Nerves

From an anatomical point of view, nerves are characterized by a complex internal structure made of nervous fibers (containing axons, myelin sheaths and Schwann cells) grouped in fascicles, and loose connective tissue (containing elastic fibers and vessels) (Fig. 3.24 a).A closer look at nerve sheaths demonstrates an external sheath - the outer epineurium - which surrounds the nerve fascicles. Each fascicle is invested in turn with a proper connective sheath - the perineurium - which encloses a variable number of nerve fibers separated by the endoneurium. The connective tissue intervening between the outer nerve sheath and the fascicles is commonly referred to as the inter-fascicular epineurium and houses the nerve vasculature.

Peripheral nerves.a Schematic drawing illustrating the inner structure of a peripheral nerve.NF = nerve fascicle. b Longitudinal 5-12 MHz US image obtained over the median nerve (empty arrows) at the middle third of the forearm.The nerve is composed of parallel linear hypoechoic areas (white arrowheads) - the fascicles - separated by hyperechoic bands (empty arrowheads) - the interfascicular epineurium. Note the outer epineurium (whitearrows)

Peripheral nerves.a Schematic drawing illustrating the inner structure of a peripheral nerve.NF = nerve fascicle. b Longitudinal 5-12 MHz US image obtained over the median nerve (empty arrows) at the middle third of the forearm.The nerve is composed of parallel linear hypoechoic areas (white arrowheads) - the fascicles - separated by hyperechoic bands (empty arrowheads) - the interfascicular epineurium. Note the outer epineurium (whitearrows)

With the current generation of high-frequency "small parts" transducers and compound technology, US has become a well-accepted and widespread imaging modality for evaluation of peripheral nerves. The improved performance of these transducers has made it possible to recognize subtle anatomical details with US at least equal to or even smaller than those depicted with surface-coil magnetic resonance (MR) imaging and to depict a wide range of pathological conditions affecting nerves [40, 41]. Apart from the availability of high-end technology, nerve US requires indepth knowledge of anatomy and close correlation of imaging findings with the patient's clinical history and the results of electrophysiological studies. With these credentials, US provides low-cost and non-invasive imaging, speed of performance, and other important advantages over MR imaging, including a higher spatial resolution and the ability to explore long segments of nerve trunks in a single study and to examine nerves in both static and dynamic states with real time scanning.

On long axis planes, nerves typically assume an elongated appearance with multiple hypoechoic parallel linear areas, which correspond to the neuronal fascicles that run longitudinally within the nerve, separated by hyperechoic bands [42] (Fig. 3.24 b). On short axis planes, high-resolution US demonstrates nerves as honeycomb-like structures composed of hypoechoic rounded areas (the fascicles) embedded in a hyperechoic background (interfascicular epineurium) (Fig. 3.25 a,b) [42].

The number of fascicles in a nerve may vary depending on the occurrence of nerve branching. In nerve bifurcations, the nerve trunk divides into two or more secondary nerve bundles, whereas each fascicle enters only one of the divisional branches without splitting. The outer boundaries of nerves are usually undefined due to the similar hypere-choic appearance of both the superficial epineuri-um and the surrounding fat. Generally speaking, nerves are compressible structures and alter their shape depending on the volume of the anatomical spaces within which they run, as well as on the bulk and conformation of the perineural structures. Across synovial joints, they pass through narrow anatomical passageways - the osteofibrous tunnels

- that redirect their course. The floor of these tunnels consists of bone, whereas the roof is made of focal thickenings of the fascia, the so-called "reti-nacula", which prevent dislocation and traumatic damage of the structures contained in the tunnel during joint activity [43]. In normal states, color and power Doppler US are able to depict blood flow signals from perineural and interfascicular vessels only occasionally and in large nerve trunks.

Careful scanning technique of nerves based on the precise knowledge of their position and analysis of their anatomical relationships with surrounding structures is essential. Systematic scanning on short axis planes is preferred to follow the nerves contiguously throughout the limbs [40]. Once detected, the nerve is kept in the center of the US image in its short axis and then followed prox-imally and distally shifting the transducer up or down according to its course. With this technique

- called the "lift technique" - the examiner is able to explore long segments of a nerve in a few seconds throughout the limbs and extremities. In the event of intrinsic or extrinsic nerve abnormalities, the US examination is more appropriately focused on the area-of-interest using oblique and longitu a

Ulnar Nerve Fascicles

Nerve echotexture.a Histologic slice demonstrates the cross-sectional appearance of a nerve (largearrows) composed of many fascicles (narrowarrows).bTransverse 17-5MHz US image of the ulnar nerve at the arm.The nerve (emptyarrows) is characterized by a honeycombing appearance made of round hypoechoic areas (narrowarrow) in a homogeneous hyperechoic background. The cross-sectional appearance of the hypoechoic rounded areas correlate well with the nerve fascicles seen in a a

Nerve echotexture.a Histologic slice demonstrates the cross-sectional appearance of a nerve (largearrows) composed of many fascicles (narrowarrows).bTransverse 17-5MHz US image of the ulnar nerve at the arm.The nerve (emptyarrows) is characterized by a honeycombing appearance made of round hypoechoic areas (narrowarrow) in a homogeneous hyperechoic background. The cross-sectional appearance of the hypoechoic rounded areas correlate well with the nerve fascicles seen in a dinal US scanning planes.Although all main nerves can readily be displayed in the extremities due to their superficial position and absence of intervening bone, depiction of the peripheral nervous system is not possible everywhere with US. In fact, most cranial nerves, the nerve roots exiting the dorsal, lumbar and sacral spine, the sympathetic chains and the splanchnic nerves in the abdomen cannot be visualized due to their course being too deep or interposition of bony structures.

Peripheral Neuropathy Natural Treatment Options

Peripheral Neuropathy Natural Treatment Options

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