Cauda Equina Syndrome — CST Interview Station Answer

Cauda equina syndrome is compression of the nerve roots below the conus that threatens bladder, bowel and sexual function, and at the CST management and clinical station the answer is the GIRFT national pathway: ask the red flag questions, record perianal sensation, scan the bladder, and get an emergency MRI at the presenting hospital within four hours of the request. According to Getting It Right First Time, whose pathway was revised in March 2026, MRI at the presenting hospital is best practice in and out of hours, and any reason for delay must be documented.

Key takeaways

The GIRFT pathway red flags are saddle or perianal numbness or altered sensation, difficulty starting or controlling urine, loss of sensation passing urine or stool, leaking or incontinence, and new sexual dysfunction, with or without bilateral leg pain
Symptoms that started within the last two weeks mean an emergency referral to the nearest hospital with an emergency MRI facility
A digital rectal examination is not necessary, but subjective perianal sensation must be recorded
A bladder scan is an adjunct and never a discriminator: a post-void residual over 200 ml makes CES 20 times more likely, under 200 ml cannot exclude it, and over 600 ml means catheterise
An emergency MRI is done as soon as possible and certainly within four hours of the request to radiology, with the report available to the referrer within one hour
Incomplete CES (CESI) is decompressed as quickly as possible as an NCEPOD E1/E2 emergency; CES with painless retention (CESR) is operated on within 24 hours of the MRI

What are the red flags for cauda equina syndrome?

The red flags for cauda equina syndrome are bilateral or severe radicular leg pain with any of: altered sensation between the inner thighs or in the genitals, numbness around the back passage or buttocks, altered feeling when wiping, difficulty starting or stopping urine, loss of sensation passing urine, leaking or a recent need for pads, not knowing whether the bladder is full or empty, faecal incontinence or loss of sensation on defecation, and a change in erection, ejaculation or genital sensation.

That list is the GIRFT pathway's own, written for a patient audience and available as a warning card in 35 languages. The panel wants you to ask each item directly, because patients do not volunteer them.

How do I assess a patient with suspected cauda equina syndrome?

Assess suspected cauda equina syndrome with the CCrISP structure: immediate analgesia and safety, then a full assessment of the red flag history, lower limb power and sensation, subjective perianal sensation and a bladder scan, then an emergency MRI as the plan.

The GIRFT pathway states a digital rectal examination is not necessary, but subjective perianal sensation should be recorded. Document the time and date of assessment, the findings, the duration and progression of symptoms, and who you referred to and when.

Say the time of symptom onset out loud. The pathway's emergency referral criterion is ongoing symptoms or signs that started within the last two weeks.

What does the bladder scan add, and what does it not?

A bladder scan adds probability, not a decision: the GIRFT pathway says it is a useful adjunct that must not be used in isolation or as a discriminator in deciding to request an MRI or to operate.

According to the pathway, a post-void residual over 200 ml in a patient with suspected CES makes the diagnosis 20 times more likely, a residual under 200 ml cannot exclude it, and 60% of patients who had emergency decompression had a residual under 200 ml.

If the residual is over 600 ml, or the patient cannot void with a scan over 600 ml, catheterise, document whether the catheter is felt, and perform a catheter tug. This avoids bladder distension injury while the MRI is arranged.

When must the MRI happen?

The MRI must happen as soon as possible and certainly within four hours of the request to radiology, at the presenting hospital, in and out of hours, with local provision required by June 2024 under the GIRFT pathway.

Where a patient has been transferred for imaging, the scan is done as soon as possible after the receiving unit's assessment and certainly within four hours of that request. The report should reach the referring clinician within one hour, and on-call surgical teams may review the images before the formal report.

MRI is the diagnostic test, not CT. If MRI is contraindicated, discuss the alternative with radiology and the spinal team rather than defaulting to a CT that cannot show the compression well.

What is the management once cauda equina syndrome is confirmed?

Once cauda equina syndrome is confirmed the management is an emergency referral to the spinal surgical team with the MRI, a Category 2 blue-light transfer if the patient must move, and surgical decompression timed by the clinical category.

According to the GIRFT pathway, surgery for incomplete CES, called CESI, should be undertaken as quickly as possible as an NCEPOD E1/E2 emergency, because the condition is time-sensitive and life-changing though not life-threatening. Any reason for delay must be documented.

For CES with painless urinary retention and overflow incontinence, CESR, timing is at the operating surgeon's discretion but surgery should still be within 24 hours of the MRI, and the pathway notes around 70% of these patients benefit from decompression.

Who do I escalate suspected cauda equina syndrome to?

Escalate suspected cauda equina syndrome to your registrar and the on-call spinal or neurosurgical service the moment the red flags are present, and request the MRI yourself rather than waiting for the spinal team to ask for it.

The GIRFT pathway is explicit that the MRI is done before the spinal referral is completed, at the presenting hospital. Ring radiology, state the four-hour standard, and document the time of the request.

The surgical team must make a time-stamped documented review of history and examination before surgery, consent the patient, and register them on the British Spine Registry.

How do I safety-net a patient who does not have cauda equina syndrome today?

Safety-net with the GIRFT warning card and the MACP video, and tell the patient to return immediately if any listed symptom appears, because CES can evolve after a normal assessment.

A patient with sudden bilateral sciatica, or unilateral pain that has become bilateral, without CES symptoms is referred urgently to be seen within two weeks by the MSK triage service, and becomes an emergency referral if anything on the card develops.

How this comes up at the CST interview

Cauda equina is set as a 40-year-old with back pain and new difficulty passing urine at 2am, and the panel wants the red flag questions, perianal sensation, a bladder scan and an MRI request with the four-hour standard said in your first minute.

Follow-ups ask whether a residual of 150 ml reassures you, what to do when the radiographer says the scanner opens at 8am, and how you consent a patient who may not regain bladder function.

The coresurgeryinterview bank includes a scored cauda equina scenario with AI-marked spoken practice among its 299 questions: /Question-Bank/Sample-Questions.

FAQ

How quickly should an MRI be done for suspected cauda equina syndrome?

The GIRFT national pathway says an emergency MRI should be undertaken as soon as possible and certainly within four hours of the request to radiology, at the presenting hospital, in and out of hours. The report should be available within one hour.

Do I need to do a rectal examination?

No. The GIRFT pathway states a digital rectal examination is not necessary, but subjective perianal sensation should be recorded, along with power and sensation in the lower limbs.

Does a small post-void residual exclude cauda equina syndrome?

No. The pathway says a residual under 200 ml cannot exclude CES, and 60% of patients who had emergency decompression had a residual under 200 ml. A residual over 200 ml makes CES 20 times more likely, and over 600 ml means catheterisation.

How urgently is cauda equina syndrome operated on?

Incomplete CES (CESI) is decompressed as quickly as possible as an NCEPOD E1/E2 emergency. CES with painless retention (CESR) is operated on at the surgeon's discretion but still within 24 hours of the MRI.

What counts as an emergency referral?

Ongoing CES symptoms or signs that started within the last two weeks, referred to the nearest hospital with an emergency MRI facility. A telephone assessment that identifies CES symptoms is enough to refer if face-to-face review would delay it.

What if the patient has bilateral sciatica but no bladder symptoms?

The GIRFT pathway says sudden bilateral radicular pain, or unilateral pain that has progressed to bilateral, without CES signs is an urgent referral to MSK triage within two weeks, with a warning card and instructions to return immediately if any red flag develops.

Cauda Equina Syndrome: Red Flags and Emergency MRI