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Biomedical subjects

M C Villanueva

Publications and source records attributed to M C Villanueva.

8 recordsLinked to original sources
PubMed2005

[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.

Cauda Equina↗
PubMed2004

Ultrastructural findings in human spinal pia mater in relation to subarachnoid anesthesia.

UNLABELLED: We examined ultrastructural details such as the cellular component and membrane thickness of human spinal pia mater with the aim of determining whether fenestrations are present. We hypothesized that pia mater is not a continuous membrane but, instead, that there are fenestrations across the pial cellular membrane. The lumbar dural sac from 7 fresh human cadavers was removed, and samples from lumbar spinal pia mater were studied by special staining techniques, immunohistochemistry, and transmission and scanning electron microscopy. A pial layer made by flat overlapping cells and subpial tissue was identified. We found fenestrations in samples from human spinal pia mater at the thoracic-lumbar junction, conus medullaris, and nerve root levels, but these fenestrations did not appear at the thoracic level. We speculate whether the presence of fenestrations in human spinal pia mater at the level of the lumbar spinal cord and at the nerve root levels has any influence on the transfer of local anesthetics across this membrane. IMPLICATIONS: The ultrastructural anatomy of the human pia mater, such as pial cells, membrane thickness, and subpial tissue at different levels of the thoracic and lumbar spinal cord and nerve roots, was studied by special staining techniques, immunohistochemistry, and transmission and scanning electron microscopy. Fenestrations were found in samples at the thoracic-lumbar junction, conus medullaris, and nerve root levels. No fenestrations were found in samples at the thoracic level. At present, we cannot determine the significance of these findings.

Aged↗
PubMed2003

[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.

Aged↗
PubMed2000

[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.

Axons↗
PubMed1998

[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.

Animals↗
PubMed1996

"Stand down for the homeless". Podiatric screening of a homeless population in Cleveland.

Health care for the homeless is a major public health concern. With the rise in antibiotic-resistant tuberculosis, the increase of human immunodeficiency virus (HIV) diseases, and other health risks, the medical community has begun to recognize the urgency of taking a proactive role in providing care for this population. Lower extremity pathology can result in limb-threatening and, in some cases, life-threatening sequelae for homeless populations. This patient group has limited access to regular hygiene, appropriate shoes, and podiatric medical care. Participation in the "Stand Down for the Homeless" projects provided an opportunity to evaluate the podiatric needs of a homeless population and to project a response to those needs. The authors define and compare this homeless population with the national homeless population, compare the podiatric needs of this homeless populations versus the general population, and respond to those needs.

Adolescent↗
PubMedDate not supplied

[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.

Adipocytes↗