells. The subdural space is opened by tearing the subdural compartment between neurothelial cells alongside the collagen fibers of the dura mater. Such a tear can be caused mechanically by injecting air or contrast media, which exert pressure on a laminar structure that tends to separate because it is weaker than neighboring ones.

[New results in the visualization of the spinal dura mater with scanning electron microscopy]

Although there are various published descriptions of the dura mater spinalis [4, 7, 9, 11, 16], some points relating to the texture of the collagen fibres in the dura have still not been adequately explained. In this study the orientation of the collagen fibril bundles was revealed with the aid of scanning electron microscopy, and our observations have yielded new insights into the three-dimensional structure of the human dura mater spinalis.

MATERIALS AND METHODS

The preparations used were taken from the bodies of four persons who had died of acute cardiac infarct at the ages of 70-78 years. The histories of these patients gave no indications of earlier neurological, endocrine or septic illnesses. The tissue examined was taken 8-12 h after death in all cases; it was immediately fixed in glutaraldehyde and then processed for scanning electron microscopy in the usual way.

RESULTS

In the outermost (epidural) layer of the dura mater spinalis the collagen fibres are bunched together in bands that run in all directions. Elastic fibres 2 mm thick are woven into this three-dimensional network of collagen systems. On the inside (the arachnoid side) thin collagen fibres are fused into layers in such a way that the innermost layer resting on the arachnoid has a smooth, shiny appearance comparable to that of a serosa. It is attached to the actual dura with a supporting band of connective tissue. Rests of the subdural neuroepithelium could contribute to the smooth appearance of the superficial aspect.

CONCLUSIONS

The outermost layer of the dura is made up mainly of collagen fibres, which run in all three directions--longitudinal, horizontal and transverse--both singly and in groups. These findings are at odds with "classic" descriptions, according to which the fibres in the dura mater spinalis all have a parallel course with a longitudinal orientation in tangential sections.

[Anatomical description of a natural perforation present in the human lumbar pia mater]

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.

[Microscopic characteristics of epidural filter pores]

OBJECTIVE

The increased use of the epidural route for administering opioids to treat chronic pain and the need to reduce complications as much as possible, has led some authors to recommend using micro filters to reduce catheter contamination. This study was motivated by the lack of technical information documenting epidural filters used routinely, as well as by the scarcity of literature describing their characteristics. Our aim was to investigate the true nature of the membrane pores, their characteristics and dimensions.

MATERIAL AND METHOD

Samples from 30 epidural filters labelled "Porosity: 0.2 microns" from three different manufacturers were studied. Filters from Vygon, Braun and Abbot were labelled A, B and C, respectively. The samples were placed in six groups of five filters each, and 15 random studies were made of each sample. Three of the six groups were used to study prefiltration surfaces and the others to study postfiltration surfaces. Each sample was metalized with gold and its center was then studied by scanning electron microscope. Given that the pores were anfractuous, they were measured by taking the diameter of the largest circle fitting inside that could predict the size of the smallest spherical non elastic body that might be retained. The samples for measuring thickness were cryofractured for determining the number of filtration planes in the 15 filters.

RESULTS

Prefiltration surface: Pore diameters were 0.70 (0.66 to 0.74), 0.45 (0.41 to 0.49), and 2.077 (2.01 to 2.15) microns on the filtration surfaces of manufacturers A, B and C, respectively. The differences were significant (p < 0.01) and the pore shapes were also different. Postfiltration surface: The function pores of filters from manufacturers A and B measured 0.26 (0.25 to 0.28) and 0.26 (0.24 to 0.28) microns, and the differences were not significant. The pores of filters from company C were significantly larger (p < 0.01), measuring 0.46 (0.43 to 0.49) microns. There were significant differences (p < 0.001) in pore size on the pre- and postfiltration surfaces from all three manufacturers. Gauge: The five A, B and C filters averaged 130, 118 and 165 microns thick, respectively, with an average number of 140, 220 and 210 filtration planes, respectively.

CONCLUSION

The pores of filters for epidural use labelled "0.2 microns" actually had much larger pores on their prefiltration surfaces and throughout the membrane thickness. On the postfiltration surface, however, the diameters of pores on filters manufactured by Vygon and Braun approached 0.2 microns. Pores on filters manufactured by Abbot, however, were approximately 0.46 microns. We believe that in the future manufacturers should include more information in the documentation accompanying their filters.

New perspectives in the microscopic structure of human dura mater in the dorsolumbar region

BACKGROUND AND OBJECTIVES

The object of this study was to describe the three-dimensional structure of the dura mater by use of scanning electron microscopy.

METHODS

Microscopic dissection of the dura mater from four fresh cadavers (aged 70, 75, 76, and 80 years) 8-12 hours after death were investigated in three different planes (longitudinal, tangential, and transverse).

RESULTS

The external surface of the dura mater, facing the epidural space, consisted of a network of randomly oriented fine collagen fibers. The thicker elastic fibers (2 microns in diameter) were observed on the surface of the dura. In the inner part of the dura mater, there were very fine lamellae of collagen fibers, which were bundled into thicker (4-5 microns) layers. The dura mater consisted of 78-82 layers, each layer including 8-12 very fine lamellae.

CONCLUSIONS

The fibers of the dura mater do not run in a longitudinal direction and are not arranged in a parallel fashion. Cytoarchitecturally the dura mater is a laminated structure built up from well-defined layers oriented concentrically around the medulla spinalis.

[Electron microscopy of the lesions produced in the human dura mater by Quincke beveled and Whitacre needles]

INTRODUCTION

Comparisons of Quincke needles and non traumatic "pencil point" needles in recent years have reported lower rates of post dural puncture headache using the later type. Our new understanding of the morphology of the human dura mater motivated us to study dural lesions caused by the Whitacre 25 G and Quincke 26 G needles, using scanning electron microscopy with the aim of determining whether there is an anatomic basis for the different outcomes.

METHOD

The dura mater from three fresh cadavers of individuals aged 65, 70 and 72 years were punctured 40 times at an angle of 90 degrees each time. The Whitacre 25 G needle was used for 20 punctures and the Quincke 26 G needle was used for the other 20. Half the punctures were performed with the bevel in the parallel alignment and the other half with the bevel perpendicular to the spinal column. Fifteen min after causing the punctures, specimens were fixed in solutions of glutaraldehyde phosphate buffer and dehydrated in acetone. After critical point removal of the acetone, after the specimens were treated with carbon and metallized with gold. The lesions were examined externally and internally and expressed as the ratio of area of lesion to diameter of the needle that had caused them.

RESULTS

Whitacre needle: each lesion consisted in the superimposition of multiple damaged layers that started to close individually. After 15 min the outermost layers were 90% closed and the innermost ones had closed entirely. Layers in the arachnoid surface of the dura mater had closed from 86 to 88%, while deeper layers in the thick part had closed 97 to 98%. Quincke needle: lesions were V-shaped or half-moon shaped, much like the opening formed by a can opener, on both the external and internal surfaces. Alignment of the bevel of the needle parallel to the spinal column did not lead to a different shape of puncture. After 15 min the lesions had closed 94 to 95% on the epidural surface and 95 to 96% on the arachnoid side, a difference attributable to the retraction of the arachnoid layers over the spinal column.

CONCLUSION

Non traumatic beveled dural needles, termed "pencil point needles", only partially separate dural fibers, and lesions caused by these needles develop in a more complex way. The Quincke 26G needle produced a puncture that is morphologically different from that caused by the Whitacre 25G needle, although lesions produced by both types close more than 94% after 15 min. We believe the size of the lesion caused by these needles does not explain the difference in post dural puncture headache due to loss of spinal fluid.

[Analysis of the external and internal surface of human dura mater with scanning electron microscopy]

INTRODUCTION

In recent years several studies have raised questions about the anatomy of the human dura mater. Our objective has therefore been to examine its tridimensional structure with the aid of the scanning electron microscope.

METHOD

Samples were taken from 4 human cadavers (70, 72, 77 and 78 years old) between 8 and 12 hours after death. After fixing in glutaraldehyde phosphate buffer, dehydration in acetone and elimination of the acetone at the critical point, treatment with carbon and metallization with gold, the external and internal surfaces were examined.

RESULTS

The external, or epidural, surface of the dura mater is made up of thin collagen fibers joined in bands running in different directions. The outer surface and lower layers of the dura contain elastic, interwoven fibers surpassing 2 microns in diameter. The inner surface, which is smooth and glossy, is formed of thin ribbons of arachnoids that are fused and tightly attached to the structure of the dura mater.

CONCLUSION

The outer surface of the dura mater consists mainly of collagen fibers which alone or in groups run in different directions: longitudinally, horizontally or obliquely, depending on the are studied. These findings contradict the classical descriptions of the dura mater as having parallel, longitudinally placed collagen fibers in the tangential plane.

[Structural analysis of the thickness of human dura mater with scanning electron microscopy]

INTRODUCTION

The only references to the thickness of the human dura mater, reporting its size at various levels, are now 50 years old. Our aim was to study its tridimensional structure with the aid of the scanning electron microscope.

METHOD

The samples, which were taken 8-12 h after death from 4 human cadavers between 70 and 78 years old, were examined on 2 orthogonal planes (radial longitudinal and transversal).

RESULTS

The architectural structure of the external membrane of the meninges was unusual. The dura mater is made up of elastic collagen fibers organized in successive parallel planes on the surface of the medulla. Each plane constitutes a unit which we will call a sub-laminae. The sub-laminae are found in groups of 8 to 12 that form larger units called laminae, which are between 4 and 5 microns thick. The full thickness of the dura mater at the level of the third lumbar vertebrate contains from 78 to 82 laminae which together measure 270 microns.

CONCLUSION

The dura mater is made up of a large number of sublaminae that are concentrically parallel to the surface of the medulla. The fibers in general run in all directions and are oriented differently in each sub-lamina. The orientation of fibers that can be seen on the outer or epidural surface corresponds only to the fibers of the outermost lamina, which has a thickness of 78 to 82 microns. A needle that pierces the dura mater passes through some 700 to 800 sublaminae, each with its own particular distribution of fibers.

[Iatrogenic spinal epidermoid tumors. A late complication of spinal puncture]

INTRODUCTION. Epidermoid tumors in the spinal canal are rare. Whether congenitally or iatrogenically caused, they form as the result of epidermal cells implanted within the spinal channel. Such implantation can occur during a variety of procedures and events such as bullet wounds, surgery, myelography or punctures for diagnosis, anesthesia or treatment. Although this complication is not discussed in books or journals on anesthesiology, we have found it mentioned in over 100 published cases reporting iatrogenically caused spinal epidermoid tumors. ETIOPATHOGENESIS. Iatrogenic epidermoid tumors of the spine derive from the implantation of epidermal tissue transported inside the spinal canal during lumbar punctures without guidance or with inadequate guidance. There is ample evidence that such tumors are iatrogenic. All cases occur in patients with a history of lumbar puncture. They are rarely associated with congenital anomalies. They are extramedullary. They tend to develop near sites of earlier lumbar puncture, usually near the conus medullaris and the cauda equina. Iatrogenic epidermoid tumors of the spine have been reproduced experimentally in two studies in which autologous skin fragments were implanted in the spinal canal. CLINICAL SIGNS. These tumors are well tolerated by patients for extended periods of time, ranging from 2 to 10 years. At the cauda equinus, tumors can grow slowly for long periods without signs of nerve compression. Symptoms are directly related to tumor size and site. All patients with tumors at the cauda equinus report severe pain radiating toward the roots of compressed nerves. Nuclear magnetic resonance makes it possible to detect the tumor without administration of intrathecal contrast. At present gadolinium-DTPA improves the image so that these tumors can be distinguished from other types. The prognosis for epidermoid tumors of the spine is good, as they are histologically benign. Treatment is always surgical. CONCLUSION. Although the causal relation between epidermoid spinal tumors and lumbar puncture is well documented, anesthesiologists are not sufficiently aware of this possible complication. Between 1977 and 1995, 28 new cases were published. We believe that a deeper understanding of such rare complications will show us how to prevent them while providing appropriate use of epidural and subarachnoid anesthesia.

[Skin fragments carried by spinal needles in cadavers]

Epidural or intradural puncture with inappropriately stiffened or improperly placed needles can carry cells or fragments of epithelial tissue into the epidural or intradural space. These skin fragments feed by imbibition, possibly leading to the development of epidermoid cysts. We aimed to study the ability of today's needles to transport cells or epithelial fragments. We studied 120 needles in 6 groups of 20, as follows: group 1, Touhy G-16; group 2, Touhy G-17; group 3, Quincke G-22; group 4, Quincke G-26; group 5, Sprotte G-22, and group 6, Sprotte G-24. These needles were used to make intradural and epidural insertions, as indicated, with stiffeners fully in place. Insertions were made into 3 cadavers, epidermal cells or skin fragments were then isolated from the solutions used to wash the needles, and the samples were studied under an optical microscope. We identified groups of cells or epidermal tissues in 45% of the Touhy G-16 samples and in 30% of the Touhy G-17 samples. Squamous epithelial cells were found in 15% of the Quincke G-22 samples and in 30% of the Sprotte G-22 samples. There was a significant difference between the amount of tissue transported by the Touhy needles in comparison with the Quincke (p < 0.01) and Sprotte (p < 0.05) needles. Needles from some manufacturers transport epithelial fragments during lumbar puncture. We believe that better quality control during manufacture of epidural and intradural needles can help to eradicate the rare neurological complications derived from the removal of epithelial cells and their subsequent deposit inside the spinal channel.