Magnetic resonance imaging (MRI) is the main imaging test used when doctors suspect a case of cauda equina syndrome (CES); however, even then there are circumstances where the right diagnosis may still be missed.

There are two main ways this can happen. Cauda equina compression may be present but missed when the MRI is reported, or the compression may be identified but its significance underestimated.

In either situation, the question in a medical negligence claim is not simply whether an MRI was carried out. It is whether the scan was interpreted correctly, whether the MRI findings were considered alongside the patient’s symptoms and whether doctors acted on the results when they should have done.

At JMW, we investigate cauda equina syndrome claims involving both delays in arranging an urgent MRI and cases where suspected cauda equina syndrome was missed despite imaging being performed.

Nicholas Young, a Partner in our Medical Negligence team with extensive experience of CES cases, explains:

“An MRI scan is an essential part of investigating suspected cauda equina syndrome, but the findings still have to be interpreted alongside the patient’s symptoms. In the cases we investigate, the issue is sometimes not that a scan was never performed, but that compression of the cauda equina nerve roots was visible and either missed or not appreciated in the context of the red flag symptoms the patient had reported.”

How is cauda equina syndrome diagnosed?

Diagnosing cauda equina syndrome involves clinical assessment alongside emergency diagnostic imaging. Doctors should consider the patient’s symptoms, medical history, neurological examination and MRI findings together as a whole rather than treating the scan as showing a simple positive or negative result.

The cauda equina is a bundle of lumbar and sacral nerve roots below the end of the spinal cord. These nerves help control movement and sensation in the lower limbs, as well as bladder and bowel function, saddle sensation and sexual function. CES develops when these nerve roots are affected, most commonly because a large lumbar disc herniation causes compression of the cauda equina nerve roots. Severe spinal stenosis can also narrow the spinal canal and compress the cauda equina nerves, while untreated spinal tumours can also cause a similar impact - a condition known as metastatic spinal cord compression.

Given that continuing spinal nerve compression can cause permanent nerve damage, suspected cauda equina syndrome requires emergency assessment.

What does an MRI show in cauda equina syndrome?

MRI is the key imaging investigation used for diagnosing cauda equina syndrome where compression is suspected based on reported red flag symptoms. The scan gives doctors a detailed view of the lumbar spine, spinal canal, discs and nerve roots, helping them identify problems such as a large lumbar disc herniation, a sequestrated disc fragment, significant lumbar spinal stenosis or compression and displacement of the cauda equina.

However, CES is not purely an MRI diagnosis but it is a clinical diagnosis based on the presence of red flag symptoms together with cauda equina nerve root compression on an MRI scan. Doctors need to consider whether the MRI findings are consistent with the clinical symptoms. If there are no red flag symptoms, it is unlikely an MRI will be performed. Where there are red flag symptoms, and an MRI scan shows nerve root compression, it is deemed a surgical emergency.

For more detail on the different forms of clinical assessment and diagnostic imaging used when CES is suspected, see our guide to common cauda equina syndrome tests.

What is the cauda equina MRI protocol?

The cauda equina MRI protocol is designed to establish quickly whether significant compression is present. The current National Suspected Cauda Equina Syndrome Pathway states that an emergency MRI should take place as soon as possible and certainly within four hours of the request being made to radiology.

The purpose of an urgent MRI is therefore not simply to obtain images. Doctors need the results quickly enough to decide whether the person requires urgent review by a spinal or neurosurgeon and to consider emergency surgery. The four-hour recommendation relates to the MRI request being made to radiology; it is not a rule that everyone with CES must have a scan within four hours of symptom onset.

How can cauda equina syndrome be missed on an MRI?

Nicholas identifies two main issues in cases where an MRI scan was carried out but the CES diagnosis was still missed: the compression was not identified at all, or it was identified but considered insufficient to cause CES.

These cases are less common than those where red flag symptoms are not recognised and an MRI is never arranged,  which is the most common issue in CES cases, but JMW Solicitors investigate both situations.

Nicholas says:

“The more common situation we see is that the significance of the patient’s red flag symptoms is not recognised and an MRI is not arranged at all. However, we also investigate cases where the right decision was made to perform an MRI, but the diagnosis was then missed when the scan was reported or its findings were not accurately considered.”

Cauda equina compression is not identified

An MRI may contain evidence of significant nerve root compression, but that finding can still be overlooked. For example, the scan may be reported to show a large disc fragment or spinal stenosis or another cause of cauda equina compression, while the report instead states that there is no significant spinal canal stenosis but the key issue of compression of the cauda equina nerve roots is missed

This can be crucial to the treatment provided to a patient. If an MRI scan is not accurately reported, a patient who attends hospital with back pain and red flag symptoms such as urinary dysfunction and altered saddle sensation may be discharged rather than referred for emergency spinal or neurosurgical assessment. Emergency surgical decompression may then be delayed while the nerve compression continues.

Image quality or patient movement can sometimes make diagnostic imaging harder to interpret, but the reporting of an MRI also requires clinical judgement. Where a scan is degraded due to these issues, it should be repeated rather than relying on a potentially substandard image and report.

The compression is identified but its significance is underestimated

The second issue can be more subtle. A radiologist or clinical team may identify a disc prolapse or narrowing of the spinal canal but consider that the degree of compression is not sufficient to cause the red flag symptoms for cauda equina syndrome.

This is why clinical diagnosis and MRI diagnosis need to work together. An MRI showing severe, compressive lumbar disc herniation is much more concerning in a person who is also reporting red flag symptoms such as urinary dysfunction and altered perineal sensation, which then becomes a surgical emergency.

Nicholas explains:

“One of the important issues in these cases is whether the scan was considered in the context of what the patient was actually reporting. If a patient has red flag symptoms such as changes in bladder function, sensation or altered perineal sensation, those symptoms can make the significance of compressive findings on the MRI very different from the same imaging finding in a patient without red flag symptoms for cauda equina syndrome.”

Communication between the emergency department, radiology team and spine surgeons can therefore be important. The doctors reporting the MRI scan need sufficient information about the symptoms that led to suspected cauda equina syndrome being suspected in the first instance.

What if the MRI does not match the symptoms?

Not everyone with red flag symptoms associated with cauda equina syndrome will have MRI-confirmed compression. Some patients have CES-type symptoms but no significant cauda equina compression on imaging, which is sometimes referred to as a scan-negative presentation.  There can be other causes for the cauda equina syndrome red flag symptoms which is why reporting of the MRI scan is key to diagnosis.

A scan negative presentation is different from a missed MRI diagnosis of cauda equina compression on an MRI scan. In a genuinely scan-negative presentation, the MRI does not show compressive CES. Where an MRI has been misreported, relevant compression was present but overlooked or its significance was underestimated. Independent expert review can help establish which situation applies.

Symptoms can also develop over time rather than appearing together at once. Some may initially experience back pain and unilateral neurological symptoms before noticing changes in urinary flow or sensation, while altered saddle sensation may develop before complete saddle anaesthesia. We discuss the way symptoms can evolve in our guide to whether cauda equina symptoms can come and go.

Severe back pain alone does not establish a clinical diagnosis of CES even where compression is seen on an MRI scan, and an MRI may not show cauda equina compression even when a person is experiencing significant pain. The concern increases when pain appears alongside red flag symptoms such as changes in bladder and bowel function, saddle sensation or neurological symptoms affecting both of the lower limbs. NHS guidance on cauda equina syndrome explains that new neurological symptoms require assessment because true cauda equina compression may require emergency surgical intervention.

What happens when cauda equina compression is missed on MRI? A real-world case study

We have investigated cases where MRI imaging was carried out but significant cauda equina compression was not correctly identified. One case handled by Nicholas Young involved a person who attended hospital with worsening back pain, urinary dysfunction and altered perineal sensation, alongside weakness and numbness affecting one lower limb.

Unilateral lower-limb symptoms are not the bilateral neurological red flag usually associated with CES. However, they can point towards a neurological problem and were relevant to the overall clinical picture.

An MRI scan was performed but reported as showing no significant spinal canal stenosis or nerve root compression. The patient was discharged without surgery. Around two weeks later, another MRI showed the disc in the same position, but on this occasion cauda equina compression was diagnosed.

What did the independent experts find?

As part of our investigation, we instructed a consultant neurosurgeon and a consultant musculoskeletal radiologist to consider the original MRI. They advised that it showed a large sequestrated disc fragment compressing the S1, S2 and S3 nerve roots and displacing the cauda equina.

The allegations included failures to identify the sequestrated disc fragment, recognise its compressive effect on the sacral nerve roots and appreciate the significance of those findings alongside the person’s urinary symptoms and altered perineal sensation. The Defendant admitted failures relating to identifying the fragment and recognising its compressive effect on the sacral nerve roots.

Nicholas explains:

“An MRI was performed and was initially interpreted as reassuring, without cauda equina compression. Around two weeks later, another MRI showed the disc in the same position, but cauda equina compression was diagnosed.

“Independent expert review later confirmed that the original MRI demonstrated significant compression of the cauda equina nerve roots. The opportunity for diagnosis and earlier treatment was there, but unfortunately it was missed, and breach of duty was admitted by the Defendant.”

The case illustrates why arranging an MRI is only one part of diagnosing cauda equina syndrome. The scan also needs to be interpreted correctly, and the findings need to be assessed in the context of the symptoms that prompted the investigation.

What happens if an MRI confirms cauda equina compression?

Where an emergency MRI confirms cauda equina compression in the presence of red flag symptoms, emergency review by the neurosurgery spinal surgical team is required. Depending on the MRI findings and clinical symptoms, emergency surgery may be necessary to relieve the pressure on the affected nerve roots.

Where lumbar disc herniation is responsible, surgical decompression may involve removing the part of the disc that is causing the compression. The aim is to prevent continuing nerve damage that could affect bladder function, bowel control, saddle sensation, sexual function together with neuropathic pain, mobility and sensation in the lower limbs.

The timing of surgical treatment is essential because surgery outside of the 48 hour window from the onset of urinary dysfunction often leads to permanent post-operative symptoms. 

However, it is not the case that surgery within a fixed number of hours always guarantees a good outcome or that treatment outside that timeframe automatically amounts to medical negligence. The legal question is whether an avoidable delay caused the person’s condition to worsen and whether earlier surgical intervention would probably have led to a better outcome.

We discuss this distinction in more detail in our guide to how long cauda equina syndrome can go untreated.

When can a missed MRI lead to a medical negligence claim?

A missed diagnosis of cauda equina syndrome does not automatically establish medical negligence. A claim needs evidence that the care fell below a reasonable standard and that this caused or materially contributed to additional injury.

Potential failings may include:

• Not recognising red flag symptoms and failing to arrange an urgent MRI.
• Delaying an emergency MRI after suspected cauda equina syndrome had been identified.
• Failing to recognise visible cauda equina compression on an MRI scan.
• Incorrectly reporting significant MRI findings as reassuring.
• Identifying nerve compression but underestimating the clinical significance.
• Failing to consider the MRI alongside the patient’s symptoms.
• Delaying referral to spinal or neurosurgeons after positive MRI findings.
• Delaying emergency surgery or surgical decompression.

Independent medical evidence is then required to address what difference the potential failings made to the outcome. A consultant neurosurgeon would consider whether earlier diagnosis and surgical intervention would probably have reduced or prevented ongoing symptoms of urinary and bowel dysfunction, saddle anaesthesia and/or lower-limb neurological symptoms. Our guide to how to prove medical negligence explains the evidence used to establish these legal tests.

How JMW investigates a missed cauda equina diagnosis

When we investigate a possible medical negligence claim involving an MRI scan, we first build a clear timeline showing the symptoms reported, the clinical assessment that took place, when imaging was requested and what happened after the MRI findings were reported.  We review GP and hospital records, emergency department notes, neurological examination findings, the original MRI images and radiology report, referral records and details of any spinal surgery.

The difference between the original images and the written MRI report can be particularly important. Where appropriate, we instruct a consultant radiologist to consider whether the MRI was correctly interpreted and a consultant neurosurgeon to assess whether earlier spinal surgery would probably have changed the outcome.

Nicholas says:

“Many cauda equina claims arise because the significance of red flag symptoms is not recognised in the first instance and MRI imaging is therefore delayed or never arranged. However, we do also see cases where the MRI scan has been performed but the diagnosis is still missed. Investigating those cases can require detailed expert review of both the original imaging, any further imaging performed and the symptoms that were recorded throughout the process.”

For a fuller explanation of what happens after we take on a case, read our guide to the medical negligence claims process.