Cauda equina syndrome

Cauda equina syndrome arises from compression of the lumbosacral nerve roots. Large herniated lumbar intervertebral discs are the most common culprit.

Other sources of compression include spinal or sacral fractures or surgery common in ICU trauma patients, lumbosacral neoplasms, spinal stenosis, nonneoplastic masses such as cysts, peripheral neuropathy, and infectious processes.

Low back pain is the fifth most common reason for all physician visits and the second most commonly reported symptom.In most cases, low back pain signals a muscular disorder that can be managed conservatively.

However, physicians should have heightened vigilance for low back pain combined with bowel and/or bladder incontinence, motor and/or sensory loss in the lower extremities, and saddle anesthesia, as this may represent a neurosurgical emergency termed cauda equina syndrome.

The cauda equina (from the Latin for horse’s tail) is the descriptive name for the lumbar nerve roots emanating from the distal tip of the spinal cord. The spinal cord terminates as the conus medullaris typically at the L1 and L2 level.

The lower lumbar and sacral nerve roots continue caudally in the cauda equina, exit their respective neural foramina, and ultimately provide motor and sensory innervation to the muscles and skin below the waist.

Signs and Symptoms of Cauda equina syndrome

Cauda equina syndrome most often can be diagnosed clinically. Compression of the lumbar and S1 nerve roots results in sensory and/or motor deficits in the lower extremities. Strength and sensation should be carefully tested in a dermatomal pattern.

The patellar (L3 and L4) and Achilles (S1) deep tendon reflexes should be tested and may be decreased. The sacral nerve roots supply motor innervation to the urethral and anal sphincters, sensation to the perineum, and in a bull’s-eye pattern to the skin surrounding the anus.

Thus, decreased resting and/or volitional rectal tone are a clinical sign of sacral nerve root compressionin Cauda equina syndrome, as is numbness in the perineum.

Anal sphincter reflexes may be tested by stretching the phallus (bulbocavernosus reflex) or by pinprick to the skin surrounding the anus (anal wink reflex).

Emergent imaging should be obtained in all patients presenting with suspected cauda equina syndrome. Magnetic resonance imaging (MRI) has emerged as the imaging modality of choice.

Computed tomography myelography is indicated for patients with a contraindication to MRI or those with spinal instrumentation.

In addition, neurosurgical consultation should be sought immediately in all cases of cauda equina syndrome. Surgical intervention aims to decompress the affected lumbosacral nerve roots within 48 hours of presentation.

The approach and extent of surgery for Cauda equina syndrome depends on the nature and location of the compressing lesion. Instrumented fusion is indicated when there is evidence of spinal instability.

Further references

Greenberg MS, ed. Handbook of Neurosurgery, Cauda equina syndrome .New York: Thieme; 2005:298–299.

Staats P, ed. Pain: Just the Facts. Philadelphia: Lippincott Williams & Wilkins; 2004:141–146.

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