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Nerve ultrasound Nerve ultrasound is a noninvasive and painless diagnostic imaging technique that’s used to evaluate peripheral nerves by using ultrasound at a very high-frequency sound wave (more than 10MHz). These sound waves at very high frequency add a worth value to ultrasonography, which is a high spatial resolution that has allowed to detect a tiny anatomical structure in detail such as small blood vessels, layers of skin, and nerves [1]. Accordingly, using diagnostic ultrasound machines has become widely used in hospitals. One of the applications of ultrasound at high frequency is evaluating peripheral nerves. To put it another way, a great deal of peripheral nerve neuropathies have become easily detectable by ultrasonogram. To assess nerves by ultrasound, the sonographers should be familiar with the normal sonographic appearance of the nerve and how to find it. The regular appearance of nerves could be described by three characteristics, which are echogenicity, size, and vascularity. Besides, landmarks are followed to make finding specific nerves easier. Also, great attention should be paid to how to distinguish nerves from other structures that may look similar to it, such as muscles, tendons, and blood vessels. Because all of these structures have a tubular shape, it might be confusing. However, it is quite possible to scan peripheral nerves by understanding its appearance, landmarks, and distinguishing criteria of the nerve ultrasound.

Typical appearance of nerve in the ultrasound:[edit]

Echogenicity:[edit]

Almost all peripheral nerves have the same sonographic mien in healthy conditions on both longitudinal and transverse views. On a longitudinal image, the nerve has a fascicular appearance, which means hyperechoic thin lines inside a hypoechogenic tubular structure. While it looks like honeycomb on axial image with hypoechoic dots within hyperechoic oval-shaped [2] [3] [4].

Vascularity:[edit]

To detect vascularity of nerves, the color doppler is applied to the area in which the nerve is present. Incidentally, no color doppler should appear inside the healthy nerves. To put it another way, increase color doppler indicate abnormalities due to increase vascularity. Hypervascularity is likely to present in some neuropathies like inflammation and tumor[5]. Not only could the defects be detected by color doppler, but the severity of the pathological condition of nerves is also liable to be determined by the vascularity level of the color doppler.

Size:[edit]

The accurate size is measured in the axial view by taking two dimensions. One is from right to left, and the other one is from anterior to posterior. To get the size, the ultrasound tranducer should placed perpendicular with gentile prerrure. Every single peripheral nerve has a specific size which is defined Iin UPSS[6] [7].

Differentiation nerves from adjacent structures:[edit]

Three anatomical structures seem to have similar presence of nerves, which are muscles, tendons, and blood vessels. Eches one has a different approach to distinguish it from nerve. Looking at echogenicity to distinguish muscular tissue from never. Also, it is very easy to distinguish blood vessels from the nerve by using color doppler. Moreover, the mobility test for the nerve tends to be discernible in case of a tendon present.

muscular tissue:[edit]

The difference in echogenicity between nerve and muscle appears to be clearly noticed because the muscle has a distinctive echogenic pattern. It is characterized by a hypoechoic area with small hyperechoic foci which represent fibrous tissue [8].

Tendon:[edit]

A mobility test is suggested to distinguish tendons from the adjacent nerve. The tendons have more ability to move than nerves when joints are flexed. Owing to the mobility, the best way to check the movement level to differentiate between tendon and nerve is by asking the patient to flex or extend the nearest joint to the area of interest [9] [10](Martinoli et al., 2002; Suk et al., 2013).

Blood vessels :[edit]

It seems to be very easy to recognize nerves that are close to the artery or vein with color doppler mode[11]. due to the effect of the blood flow inside blood vessels, the lumen of the blood vessels have a red or blue color depending on the direction of blood flow and the orientation of the ultrasound transducer.

Landmarks and peripheral nerves can be evaluated by ultrasound:[edit]

Landmark in ultrasound is defined as a clear structure that is easy to be detected during scanning and used as a guide to find out a structure that is difficult to visualize in ultrasound imaging. To express it differently, it might be better to find a prominent structure and then look at the area of unclear structure related to the obvious one. In the table below, there are some peripheral nerves and their landmarks.

Peripheral nerve Headerlandmark text
Median nerve in the upper arm Brachial artery.
Median nerve in the forearm Superficial and deep flexor muscle.
Median nerve at the wrist Carpal tunnel.
Ulnar nerve at the wris Ulnar artery.
Ulnar nerve at the elbow Medial epicondyle.
Radial nerve Radial groove.
Brachial plexus Anterior and middle scalene muscle and proximal subclavian artery.
Distal sciatic nerve Popliteal artery.
peroneal nerve head of fibula.
Tibial nerve at the ankle Posterior tibial artery.

Peripheral nerve pathologies can be diagnosed by sonogram:[edit]

Peripheral nerve pathologies associated usually with the inflammatory process or swelling or lesion or bleeding which leads to a change in one or more of the characteristics of a healthy nerve. Consequently, these changes would make the anomalies remarkable [12](Lawande, Warrier, & Joshi, 2014). Numerous peripheral diseases and condition are likely to be evaluated by ultrasound like:

Other nerve ultrasound application:[edit]

Nerve ultrasound is commonly used as a guidance for peripheral nerve block in regional anesthesia[16].

Advantages of nerve ultrasound:[edit]

  • When ultrasound is compared to MRI in nerve scanning, ultrasound is superior to MRI in sensitivity and specificity[17] [18].
  • It is higher than MRI in edge to edge resolution[19].
  • It cost much less than other diagnostic imaging.

Limitation:[edit]

• Only the peripheral nerves can be imaged by ultrasound because the sound wave at high frequency is fragile and can not go deep to detect deep nerves. • Detecting some peripheral nerves might be challenging in obese patients because increasing the volume of fatty layer leads to increases in the depth of nerves.





References[edit]

  1. ^ Bhatta, A. K., Keyal, U., & Liu, Y. (2018). Application of High Frequency Ultrasound in Dermatology. Discovery medicine, 26(145), 237-242.
  2. ^ Gallardo, Elena, Yu-Ichi Noto, and Neil G Simon. "Ultrasound in the Diagnosis of Peripheral Neuropathy: Structure Meets Function in the Neuromuscular Clinic." Journal of Neurology, Neurosurgery & Psychiatry 86.10 (2015): 1066-1074. Web.
  3. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  4. ^ Martinoli, Carlo, Stefano Bianchi, M'Hamed Dahmane, Francesca Pugliese, Maria Bianchi-Zamorani, and Maura Valle. "Ultrasound of Tendons and Nerves." European Radiology 12.1 (2002): 44-55. Web.
  5. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  6. ^ Grimm, Alexander, Bernhard F Décard, Hubertus Axer, and Peter Fuhr. "The Ultrasound Pattern Sum Score – UPSS. A New Method to Differentiate Acute and Subacute Neuropathies Using Ultrasound of the Peripheral Nerves." Clinical Neurophysiology 126.11 (2015): 2216-225. Web.
  7. ^ Grimm, Alexander, Hubertus Axer, Bianka Heiling, and Natalie Winter. "Nerve Ultrasound Normal Values – Readjustment of the Ultrasound Pattern Sum Score UPSS." Clinical Neurophysiology 129.7 (2018): 1403-409. Web.
  8. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  9. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  10. ^ Martinoli, Carlo, Stefano Bianchi, M'Hamed Dahmane, Francesca Pugliese, Maria Bianchi-Zamorani, and Maura Valle. "Ultrasound of Tendons and Nerves." European Radiology 12.1 (2002): 44-55. Web.
  11. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  12. ^ Lawande, Ashwin, Sudhir Warrier, and Mukund Joshi. "Role of Ultrasound in Evaluation of Peripheral Nerves." The Indian Journal of Radiology and Imaging (2014): 254-58. Web.
  13. ^ Kerasnoudis, Antonios, and Georgios Tsivgoulis. "Nerve Ultrasound in Peripheral Neuropathies: A Review." Journal of Neuroimaging 25.4 (2015): 528-38. Web.
  14. ^ Lawande, Ashwin, Sudhir Warrier, and Mukund Joshi. "Role of Ultrasound in Evaluation of Peripheral Nerves." The Indian Journal of Radiology and Imaging (2014): 254-58. Web.
  15. ^ Kele, Henrich. "Ultrasonography of the Peripheral Nervous System." Perspectives in Medicine 1.1-12 (2012): 417-21. Web.
  16. ^ Koscielniak‐Nielsen, Z. J. "Ultrasound‐guided Peripheral Nerve Blocks: What Are the Benefits?" Acta Anaesthesiologica Scandinavica 52.6 (2008): 727-37. Web.
  17. ^ Suk, Jung, Im Walker, and Francis Cartwright. "Ultrasonography of Peripheral Nerves." Current Neurology and Neuroscience Reports 13.2 (2013): 1-9. Web.
  18. ^ Zaidman, C. M., Seelig, M. J., Baker, J. C., Mackinnon, S. E., & Pestronk, A. (2013). Detection of peripheral nerve pathology: comparison of ultrasound and MRI. Neurology, 80(18), 1634-1640.
  19. ^ Zaidman, C. M., Seelig, M. J., Baker, J. C., Mackinnon, S. E., & Pestronk, A. (2013). Detection of peripheral nerve pathology: comparison of ultrasound and MRI. Neurology, 80(18), 1634-1640.
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