The accuracy of clinical symptoms in detecting cauda equina syndrome in patients undergoing acute MRI of the spine

Abstract

A large number of patients do not have cauda equina syndrome (CES) on MRI to account for their clinical findings; consequently, the majority of urgent scans requested are normal. We aimed to determine whether any clinical manifestation of CES, as stated in Royal College of Radiology guidelines, could predict the presence of established CES on MRI. We also aimed to support a larger study to develop a more universal assessment tool for acute lower back pain.

A retrospective analysis of consecutive patients who warranted urgent MRI was conducted. Seventy-nine patients were eligible for study. The Kendall’s tau test was used for statistical analysis of all data. A p value of less than 0.05 was considered to be significant. MRI was performed in 62 patients out of 79.

A total of 32.9% of patients had scans within 24 hours of admission. Nine of these patients were referred to neurosurgery for urgent neurosurgical review. Of these, 6.3% of patients had an established CES on MRI scan. One patient who had an out-patient MRI spine (15 days from hospital presentation) was found to have an established CES, was urgently referred to spinal surgery and underwent primary fenestration excision of the lumbar vertebra. No clinical features that were able to predict the presence of an established CES on MRI were elucidated. Findings included decreased anal tone 7.6% (p = 0.282), faecal incontinence 3.8% (p = 0.648), urinary retention 7.6% (p = 0.510), bladder incontinence 8.9% (p = 0.474), constipation 2.5% (p = 0.011) and saddle anaesthesia 8.9% (p = 0.368). Patients who had an abnormal MRI spine for back pain prior to this presentation showed a correlation with a newly diagnosed CES on MRI (p = 0.016) with a correlation coefficient of 0.272.

Introduction

The adult spinal cord terminates at the level of the L1–L2 vertebrae, with the terminal lumbar and sacral nerve roots within the spinal canal. The lower distal part of the spinal cord is known as the conus medullaris, and its tapered end forms the filum terminale. Distal to this area is a gathering of nerve roots (horsetail-like) forming the cauda equina distally. The squeezing of multiple lumbosacral nerve roots below the conus medullaris causes specific symptoms. These symptoms consist of low back pain, sciatica, saddle sensory problems, bladder and bowel problems, and lower extremity motor and sensory loss.^1,2

Cauda equina syndrome (CES) is most commonly caused by herniation of a lumbar disc, and presents as a complication in 2% of lumbar disc herniation cases.^3,4 Clinical features of CES include perineal anaesthesia and other lumbosacral root sensory deficits, lower extremity weakness, difficulty with bladder and bowel control, sexual dysfunction, low back pain, and unilateral or bilateral sciatica.^2,5 CES could be of two types, complete or incomplete. Complete CES patients usually have saddle anaesthesia and bladder or bowel retention/incontinence, while incomplete CES patients have saddle anaesthesia but with minor bladder and bowel dysfunction like loss of urgency or altered urinary sensorium.^6,7

A thorough neurological examination (including an assessment of perineal sensation and anal sphincter tone) should be performed. Patients with back pain and urinary incontinence should have a urinary post-void residual volume measured; greater than 100–200 ml indicates urinary retention and mandates further evaluation.⁸

Magnetic resonance imaging (MRI) should be urgently obtained when a diagnosis of CES is suspected. Treatment with high-dose steroids (dexamethasone 4–100 mg intravenously (IV)) may provide pain relief and improved neurological function (by reducing oedema) while awaiting diagnostic studies and surgical decompression.^8,9

CES is an absolute indication for emergency surgical decompression; laminectomy with gentle traction of the cauda equina and discectomy is the technique of choice.³ The outcome for patients with CES is determined primarily by their symptoms at presentation. Patients who can ambulate at presentation will generally remain ambulatory.⁹ Patients who present with paresis but are ambulatory with assistance have approximately a 50% chance of walking again, and as many as 79% of patients presenting with urinary retention will continue to require a urinary catheter after treatment.⁹ Other modes of surgical treatment have also been commonly used if lumbar disc herniation is involved, like microsurgery for lumbar disc herniation that requires surgical intervention. Discectomy and minimally invasive techniques have also been adopted by many surgeons.¹⁰ Some patients, however, need emergency surgery.^11–14

The primary aims of this study were to look at our recent experience at the Royal Alexandra Hospital, Paisley, United Kingdom (UK) and to determine how many of the patients who warranted MRI for CES possessed the above clinical findings and how many of them had positive MRI for established CES. As a secondary objective, we aimed to determine whether any clinical feature(s) could accurately predict the presence of structural abnormality on MRI and what the main radiological findings are for these patients. We aimed also to support a larger study to develop a more universal assessment tool for acute lower back pain.

Materials and methods

We conducted a retrospective analysis of consecutive patients for whom urgent spinal MRI was requested over an eight-month period between August 2012 and March 2013. All scans were performed in the radiology department of Royal Alexandra Hospital, Paisley. Criteria for inclusion into the study were the presence of medical notes and images that had been reported by a radiologist. Medical notes were then reviewed to identify duration of symptoms, clinical features on examination, result of the scan and the urgency and type of treatment provided. Clinical features were subdivided for analysis. Urinary symptoms were classified as acute incontinence, retention, frequency and other. Bowel symptoms were divided into acute incontinence and change in bowel habits. Perianal findings per rectal examination were divided into saddle anaesthesia, decreased anal tone or the presence of both.

The Kendall’s tau test was used for statistical analysis of all the data. A p value of less than 0.05 was considered to be significant.

Results

Based on inclusion criteria, 79 patients were eligible for the study. The cohort consisted of 24 males and 55 females with a mean age of 52.5 years (range, 18–89 years; median, 52 years).

MRI of the spine was performed within 24 hours of admission in 26 patients (32.9%). The mean time interval between hospital admission and scan was 149.17 hours/6.21 days (range, one hour to nine weeks; median, four days). Eleven patients had scans within 24–48 hours of admission. Only one MRI spine was performed out of hours during the eight-month period. The rest were performed beyond 48 hours of admission.

Nine patients who were admitted with questionable CES had been reviewed and decided to have out-patient MRI scans. Among them, back pain with radiation down the legs (sciatica) was found in seven of nine patients; the other two patients had bilateral lower limb weakness. One of the patients who had out-patient MRI spine (15 days from hospital presentation) was found to have an established CES, was urgently referred to spinal surgery and underwent primary fenestration excision of the lumbar vertebra.

The range of duration of symptoms prior to hospitalization was 24 hours to six months. Amongst a range of symptoms, acute onset of lower lumbar pain was the most commonly encountered symptom among patients.

Decreased power in the lower limbs was noted in 21 patients (26.6%), making it the most frequently encountered focal neurological deficit. Of these, 12 patients showed decreased power in one leg (unilateral), while nine patients had both legs affected (bilateral).

Sensory deficit in the lower limbs below the knee was the second most common focal neurological deficit noted in 16 patients (20.2%). Further details of neurological signs specific to CES and population size percentages can be found in Table 1.

Table 1.

Percentages of population size with neurological symptoms/signs specific to CES.

Neurological signs	Number of patients (out of 79)
Bladder incontinence	8.9%
Saddle anaesthesia	8.9%
Decrease anal tone	7.6%
Urinary retention	7.6%
Faecal incontinence	3.8%
Constipation	2.5%
Motor weakness lower limbs	26.6%
Sensory deficit/numbness/altered sensation	20.2%

CES: cauda equina syndrome.

Decreased ankle and knee reflexes were found in two patients (0.25%), and foot drop was encountered in two patients (0.25%).

Patients with decreased anal tone, faecal incontinence, urinary retention, saddle anaesthesia and urinary incontinence had been scanned within 24 hours. Patients with acute onset of constipation were scanned within the range of two to four days. MRI consistent with CES was found in five patients. All of them confirmed to have CES on MRI scan had been referred to spinal surgery and underwent surgical intervention: primary fenestration excision of the lumbar vertebral disc.

A total of 27.8% patients were previously admitted to hospital with lower lumbar back pain. Of these, 15 (19%) had previous MRI spine. Lumbar disc prolapse was the most common radiological finding on previous MRI. Patients who had an abnormal MRI spine for back pain prior to this presentation showed a correlation with a newly diagnosed CES on MRI (p = 0.016) with a correlation coefficient of 0.272 (Table 2). Only six patients (7.6%) had a history of lumbar spinal surgery.

Table 2.

The relationship between previous admission/previous MRI and a new diagnosed CES on MRI of spine (Kendall’s tau test).

	% Patients	p value	Correlation coefficient
Previous admission for back pain	27.8%	p = 0.1	0.186
Previous MRI for back pain	19.0%	p = 0.016	0.272
Abnormal findings on previous MRI scan	19.0%	p = 0.016	0.272
Previous history of spinal surgery	7.6%	p = 0.282	0.122

CES: cauda equina syndrome; MRI: magnetic resonance imaging.

Using the Kendall’s tau test, we tested the relationship between clinical manifestations and established CES on MRI of the spine. We found that none of the clinical manifestations was closely related to a diagnosis of CES. We also tried to test with non-urgent lumbar disc pathology. Further details of all variables examined with their corresponding percentages and p values can be found in Tables 1 and 3.

Table 3.

Correlation of neurological symptoms/signs with MRI consistent with CES and evidence of non-urgent lumbar disc pathology (Kendall’s tau test).

	MRI consistent with CES (p value)	Non-urgent lumbar disc pathologya (p value)
Decrease anal tone	0.282	0.185
Faecal incontinence	0.648	0.358
Urinary retention	0.510	0.034
Bladder incontinence	0.474	0.149
Constipation	0.011	0.456
Saddle anaesthesia	0.102	0.055
Motor weakness lower limbs	0.486	0.176

^aNon-urgent lumbar disc pathology: disc prolapse, degenerative changes, disc desiccation, etc. CES: cauda equina syndrome; MRI: magnetic resonance imaging.

Other systemic factors like weight loss, previous cancer, human immunodeficiency virus (HIV)/drug abusers and steroids had shown no correlation with CES diagnosis.

Sixty-two patients (78.5%) showed evidence of lumbar disc pathology on MRI of the spine. Disc prolapse was the most common pathology, noted in 45 patients (57%). Of these, 29 occurred at L4–L5, making it the most common level of disc prolapse found on MRI of the spine. Various shapes/types of disc prolapsed were found, including annular, diffuse, circumferential, right lateral, left lateral, posterior and central. Of these, central and diffuse disc prolapse were the most common shapes of prolapsed evidenced on MRI spine.

The scans of 19 patients (24.1%) were characterized by degenerative changes including osteoarthritis, spinal stenosis and osteoporosis. Further details can be found in Table 4.

Table 4.

Lumbar disc pathology on MRI and their correlation with diagnosed CES (Kendall’s tau test).

	Percentage %	p value
Disc prolapse	57%	0.049
Degenerative changes	24.1%	0.053
Disc desiccation	8.9%	0.474

CES: cauda equina syndrome; MRI: magnetic resonance imaging.

Disc desiccation was the third most common pathology noted in seven patients (8.9%). Of these, four occurred at L4–L5 and two at L5–S1, and one patient demonstrated widespread disc desiccation involving all the disc space.

Neoplastic disease was found in three patients (3.7%), of whom one had a known primary lesion, which was lung carcinoma with adrenal metastasis. This patient had lumbar metastasis with significant compression of the thoracic spine at T5 by a large spinal metastasis evident on whole MRI spine and received radiotherapy. The remaining two patients with spinal neoplastic disease presented with established CES on MRI of the spine. One of them had a large L3–L4 superiorly migrated intracanalicular sequestrated disc fragment in an epidural space. (That disc fragment was encroaching the right L3–L4 traversing nerve roots. Later, a nuclear medicine whole-body bone scan demonstrated widespread osteoblastic skeletal malignancy arising from the prostate.) The other patient had a severe biconcave fracture at T10–T11 demonstrated on whole MRI spine along with retropulsion of the posterior wall consistent with metastatic disease. Both of them were managed non-operatively and received specific oncological therapy, palliative care and medical management. A further five patients (6.3%) had primary neoplastic lesions but had no evidence of spinal metastases.

Discitis was demonstrated in four patients (5.0%); of these, two occurred at L5–S1 and one each at L2–L3 and L3–L4, respectively.

Other pathologies demonstrated on MRI spine included incidental haemangioma at L1–L2, meningocele at L4–L5, Tarlov cyst in the sacral canal, small peri-neural cyst at S1–S2, fatty infiltration of paraspinal muscles and Schmörl’s node at T10.

Discussion

In our study, only 26 patients received an MRI scan within 24 hours of hospital admission. The remaining patients, despite having urgent requests for MRI, were scanned only within a mean of 6.21 days, during which time the majority remained as in-patients. Five patients were found to have an established CES on MRI and underwent surgical intervention; one of them had an out-patient MRI scan. This highlights the limitation of the clinical assessment tool given those patients who were initially thought to have warranted MRI less urgently than others but still underwent surgery.

As a primary objective, we examined whether a single clinical feature could predict the presence of CES on MRI scan. This can help to propose a more universal rule to study patients with lower back pain. A Canadian computed tomography (CT) rule for patients after minor or mild head injury has been developed, and our study can support a larger study to develop a similar rule for acute lower back pain. We found that none of the single clinical features could predict the presence of the syndrome. In contrast, Balasubramanian et al.¹⁵ found that the presence of saddle sensory deficit has a higher predictive value than other clinical features in diagnosing CES. Interestingly, one more study, by Gooding et al.,¹⁶ found that digital rectal examination has no significant value in the acute diagnosis of CES with a p value of 0.897. To explain the disparity, Rooney et al.¹⁷ postulated that an abnormally persistent physiological response to acute back pain may lead to apparent neurological symptoms in the absence of an organic cause. Visceral dysfunction too may occur as a result of acute back pain and may, therefore, be regarded as functional symptoms. Functional paralysis, for instance, has an incidence of three to five per 100,000 and has been known to mimic CES.¹⁷

Despite both a history and clinical examination suggesting CES, MRI of the spine was still completely normal in eight patients. In our study disc prolapse was the most common cause of sciatica/symptoms, most often involving L4–L5. Levis¹⁸ also found that L4–L5 is the most common site for herniation.

Due to the small sample size, it is beyond the scope of this study to provide a greater in-depth analysis of individual symptoms or combination of symptoms. This is the main limitation of the results we have presented. Other weaknesses are predominantly due to the method of data collection and study design. Due to the retrospective nature of this study, it is conceivable that data may not have been recorded as diligently as they would have been in a prospective study and thus important findings may have been omitted. Although decisions to perform MRI were made by senior clinicians, these may have been influenced by the clinical assessments conducted by more junior members of medical team. Furthermore, with several radiologists interpreting the images, there may be a degree of inter-observer variability.

Conclusion

We were unable to elucidate any clinical features that were able to predict the presence of an established CES on MRI. Our findings included decreased anal tone 7.6% (p = 0.282), faecal incontinence 3.8% (p = 0.648), urinary retention 7.6% (p = 0.510), bladder incontinence 8.9% (p = 0.474), constipation 2.5% (p = 0.011), saddle anaesthesia 8.9% (p = 0.368). Patients who had an abnormal MRI spine for back pain prior to this presentation showed a correlation with a newly diagnosed CES on MRI (p = 0.016) with a correlation coefficient of 0.272.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Conflict of interest

None declared.