What are the typical symptoms, signs, and common causes of cauda equina syndrome?

Cauda Equina Syndrome: Symptoms and Causes

Critical Symptoms Requiring Immediate Action

Bilateral radiculopathy—pain, numbness, tingling, or weakness radiating down both legs below the knee—is the most sensitive early warning sign (90% sensitivity) and demands immediate emergency MRI and neurosurgical consultation without waiting for urinary retention or complete saddle anesthesia. 1, 2

Early "Red Flag" Symptoms (Reversible Stage)

• New bladder symptoms including hesitancy, poor stream, urgency, or any change in urinary function with preserved control constitute early warning signs requiring urgent imaging 1, 2
• Perineal sensory changes manifesting as subjective numbness or tingling in the "saddle" distribution (perineum, genitals, inner thighs) or objective loss of sensation on examination 1, 2
• Progressive neurological deficits in the lower extremities, including worsening motor weakness in foot dorsiflexion, plantarflexion, or knee extension on both sides 1, 2
• Severe low back pain that overshadows leg pain, often accompanied by sciatica in a typical lumbar nerve root distribution 1

Late "White Flag" Symptoms (Irreversible Damage)

• Painless urinary retention—inability to void despite a distended bladder without discomfort—occurs in approximately 90% of established cases and indicates advanced, often irreversible disease 1, 2
• Complete saddle anesthesia rather than partial sensory loss in the perineal region 1
• Fecal incontinence due to loss of bowel control from sphincter dysfunction 1, 2
• Loss of anal tone or patulous anus on rectal examination, representing late sphincter dysfunction 1, 2
• Complete loss of bladder and bowel control indicating severe, established injury 1

Common Causes

Massive midline lumbar disc herniation is the most common cause, occurring in approximately 0.04% of patients with low back pain, with over 90% of symptomatic herniations occurring at the L4-L5 or L5-S1 intervertebral levels. 1, 3

Primary Etiologies

• Lumbar disc herniation at L4-L5 and L5-S1 levels causing direct mechanical compression of the cauda equina nerve roots 1, 3
• Spinal stenosis with progressive narrowing of the spinal canal 1
• Neoplasm including primary spinal tumors or metastatic disease causing epidural compression 1, 3
• Infection or inflammation such as epidural abscess or vertebral osteomyelitis 1
• Hemorrhage within the spinal canal causing acute compression 1
• Postoperative complication following lumbar spinal surgery, though rare 4

Pathophysiology

• Compression results from direct mechanical pressure on the nerve roots composing the cauda equina below the level of the conus medullaris 1, 5
• Venous congestion and ischemia contribute to nerve root damage beyond direct compression 5
• Vertebral bone destruction, neural foramina blockage, and vascular obstruction can lead to spinal cord edema 3

Clinical Staging and Prognosis

Treatment at the suspected or incomplete stage (before urinary retention develops) yields normal or socially normal bladder, bowel, and sexual function, whereas treatment after complete retention develops results in variable recovery (48-93% show some improvement) but many require lifelong catheterization and manual fecal evacuation. 1, 2

Stage-Specific Outcomes

• Cauda Equina Syndrome Suspected (CESS): Bilateral radiculopathy without objective bladder/bowel dysfunction—early treatment prevents progression and preserves normal function 1
• Cauda Equina Syndrome Incomplete (CESI): New bladder symptoms with preserved control plus perineal sensory loss—early decompression yields normal or socially normal long-term function 1, 2
• Cauda Equina Syndrome with Retention (CESR): Painless urinary retention, complete perineal anesthesia, or fecal incontinence—even with urgent surgery, only 48-93% achieve any improvement, and many face permanent disability requiring intermittent self-catheterization and manual fecal evacuation 1, 2
• Only a minority of patients with severe deficits post-CES return to work 1

Critical Diagnostic Pitfalls to Avoid

• Never wait for complete urinary retention before referral—this represents a late sign of irreversible damage 1, 2
• Do not catheterize before assessing post-void residual volume, as this obscures whether the patient is in the CESI or CESR stage 1
• No single symptom has high positive predictive value in isolation—even combinations have low predictive value until features of severe, irreversible lesions appear, making emergent MRI essential 1, 2
• Sensory testing is subjective and subtle impairment of perineal sensation is easily missed or misinterpreted 1
• Anal tone assessment has low interobserver reliability, especially among inexperienced clinicians 1
• Symptoms develop gradually over weeks to months, leading to attribution to more benign causes and delaying appropriate imaging 1

Immediate Diagnostic Action Required

MRI of the lumbar spine without IV contrast is the gold standard (96% sensitivity, 94% specificity) and must be performed emergently in all suspected cases—CT alone has only 6% sensitivity for neural compression and cannot adequately visualize the cauda equina nerve roots or epidural space necessary for surgical decision-making. 1, 2, 3