How should an adult presenting with acute low‑back pain, progressive lower‑extremity weakness, saddle anesthesia, loss of anal tone, and urinary or bowel retention (suspected cauda equina syndrome) be diagnosed and managed?

Diagnosis and Management of Cauda Equina Syndrome

Cauda equina syndrome (CES) requires immediate emergency MRI and neurosurgical consultation the moment bilateral radiculopathy, new bladder symptoms, or perineal sensory changes appear—do not wait for urinary retention, which represents irreversible neurological damage. 1

Clinical Staging and Recognition

Early "Red Flag" Symptoms (Reversible Stage)

• Bilateral radiculopathy (leg pain, numbness, tingling, or weakness radiating below the knee in both legs) demonstrates 90% sensitivity for cauda equina involvement and mandates immediate action. 1
• New bladder symptoms including hesitancy, poor stream, or urgency with preserved urinary control constitute early warning signs requiring urgent imaging. 1
• Perineal sensory changes (subjective numbness or objective loss in the saddle distribution) are critical early indicators. 1
• Progressive bilateral lower extremity weakness signals advancing neural compromise. 1

Late "White Flag" Symptoms (Irreversible Damage)

• Painless urinary retention occurs in approximately 90% of established CES cases and indicates advanced disease with poor prognosis. 2, 1
• Fecal incontinence represents late sphincter dysfunction. 1
• Complete saddle anesthesia rather than partial sensory loss indicates established damage. 1
• Loss of anal tone or patulous anus are late findings. 2, 1

Diagnostic Algorithm

Physical Examination

• Test perineal sensation systematically, recognizing that subtle impairment is easily missed or misinterpreted. 3
• Assess anal tone via digital rectal examination, though interobserver reliability is low among inexperienced clinicians. 1
• Check bulbocavernosus reflex—a combination of normal reflex, voluntary rectal tone, and perianal sensation effectively rules out CES. 1
• Evaluate bladder function but do not catheterize before assessing post-void residual volume, as this obscures whether the patient is in incomplete versus complete retention stage. 3
• Perform straight-leg-raise test—91% sensitivity for lumbar disc herniation when pain reproduces between 30-70 degrees. 1

Emergency Imaging

• MRI of the lumbar spine without IV contrast is mandatory with 96% sensitivity and 94% specificity for cauda equina pathology. 1
• CT scan alone is inadequate with only 6% sensitivity for epidural abscess or neural compression and cannot visualize intraspinal contents sufficiently for surgical planning. 1
• Emergency MRI must be performed immediately in all suspected cases—only 14-33% of scans confirm significant compression, but this high true-negative rate minimizes false negatives. 1

Surgical Management Based on Clinical Stage

Cauda Equina Syndrome Suspected (CESS)

• Presentation: Bilateral radiculopathy without objective bladder/bowel dysfunction. 1
• Management: Emergency surgical decompression as soon as possible to prevent progression. 1
• Outcome: CES fully prevented with normal bladder, bowel, and sexual function. 1

Cauda Equina Syndrome Incomplete (CESI)

• Presentation: New bladder symptoms with preserved control plus perineal sensory loss. 1
• Management: Emergency surgical decompression immediately. 1
• Outcome: Normal or socially normal long-term bladder, bowel, and sexual function. 1

Cauda Equina Syndrome with Retention (CESR)

• Presentation: Painless urinary retention, complete perineal anesthesia, fecal incontinence, or patulous anus. 1
• Management: Urgent surgery within 12 hours when feasible; outcomes superior when performed within 12-72 hours. 1
• Outcome: Variable recovery with only 48-93% achieving any improvement; many require lifelong intermittent catheterization, manual fecal evacuation, and lose sexual function. 1

Surgical Timing and Prognosis

• Preservation of any perineal sensation preoperatively predicts higher likelihood of postoperative recovery. 1
• Better outcomes occur with surgery within 12-72 hours of symptom onset compared to further delayed intervention. 1
• Treatment at CESS or CESI stage results in normal functional recovery, while treatment at CESR stage carries high risk of permanent disability. 1

Critical Pitfalls to Avoid

• Do not wait for complete urinary retention before referral—this represents a late sign of irreversible damage. 1, 3
• Do not dismiss bilateral leg symptoms as "just sciatica"—bilateral radiculopathy is the earliest red flag for CES. 3
• Do not delay MRI when CES is suspected, even if clinical findings are subtle, as no single symptom has high positive predictive value in isolation. 1, 3
• Do not catheterize before determining retention status, as this obscures whether the patient is CESI or CESR. 3
• Do not rely on CT scan alone to rule out CES given its extremely low sensitivity. 1

Differentiating from Isolated Sciatica

• Unilateral radicular pain following a single nerve root distribution (typically L5 or S1) with preserved bladder/bowel function, normal perineal sensation, and normal anal tone indicates sciatic nerve impingement rather than CES. 3
• Conservative management is appropriate for isolated sciatica, while any bilateral symptoms mandate emergency evaluation for CES. 3

Epidemiology

• CES occurs in approximately 0.04% of patients with low back pain, most commonly from massive midline disc herniation. 2
• Over 90% of symptomatic lumbar disc herniations causing radiculopathy occur at L4/L5 or L5/S1 levels. 1
• Among patients presenting with suspected CES, only 19% have radiological and clinical confirmation, emphasizing the need for high clinical suspicion and liberal use of emergency MRI. 4