Small Central Disc Herniation: Pathophysiology, Symptoms, and Treatment Algorithm

A small central disc herniation at L4-L5 or L5-S1 indenting the ventral thecal sac is a common MRI finding. Clinical significance depends on correlation with symptoms.

Pathophysiology

• Nucleus pulposus protrudes through annular fissure → central/paracentral extrusion → compresses thecal sac → may impinge traversing nerve roots (L5 at L4-L5, S1 at L5-S1) or cauda equina.
• "Small" = <5–7 mm; "indenting" = deforming but not obliterating CSF space.

Symptoms (If Symptomatic)

• Radiculopathy: Dermatomal pain (L5: lateral leg/dorsum foot; S1: posterior leg/lateral foot), paresthesia, weakness (dorsiflexion/L5, plantarflexion/S1), diminished reflex (S1).
• Axial Back Pain: Discogenic (annular tear, chemical inflammation).
• Cauda Equina Syndrome (Rare): Saddle anesthesia, bowel/bladder dysfunction, bilateral leg weakness – surgical emergency.

Natural History

• ~66% resorb spontaneously (macrophage phagocytosis) within 6–12 months.
• Symptoms often improve faster than imaging changes.

Treatment Algorithm

1. Conservative (6–12 weeks):
   • Activity modification (avoid flexion/rotation), not bed rest.
   • NSAIDs, acetaminophen; short-course oral steroids (taper) for radiculopathy.
   • Physical therapy: McKenzie extension, core stabilization, nerve glides.
   • Epidural steroid injection (transforaminal) if radiculopathy >4–6 weeks.
2. Surgical Indications:
   • Progressive motor deficit.
   • Cauda equina syndrome.
   • Intractable pain >6–12 weeks despite conservative care.
   • Large fragment sequestered.
3. Surgery: Microdiscectomy (gold standard) – 90% leg pain relief. Fusion rarely needed for primary herniation.

Red Flags for Urgent Imaging

• Saddle paresthesia, urinary retention/overflow, bilateral leg weakness, fever + back pain (infection), history of cancer.

Most small central herniations are managed non-operatively. Shared decision-making based on symptom severity and patient goals.