Reference values of sonographic nerve size
| Nerve site | Normal values (CSA in mm2) | Disease specific cut-off values for suspected CIN (CSA in mm2) | |
| Median nerve | Wrist | 11 | – |
| Forearm | 9 | >10 | |
| Upper arm | 9 | >13 | |
| Ulnar nerve | Wrist | 7 | – |
| Forearm | 6 | – | |
| Distal to sulcus | 9 | – | |
| At ulnar sulcus | 9 | – | |
| Proximal to sulcus | 9 | – | |
| Upper arm | 9 | – | |
| Brachial plexus | C5 nerve root* | 8 | >8 |
| Fibular nerve | Popliteal fossa | 9 | – |
| Fibular head | 11 | – | |
| Tibial nerve | Popliteal fossa | 22 | – |
| Distal lower leg | 13 | – | |
| At medial malleolus | 13 | – | |
| Sural nerve | Distal lower leg | 3 | – |
This table shows the upper limit of normal nerve cross-sectional area (CSA) and cut-off value for nerve enlargement suspect of chronic inflammatory neuropathy (CIN) in upper and lower extremity nerve sites. Normal values shown were obtained in a mainly Caucasian general Dutch population and a population suspected of CIN.
*Elements of the brachial plexus are commonly measured intra-scalenic; normal nerve root sizes at the exit of the neuroforamina are often larger (ie, up to 12 mm2), whereas C6 and particularly C7 nerve roots may be less reliable to assess accurately.35