MR imaging characteristics of normal and abnormal peripheral nerves
| MR Imaging Characteristic | Normal Peripheral Nerve | Abnormal Peripheral Nerve |
|---|---|---|
| Size | Decreases distally, similar or smaller than accompanying artery | Focal or diffuse enlargement, larger than accompanying artery |
| Signal intensity on T1WI | Isointense to skeletal muscle | Isointense to skeletal muscle |
| Signal intensity on fluid-sensitive sequences (SPAIR, T2WIFS or STIR images) | Isointense (SPAIR/fat sat T2WI) to minimal hyperintensity (STIR) | Moderate-to-marked hyperintensity approaching fluid signal similar to that in adjoining veins |
| Fascicular pattern | Seen on both T1WI and T2WI, especially in larger nerves | Enlarged single or multiple fascicles, loss of normal fascicular pattern |
| Course | Well-outlined by perineural fat, which is best seen on T1WI | Deviated from normal course |
| Enhancement with intravenous gadolinium | No appreciable enhancementa | Abnormal enhancement when blood-nerve barrier is breached |
| Indirect signs, muscle denervation changes | Absent | Muscle edema or fatty atrophy may be present |
a Exception: enhancement may be seen in dorsal nerve root ganglia of normal peripheral nerves, where blood-nerve barrier is absent.