A patient with a central disc herniation at L4–L5 level presents with bilateral leg weakness, saddle anaesthesia, and urinary retention. The compressed neural elements are:

• A L4 and L5 spinal cord segments
• B Cauda equina nerve roots (multiple sacral and lower lumbar roots) ✓
• C Conus medullaris
• D Only the L5 nerve root bilaterally

Explanation

At the L4–L5 disc level, the spinal cord has already ended (conus medullaris at L1–L2), so only cauda equina nerve roots are present. A large central disc herniation compresses multiple lower lumbar and sacral roots of the cauda equina simultaneously, producing cauda equina syndrome: bilateral lower limb weakness/numbness, saddle anaesthesia (perianal/perineal numbness from S3–S5 compression), bladder retention (loss of S2–S4 parasympathetic detrusor control), and bowel incontinence. This is a surgical emergency. Pure L5 root compression would cause unilateral foot drop only.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.