Cauda equina syndrome

Consultant orthopaedic surgeons Alan Gardner and Tim Morley provide the medicolegal background and a review of the clinical literature

Medicolegal considerations

Cauda equina syndrome (CES) is a rare condition with a disproportionately high medicolegal profile and figures significantly in terms of medicolegal costs.

During the five years between 1 January 2003 and 31 December 2007, MPS was notified of 63 likely claims worldwide relating to CES, of which 46 were in the UK.

Of the 20 concluded cases, damages were paid in 55%, with an average payment of £117,331 per case. This represents a total payout of £1,290,641 over the five years (£258,128 per annum), with only one third of the cases concluded.

The highest settlement was £584,000. Forty-three of the 63 cases related to general practice and 11 to orthopaedic surgery, with two each to radiology and neurosurgery and the remaining five to other specialties.

Such substantial costs are a reflection of the damaging and distressing nature of the condition. The statistics also indicate the vital importance of getting the diagnosis right and the potential difficulties surrounding surgery.

Although there are a number of potential causes, CES occurs most frequently following a large lower lumbar disc herniation, prolapse or sequestration. This article looks at the problem of CES resulting from compression by lumbar disc herniation, prolapse or sequestration, about which most has been written.

Diagnosis

CES is usually characterised by the following so-called “red flag” symptoms:

• Severe low back pain (LBP)
• Sciatica – often bilateral but sometimes absent – especially at L5/S1 with an inferior sequestration
• Saddle and genital sensory deficit
• Bladder, bowel and sexual dysfunction.

Three types of cauda equina syndrome have been identified:

• Rapid onset without a previous history of back problems.
• Acute bladder dysfunction with a history of low back pain and sciatica.
• Chronic backache and sciatica with gradually progressing CES.¹

Within these groups, CES may be complete or incomplete and its onset may be either acute within hours or gradual over weeks or months.²

CES-incomplete (CES-I) and CES-retention (complete) (CES-R)

Although the above description is clinically useful, in medicolegal terms the important distinction is whether, at any given time, CES is complete or incomplete in relation to urinary function and perineal sensation. These are both relatively easy to assess – urinary dysfunction is often the most distressing sequel of CES.

When the syndrome is incomplete (CES-I), the patient has urinary difficulties of neurogenic origin, including altered urinary sensation, loss of desire to void, poor stream and the need to strain. Saddle and genital sensory deficit is often unilateral or partial.

The complete syndrome (CES-R) is characterised by painless urinary retention and overflow incontinence. There is usually extensive or complete saddle and genital sensory deficit.

The outcome for patients with CES-I at the time of surgery is generally favourable, whereas those who have deteriorated to CES-R by the time the compression is relieved have a poorer prognosis – although around 70% have a socially acceptable long-term outcome.³

Low back pain and sciatica are of course common, but bilateral neurogenic sciatica should always ring alarm bells. Its occurrence with any “red flag” symptoms must trigger immediate action, generally involving emergency referral to an A&E department with ready access to a Spinal Surgery Unit – preferably accompanied by an explanatory telephone call to reduce delays. The diagnosis is confirmed by prompt MRI scanning.⁴

Background

CES is a significant indication for surgery in around 2-3% of all operations for lumbar disc prolapse, with an incidence in the population thought to be between 1 in 33,000 to 1 in 100,000. ^3,5,6 It generally requires urgent surgical treatment, so it is difficult to carry out high-quality prospective studies with statistical power sufficient to establish conclusions concerning the principal contentious issues. These are:

• The significance of delays in diagnosis and referral to hospital
• The risks and benefits of emergency versus urgent surgery
• The significance of surgical delay beyond 24 and 48 hours
• The prognostic significance of complete versus incomplete sphincter involvement and complete versus incomplete sensory deficit
• The prognostic significance of unilateral and bilateral leg signs
• The medicolegal implications of the above.

The most regrettable and life-affecting consequence of CE compression is bladder dysfunction. The terms CES-incomplete (CES-I) and CES-retention (CES-R) are useful and usually identifiable reference points with some relevance to the timing of surgery and clinical outcome.

CES may develop relatively acutely, usually with severe low back pain and often with complete anal and bladder motor and sensory loss and usually, but not always, with motor and sensory deficits in the lower limbs, all within 24 hours (CES-R, Tandon and Sankaran Group 1).¹ At the other end of the spectrum, low back pain may be mild, with gradually developing or intermittent sciatica over weeks or months in one or both legs, and incomplete or intermittent deficits of bowel and bladder function (CES-I, Tandon and Sankaran Group 3); there may be a relatively modest central disc prolapse causing compression because of a degree of stenosis of the spinal canal.

Questions arise as to what extent these variations in time and severity of compression are of prognostic significance. First, in relation to the delicate unmyelinated preganglionic fibres of the cauda equina in or near the midline, accompanied by the pudendal nerves, and secondly, for the more robust sciatic nerve roots laterally at the exit foramina in which the sensory nerves are smaller and more sensitive to compression than the motor nerves.⁷

The answer is unclear, with conflicting conclusions in the literature, and especially in individual cases where vital reference data may be missing from the record. One can only advise that, the longer compression continues, the more likely is long-term neurological damage initially to the autonomic, and subsequently to the somatic, components of the cauda equina.

A further factor may be at work, and that is the possibility of chemical interference with the function of nerves in contact with the irritating components in prolapsed nuclear disc material.⁸ Involved nerve roots are sometimes noted to be grossly swollen and inflamed at surgery. It may be that nerve recovery, after three days or more have passed before surgical decompression, may at least be partly explained by resolution of this chemical effect.

In other situations, such as the use or misuse of a tourniquet, the effect of nerve compression for more than four to six hours is usually considered to be irreversible. On the other hand, it may be that the clinical diagnosis of CES-R, with its less good prognosis – often on the basis of scanty information – may be overly pessimistic in some cases when they are in fact still CES-I at the time of surgery.

The traditional view was that “early operation is an essential prerequisite for an improved prognosis”.⁹ This seems logical and intuitive, if somewhat simplistic, as examination of the available evidence provides inconsistent support for this point of view.

It begs the questions: how early is early? And when does the clock start ticking? Is it at the onset of CES symptoms or from the loss of bladder control, or from the time of admission to hospital or surgical unit? Also, what symptomatic characteristics, if any, are good indicators of prognosis? Is it the presence or absence of perineal sensory loss or unilateral or bilateral sciatica or motor weakness in the lower limbs, or the presence or absence of bladder and/or anal motor or sensory function?

Finally, from a medicolegal perspective, at what stage, if at all, was the situation retrievable by surgical decompression? If there was demonstrable delay, what difference did this make and what would have been the outcome if that delay had not occurred? As involved clinicians, or expert witnesses, we have not only to admit our uncertainty, where necessary, but also not stray from the validated behaviour patterns of this complex and variable condition.

The literature

In reviewing the literature, we may start with the meta-analysis by Ahn et al which indicates: “There was a significant advantage to treating patients within 48 hours, versus more than 48 hours after the onset of cauda equina syndrome. A significant improvement in sensory and motor deficits as well as urinary and rectal function occurred in patients who underwent decompression within 48 hours versus after 48 hours.”¹⁰ They also stated that “no significant improvement in surgical outcome was identified with interventions less than 24 hours from the onset of cauda equina syndrome compared with patients treated within 24-48 hours”.

However, Kohles et al (2004) critically reassessed the Ahn paper and concluded that, although an advantage existed in treating patients within 48 hours, there was further benefit in treating patients within 24. They make the logical point that the earlier the surgery, including within 24 hours, the better the outcome.¹¹

Gleave and Macfarlane (1990) reported that retention developing less than 48 hours after an acute prolapse was associated with a poorer prognosis.³ They believe that in the majority of such cases “the die is cast at the time of the prolapse”, depending on the rapidity of its development and the severity of the nerve compression and that “there is no evidence to support the view that emergency surgery influences the degree of recovery”. Indeed, emergency surgery in the middle of the night by inexperienced staff may not be in the patient’s best interest. Decompression of a large midline disc prolapse or sequestration is often a demanding procedure. An appropriately experienced surgeon is essential.

They conclude, however, that a diagnosis of incomplete CES requires urgent surgery in order to prevent progression of the condition. In a review of the literature in 2002, they go on to highlight the following points:³

• Patients with incomplete CES are best treated by early surgery and tend to show a favourable outcome. However, around 70% of their CES-retention patients had a good result from surgery carried out a mean of 3.7 days after onset; a similar figure to Shapiro’s group who were operated upon within 48 hours.¹² They agree that incomplete CES is best treated by early surgery.
• Urodynamic studies can show a serious disturbance of bladder function after CE compression and yet the patient may have no symptoms at all.¹²
• Recovery of bladder and sexual function may continue for a number of years after injury.^13,14 This is unlikely to be due to neural regeneration, but reflects the patient’s ability to develop compensatory strategies for coping with bladder sphincter denervation. Length of follow-up is therefore an important variable.
• Recovery of sexual function appears to mirror sphincter outcome.
• Surgical exposure should generally be via full laminectomy rather than microdiscectomy. Permanent damage can result from excessive manipulation of the dura and occasionally transthecal excision may be necessary.
• Nerve ischaemia for more than around four hours is irreversible. “That window of opportunity is manifestly impossible to achieve in the clinical situation; it must be concluded that the outcome of CES-R has already been decided by the time the patient is admitted to hospital.”

Gleave and Macfarlane conclude that whilst urgent surgery remains indicated for patients with an incomplete lesion, to prevent them from progressing to complete CES, examination of the literature does not support a role for emergency surgery to treat a condition which is complete at the time of presentation to hospital.

Conclusion

CES occupies a prominent position in the medicolegal field, partly perhaps through lack of awareness and urgency in its management, and partly because of the devastating consequences of inadequate management which may lead to bowel, bladder, sexual and lower limb dysfunction.

However, it is now established that, in around half of cases, the die is cast within the first four-six hours of a severe central disc prolapse resulting in CES-R. This is a very small window of opportunity in which to achieve referral to an appropriate hospital, confirmation of diagnosis by MRI scan and surgical decompression. It follows that minor delays are probably not significantly related to causation in these cases.

Nevertheless, prompt diagnosis and investigation, followed by a full explanation and consent procedure before timely and skilful surgery and rehabilitation, are the essentials of best practice in the treatment of this rare, but often very damaging, condition. It is a tragedy, sometimes avoidable, if an incomplete syndrome becomes complete while under medical supervision (see also the case report on CES from this issue).

Essential questions to ask:

• History of back pain. Put your finger(s) on the worst place.
• Where is your leg pain?
• When did you last pass urine/open your bowels?
• Does your backside/genital area feel normal? 
• Can you feel whether your bladder is full?
• Can you tighten your anus?
• Have you had any dribbling/leakage?

Major causes of delay and dissatisfaction in practice are:

• Patients, often previously asymptomatic, who delay seeking advice.
• GPs not recognising the urgency of “red flag” symptoms (see below).
• Junior A&E staff missing the diagnosis and not calling a senior.
• Hospital delays in admission to a surgical unit and arranging MRI and surgery at an appropriate time by a suitably experienced surgical team.
• Failure to warn of persistent neurological symptoms in the preoperative consent procedure.
• Deficiencies in aftercare and multi-disciplinary rehabilitation.

References

1. Tandon PN and Sankaran B, Cauda equina syndrome due to lumbar disc prolapse, Indian J. Orthop 1:112-119 (1967).

2. Gleave JRW and Macfarlane R, Prognosis for recovery of bladder function following lumbar central disc prolapse, Brit J. Neurosurg 4:205-210 (1990).

3. Gleave JRW and Macfarlane R, Cauda equina syndrome: what is the relationship between timing of surgery and outcome? Brit J. Neurosurg 16(4):325-328 (2002).

4. Coscia M, et al, Acute cauda equina syndrome: diagnostic advantage of MRI, Spine 1994; 19:475-478.

5. O’Connell JEA, The indications for and results of the excision of lumbar intervertebral disc protrusions; a review of 500 cases, Ann. R.Coll. Surg. Engl 6:403-412 (1950).

6. Anthony S, Cauda equina syndrome, MPS Casebook Spring 2003; 20: 9-13.

7. Olmarker K, The spinal nerve roots, Acta. Orth. Scand Suppl 242:1-27 (1991).

8. Rydevik BL, Brown M, Lundborg G: Pathoanatomy and pathophysiology of spinal nerve root compression, Spine 1984 Jan-Feb; 9(1): 7-15.

9. Shephard RH, Diagnosis and prognosis of cauda equina syndrome produced by protrusion of lumbar disc, Brit Med J 2:1434-39 (1959).

10. Ahn UM, et al, Cauda equina syndrome secondary to lumbar disc herniation – a meta-analysis of surgical outcomes, Spine 25; 12:1515-1522 (2000).

11. Kohles SS, et al, Time-dependent surgical outcomes following cauda equina syndrome diagnosis – Comments on a meta-analysis, Spine 29; 11:1281-1287 (2004).

12. Shapiro S, Cauda equina syndrome secondary to lumbar disc herniation, Neurosurgery 1993; 8: 317-322 (1993).

13. Dinning TAR and Schaeffer HR, Discogenic compression of the cauda equina: a surgical emergency, Aus. N.Z. J. Surg 63: 927-934 (1993).

14. Chang HS, et al, Lumbar herniated disc presenting with cauda equina syndrome: Long-term follow-up of 4 cases, Surg. Neurol 53:100-5 (2000).