Ultrasonography of nerves

The emergence of new high-frequency matrix and wide-band sensors, new technologies for processing the ultrasound signal (tissue harmonics, compound scanning) provided ultrasound priority in the study of peripheral nerves. It is customary to correlate the nerve path with its projection on the skin.

Methods of ultrasound of nerves.

For more accurate diagnosis of the pathology of nerves, it is necessary to study neurologic symptoms, to conduct appropriate tests and tests. It is important to inquire about the presence of pain, hyperesthesia, weakness in certain muscle groups or their fatigue, impaired function, muscle atrophy, dermal sensitivity disorders.

For the study, as a rule, sensors with a frequency of 3-5 (sciatic nerve) and 7-15 MHz are used. In the study, it is better to apply a large amount of gel to the surface of the sensor, while fixing the edge of the sensor with the little finger, thereby preserving the gel layer and ensuring a minimum pressure on the area under investigation.

Knowing the exact course of the nerves greatly helps in their search. Starting a nerve scan is necessary with its topographic search. Then a minimum amount of time will be spent to find the corresponding department of damage.

The medial nerve in the wrist area is located behind the long palmar tendon, just behind the flexor tendon retina. Thus, in the process of scanning, even with a loss of visualization of the nerve, one can always return to its topographic initial search point.

First, a transverse section of the nerve is obtained with its small increase, and then, by analyzing the structure of the nerve in the longitudinal section, the image is enlarged.

Energy Doppler mapping is used not only to assess the vascularization of peripheral nerve tumors, but also in the search for small branches of the nerves that are always accompanied by the artery. Some pathological processes are detected only when performing dynamic functional tests. For example, the ulnar nerve can move from the ulnar fossa medially to the epicondyle only when flexed at the elbow joint.

Or a medial nerve that can reduce its displacement in the frontal plane within the carpal tunnel when flexing and flexing the fingers. This, by the way, serves as the first symptom of carpal tunnel syndrome. It is also possible to detect an osteophyte that damages the nerve when moving in the joint.

Echocardiograms of nerves are normal.

It is necessary to measure the transverse and antero-posterior dimensions of the nerve, to assess the shape of its transverse section, the contours, the echostructure. Compare with the distal or proximal or contralateral side. In the transverse section, they acquire a granular structure of the "salt and pepper" type, encased in a hyperechoic membrane. When longitudinal scanning along the long axis, the nerves look like fine hyperechoic fibrillar structures, bounded above and below by the hyperechogenic line. The nerve consists of a multitude of nerve fibers encased in a shell. Unlike tendons and ligaments, nerves have rarer and thicker fibers. They are less susceptible to anisotropy, less shift when the limb moves.

Pathology of nerves on ultrasound.

Tumors. There are two most commonly occurring tumors of the peripheral nerves: schwannoma and neurofibroma. They develop from the shells of nerves.

Neurofibroma is the proliferation of cells resembling Schwann cells. It grows from the inside of the nerve, among the nerve fibers, making the tumor resection without crossing the nerve impossible. Schwannoma also grows from Schwann cells, but unlike neurofibroma displaces the nerve to the periphery in the process of growth, which provides the possibility of resection of the tumor without the intersection of the nerve. These tumors, as a rule, have the form of hypoechoic with clear contours of a spindle-shaped thickening along the nerve trunk with an increase in the ultrasound signal behind the tumor. With ultrasound angiography, the Schwannomas are quite vascular.

Injury. There are acute and chronic nerve injuries. Acute occurs as a result of stretching or rupturing of nerve fibers during muscle injuries or bone fractures. Nerve rupture manifests itself in violation of the integrity of its fibers, thickening of its ends. As a result of trauma, neuromas are formed at the distal ends, which are not true tumors, but a thickening due to the regeneration of nerve fibers.

Compression (tunnel syndrome). Typical manifestations of compression of the nerve are its deformation at the site of compression, a thickening proximal to compression and, sometimes, the formation of a neuroma. In the distal department, nerve atrophy is observed.

With compression, the width of the nerve increases. Compression of the nerve in the bone or fibrous tunnel is called tunnel syndrome. Osteophytes, bursitis, synovial cysts, ganglia can lead to nerve infringement. Ischemia can lead to a thickening of the nerve, as, for example, in the case of the Morton's neuroma.

Morton's neuroma. This pseudotumor is a tumor-like thickening of the interdigital nerves on the foot, typically between 3 and 4 fingers, where the interdigital nerve includes the fibers of the medial and lateral plantar nerves.

Often the diagnosis is established clinically, when a local plantar pain occurs. The absence of thickening along the interdigital nerve does not exclude a diagnosis.