Last Updated on March 17, 2025
Cauda equina syndrome refers to a characteristic pattern of neuromuscular and urogenital symptoms resulting from the compression of multiple lumbosacral nerves in cauda equine [see below].
The spinal cord ends at L1- L2 level. It tapers before ending. The most distal bulbous part of the spinal cord is called the conus medullaris, and its tapering end as the filum terminale.
After spinal cords ends, there is a collection of nerve roots. This is called cauda equina as it resembles the tail of a horse.
Cauda equina syndrome may often be a surgical emergency.
Cauda equina syndrome is relatively rare.
Relevant Anatomy
The spinal cord projects 31 pairs of spinal nerves on either side (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal) of the vertebrae that are connected to the peripheral nerves.
During development, the vertebral column grows more rapidly than the spinal cord. Spinal nerves exit the vertebral column at progressively more oblique angles because of the increasing distance between the spinal cord segments and the corresponding vertebrae. Lumbar and sacral nerves travel nearly vertically down the spinal canal to reach their exiting foramen.
The cauda equina is a bundle of intradural nerve roots at the end of the spinal cord, in the subarachnoid space distal to the conus medullaris
The nerves in the cauda equina region are lower lumbar and all the sacral nerve roots arranged anatomically according to the spinal segments from which they originated.
These nerves carry sensations from the lower limbs, perineal dermatomes, and supply muscles of lower limbs.
The conus medullaris obtains its blood supply primarily from 3 spinal arterial vessels
- Anterior median longitudinal arterial trunk
- Two posterolateral trunks.
Radicular arterial branches from the aorta also contribute. The nerve roots may also be supplied by diffusion from the surrounding CSF.
Pathophysiology and Causes of Cauda Equina Syndrome
Cauda equina syndrome may result from any lesion that compresses cauda equina nerve roots. Due to proximity to conus medularis, the lesions that cause cauda equina syndrome may also affect conus medularis and result in the mixed picture.
Studies showed that not only the magnitude but also the length and the speed of obstruction were also important in damaging the CE region
The most common causes of cauda equina and conus medullaris syndromes are the following –
Trauma
- Fracture dislocations causing compression of the cauda equina
- Penetrating trauma
- Stabs
- Gunshots
- Hematomas and posttraumatic arachnoid cysts
Disc Herniation
- Large central disc
- Extruded disc fragment causing stenosis
- Intradural disc herniation [Rare]
Spinal stenosis
- Developmental abnormality
- Degenerative process
Tumors
- Primary tumors
- Myxopapillary ependymoma [most common]
- Schwannoma
- Metastases
Inflammatory Conditions [By causing stenosis]
Infections
- Epidural abscess
- Pyogenic
- Tuberculous
- Nocardia infections
- Herpes simplex virus
- Meningovascular syphilis
- Cytomegalovirus
- Schistosomiasis
Congenital
Iatrogenic [Caused as a complication of medical procedures]
- Spinal instrumentation
- Misplaced pedicle screws
- Laminar hooks
- Continuous spinal anesthesia
- Epidural steroid injections
- Lumbar arthrodesis for spondylolisthesis
- Lumbar discectomy
- Intradiscal therapy
- Lumbar puncture causing an epidural hematoma
- Chiropractic manipulation
Clinical Presentation of Cauda Equina Syndrome
Patients can present with symptoms of isolated cauda equina syndrome or mixed with a picture of conus medullaris syndrome. The symptoms and signs of cauda equina syndrome tend to be of lower motor neuron in nature, while those of conus medullaris syndrome are a combination of lower and upper motor neuron.
Symptoms of cauda equina syndrome include the following:
- Low back pain
- Unilateral or bilateral radiculopathy
- Saddle [area of the buttocks, perineum and inner surfaces of the thighs] anesthesia and perineal hypoesthesia or anesthesia
- Urinary Disturbances
- Retention
- Difficulty initiating micturition
- Urethral numbness
- Overflow urinary incontinence
- Bowel Disturbances
- Incontinence
- Constipation
- Loss of anal tone and sensation [characteristic of cauda equina syndrome]
- Lower limb motor and sensory deficits
- Decreased or absent reflexes in lower limb
The initial presentation of bladder/bowel dysfunction may be of difficulty starting or stopping a stream of urine. It may be followed by frank incontinence, first of urine, then stool.
Presence of Babinski sign or other signs suggesting upper motor neuron involvement suggest a spinal cord compression. It not seen in isolated cauda equina syndrome. Its presence indicates a mixed picture or some other diagnosis.
Association (ASIA) impairment scale is used in determining the level and extent of the injury.
Differentiation from Conus Medullaris Syndrome
Here are the differentiating features
| Feature | Conus Medullaris Syndrome | Cauda Equina Syndrome |
| Presentation | Sudden and bilateral | Gradual and unilateral |
| Reflexes | Knee jerks preserved but ankle jerks affected | Both ankle and knee jerks affected |
| Sensory symptoms and signs | Numbness more localized to the perianal area; symmetrical and bilateral; sensory dissociation occurs | Numbness more localized to saddle area; asymmetrical, maybe unilateral; no sensory dissociation; loss of sensation in specific dermatomes in lower extremities, pubic area, and glans penis or clitoris |
| Motor strength | Typically symmetric, hyperreflexia Fasciculations may be present | Asymmetric areflexic paraplegia that is more marked; fasciculations rare; atrophy more common |
| Sphincter dysfunction | Urinary retention and atonic anal sphincter cause overflow urinary incontinence and fecal incontinence; tend to present early in course of the disease | Urinary retention tends to present late in the course of the disease |
Differential Diagnoses
- Acute inflammatory demyelinating polyradiculoneuropathy
- Amyotrophic lateral sclerosis
- Diabetic neuropathy
- Guillain-Barré syndrome
- Multiple sclerosis
- Tumors of spinal cord
- Neurosarcoidosis
- Spinal cord infections
- Traumatic peripheral nerve lesions
Imaging Studies
X-rays
Plain x-rays are not helpful in cauda equina syndrome but may be done in cases of trauma, bony lesions and degenerative changes.
Chest X-ray is done in suspected cases of metastases.
Magnetic Resonance Imaging
MRI generally has been the favored imaging study in cauda equina syndrome A patient with new-onset urinary symptoms with associated back pain or sciatica need urgent MRI for diagnosis making and treatment.
MRI with gadolinium enhancement is the diagnostic test of choice.
Other Studies
Needle electromyography may show evidence of acute denervation and could help in predicting prognosis and monitoring recovery.
Nerve conduction studies may rule out more distal peripheral nerve lesions. [usually done in pudendal nerve]
Duplex ultrasound of peripheral vessels may rule out compromised vasculature as a possible cause of associated claudication.
Lab Studies
- Basic blood tests including blood biochemistry, sedimentation rate, and syphilis and Lyme serologies.
- Lumbar puncture and CSF examination to rule out inflammatory disease of the meninges or spinal cord.
- Ultrasonography to estimate or measure residual bladder volume after voiding.
- Urodynamic studies to evaluate the degree and cause of sphincter dysfunction
Treatment
The general treatment goals are to minimize the extent of the injury and to treat ensuing general complications.
In acute onset cauda equina syndrome, methylprednisolone should be administered if the patient is seen within 8 hours of injury.
Administration of ganglioside GM1 sodium salt beginning within 72 hours of injury may be beneficial. It is given as iv infusion and continued for about 3-5 weeks.
A patient with acute cauda equina syndrome [saddle anesthesia, bilateral lower limb weakness, loss of bowel or bladder control] should not be continued on medical treatment beyond 24 hours.
Failure of relief during this is an indication for surgical decompression.
In acute compression of cauda equina, surgical decompression as soon as possible is desirable. It is a kind of surgical emergency. A patient with a history of back pain/ radiculopathy who presents with bladder/bowel disturbances mandates MRI study.
Decompression surgery aims at removing the compression and increasing the space and thus relieves the pressure on the nerves of the cauda equina.
Surgical decompression considered necessary within 48 hours after the onset of symptoms, and preferably performed within 6 h of injury.
For example, in the case of disc herniation causing cauda equine syndrome, a laminotomy or laminectomy, followed by gentle retraction and discectomy is advisable.
When the presentation is chronic, decompression could be performed when feasible.
The decompression is aided by instrumentation/fusion for stabilization.
Depending on the causation of cauda equine, drugs are administered
- Anti-inflammatory agents and steroids in inflammatory processes such as ankylosing spondylitis
- Antibiotics therapy in infection
- Chemotherapy and radiation therapy of tumors, if feasible
Rehabilitation
Rehabilitation aims to maximize the function [physical, psychological and social].
- The range of motion and strengthening exercises
- Sitting balance
- Functional electrical stimulation for increased muscle tone
- Lower extremity orthoses to aid balance and walking
- Assistive devices for ambulation
- Ambulation exercises
- Family training and community skills
- A home exercise program
Complications of Cauda Equina Syndrome
- Thromboembolic phenomena
- Neurogenic bladder/bowel
- Erectile dysfunction
- Pressure ulcers
- Heterotopic ossification
- Osteoporosis
- Chronic neuropathic pain
- Spasticity/contractures
- Recurrent urinary tract infections
- Urethral Stricture
- Bladder calculi
- Depression
For deep venous thrombosis/pulmonary embolism, patients should be put on thrombolytic agents.
For neurogenic bladder, patients may require bladder catheterization.
The problem of erectile dysfunction could be effectively addressed by the use of a phosphodiesterase type 5 inhibitor like sildenafil [Viagra]
Pressure ulcers may be prevented by eliminating pressure and wound care.
The stool softener or manual evacuation for fecal incontinence may be advised for constipation.
For heterotopic ossification stretching exercises, disodium, radiation, and surgical excision are the treatment options.
Pain relieving drugs are beneficial for control of pain.
Use of orthoses is advised to prevent contractures.
In case of spasticity, antispasticity drugs like baclofen should be used.
Prognosis
Cause of cauda equine and promptness of the treatment are two major factors in cauda equine syndrome.
Complications are more common if treatment is delayed.
Patients with a history of bilateral radiculopathy have a less favorable prognosis than patients with unilateral pain.
Patients with complete perineal anesthesia are more likely to have permanent paralysis of the bladder.
The extent of perineal or saddle sensory deficit has been reported to be the most important predictor of recovery. Patients with unilateral deficits have a better prognosis than patients with bilateral deficits. Females and patients with bowel dysfunction have been reported to have worse outcomes postoperatively.
Prognosis can be predicted with the American Spinal Injury Association (ASIA) impairment scale as follows:
ASIA A
90% of patients fail to achieve functional ambulation.
ASIA B
72% fail to attain functional ambulation.
ASIA C/D
13% fail to attain functional ambulation 1 year after injury.
