Ultrasound Examination of Peripheral Nerves

For any questions regarding ultrasound examination of peripheral nerves, existing contraindications and the specifics of the procedure, you may contact the physicians of our center.

In recent years there has been growing interest in neuroimaging methods for peripheral nerves, such as MRI and ultrasound, across different types of neuropathies of both acquired and hereditary origin. The main goal of using neuroimaging methods together with neurophysiological and laboratory testing is to facilitate the differential diagnostic process. Previously, the use of peripheral nerve ultrasound was limited to verifying the anatomical integrity of nerve trunks in cases of traumatic injury and visualizing tumor processes. Subsequently, the advantages of the ultrasound method were demonstrated in various peripheral nerve diseases.

An undoubted advantage of the peripheral nerve ultrasound method is its non-invasiveness, safety for the patient, and the possibility of performing it an unlimited number of times. At the same time, the method is highly informative across a broad range of peripheral nerve pathologies.

On cross-sectional ultrasound scanning, a peripheral nerve appears as an oval or round structure with a clear hyperechoic border and an internal heterogeneous ordered structure (a "honeycomb" pattern); on longitudinal scanning, the peripheral nerve is visualized as a linear structure with a clear hyperechoic border, within which hypoechoic and hyperechoic bands alternate (a "cable-like" pattern). The parameters analyzed on ultrasound can be divided into two large groups: qualitative and quantitative. One of the main quantitative parameters assessed is the cross-sectional area (CSA) of the nerve. This parameter is highly reproducible, and reference values exist for each nerve in adults at standard measurement levels. Measurements are taken at several points, including nerves in the arms at the proximal and distal segments (median, ulnar), the spinal nerves of the brachial plexus (C5/C6/C7), and nerves in the legs (the sciatic nerve and its branches).

Protocols do not differ significantly between laboratories, mainly due to the inclusion of additional points for the ulnar nerve and a point for the posterior tibial nerve at the ankle level. The ultrasound protocol we have developed for assessing cross-sectional area includes 13 measurements on each side (26 measurements in total).

The qualitative characterization of peripheral nerve remodeling is based on the work of L. Padua. It is based on the visually determined principle of preserved differentiation of the nerve into fascicular groups, applicable to the median and ulnar nerves at the level of the arm and forearm on cross-sectional scanning.

Changes in peripheral nerves have been described by many researchers not only in dysimmune but also in hereditary neuropathies. The main principles for describing nerve changes in neuropathies are the symmetry and extent of nerve trunk enlargement. Researchers today consider the cause of CSA enlargement to be edema and the alternation of demyelination and remyelination processes during periods of exacerbation and remission of CIDP, which is confirmed on histological examination of the nerve by the detection of "onion bulb"-type changes.

Patients with a disease duration of 6 months or more show, on ultrasound scanning, diffuse CSA enlargement, in contrast to newly diagnosed patients, in whom CSA enlargement is noted only in the proximal segments of the nerve trunks.

Accordingly, several scales have been validated, the use of which in routine practice is difficult due to their cumbersome nature. The table shows some of them, along with the nosological forms being compared.

In addition, it turned out to be highly significant at what point relative to the onset of the pathological process and its treatment the examination was performed. Thus, in treatment-naive patients with CIDP undergoing therapy, the previously detected diffuse symmetric CSA enlargement of all nerves regresses. Assessment of parameters such as nerve vascularization and echogenicity has not become widespread due to the technical limitations of modern ultrasound scanners.

The search for optimal peripheral nerve ultrasound protocols continues today for patients with suspected polyneuropathy of both dysimmune and hereditary origin.

Despite the limitations discussed, the main advantage of ultrasound over MRI is its low cost, its mobility, and the possibility of performing it an unlimited number of times to assess the dynamics of changes in peripheral nerve ultrasound parameters, which studies have shown to be important when evaluating the effectiveness of therapy in patients with dysimmune neuropathies.

We can offer the full range of peripheral nerve ultrasound examinations using accepted examination protocols. The examination and interpretation of data are performed at a high level by specialists who have proven their professional standing through experience and publications.

Author: Dmitry S. Druzhinin, MD, DSc