The spinal cord tapers and ends at the level between the first and second lumbar vertebrae in an average adult. The most distal bulbous part of the spinal cord is called the conus medullaris, and its tapering end continues as the filum terminale. The upper border of the conus medullaris is often not well defined. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the cauda equina (Latin for horse's tail). These nerve roots constitute the anatomic connection between the central nervous system (CNS) and the peripheral nervous system (PNS). They are arranged anatomically according to the spinal segments from which they originated and are within the cerebrospinal fluid (CSF) in the subarachnoid space with the dural sac ending at the level of second sacral vertebra.
The conus medullaris part of the spinal cord obtains its blood supply primarily from 3 spinal arterial vessels-the anterior median longitudinal arterial trunk and 2 posterolateral trunks. Less prominent sources of blood supply include radicular arterial branches from the aorta, lateral sacral arteries, and the fifth lumbar, iliolumbar, and middle sacral arteries. The latter contribute more to the vascular supply of the cauda equina, although not in a segmental fashion, unlike the blood supply to the peripheral nerves. The nerve roots may also be supplied by diffusion from the surrounding CSF. Moreover, a proximal area of the nerve roots may have a zone of relative hypovascularity.
In understanding the pathological basis of any disease involving the conus medullaris, keep in mind that this structure constitutes part of the spinal cord (the distal part of the cord) and is in proximity to the nerve roots. Thus, injuries to this area often yield a combination of upper motor neuron (UMN) and lower motor neuron (LMN) symptoms and signs in the dermatomes and myotomes of the affected segments. On the other hand, a cauda equina lesion is a LMN lesion because the nerve roots are part of the PNS. Cauda equina and conus medullaris syndromes are classified as clinical syndromes of the spinal cord; epidemiological data on the 2 syndromes are often not available separately from the general data on spinal cord injury.
Frequency is determined by the underlying etiology. Multiple conditions can result in a cauda equina or conus medullaris syndrome as outlined later in this article.
Morbidity and especially mortality rates are determined by the underlying etiology. Multiple conditions can result in cauda equina or conus medullaris syndrome, as outlined later in this article.
The history of onset, the duration of symptoms, and the presence of other features or symptoms could point to the possible causes. Patients can present with symptoms of isolated cauda equina syndrome, isolated conus medullaris syndrome, or a combination. The symptoms and signs of cauda equina syndrome tend to be mostly LMN in nature, while those of conus medullaris syndrome are a combination of lower and upper motor neurons
Presentation Sudden and bilateral Gradual and unilateral Reflexes Knee jerks preserved but ankle jerks affected Both ankle and knee jerks affected Radicular pain Less severe More severes
Sensory symptoms and signs
Numbness tends to be more localized to perianal area; symmetrical and bilateral; sensory dissociation occurs Numbness tends to be more localized to saddle area; asymmetrical, may be unilateral; no sensory dissociation; loss of sensation in specific dermatomes in lower extremities with numbness and paresthesia; possible numbness in pubic area, including glans penis or clitoris.
Typically symmetric, hyperreflexic distal paresis of lower limbs that is less marked; fasciculations may be present Asymmetric areflexic paraplegia that is more marked; fasciculations rare; atrophy more common
Erectile dysfunction that includes inability to have erection, inability to maintain erection, lack of sensation in pubic area (including glans penis or clitoris), and inability to ejaculate
Urinary retention and atonic anal sphincter cause overflow urinary incontinence and fecal incontinence; tend to present early in course of disease Urinary retention; tends to present late in course of disease
Signs of cauda equina syndrome include the following:
- Muscle strength in the lower extremities is diminished. This may be specific to the involved nerve roots as listed below, with the lower lumbar and sacral roots more affected, leading to diminished strength in the glutei muscles, hamstring muscles (ie, semimembranosus, semitendinosus, biceps femoris), and the gastrocnemius and soleus muscles.
- Sensation is decreased to pinprick and light touch in a dermatomal pattern corresponding to the affected nerve roots. This includes saddle anesthesia (sometimes including the glans penis or clitoris) and decreased sensation in the lower extremities in the distribution of lumbar and sacral nerves. Vibration sense may also be affected. Sensation of the glans penis or clitoris should be examined.
- Muscle stretch reflexes may be absent or diminished in the corresponding nerve roots. Babinski reflex is diminished or absent.
- Bulbocavernosus reflexes may be absent or diminished. This should always be tested.
- Anal sphincter tone is patulous and should always be tested since it can define the completeness of the injury (with bulbocavernosus reflex); it is also useful in monitoring recovery from the injury.
- Urinary incontinence could also occur secondary to loss of urinary sphincter tone; this may also present initially as urinary retention secondary to a flaccid bladder.
Signs of conus medullaris syndrome include the following:
- Muscle tone in the lower extremities is decreased, which is consistent with an LMN lesion.
Patients may exhibit hypertonicity, especially if the lesion is isolated and primarily UMN.
Signs are almost identical to those of the cauda equina syndrome, except that in conus medullaris syndrome signs are more likely to be bilateral; sacral segments occasionally show preserved bulbocavernosus reflexes and normal or increased anal sphincter tone; the muscle stretch reflex may be hyperreflexic, especially if the conus medullaris syndrome (ie, UMN lesion) is isolated; Babinski reflex may affect the extensors; and muscle tone might be increased (ie, spasticity).
Other signs include papilledema (rare, occurs in lower spinal cord tumors), cutaneous abnormalities (eg, cutaneous angioma, pilonidal sinus that may be present in dermoid or epidermoid tumors), distended bladder due to areflexia, and other spinal abnormalities (noted on lower back examination) predisposing the patient to the syndrome.
The most common causes of cauda equina and conus medullaris syndromes are the following:
Other, rare causes include the following:
- Lumbar stenosis (multilevel)
- Spinal trauma including fractures1
- Herniated nucleus pulposus (cause of 2-6% of cases of cauda equina syndrome)
- Neoplasm, including metastases, astrocytoma, neurofibroma, and meningioma: Twenty percent of all spinal tumors affect this area.
- Spinal infection/abscess, such as tuberculosis, herpes simplex virus, meningitis, meningovascular syphilis, cytomegalovirus, or schistosomiasis5
- Idiopathic, eg, spinal anesthesia : These syndromes may occur as complications of the procedure or of the anesthetic agent (eg, hyperbaric lidocaine, tetracaine).
- Spina bifida and tethered cord syndrome7
- Spinal hemorrhage, especially subdural and epidural hemorrhage causing compression within the spinal canal
- Intravascular lymphomatosis
- Congenital anomalies of the spine/filum terminale including tethered cord syndrome
- Conus medullaris lipomas
- Multiple sclerosis
- Spinal arteriovenous malformations
- Late-stage ankylosing spondylitis
- Deep venous thrombosis of the spinal veins (propagated
Differential Diagnoses & Workup
Other Problems to Be Considered
- Differential Diagnoses
- Acute Inflammatory Demyelinating Polyradiculoneuropathy
- Multiple Sclerosis
- Alcohol (Ethanol) Related Neuropathy
- Amyotrophic Lateral Sclerosis
- Pathophysiology of Chronic Back Pain
- Chronic Inflammatory Demyelinating Polyradiculoneuropathy
- Spinal Cord Hemorrhage
- Spinal Cord Infarction
- Diabetic Neuropathy
- Spinal Cord Trauma and Related Diseases
- Femoral Mononeuropathy
- Spinal Epidural Abscess
- HIV-1 Associated Distal Painful Sensorimotor Polyneuropathy
- HIV-1 Associated Multiple Mononeuropathies
- Traumatic Peripheral Nerve Lesions
- HIV-1 Associated Myopathies
- Tropical Myeloneuropathies
- HIV-1 Associated Neuromuscular Complications (Overview)
- Abdominal aortic aneurysm
- Amyloidosis with deposits in the spinal cord
- Ankylosing spondylitis and other spondyloarthropathy
- Charcot-Marie-Tooth disease (types 1 and 3)
- Guillain-Barré syndrome
- Herniated lumbar or sacral disk
- Intravascular lymphomatosis
- Lipomas within the spine
- Lumbar stenosis (multilevel)
- Neoplasm in the spine
- Paget disease of the spine
- Peripheral neuropathy and its various causes
- Retroperitoneal mass, including neoplasm and hematoma
- Sacral plexus injury (eg, after surgery, such as abdominal-perineal resection, sacral excision, or radical hysterectomy)
- Spinal infection/abscess and meningitis
- Spina bifida/congenital anomalies of the spine/filum terminale
- Spinal degenerative diseases
- Spinal hemorrhage
- Tethered cord syndrome/short filum terminale
- Vascular intermittent claudication
- Back pain
These studies may help to define possible causes and any associated pathology, especially other causes of lesions in the lower spinal cord or cauda equina.
- CBC count, blood glucose, electrolytes, blood urea nitrogen (BUN), and creatinine - As part of the workup to rule out associated anemia, infection, and renal dysfunction, especially in associated retroperitoneal mass
- Elevated erythrocyte sedimentation rate (ESR) - May point to an inflammatory pathology
- Syphilitic serology to rule out meningovascular syphilis
MRI with contrast of the lumbosacral spine is the diagnostic test of choice and provides a more complete radiographic assessment of the spine than other tests. Gadolinium contrast MRI is currently the most sensitive imaging for detecting intradural neoplasms. It also may be able to rule out abdominal aneurysm, which could be the source of emboli causing conus medullaris infarction. See the following images for representative MRIs.
CT scan myelogram may reveal an intradural or extradural mass or lesions affecting the conus medullaris.
Plain radiographs of the lumbosacral spine are still useful and may depict early changes in vertebral erosions secondary to tumors and spina bifida. Chest radiography is indicated to rule out a pulmonary source of pathology that could affect the lumbosacral spine (eg, malignant tumor, tuberculosis). Follow-up chest CT may be required.
Bone scan may detect malignant tumor or metastases and inflammatory conditions affecting the vertebrae.
Needle electromyography (EMG)11 may show evidence of acute denervation, especially in cauda equina lesions and multilevel lumbar spinal stenosis. EMG studies also could help in predicting prognosis and monitoring recovery. Performing needle EMG of the bilateral external anal sphincter muscles is recommended.
Nerve conduction studies, especially of the pudendal nerve, may rule out more distal peripheral nerve lesions.
Cauda Equina and Conus Medullaris Syndromes: Treatment & Medication
Specific treatment is directed at the primary cause; these are discussed in other articles. As discussed below, the general treatment goals are to minimize the extent of injury and to treat ensuing general complications.
In an acute setting, treatment options entail minimizing possible inflammation and preventing further trauma that might cause worsening of the injury. This is of even greater importance if the cause is trauma.
Maintenance of adequate airway, cardiopulmonary resuscitation, fluid management, and initial immobilization (using a molded thoracolumbosacral orthosis) are necessary to limit further damage.
Methylprednisolone must be started within 8 hours of injury. No evidence exists of any benefit if it is started more than 8 hours after injury; on the contrary, late treatment may have detrimental effects.
Administration of GM1 ganglioside sodium salt beginning within 72 hours of injury may be beneficial.
Any specific causal factor should be treated as soon as it has been identified.
Treatment/prevention of possible complications should begin immediately, including the following:
- Deep venous thrombosis/pulmonary embolism: Patients should use antiembolic compression stockings and subcutaneous heparin for 3 months as prophylaxis. Low-molecular-weight heparin also has been approved for prophylaxis. Ultrasound of the lower extremities may need to be done as an initial screening test with follow-up later.
- Neurogenic bladder: Patients may require bladder catheterization.
- Pressure ulcers: These may be prevented by eliminating pressure, optimizing wound-healing environment, and debriding if necessary.
- Impotence: Use of sildenafil (Viagra) is becoming popular. Other drugs include yohimbine, papaverine, and alprostadil. Methods to promote coitus and/or ejaculation could also be used; these include implantable penile prostheses or vibrator stimulation.
- Fecal incontinence: Patients may require use of stool softener or manual evacuation.
- Heterotopic ossification: Heterotropic ossification (HO) can be confirmed by a triple-bone scan with associated elevated alkaline phosphatase and phosphate, especially in the early stage. Treatment includes stretching exercises, disodium etidronate, radiation, and surgical excision. Surgery is done only when the HO has matured or stabilized, which is evident by stable plain x-ray, normal alkaline phosphatase level, and decline in triple-phase bone scan activity.
Pain should be treated appropriately based on its origin; treatment may include narcotics in the acute setting and tricyclic antidepressants later. Patient education, biofeedback, and relaxation techniques may also be used.
Use of orthoses is advised to prevent contractures. Use of antispasticity medications also is encouraged. Other medications include dantrolene, diazepam, clonidine, and tizanidine. Nerve blocks also could be done to relieve spasticity; appropriate agents include phenol, botulinum toxin, or local anesthetics.
In acute compression of the conus medullaris or cauda equina, surgical decompression as soon as possible (preferably within 6 h of injury) becomes mandatory. In a more chronic presentation with less severe symptoms, decompression could be performed when medically feasible and should be delayed to optimize the patient's medical condition; with this precaution, decompression is less likely to lead to irreversible neurological damage.
Surgical treatment may be necessary for decompression or tumor removal, especially if the patient presents with acute onset of symptoms.
Surgical treatment may include any of the following:
- Laminectomy and instrumentation/fusion for stabilization
- Other surgical care may entail wound care, eg, debridement, skin graft, and skin flap/myocutaneous flap.
The rehabilitation team, especially the spinal cord injury rehabilitation physician and occupational and physical therapists, should be involved as soon as possible.
This entails setting goals in the rehabilitation unit toward maintaining and improving endurance, with the ability to be independent in activities of daily living on discharge from the hospital or long-term care facility.
The rehabilitation goals are to maximize the medical, physical, psychological, educational, vocational, and social function of the patient.
This involves the following rehabilitation modalities:
Further care includes the following:
- Medical Ensure adequate prevention and treatment of possible medical complications already discussed, especially deep venous thrombosis, bladder and bowel problems, and decubitus ulcers
- Physical therapy Range of motion and strengthening exercises, sitting balance, transfer training, and tilt table as tolerated (because of tendency to orthostatic hypotension). Tilt table should start at 15 degrees, progressing by 10 degrees every 15 minutes up to about 80 degrees with the necessary precautions. Other activities include wheelchair propulsion training, standing table exercises, functional electrical stimulation for increased muscle tone, use of lower extremity orthoses to aid balance and walking, along with ambulation exercises, family training and community skills, and a home exercise program.
- Occupational therapy - Wheelchair training, especially for advanced wheelchair activities; transfer training; activities of daily living program with assistive devices for dressing, feeding, grooming, bathing, and toileting; motor coordination skills training; shower program; upper extremities training to increase strength for the increased demands of wheelchair propulsion and walking with assistive devices; home evaluation; family training; and a home exercise program.
- Orthotic/assistive devices - May be needed for functional household ambulation and, if possible, community ambulation. This entails prescribing and training in proper use of knee-ankle-foot orthoses (KAFO) with forearm crutches for support; for lower lesions, KAFOs or AFOs with canes or crutches may be needed. In addition to the above, bathtub bench, transfer boards, pressure-relieving seats, and wheelchairs are devices that may be needed. The patient should be assessed for these needs prior to discharge from the acute rehabilitation setting.
- Rehabilitation - Physical therapy and occupational therapy for muscle strengthening, endurance, mobility, activities of daily living, gait/balance, use of assistive devices, and adaptation to home environment
- Surgical follow-up for postoperative spinal care, depending on the cause
- Urology4 - Cystometrography to define bladder pathology (Patients should undergo regular follow-up on discharge for any renal or bladder complications and impotence, because they have an increased tendency for recurrent urinary tract infection and calculi.)
Further Outpatient Care
Follow-up with the rehabilitation team, including the spinal cord injury rehabilitation physician, physical therapist, and occupational therapist. These professionals are responsible for monitoring community and home integration and following improvements in the patient's strength, coordination, transfer, activities of daily living, and ambulation.
- Follow-up with consulting physicians within a week after discharge
- Follow-up with a primary care physician to monitor posthospital medications and other laboratory tests
- Yearly cystoscopy for patients with suprapubic catheters to help detect early bladder malignancies
- Regular follow-up urodynamic studies, renal ultrasound, and general cancer screening
Inpatient & Outpatient Medications
This includes continuation of anticoagulation medications (if necessary), antispasticity medications, and other medications being given to ameliorate possible complications, including bladder and bowel problems and heterotopic ossifications. If a patient is on warfarin, one of the team physicians looking after the patient must be designated to monitor the international normalized ratio (INR) at regular intervals.
Complications include the following:
- Thromboembolic phenomena
- Neurogenic bladder/bowel
- Erectile dysfunction
- Pressure ulcers
- Heterotopic ossification
- Chronic neuropathic pain
- Recurrent urinary tract infections
- Urethral stricture
- Bladder calculi
Prognosis can be predicted based on the ASIA impairment scale.
- ASIA A: Ninety percent of patients remain neurologically complete and unable to have functional ambulation.
- ASIA B: Seventy-two percent of patients are unable to attain functional ambulation.
- ASIA C/D: Thirteen percent are unable to attain functional ambulation (reciprocal gait of 200 feet or more) 1 year after injury.
Ambulatory motor index also is used to predict ambulatory capability, it is calculated using a 4-point scale (0=absent, 1=trace/poor, 2=fair, 3=good or normal) and then calculating hip flexion, hip abduction, hip extension, knee extension, and knee flexion on both sides; the score is expressed as a percentage of the maximum score of 30.
- A score of 60% or more shows a good chance for community ambulation with no more than one knee-ankle-foot orthosis (KAFO).
- A patient with a score of 79% or higher may not need an orthosis.
- A patient with a score of 40% or less may require 2 KAFOs for community ambulation.