The cauda equina is a collection of spinal nerves and nerve roots distal to the tapered end of the spinal cord, or conus medullaris.1 It consists of the second through fifth lumbar nerve pairs, all sacral nerve pairs and the coccygeal nerve. These nerve roots supply sensory and motor innervation to the pelvic organs, lower limbs and the external anal and urinary sphincters. They also provide parasympathetic innervation to the bladder. The cauda equina syndrome (CES) is a serious pathologic condition that is caused by compression of these nerve roots. It can cause various symptoms such as back pain, sciatica, motor weakness, and sensory deficits, but the term cauda equina syndrome is used only when bladder, bowel, and/or sexual dysfunction, and/or saddle anesthesia occur.2,3 Some patients may go on to develop permanent weakness, sensory deficits, and incontinence.4
Although rare, CES is an important condition for emergency physicians to understand due to its potential to cause permanent neurologic deficits.5 The history and examination can be helpful in diagnosing CES but as discussed below, the history and exam do not always correlate with the final diagnosis.6 Magnetic resonance imaging (MRI) is considered the best test in confirming a diagnosis of CES.4
CES carries a high risk of litigation, especially when patients are left with long-term deficits.5 Surgical intervention remains the first-line therapy. Historically, urgent surgery has been touted as the best treatment for patients, however recent studies have suggested that the timing of surgery may be less important for overall outcomes. Rather, outcomes may be more related to the extent of cord compression at presentation. Nevertheless, CES is a serious condition that must be recognized in order to give patients the best chance at full neurologic recovery.
CES is rare, estimated at 7 out of 100,000 person years in the US military and in 0.12% of herniated discs each year.2,7 In 1967, Tandon and Sankaran proposed three main types of CES (a) sudden onset, either primarily or acute on chronic, (b) Slow onset with progressively worsening symptoms and (c) progressive onset of visceral impairment with urinary retention.8 Today, most clinicians now divide CES into two main categories: CES with retention and incomplete CES, in which there is reduced urinary sensation and or poor stream but no established retention or overflow.9
The most common cause of CES is herniation of a lumbar disk causing pressure on the cauda equina.2,3,4 However, many other causes have been reported such as trauma, spinal stenosis, malignancy, spinal abscess, chiropractic manipulations, and aortic obstruction.10,11,12,13,14,15 Other rare causes include interspinous device placements, and IVC thrombosis.16,17 Obesity has also recently been shown to be related to an increased risk of CES.18
Symptoms of CES vary but the most common symptoms include severe back pain and radiculopathy.11 However, radicular pain may not be present if central herniation occurs at L5-S1 where motor roots are spared.19 Other symptoms include motor weakness of lower extremities, sensory disturbance in the saddle area, and loss of visceral function.11,19 Clinicians should suspect CES if any patient has dysfunction of bowel, bladder or sexual function and/or sensory changes in the perianal area.2 Since urination occurs more often than bowel evacuation, a diagnosis is most often based on urinary dysfunction. Certain examination findings can also be suggestive of the diagnosis, including decreased or absent rectal tone, sensory loss in the lower extremities, and/or complete anesthesia in the perianal area.19
Recent studies have been conducted to determine whether sole history and physical examination findings can accurately predict the presence or absence of CES. In 2011, Fairbank et al conducted a literature review of studies that evaluated patients with signs and/or symptoms concerning for CES and compared them with findings on MRI.6 Symptoms included low back pain, bilateral sciatica, bladder retention and/or incontinence, frequent urination, decreased urinary sensation, and bowel incontinence. Signs included saddle numbness and reduced anal tone. Overall, the authors found that no signs or symptoms demonstrated high sensitivity and specificity. In addition, all likelihood ratios were low. Essentially, the authors determined that there is minimal evidence that any particular sign or symptom can accurately diagnose CES.6
In 2007, Bell et al conducted a prospective cohort study that evaluated the ability of neurosurgical residents to predict which patients with symptoms of CES required urgent MRI imaging.20 Overall, the authors found that 43% of patients suspected of CES had normal MRI findings. They also found urinary incontinence, saddle anesthesia, and altered urinary sensation are poorly predictive of CES. The authors conclude that it is impossible to exclude the diagnosis of CES clinically and thus, urgent MRI should be obtained in any patient with urinary symptoms, back pain, and/or sciatica.20
As noted above, MRI should be obtained immediately if one suspects CES as this is the gold standard test for diagnosis.4 CT myelography can also be obtained if a patient has contraindications to MRI, such as a specific pacemaker.2 The important point to note is that clinicians should not rely on signs or symptoms to rule out or rule in CES. Clinicians should order the appropriate imaging immediately once diagnosis is suspected.
Historically, literature has shown that patients have better outcomes with early surgical intervention.11,21 However, some authors have noted that even expeditious surgery may not lead to full recovery.5,10,22,23 Recent studies have evaluated the urgency of surgery and some have shown that immediate surgery does not necessarily improve long term outcomes but rather, outcomes tend to vary based on initial presentation and the severity of each patient’s condition.22 In 2003, Hussain et al conducted a retrospective study on a group of patients with CES who underwent surgery within five hours and another group who had surgery within 24 hours. They found no significant outcomes between the two groups and concluded that emergency decompressive surgery for CES did not improve overall outcomes compared with a delayed approach.23
In 2007, Qureshi et al conducted a prospective cohort study of 33 patients undergoing surgery for CES. Their goal was to determine what factors, specifically onset of symptoms and timing of surgical decompression, influence spine and urinary outcome measures at three months and one year. Overall, surgery was performed on 36% of patients within 48 h of the onset of symptoms and the rest in greater than 48 hours. At follow up, there was no statistically significant difference in outcome with respect to length of time from symptom onset to surgery. Outcomes were better in those who were continent of urine at presentation compared with those who were incontinent. Overall the authors conclude that the severity of bladder dysfunction at the time of surgery was the dominant factor in long-term recovery of bladder function.22
Similarly, in 2011, Harrop et al reviewed current literature regarding traumatic CES and urgent surgical intervention and found that immediate surgical decompression did not result in improved neurologic outcomes compared to delayed or nonsurgical treatment.10 Other studies, such as a 2008 meta-analysis by Delong, show that urgent surgery may only be helpful for those with complete CES and less so for incomplete CES.9 That being said, the data is still inconclusive. Despite new studies emerging on the timing of surgery, the above studies still infer that patients will need surgery but may not require it as urgently as previously thought. From an emergency medicine perspective, we should remain vigilant in ordering all patients urgent imaging and surgical referral.
From a malpractice standpoint, the urgency of CES remains to be true. Although there are many factors involved in lawsuits concerning CES, a positive association has been found between time to surgery > 48 hours and an adverse decision for the clinician.5 Other medicolegal factors include failure to document an appropriate history and physical exam, including a rectal exam and perianal sensation to pin prick.19 Failure to provide patients with strict return precautions and failure to refer patients to a surgeon also have been positively associated with a negative verdict for the plaintiff.5,19 Interestingly, in a 2012 study by Daniels et al, actual degree of functional loss did not appear to affect the verdicts.5,19
In the ED setting, it can be a challenge to suspect CES, obtain an emergent MRI, and provide the patient with adequate referral. In 2007, Jalloh et al conducted a retrospective study on 32 patients with CES. Their purpose was to identify reasons for delay in diagnosis and management of CES.24 In all 32 patients presented to nine different emergency departments and were subsequently diagnosed with CES. In general, the authors found certain factors that delayed the diagnosis and management. These included patients presenting too late, CES not considered a diagnosis, inappropriate advice from consultants, mechanical failure of the MRI scanner, referral to inappropriate specialty, and lack of beds in the tertiary referral center. Overall, the authors found that delay in treatment was most often due to delay in making the diagnosis. They attributed this to the fact that the majority of patients did not present with the classic symptoms of CES. They found that the strongest predictor was sacral sensory loss and thus, strongly recommend a sacral sensory exam in all patients who present with concerning symptoms of CES.24
Bottom Line/Pearls & Pitfalls
The bottom line is to keep a high level of suspicion and do a full sensory and rectal exam on any patient who may present with concerning symptoms of CES. The diagnosis cannot be confirmed by history and examination alone, so consider imaging strongly. Continue to refer all patients early as the proper timing of surgery and long-term outcomes has not yet been determined. Always document thoroughly and keep patients informed. If a patient with sciatica has no concerning signs of CES on history and exam, make sure to provide strict return precautions and tell him or her to return immediately if there are symptoms of CES such as incontinence, saddle anesthesia, and/or lower limb weakness.
- Lavy C. Cauda Equina Syndrome. BMJ 2009; 338: b936.
- Kostuik JP. Medicolegal Consequences of Cauda Equina Syndrome: An Overview. Neurosurg Focus 2004; 16(6): e8.
- Qureshi, A, Sell P. Cauda Equina Syndrome Treated by Surgical Decompression: The Influence of Timing on Surgical Outcome. Eur Spine J 2007; 16(12): 2143–51.
- Levis JT. Cauda Equina syndrome. West J Emerg Med. 2009 Feb;10(1):20.
- Small SA, et al. Orthopedic pitfalls: cauda equina syndrome. Am J Emerg Med. 2005 Mar;23(2):159-63.
- Chau AM, et al. Timing of Surgical Intervention in Cauda Equina Syndrome: A Systematic Critical Review. World Neurosurg. 2013 Nov 13. pii: S1878-8750(13)01418-6.
- What is the optimum timing for surgical intervention on patients with CES?
- How can emergency physicians better determine “at risk” patients for CES?