A 25-year-old motorcyclist sustains a high-velocity road traffic accident and presents with a flail right upper limb. MRI of the brachial plexus reveals pseudo-meningoceles at C5, C6, C7 levels. Electrodiagnostic study shows absent SNAP but preserved CMAP. These findings are consistent with:

• A Preganglionic avulsion of C5–C7 roots ✓
• B Postganglionic rupture of upper trunk
• C Neuropraxia of the entire brachial plexus
• D Sunderland Grade II axonotmesis

Explanation

Pseudo-meningoceles on MRI indicate nerve root avulsion from the spinal cord (preganglionic injury). In preganglionic avulsion, the dorsal root ganglion (DRG) remains intact; therefore, sensory nerve action potentials (SNAPs) are paradoxically preserved (because DRG cell bodies are intact) despite complete clinical sensory loss. Compound muscle action potentials (CMAPs) are absent due to interruption of motor fibers proximal to the anterior horn cell. This pattern — preserved SNAP, absent CMAP, with meningoceles — is pathognomonic of preganglionic root avulsion.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.