# Cauda Equina Syndrome

> Cauda equina syndrome for NEET-PG Orthopaedics, covering saddle anaesthesia, bladder involvement, emergency MRI, retention and surgical timing.

- Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/cauda-equina-syndrome
- Exam / course: NEET-PG · Subject: Orthopaedics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Maheshwari's Essential Orthopaedics; Apley's System of Orthopaedics and Fractures; Miller's Review of Orthopaedics
- How to cite: "Cauda Equina Syndrome", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/cauda-equina-syndrome

## Direct answer

Cauda equina syndrome is a surgical emergency caused by compression of the lumbosacral nerve roots below the conus, most often by a large central disc prolapse. Its hallmarks are sciatica that may be bilateral, saddle sensory loss, bladder and bowel dysfunction and reduced anal tone, and emergency MRI confirms it. Decompression should be urgent, ideally within 48 hours of symptom onset, a timeframe commonly quoted in UK guidance.

## What you must remember

- **Sphincter disturbance:** urinary retention, incontinence or reduced anal tone marks established disease, and painless retention with overflow is a late sign of established disease, whereas altered bladder sensation or loss of urgency comes earlier.
- **Saddle anaesthesia:** numbness over the perineum and buttocks, from the S2 to S4 segments, and patchy or absent perianal sensation is a red flag.
- **Bilateral sciatica:** new bilateral leg pain or weakness is more significant than unilateral sciatica and warrants urgent assessment.
- **Commonest cause:** a large central or paracentral disc prolapse at L4-L5 or L5-S1, although tumour, haematoma and infection can also compress the roots.
- **Investigation:** urgent MRI of the lumbosacral spine, with a post-void bladder scan to measure residual urine.
- **Retention versus incomplete:** the retention form carries the poorest bladder prognosis, while the incomplete form has preserved emptying with altered sensation or incontinence.
- **Outcome:** earlier decompression is linked to better bladder recovery, and delayed diagnosis risks permanent bladder and sexual dysfunction.

## Acting on red flags in a patient with back pain

A 45-year-old labourer has back pain and sciatica two days after lifting, and wakes up unable to pass urine with numbness around the buttocks. The sequence below moves from screening to decompression without waiting for routine referral.

1. **Screen for red flags:** new bilateral sciatica, saddle sensory loss, urinary retention or incontinence and reduced anal tone must be asked about specifically.
2. **Examine the perineum:** perianal sensation, anal tone and lower limb reflexes are recorded, and a post-void bladder scan measures residual urine.
3. **Request emergency MRI:** lumbosacral MRI is requested immediately, not placed in a routine queue, because the decision depends on it.
4. **Involve the spinal team:** the on-call spinal surgeon is informed at once, with the neurological and urinary findings documented.
5. **Decompress urgently:** surgery, usually laminectomy and discectomy, is performed as an emergency, ideally within 48 hours of symptom onset.
6. **Follow bladder recovery:** serial residual volumes and urodynamic assessment guide catheter management, and bladder recovery can take months.

## Where the exam tries to catch you

Cauda equina questions test recognition of red flags and the importance of timing.

- **Trap:** dismissing urinary retention with sciatica as a simple urinary tract infection — **Correct:** retention with back pain is a cauda equina red flag, requiring urgent MRI and surgical review.
- **Trap:** relying on normal reflexes or a negative straight-leg test to exclude the syndrome — **Correct:** the diagnosis rests on sphincter and saddle findings and bladder scanning, because reflexes can remain normal.
- **Trap:** waiting for the MRI report before involving the spinal team — **Correct:** the team is alerted immediately, since the timing of decompression drives bladder outcome.

## Frequently asked questions

### What is an early sign of cauda equina syndrome?

Altered bladder sensation, such as loss of the urge to void or a reduced stream, with saddle sensory change is an early sign of cauda equina syndrome, whereas painless retention with overflow is a late sign. Either finding in a patient with back pain prompts urgent MRI.

### Which MRI findings confirm cauda equina syndrome?

MRI of the lumbosacral spine shows compression of the cauda equina nerve roots within the thecal sac, most often by a large central disc prolapse. Urgent MRI is requested whenever clinical features suggest cauda equina syndrome, and the findings guide emergency decompression.

### How is cauda equina retention differentiated from incontinence?

Cauda equina retention means the bladder cannot empty, with a raised post-void residual, whereas the incomplete form preserves emptying but alters sensation or causes incontinence. Retention is the more serious form, with a poorer bladder prognosis after decompression.

### When should decompression be performed in cauda equina syndrome?

Decompression in cauda equina syndrome is performed as an emergency, ideally within 48 hours of symptom onset, a timeframe commonly quoted in UK guidance. Earlier decompression is linked to better bladder recovery, so delays are avoided.