Nerve ultrasound

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

Ultrasound technique of nerves.

For a more accurate diagnosis of nerve pathology, it is necessary to study neurological symptoms, conduct appropriate tests and examinations. It is important to inquire about the presence of pain, hyperesthesia, weakness in certain muscle groups or their fatigue, dysfunction, muscle atrophy, and impaired skin sensitivity.

For examination, as a rule, sensors with a frequency of 3-5 (sciatic nerve) and 7-15 MHz are used. During examination, it is better to apply a large amount of gel to the surface of the sensor, while you can fix the edge of the sensor with your little finger, thereby preserving the gel layer and providing minimal pressure on the area being examined.

Knowing the exact course of nerves significantly helps in their search. It is necessary to start scanning the nerve with its topographic search. Then the minimum amount of time will be spent to find the corresponding section of damage.

The medial nerve in the wrist area is located behind the long palmar tendon, just behind the flexor tendon retinaculum. Thus, during the scanning process, even if the visualization of the nerve is lost, it is always possible to return to its topographic initial search point.

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

Power Doppler mapping is used not only to assess the vascularization of peripheral nerve tumors, but also to search for small nerve branches, which are always accompanied by an artery. Some pathological processes are detected only during dynamic functional tests. For example, the ulnar nerve can shift from the cubital fossa medially to the epicondyle only during flexion of the elbow joint.

Or the medial nerve, which can reduce its displacement in the frontal plane inside the carpal tunnel when bending and unbending the fingers. This, by the way, is the first symptom of carpal tunnel syndrome. An osteophyte that damages the nerve can also be detected when moving the joint.

The echo picture of the nerves is normal.

It is necessary to measure the transverse and anteroposterior dimensions of the nerve, evaluate the shape of its cross-section, contours, echostructure. Compare with the distal or proximal section or the contralateral side. In a cross-section, they acquire a granular structure like "salt and pepper" enclosed in a hyperechoic membrane. In longitudinal scanning along the long axis, the nerves look like thin hyperechoic fibrillar structures, limited at the top and bottom by a hyperechoic line. The nerve consists of many nerve fibers enclosed in a membrane. Unlike tendons and ligaments, nerves have thinner and thicker fibers. They are less subject to anisotropy and shift less when the limb moves.

Nerve pathology on ultrasound.

Tumors. There are two most common tumors of the peripheral nerves: schwannoma and neurofibroma. They develop from the nerve sheaths.

Neurofibroma is a proliferation of cells similar to Schwann cells. It grows from within the nerve, among the nerve fibers, making tumor resection impossible without cutting the nerve. Schwannoma also grows from Schwann cells, but unlike neurofibroma, it displaces the nerve to the periphery during growth, which makes it possible to resect the tumor without cutting the nerve. These tumors usually have the appearance of a hypoechoic, well-defined spindle-shaped thickening along the nerve trunk with an increase in the ultrasound signal behind the tumor. Schwannomas are quite vascular on ultrasound angiography.

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

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

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

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

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