Nerve block, nerve damage, and fluid injection pressure: overturning the myth.

Histological and micro-ultrasound evidence rebuffs deep-rooted views on the nature of nerve block, nerve damage, and injection pressure monitoring. We propose that the ideal position of the needle tip for nerve block is between the innermost circumneural fascial layer and outer epineurium, with local anaesthetic passing circumferentially through adipose tissue. Thin, circumferential, subepineural expansion that is invisible to the naked eye was identified using micro-ultrasound, and could account for variability of outcomes in clinical practice. Pressure monitoring cannot differentiate between intrafascicular and extrafascicular injection. High injection pressure only indicates intraneural extrafascicular spread, not intrafascicular spread, because it is not possible to inject into the stiff endoneurium in most human nerves.

Anatomical study with clinical significance of communicating and visceral branching of the cervical and upper thoracic sympathetic trunk.

Current advances in the management of the autonomic nervous system in various cardiovascular diseases, and in treatments for pain or sympathetic disturbances in the head, neck, or upper limbs, necessitate a thorough understanding of the anatomy of the cervicothoracic sympathetic trunk. Our objective was to enhance our understanding of the origin and distribution of communicating branches and visceral cervicothoracic sympathetic nerves in human fetuses. This was achieved through a comprehensive topographic systematization of the branching patterns observed in the cervical and upper thoracic ganglia, along with the distribution of communicating branches to each cervical spinal nerve. We conducted detailed sub-macroscopic dissections of the cervical and thoracic regions in 20 human fetuses (40 sides). The superior and cervicothoracic ganglia were identified as the cervical sympathetic ganglia that provided the most communicating branches on both sides. The middle and accessory cervical ganglia contributed the fewest branches, with no significant differences between the right and left sides. The cervicothoracic ganglion supplied sympathetic branches to the greatest number of spinal nerves, spanning from C5 to T2 . The distribution of communicating branches to spinal nerves was non-uniform. Notably, C3 , C4 , and C5 received the fewest branches, and more than half of the specimens showed no sympathetic connections. C1 and C2 received sympathetic connections exclusively from the superior ganglion. Spinal nerves that received more branches often did so from multiple ganglia. The vertebral nerve provided deep communicating branches primarily to C6 , with lesser contributions to C7 , C5 , and C8 . The vagus nerve stood out as the cranial nerve with the most direct sympathetic connections. The autonomic branching pattern and connections of the cervicothoracic sympathetic trunk are significantly variable in the fetus. A comprehensive understanding of the anatomy of the cervical and upper thoracic sympathetic trunk and its branches is valuable during autonomic interventions and neuromodulation. This knowledge is particularly relevant for addressing various autonomic cardiac diseases and for treating pain and vascular dysfunction in the head, neck, and upper limbs.

A histology guide for performing human cadaveric studies: SQIP 2024 what to look for with light microscopy.

Histological observation under light microscopy has long been used in human cadaveric studies. However, it can distort the interpretations of findings if not used appropriately; there is no guide for its proper use. The aim of this article is to revisit and discuss the correct use of histology in human cadaveric studies, following discussions with experts in multiple fields of medicine, and to create the first guide for such usage. We reached a consensus with the experts, agreeing that when this principle (structure, quantification, interaction, position: SQIP) is applied to histological observations, the findings will be interpreted correctly. Appropriate use of this recommendation can make human cadaveric studies more accurate and informative. This is the first histology guide for human cadaveric studies.

Human lumbar sympathetic blockade: An anatomical study to address potential block failure.

The lumbar sympathetic block is often used to treat complex regional pain syndrome, but it seems to have a high failure rate. This study seeks anatomical explanations for this apparent failure in order to refine our block procedure. Two simulated sympathetic trunk blocks were carried out on four fresh, cryopreserved unembalmed human cadavers under fluoroscopic control at the L2 vertebral body level, followed by two further simulated blocks at the L4 vertebral body level on the other side. Dye was injected, and the areas were dissected following a specific protocol. We then describe the anatomy and the spread of the dye compared to the spread of the contrast medium on fluoroscopy. The ganglia were differently located at different vertebral levels, and differed among the cadavers. Following this anatomical clarification, we now prefer to perform lumbar sympathetic blocks at the fourth lumbar vertebra level, using an extraforaminal approach at the caudal end of ​​the vertebra, avoiding the anterolateral margin of the vertebral body at the midpoint.

Innervation of the heart: Anatomical study with application to better understanding pathologies of the cardiac autonomics.

Current advances in management of the cardiac neuroaxis in different cardiovascular diseases require a deeper knowledge of cardiac neuroanatomy. The aim of the study was to increase knowledge of the human fetal extrinsic cardiac nervous system. We achieved this by systematizing the origin and formation of the cardiac nerves, branches, and ganglia and their sympathetic/parasympathetic connections. Thirty human fetuses (60 sides) were subjected to detailed sub-macroscopic dissection of the cervical and thoracic regions. Cardiac accessory ganglia lying on a cardiac nerve or in conjunction with two or more (up to four) nerves before entering the mediastinal cardiac plexus were observed in 13 sides. Except for the superior cardiac nerve, the sympathetic cardiac nerves were individually variable and inconstant. In contrast, the cardiac branches of the vagus nerve appeared grossly more constant and invariable, although the individual cardiac branches varied in number and position of origin. Each cervical cardiac nerve or cardiac branch of the vagus nerve could be singular or multiple (up to six) and originated from the sympathetic trunk or the vagus nerve by one, two, or three roots. Sympathetic nerves arose from the cervical-thoracic ganglia or the interganglionic segment of the sympathetic trunk. Connections were found outside the cardiac plexus. Some cardiac nerves were connected to non-cardiac nerves, while others were connected to each other. Common sympathetic/parasympathetic cardiac nerve trunks were more frequent on right (70%) versus left sides (20%). The origin, frequency, and connections of the cardiac nerves and branches are highly variable in the fetus. Detailed knowledge of the normal neuroanatomy of the heart could be useful during cardiac neuromodulation procedures and in better understanding nervous pathologies of the heart.

Microscopy of structures surrounding typical acupoints used in clinical practice and electron microscopic evaluation of acupuncture needles.

Although the general functionality and structures of acupoints have been studied, there has been little insight into their underlying morphology and physical characteristics. We describe the microanatomical structures surrounding acupoints, the electron microscopic appearance of the needles, and the physical effects of acupuncture needling on the fascia. We injected heparinized blood solution through thin needles at seven known and commonly used "sweat acupoints" in eight fresh, unembalmed, cryopreserved human cadavers to mark the needle positions, and later, during histological examination, to identify them. After the solution was injected, samples were dissected and prepared for histological examination. We examined 350 cross-sections of five different paraffin wax sections from each acupoint microscopically. Acupuncture needles were photographed and superimposed on the cross-sectioned tissues at similar magnifications. Needles were also examined under a scanning electron microscope to judge the roughness or smoothness of their surfaces. A greater conglomeration of nerve endings surrounded the acupoints than in tissues more than 1-3 cm distant from them. Nerve endings and blood vessels were in close contact with a complex network of membranes formed by interlacing collagen fibers, and were always enclosed within those collagen membranes. Nerve endings were found within hypodermis, muscles, or both. Scanning electron microscopy demonstrated the three-dimensional shapes and sizes of the needles, and the degree of roughness or smoothness of their polished external surfaces. We demonstrate a delicate arrangement of nerve endings and blood vessels enclosed within complex collagen membrane networks at acupoints within the hypodermis and muscle. This arrangement could explain why needling is an essential step in the acupuncture process that provides favorable outcomes in clinical practice.

Did she have an epidural? The long-term consequences of postdural puncture headache and the role of unintended dural puncture.

OBJECTIVE: This narrative literature review examines the long-term impact of postdural puncture headache (PDPH) in postpartum women following an unintended dural puncture (UDP) with a large bore needle commonly used for epidural catheter placement. It seeks to bridge the knowledge gap for the neurologist as to the mounting body of obstetric anesthesia literature on the development of chronic headache after PDPH with this unique needle. BACKGROUND: Headache is the most common complication of dural puncture, and the risk is greatest in the parturient population. Preexisting risk factors for this population include youth and sex, and after UDP with a large bore needle, almost 70%-80% report a headache. Additionally, there appears to be a significant cohort who experience long-term, persistent headache after UDP. METHODS: We performed a narrative review of literature using PubMed, searching terms that included long-term follow-up after UDP with a large bore needle in the postpartum population. RESULTS: In women who had UDP with a large bore needle used for epidural catheter placement at delivery, the rate of chronic debilitating headache is around 30% in the months following delivery and may persist for up to a year or longer. CONCLUSION: Based on the existing literature, we have mounting evidence that UDP with the large bore needle used to place an epidural catheter should be understood as a high-risk inciting event for the development of long-term headaches not simply a high risk of acute PDPH. Additionally, consideration should be given to stratifying the etiology of PDPH, based on needle type, and recognizing the entity of chronic PDPH, thus allowing for improvements in research and diagnosis.

Spinal arachnoid sleeves and their possible causative role in cauda equina syndrome and transient radicular irritation syndrome.

INTRODUCTION: We have previously described arachnoid sleeves around cauda equina nerve roots, but at that time we did not determine whether injections could be performed within those sleeves. The purpose of this observational study was to establish whether the entire distal orifice of a spinal needle can be accommodated within an arachnoid sleeve. MATERIALS AND METHODS: We carefully dissected the entire dural sacs off four fresh cadavers, opened them by longitudinal incision, and immersed them in saline. Under direct vision, we penetrated the cauda equina roots nerves traveling almost vertically downward at 30 locations each with a 27- and a 25-G pencil-point needle (60 punctures total). We captured the images with a stereoscopic camera. RESULTS: The nerve root offered no noticeable resistance to needle entry. Although the arachnoid sleeves could not be identified with the naked eye, they were translucent but visible under microscopy. In 21 of 30 attempts with a 27-gauge needle, and in 20 of 30 attempts with a 25-gauge needle, the distal orifice of the spinal needle was completely within the arachnoid sleeve. CONCLUSION: It seems possible to accommodate the distal orifice of a 25- or a 27-gauge pencil-point spinal needle completely within the space of the arachnoid sleeve. An injection within this sleeve could potentially lead to a neurological syndrome, as we have previously proposed.

Case series of fluoroscopic findings and 3D reconstruction of human spinal MRIs of the space of Okada.

OBJECTIVE: To better understand the unexpected spread of contrast medium observed by conventional fluoroscopic X-ray images during standard neuraxial techniques used in the treatment of pain. The support of 3D reconstruction of MRI images of structures within the lumbar spine was used to better understand the space of Okada. METHODS: Lumbar facet joint and epidural corticosteroid injections in five patients under fluoroscopic guidance with loss of resistance to air or saline to identify the facet joints or epidural space. Next, in a retrospective study, the authors examined the retrodural space of Okada and the neighboring tissues with 3D reconstruction of spinal MRIs of seven patients without any demonstrable spinal pathology to better understand the characteristics of the space of Okada. RESULTS: Contrast medium spread to the ipsilateral and contralateral sides was observed in five patients. The contralateral spread was thought to be through the retrodural space of Okada, which is a potential space between the anterior surface of the vertebral lamina and the posterior surface of the ligamentum flavum. It facilitates communication between the contralateral articular facet joints of the spine. CONCLUSIONS: This study provides new evidence for the existence of the space of Okada where an unexpected contralateral spread occurred following facet joint and attempted epidural injection. The 3D reconstructions of MRIs may help us better understand the nature of the retrodural space of Okada and its clinical implications.

"Triceps Brachii Muscle Response to Neurostimulation of the Radial Nerve during Axillary Plexus Blockade: Clinical, Anatomical and Histological Correlation".

Axillary plexus blockade is a common technique in clinical practice with a well-known pattern of structures around the brachial artery. Historically, the only proper response to radial nerve stimulation was considered to be extension of the hand and wrist. Twenty-five axillary blockades were assessed by ultrasound and neurostimulation; the principal objective was to correlate the needle position over the radial nerve with the anatomical and histological structure of that nerve. During the procedure, the needle was directed in two ways to reach the medial or lateral margin of the nerve: above the brachial artery or beneath it. Once the needle reached the nerve, the current was augmented gradually until a response was elicited. For the cadaveric anatomical study, eight axillae were dissected and histological samples were examined. The response of the triceps brachii muscle differed significantly between the two approaches to the radial nerve (P < 0.001), and the mean intensity of stimulation was significantly lower when the nerve was accessed above the artery (0.44 ± 0.15 mA) than below it (0.57 ± 0.17 mA) (P = 0.015). A triceps brachii motor response occurs at lower current intensity and lower needle-nerve distance when the radial nerve is accessed above the artery and over the latissimus dorsi tendon. These findings were correlated with the topography of the radial nerve in the axillary fossa. Clin. Anat. 33:578-584, 2020. © 2019 Wiley Periodicals, Inc.

Another (Internal) Epineurium: Beyond the Anatomical Barriers of Nerves.

The epineurium has been accepted as the outer anatomical barrier of the peripheral nerves. Our objective was to characterize the microanatomy of the layers surrounding nerves using different tissue-specific staining methods. Two hundred forty-two cross sections of human sciatic and median nerves, and brachial plexuses of eight fresh unembalmed cadavers, were examined. The samples were fixed in formaldehyde solution and stained with hematoxylin-eosin, Masson's trichrome, or epithelial membrane antigen under standard conditions. Because epithelial membrane antigen only stains the perineurium, we demonstrated using hematoxylin-eosin and Masson's trichrome that there were different collagen layers inside and outside the nerves. All fascicles had a collagen layer that surrounded the perineurium and were in close contact with it, with no adipose tissue between them. Unlike the perineurium, this layer, an "internal epineurium," contained no cells, and it surrounded one or a small group of fascicles. Bundling these fascicles or small groups of fascicles together was the true epineurium, and between the true and internal epineurium, we consistently found an adipose-containing compartment. More proximal to this, the tibial and common peroneal nerves were bundled together by another collagen layer, the circumneurium, which also had a fat-cell-containing compartment deep to it. There were scattered collagen fibers among the adipocytes. Using tissue-specific staining, we were able to demonstrate a collagen layer, the "internal epineurium." Outside the nerves, we identified several fat-containing concentric compartments. Those compartments were limited by collagen fiber layers that were also similar to the epineurium. Clin. Anat. 33:199-206, 2020. © 2019 Wiley Periodicals, Inc.

Extrafasicular and Intraperineural, but No Endoneural, Spread after Deliberate Intraneural Injections in a Cadaveric Study.

BACKGROUND: There is confusion regarding the spread of intraneurally injected local anesthetic agents during regional anesthesia. The aim of this research was to deliberately inject a marker that does not leave the neural compartment into which it is injected, and then to study the longitudinal and circumferential spread and possible pathways of intraneural spread. METHODS: After institutional review board approval, we intraneurally injected 20 and 5 ml of heparinized blood solution under ultrasound guidance into 12 sciatic nerves in the popliteal fossa and 10 median nerves, respectively, of eight fresh, unembalmed cadavers using standard 22-gauge "D" needles, mimicking the blocks in clinical conditions. Ultrasound evidence of nerve swelling confirmed intraneural injection. Samples of the nerves were then examined under light and scanning electron microscopy. RESULTS: Extrafascicular spread was observed in all the adipocyte-containing neural compartments of the 664 cross-section samples we examined, but intrafascicular spread was seen in only 6 cross-sections of two nerves. None of the epineurium, perineurium, or neural components were disrupted in any of the samples. Spread between the layers of the perineurium was a route of spread that included the perineurium surrounding the fascicles and the perineurium that formed incomplete septa in the fascicles. Similar to the endoneurium proper, subepineural compartments that did not contain any fat cells did not reveal any spread of heparinized blood solution cells. No "perineural" spaces were observed within the endoneurium. We also did not observe any true intrafascicular spread. CONCLUSIONS: After deliberate intraneural injection, longitudinal and circumferential extrafascicular spread occurred in all instances in the neural compartments that contained adipocytes, but not in the relatively solid endoneurium of the fascicles.

The Posterior Lumbar Epidural Space: Three-Dimensional Reconstruction of High-Resolution MRI: Real and Potential Epidural Spaces and Their Content In Vivo.

OBJECTIVE: Our aim was to study the posterior lumbar epidural space with 3D reconstructions of magnetic resonance images (MRIs) and to compare and validate the findings with targeted anatomic microdissections. DESIGN: We performed 3D reconstructions of high-resolution MRIs from seven patients and normal-resolution MRIs commonly used in clinical practice from 196 other random patients. We then dissected and photographed the lumbar spine areas of four fresh cadavers. RESULTS: From the 3D reconstructions of the MRIs, we verified that the distribution of the posterior fat pad had an irregular shape that resembled a truncated pyramid. It spanned between the superior margin of the lamina of the caudad vertebra and beyond the inferior margin to almost halfway underneath the cephalad lamina of the cranial vertebra, and it was not longitudinally or circumferentially continuous. The 3D reconstructions of the high-definition MRI also consistently revealed a prelaminar fibrous body that was not seen in most of the usually used low-definition MRI reconstructions. Targeted microdissections confirmed the 3D reconstruction findings and also showed the prelaminar tissue body to be fibrous, crossing from side to side anterior to the cephalad half of each lamina, and spanning from the dural sac to the laminae. CONCLUSIONS: Three-dimensional reconstructions and targeted microdissection revealed the unique appearance of posterior fat pads and a prelaminar fibrous body. The exact consistency, presence, prevalence with age, presence in other regions, and function of this body are unknown and require further research.

3D reconstruction of peripheral nerves from optical projection tomography images: A method for studying fascicular interconnections and intraneural plexuses.

The general microscopic characteristics of nerves are described in several textbooks of histology, but the specific microanatomies of most nerves that can be blocked by anesthesiologists are usually less well known. Our objective was to evaluate the 3D reconstruction of nerve fascicles from optical projection tomography images (OPT) and the ability to undertake an internal navigation exploring the morphology in detail, more specifically the fascicular interconnections. Median and lingual nerve samples were obtained from five euthanized piglets. OPT images of the samples were acquired and 3D reconstruction was performed. The OPT technique revealed the inner structure of the nerves at high resolution, including large and small fascicles, perineurium, interfascicular tissue, and epineurium. The fascicles were loosely packed inside the median nerve and more densely so in the lingual nerve. Analysis of the 3D models demonstrated that the nerve fascicles can show six general spatial patterns. Fascicular interconnections were clearly identified. The 3D reconstruction of nerve fascicles from OPT images opens a new path for research into the microstructure of the inner contents of fascicular nerve groups and their spatial disposition within the nerve including their interconnections. These techniques enable 3D images of partial areas of nerves to be produced and could became an excellent tool for obtaining data concerning the 3D microanatomy of nerves, essential for better interpretation of ultrasound images in clinical practice and thus avoiding possible neurological complications. Clin. Anat. 31:424-431, 2018. © 2017 Wiley Periodicals, Inc.

A novel marker for identifying and studying the membranes, barriers, and compartments surrounding peripheral nerves microscopically.

Recent anatomical discoveries indicate the importance of identifying membranes and compartments surrounding peripheral nerves into which local anesthetic agents can be injected and continuous nerve block catheters placed during regional anesthetic procedures. However, current markers used in anatomical studies have multiple drawbacks, specifically extravasation into noninjected locations, which can result in inadequate treatment. We studied a readily-available new marker, heparinized blood solution (HBS), which is easy to identify by microscopy and can remain in the nerve compartment into which it is deposited without distorting the tissue. We collected blood from 22 patients and prepared it as HBS. This was then injected into four fresh cadavers as in routine clinical practice for ultrasound-guided nerve blocks to form a so-called "doughnut" by "hydro-dissecting" at 32 sites. All samples, including nerves and neighboring tissues, were then prepared and examined by light microscopy. Although no deliberate intraneural injection was attempted, the marker was identified inside all the nerve compartments except the fascicles. Apart from leaking through the needle entry site in some instances, there was no extravasation of the HBS into neighboring nerve compartments in either direction. The tissues were not distorted and the erythrocytes did not form a thrombus. Nerve membranes and compartments could be clearly identified with routine staining. This technique enabled us to study the longitudinal and circumferential spread in all nerve compartments and to collect data for better interpretation of factors influencing an anesthetic nerve block and situations in which complications could possibly arise. HBS seemed superior to other markers because it did not leave the compartments into which it had been injected, did not distort the tissue, and was easily visible under the light microscope. Clin. Anat., 31:1050-1057, 2018. © 2018 Wiley Periodicals, Inc.

Human Lumbar Ligamentum Flavum Anatomy for Epidural Anesthesia: Reviewing a 3D MR-Based Interactive Model and Postmortem Samples.

The ligamentum flavum (LF) forms the anatomic basis for the loss-of-resistance technique essential to the performance of epidural anesthesia. However, the LF presents considerable interindividual variability, including the possibility of midline gaps, which may influence the performance of epidural anesthesia. We devise a method to reconstruct the anatomy of the digitally LF based on magnetic resonance images to clarify the exact limits and edges of LF and its different thickness, depending on the area examined, while avoiding destructive methods, as well as the dissection processes. Anatomic cadaveric cross sections enabled us to visually check the definition of the edges along the entire LF and compare them using 3D image reconstruction methods. Reconstruction was performed in images obtained from 7 patients. Images from 1 patient were used as a basis for the 3D spinal anatomy tool. In parallel, axial cuts, 2 to 3 cm thick, were performed in lumbar spines of 4 frozen cadavers. This technique allowed us to identify the entire ligament and its exact limits, while avoiding alterations resulting from cutting processes or from preparation methods. The LF extended between the laminas of adjacent vertebrae at all vertebral levels of the patients examined, but midline gaps are regularly encountered. These anatomical variants were reproduced in a 3D portable document format. The major anatomical features of the LF were reproduced in the 3D model. Details of its structure and variations of thickness in successive sagittal and axial slides could be visualized. Gaps within LF previously studied in cadavers have been identified in our interactive 3D model, which may help to understand their nature, as well as possible implications for epidural techniques.

Pythagoras and Cosines: The skin-dural sac distance and optimal angles in paramedian spinal anesthesia.

The classical recommendation for paramedian approaches is needle insertion 1-2 cm paramedian and an angle of 10°-15° medial-cephalad to the plane of the back, but contact with vertebrae is frequent. A mathematical approach to individualizing punctures is proposed on the basis of skin-dural sac distance (d): Optimal angle ∼ inverse cosine [d/ √(1+d^2) ] and the distance covered by the needle ∼ √(1+d^2) for 1 cm paramedian punctures. The inferred angles were compared to optimal angles leading to the central dorsal part of the dural sac from 1 to 2 cm paramedian, measured by Magnetic Resonance Imaging (MRI) in seven cases and in a short stature volunteer (1.58 m, Body Mass Index (BMI) 23.2), to study supine and fetal positions using both closed MR and ultrasound. The average (d) decreased rostrally [6.8 cm (L4-L5)-4.3 cm (T11-T12)] while the mean optimal incidence angles increased [8.3°-16.5° (L4-L5) to 12.7°-24.1° (T11-T12) at 1-2 cm paramedian, respectively] and coincided with the estimated angles with a correlation coefficient = 0.98. In the volunteer, the optimal lateromedial angles increased from 14.4° to 26.7° (L3-L4) to 17.1°-30.3° (T11-T12) for a (d) = 3.7 cm (L3-L4)-3.1 cm (T11-T12) and increased ≤3.7° and ≤5.1° at 1 and 2 cm paramedian, respectively, in fetal positions in MR. Ultrasound yielded comparable figures. The range of possible angles for dural punctures is wider at 1 cm paramedian in lower approaches in lateral decubitus [from 3.6° at T12L1 (12.2°-15.8°) to 9° at L3L4 (8.8°-18.7°)]. The classically recommended angles of 10°-15° differ from the optimal angles, particularly in small patients, suggesting the need for ultrasound guidance or for inferring angles prior to spinal anesthesia. Clin. Anat. 29:1046-1052, 2016. © 2016 Wiley Periodicals, Inc.

3D interactive model of lumbar spinal structures of anesthetic interest.

A 3D model of lumbar structures of anesthetic interest was reconstructed from human magnetic resonance (MR) images and embedded in a Portable Document Format (PDF) file, which can be opened by freely available software and used offline. The MR images were analyzed using a specific 3D software platform for biomedical data. Models generated from manually delimited volumes of interest and selected MR images were exported to Virtual Reality Modeling Language format and were presented in a PDF document containing JavaScript-based functions. The 3D file and the corresponding instructions and license files can be downloaded freely at http://diposit.ub.edu/dspace/handle/2445/44844?locale=en. The 3D PDF interactive file includes reconstructions of the L3-L5 vertebrae, intervertebral disks, ligaments, epidural and foraminal fat, dural sac and nerve root cuffs, sensory and motor nerve roots of the cauda equina, and anesthetic approaches (epidural medial, spinal paramedial, and selective nerve root paths); it also includes a predefined sequential educational presentation. Zoom, 360° rotation, selective visualization, and transparency graduation of each structure and clipping functions are available. Familiarization requires no specialized informatics knowledge. The ease with which the document can be used could make it valuable for anatomical and anesthetic teaching and demonstration of patient information.

No evidence of fascicular injury following a low-volume intraneural injection of the median nerve: a cadaveric study.

BACKGROUND: The test dose or hydrolocation technique allows rapid detection of spread location. Though its primary aim is to enhance safety in peripheral nerve blocks, evidence on the potential risks of an intraneural test aliquot is lacking. We conducted a cadaveric study to evaluate the risk of fascicular injury following a low-volume (<1 mL) intraneural injection of the median nerve. METHODS: Ten upper limbs from fresh unembalmed human cadavers were studied. In-plane ultrasound-guided intraneural injections of the median nerve were performed at mid, proximal, and distal locations using 1 mL of methylene blue and heparinized blood solution. Nerves were extracted and samples immersed in 10% buffered formalin for 4 weeks. Perpendicular 3 mm slices were obtained for H&E staining and light microscopy analysis. Our main objective was to assess the number of injured fascicles. Secondarily, we evaluated the pattern of intraneural spread. Fascicular injury was defined as the presence perineurium or axonal disruption and/or the presence of erythrocytes inside a nerve fascicle. RESULTS: Thirty injections were performed in 10 median nerves. Sonographic swelling was confirmed in 100% of the cases. 352 histological sections were analyzed to assess study outcomes. The mean number of fascicles on each section of median nerve was 20±6 covering 49%±7% of the nerve area. No evidence of axonal disruption nor intra-fascicular erythrocytes was found in any of the analyzed sections. CONCLUSIONS: Low-volume intraneural injections do not result in evident fascicular injury. Our findings support the use of a test dose in ultrasound-guided regional anesthesia.

Newly revealed anatomy of the bucinator muscle: An anatomical and histological study.

BACKGROUND: Current anatomical knowledge of the origin of the bucinator muscle (BM), i.e., long thin attachments on the maxilla and mandible and the pterygomandibular raphe (PMR), is not supported by anatomical dissection of this muscle. The aim of this study was therefore to investigate the detailed morphology of the BM and associated structures and to discuss its function. METHODS: The anatomy of the BM and related structures was investigated in 15 cadaveric heads using a surgical microscope and histological analysis. RESULTS: The inferior fibers of the BM originated from a small retromolar area (internal oblique line), which shared a common tendon with the deep tendon of the temporalis. The superior fibers of the BM originated from the maxillary tuberosity. The middle fibers originated the pterygoid hamulus. No PMR was identified in any of the specimens, but the border between the BM and superior pharyngeal constrictor muscle (SC) was clear because the muscle fibers followed different directions. Some horizontal fibers were continuous between the BM and SC. CONCLUSIONS: Our results suggest the need to revise established accounts of the origins of the bucinator (the maxillary tuberosity, conjoint tendon of the temporalis, and pterygoid hamulus without a pterygomandibular raphe. It also needs to be noted that some of its fibers merge directly with the SC.