Ultrasound (US) is an imaging technique that continues to expand its field of use. In the last decade, we dealt with its use on peripheral nerve involvement and the contribution changed the approach to most acute and chronic diseases. All clinical neurophysiological meeting now includes a session on nerve US. Nevertheless, from the assessment of the nerve we moved to the nearby structures discovering new possible uses. Neurophysiology is the gold standard in assessing nerve function and hence is crucial in the diagnosis of nerve involvement. US is now a precious tool useful in assessing peripheral nerve impairments as entrapments, tumors, extrinsic compressions, traumatic lesions, immune-mediated and inherited neuropathies.
A wide literature shows that US integrates neurophysiological assessment in routine practice: by a combined use of electrodiagnosis and US we obtain more information than we do if they are separately used. If neurophysiology allows to detect nerve function, US provides detailed imaging of nerve morphology and size and of the surrounding structures. A multidimensional evaluation of peripheral nervous system impairments improves diagnostic precision and therapeutic accuracy, even providing data about prognosis and disease evolution.
The main quantitative measure that US provides, owing to its sensitivity, is the nerve cross-sectional area (CSA), which is the area of the nerve structure visualized by a transverse US scan, calculated using the ellipse or the tracing method. Usually, an increase CSA indicates nerve involvement. Besides this, we can evaluate echogenicity, alteration of nerve elements (e.g. fascicles), variations in nerve shape. US report is based on characterization of nerve abnormalities and localization and extension of these findings.
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