Summary: Your report dictates the decision directly: normal signal = Grade I (rest); edema + continuous nerve = Grades II–IV (monitor); discontinuous nerve trunk = Grade V (repair).
Rend a Sunder: Severity scales with Sunderland, distinguishing mild lesions which resolve with rest from structural disruptions requiring surgery. As Dr. Laura M. Fayad reminded us at the Annual Meeting, it’s a spectrum, too:
- Grade I
- Neurapraxia—focal demyelination without axonal disruption, maintaining normal muscle signal. Resolution with 4–6 weeks of rest.
- Grades II–IV
- Axonotmesis—progressive connective tissue breakdown, ranging from isolated axonal disruption to endoneurial and perineurial damage. Outer epineurium remains intact.
- Grade V
- Neurotmesis—complete nerve transection or avulsion with full disruption of all surrounding connective tissue layers. Intervention required.
Injured nerves demonstrate altered caliber, loss of normal fascicular architecture, and focal or diffuse T2 hyperintensity from edema or distal Wallerian degeneration.
Muscle Denervation: Increased fluid signal appears as early as 4 days post-injury…effectively ruling out Grade I.
- High-res MRI delineates focal sites of compression and continuity, overcoming electrodiagnostic limitations in distinguishing IV versus V.
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