05/08/2026
🧠 Exiting or Traversing : One Anatomical detail that changes Everything 🔍
EXITING VS TRAVERSING NERVE ROOT
One of the most important concepts in spine imaging and interventional pain medicine is understanding which nerve root is actually being compressed.
At each lumbar level, there are two nerve roots related to an intervertebral disc :
• Exiting nerve root – leaves the spinal canal through the neural foramen at that level.
• Traversing nerve root – descends past that disc level inside the spinal canal before exiting one level below.
Many clinicians look at the MRI level—but the level of the disc herniation is not always the same as the affected nerve root.
📍 At the L4–L5 Disc Level
✅ Exiting nerve root: L4
• Leaves through the L4–L5 neural foramen.
• Commonly compressed by foraminal or extraforaminal disc herniations.
✅ Traversing nerve root: L5
• Continues downward within the spinal canal before exiting at L5–S1.
• Commonly compressed by central or paracentral disc herniations.
🔑 Key Points
➡️ Central / Paracentral Disc → Traversing Nerve Root
➡️ Foraminal / Extraforaminal Disc → Exiting Nerve Root
📖 Clinical Examples
🔹 L4–L5 Paracentral Disc Herniation
➡️ Compresses the L5 traversing nerve root
• Pain along the lateral leg and dorsum of the foot
• EHL weakness
• Difficulty with heel walking
🔹 L4–L5 Foraminal Disc Herniation
➡️ Compresses the L4 exiting nerve root
• Pain over the anterior thigh and medial leg
• Quadriceps weakness
• Reduced patellar reflex
🔹 L5–S1 Paracentral Disc Herniation
➡️ Compresses the S1 traversing nerve root
• Posterior leg pain radiating to the lateral foot
• Plantarflexion weakness
• Reduced ankle reflex
• Difficulty with toe walking
🎯 TAKE-HOME MESSAGE
Knowing the relationship between the exiting and traversing nerve roots is essential for accurate clinicoradiological correlation.
It helps us :
✅ Identify the correct symptomatic nerve root.
✅ Interpret MRI findings accurately.
✅ Choose the appropriate target for selective nerve root blocks and transforaminal epidural injections.
✅ Improve diagnostic accuracy and optimize interventional pain management.
Treat the patient—not just the MRI. Anatomy is the key to successful intervention.