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Cauda Equina and Conus Medullaris Syndromes

Author: Segun T Dawodu, MD, JD, MBA, LLM, FAAPMR, FAANEM; Chief Editor: Nicholas Lorenzo, MD,CPE more...

Updated: Mar 6, 2013

Background

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 asthe filum terminale. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like inappearance and hence called the cauda equina (Latin for horse's tail). (See the image of cauda equina anatomybelow.)

Illustration demonstrating the relevant anatomy of the cauda equina region

These nerve roots constitute the anatomic connection between the central nervous system (CNS) and theperipheral nervous system (PNS). They are arranged anatomically according to the spinal segments from whichthey originated and are within the cerebrospinal fluid (CSF) in the subarachnoid space with the dural sac ending atthe level of second sacral vertebra.

Cauda equina syndrome refers to a characteristic pattern of neuromuscular and urogenital symptoms resultingfrom the simultaneous compression of multiple lumbosacral nerve roots below the level of the conus medullaris(see the image below). These symptoms include low back pain, sciatica (unilateral or, usually, bilateral), saddlesensory disturbances, bladder and bowel dysfunction, and variable lower extremity motor and sensory loss (seeClinical).

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Although the lesion is technically involves nerve roots and represents a "peripheral" nerve injury, damage may be

irreversible and cauda equina syndrome may be a surgical emergency (see Treatment).[1]

Illustration demonstrating an example of cauda equina syndrome secondary to a spinal neoplasm

Lesions involving the termination of the spinal cord (conus medullaris) are not discussed in this article. Please seethe article Spinal Cord Injuries.

Anatomy

The spinal cord, which is the downward continuation of medulla that starts just below the foramen magnum, servesas a conduit for the ascending and descending fiber tracts that connect the peripheral and spinal nerves to thebrain. The cord projects 31 pairs of spinal nerves on either side (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1coccygeal) that are connected to the peripheral nerves.

A cross-section of the spinal cord reveals butterfly-shaped gray matter in the middle, surrounded by white matter.As in the cerebrum, the gray matter is composed of cell bodies. The white matter consists of various ascendingand descending tracts of myelinated axon fibers, each with specific functions.

During development, the vertebral column grows more rapidly than the spinal cord. Spinal nerves exit the vertebralcolumn at progressively more oblique angles because of the increasing distance between the spinal cordsegments and the corresponding vertebrae. Lumbar and sacral nerves travel nearly vertically down the spinal canalto reach their exiting foramen.

The spinal cord ends at the intervertebral disc between the first and second lumbar vertebrae as a taperedstructure called the conus medullaris, consisting of sacral spinal cord segments. The upper border of the conusmedullaris is often not well defined. The fibrous extension of the cord, the filum terminale, is a nonneural elementthat extends down to the coccyx.

The cauda equina (CE) is a bundle of intradural nerve roots at the end of the spinal cord, in the subarachnoidspace distal to the conus medullaris. Cauda is Latin for tail, and equina is Latin for horse (ie, the "horse's tail").The CE provides sensory innervation to the saddle area, motor innervation to the sphincters, and parasympatheticinnervation to the bladder and lower bowel (ie, from the left splenic flexure to the rectum).

The nerves in the CE region include lower lumbar and all of the sacral nerve roots. The pelvic splanchnic nervescarry preganglionic parasympathetic fibers from S2-S4 to innervate the detrusor muscle of the urinary bladder.Conversely, somatic lower motor neurons from S2-S4 innervate the voluntary muscles of the external analsphincter and the urethral sphincter via the inferior rectal and the perineal branches of the pudendal nerve,respectively.

Hence, the nerve roots in the CE region carry sensations from the lower extremities, perineal dermatomes, andoutgoing motor fibers to the lower extremity myotomes.

The conus medullaris obtains its blood supply primarily from 3 spinal arterial vessels: the anterior medianlongitudinal arterial trunk and 2 posterolateral trunks. Less prominent sources of blood supply include radiculararterial branches from the aorta, lateral sacral arteries, and the fifth lumbar, iliolumbar, and middle sacral arteries.

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The latter contribute more to the vascular supply of the cauda equina, although not in a segmental fashion, unlikethe blood supply to the peripheral nerves.

The nerve roots may also be supplied by diffusion from the surrounding CSF. Moreover, a proximal area of thenerve roots may have a zone of relative hypovascularity.

Pathophysiology

In understanding the pathological basis of any disease involving the conus medullaris, keep in mind that thisstructure 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 caudaequina lesion is an LMN lesion because the nerve roots are part of the PNS.

Cauda equina syndrome may result from any lesion that compresses CE nerve roots. These nerve roots areparticularly susceptible to injury, since they have a poorly developed epineurium. A well-developed epineurium, asperipheral nerves have, protects against compressive and tensile stresses.

The microvascular systems of nerve roots have a region of relative hypovascularity in their proximal third. Increasedvascular permeability and subsequent diffusion from the surrounding cerebral spinal fluid supplement the nutritionalsupply. This property of increased permeability may be related to the tendency toward edema formation of thenerve roots, which may result in edema compounding initial and sometimes seemingly slight injury.

Several studies in different animal models have assessed the pathophysiology of cauda equina syndrome.[2, 3]

Olmarker et al, using a graded balloon pressure method in a porcine model, reported that the venules in the CEregion begin to compress at a pressure as low as 5 mm Hg and the arterioles begin to occlude as the balloon

pressure surpasses the mean arterial pressure.[4, 5, 6, 2, 7] Despite this, even a pressure as high as 200 mm Hgfailed to completely shut off nutritional supply to the CE.

These studies showed that not only the magnitude but also the length and the speed of obstruction were also

important in damaging the CE region.[8] Similar results were reported in other studies. Takahashi et al reported areduction in blood flow to the intermediate nerve segment when 2 pressure points were applied along the path of

the nerve in the CE.[9]

Others have studied compound action potentials in afferent and efferent segments of nerves in the CE region after

application of balloon compression.[10, 11, 12] These researchers reported that 0-50 mm Hg of pressure did notaffect the action potentials (the threshold for disturbances in action potentials was 50-75 mm Hg), and significantdeficits were observed when pressure rose to 100-200 mm Hg.

Etiology

Cauda equina syndrome is caused by any narrowing of the spinal canal that compresses the nerve roots below the

level of the spinal cord.[13] Numerous causes of cauda equina syndrome have been reported, including discherniation, intradural disc rupture, spinal stenosis secondary to other spinal conditions, traumatic injury, primarytumors such as ependymomas and schwannomas, metastatic tumors, infectious conditions, arteriovenous

malformation or hemorrhage, and iatrogenic injury.[13, 14]

The most common causes of cauda equina and conus medullaris syndromes are the following:

Lumbar stenosis (multilevel)

Spinal trauma including fractures[15]

Herniated nucleus pulposus (cause of 2-6% of cases of cauda equina syndrome)[16, 17, 18]

Neoplasm, including metastases, astrocytoma, neurofibroma, and meningioma; 20% of all spinal tumorsaffect this areaSpinal infection/abscess (eg, tuberculosis, herpes simplex virus, meningitis, meningovascular syphilis,

cytomegalovirus, schistosomiasis)[19]

Idiopathic (eg, spinal anesthesia[20] ): these syndromes may occur as complications of the procedure or of

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the anesthetic agent (eg, hyperbaric lidocaine, tetracaine)

Spina bifida and subsequent tethered cord syndrome[21]

Other, rare causes include the following:

Spinal hemorrhage, especially subdural and epidural hemorrhage causing compression within the spinalcanalIntravascular lymphomatosisCongenital anomalies of the spine/filum terminale, including tethered cord syndromeConus medullaris lipomasMultiple sclerosisSpinal arteriovenous malformationsLate-stage ankylosing spondylitisNeurosarcoidosisDeep venous thrombosis of the spinal veins (propagated)

Inferior vena cava thrombosis[22]

A retrospective study of 66 consecutive cases of patients admitted to a neurosurgical unit with suspected cauda

equina syndrome found that almost half had no evidence of structural pathology on MRI.[23] These researcherssuggested that the symptoms have a functional origin in such cases.

Trauma

Traumatic events leading to fracture or subluxation can lead to compression of the cauda equina.[15, 24, 25, 26, 27]

Penetrating trauma can cause damage or compression of the cauda equina. Spinal manipulation resulting in

subluxation has caused cauda equina syndrome.[28] Rare cases of sacral insufficiency fractures have been

reported to cause cauda equina syndrome.[29] Acute and delayed presentations of CES due to hematomas and

posttraumatic arachnoid cysts have also been reported.[30, 31, 32]

Herniated disk

The reported incidence of cauda equina syndrome resulting from herniated lumbar disk (see the image below)

varies from 1-15%.[33, 34, 18] Ninety percent of lumbar disk herniations occur either at L4-L5 or L5-S1.[35, 36]

Sagittal MRI of a patient w ith cauda equina syndrome secondary to a large lumbar disk herniation

Of cases of herniated disks leading to cauda equina syndrome, 70% occur in patients with a history of chronic low

back pain; in 30%, cauda equina syndrome is the first symptom of lumbar disk herniation.[17] Men in the fourth

and fifth decades of life are most prone to cauda equina syndrome secondary to disk herniation.[37]

Most cases of cauda equina syndrome secondary to disk herniation involve either a large central disc or an

extruded disc fragment that compromises a significant amount of the spinal canal diameter.[38] The presentation

may be acute or that of a more protracted course, with the latter bearing a better prognosis.[34] Individuals withcongenital stenosis who sustain a disk herniation are more likely to develop cauda equina syndrome because even

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a small herniation can drastically limit the space available for the nerve roots.

Rare cases of intradural disk herniations have been reported to cause cauda equina syndrome.[39] Myelography inthese instances typically demonstrates a complete block of the contrast material. If an intradural disc fragment isidentified, transdural removal of the extruded disc fragment may be helpful to prevent further stretching of thealready compromised nerve root.

Spinal stenosis

Narrowing of the spinal canal can be due to a developmental abnormality or degenerative process. Althoughunusual, cauda equina syndrome from spinal stenosis secondary to spinal disorders such as ankylosing

spondylitis, spondylosis, and spondylolisthesis have all been reported.[40, 41, 42, 43, 44, 45, 46]

Neoplasms

Cauda equina syndrome can be caused by primary or metastatic spinal neoplasms. Among the primary tumorsable to cause CES include myxopapillary ependymoma, schwannoma, and paraganglioma.

Myxopapillary ependymoma is the most common tumor of the filum. Recovery of the function after surgery

depends on the duration of symptoms and the presence or absence of sphincter dysfunction[47] Paraganglioma of

the filum, when present, needs to be differentiated from other tumors of this region.[48] Although rare, this entitymay present as CES.

Schwannomas are benign encapsulated neoplasms that are structurally identical to a syncytium of Schwann

cells.[49] These growths may arise from peripheral or sympathetic nerves. Schwannomas, whether solitary or as apart of a syndrome, may cause CES if present at the level of the conus or filum terminale. Primary tumors thataffect the sacrum, such as chordoma and giant cell tumor of the bone, may produce similar symptoms as a result

of bony destruction and collapse.[50]

Ependymomas are gliomas derived from relatively undifferentiated ependymal cells. They often originate from thecentral canal of the spinal cord and tend to be arranged radially around blood vessels. Ependymomas are foundmost commonly in patients aged approximately 35 years. They can lead to increased intracranial pressure (ICP),and cerebrospinal fluid (CSF) has an increased protein level.

Metastatic lesions of the spine are being reported with increasing frequency because of earlier diagnosis, betterimaging, and more effective treatment modalities. Although metastasis accounts for most tumors in the spine ingeneral, metastatic tumors in the cauda equina are relatively rare compared with primary tumors.

For the spine in general, sources of spinal metastases are as follows[51] :

Lung cancer (40-85%)Breast cancer (11%)Renal cell carcinoma (4%)Lymphatic cancer (3%)Colorectal cancer (3%)

Although lung cancer is the most common source of spine metastases, in one study, only 0.7% of the lungcancer metastases to the spine produced cauda equina syndrome; most of the metastatic lesions were not at the

level of the cauda equina.[51] Up to 8% of patients with prostate cancer experience malignant spinal cord

compression; however, the percentage of cases involving cauda equina syndrome is unknown.[52]

The CE region is also a favored site for drop metastases from intracranial ependymoma, germinoma, and other

tumors.[53] Other unusual metastatic spread from genitourinary and gynecologic cancer have also been reported at

the conus region, causing neurological compromise.[54, 55]

Inflammatory and infectious conditions

Long-lasting inflammatory conditions of the spine, including Paget disease and ankylosing spondylitis, can lead to

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cauda equina syndrome secondary to spinal stenosis or fracture.

Infectious conditions, including epidural abscess, can lead to deformity of the nerve roots and spinal cord.[56]

Symptoms generally include severe back pain and a rapidly progressing motor weakness.

Infectious causes for cauda equina syndrome may be pyogenic or nonpyogenic. Pyogenic abscesses aregenerally found in an immunocompromised or poorly nourished host. Staphylococcus aureus causes epiduralabscesses in 25-60% of cases, but, recently, an increasing incidence of infections with methicillin-resistant Saureus, Pseudomonas species, and Escherichia coli have been recorded. A high index of suspicion is helpful in

correct diagnosis and management.[56]

Nonpyogenic causes for abscess are rare and include tuberculosis. Resurgence of tuberculosis secondary toimmunocompromise in individuals with HIV infection requires a high index of suspicion, as the development of

cauda equina syndrome may follow an indolent course.[57] Other uncommon organisms, such as Nocardiaasteroides and Streptococcus milleri, have also been reported as a cause of abscess that leads to the

development of CES.[58, 59]

Iatrogenic causes

Complications of spinal instrumentation have been reported to cause cases of cauda equina syndrome, including

misplaced pedicle screws[60] and laminar hooks.[61, 62] Continuous spinal anesthesia also has been linked to

cases of cauda equina syndrome.[63]

Rare cases of cauda equina syndrome caused by epidural steroid injections, fibrin glue injection,[64] and

placement of a free-fat graft have been reported.[65]

Several cases have involved the use of hyperbaric 5% lidocaine for spinal anesthesia. Recommendations are thathyperbaric lidocaine not be administered in concentrations greater than 2%, with a total dose not to exceed 60

mg.[66, 67]

Medical and surgical situations such as bone screw fixation, fat grafts, lumbar arthrodesis for spondylolisthesis,lumbar discectomy, intradiscal therapy, lumbar puncture forming an epidural hematoma, chiropractic manipulation,and a bolus injection of anesthetic during spinal anesthesia have been related to the development of cauda equina

syndrome–like syndromes.[34, 68, 69, 70, 71, 72]

Epidemiology

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 cordinjury.

Cauda equina syndrome is uncommon, both atraumatically as well as traumatically. It is often reported as a casereport due to its rarity. Although infrequent, it is a diagnosis that must be considered in patients who complain oflow back pain coupled with neurologic complaints, especially urinary symptoms.

Age-related differences in incidence

Traumatic cauda equina syndrome is not age specific. Atraumatic cauda equina syndrome occurs primarily inadults as a result of surgical morbidity, spinal disk disease, metastatic cancer, or epidural abscess.

Prognosis

Morbidity and especially mortality rates are determined by the underlying etiology. Multiple conditions can result incauda equina or conus medullaris syndrome. The prognosis improves if a definitive cause is identified andappropriate treatment occurs early in the course. Surgical decompression may be performed emergently, or, insome patients, delayed, depending on the etiology. Residual weakness, incontinence, impotence, and/or sensory

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abnormalities are potential problems if therapy is delayed.

Investigators have attempted to identify specific criteria that can aid in predicting the prognosis of patients withcauda equina syndrome. Patients with bilateral sciatica have been reported to have a less favorable prognosis thanpatients with unilateral pain. Patients with complete perineal anesthesia are more likely to have permanent

paralysis of the bladder.[38]

The extent of perineal or saddle sensory deficit has been reported to be the most important predictor of recovery.[73] 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.[74]

Prognosis can be predicted with the American Spinal Injury Association (ASIA) impairment scale (see PhysicalExamination ), as follows:

ASIA A: 90% of patients remain incapable of functional ambulation (reciprocal gait of 200 feet or more)ASIA B: 72% of patients are unable to attain functional ambulationASIA C/D: 13% are unable to attain functional ambulation 1 year after injury

Ambulatory motor index also is used to predict ambulatory capability. It is calculated by scoring hip flexion, hipabduction, hip extension, knee extension, and knee flexion on both sides, using a 4-point scale (0=absent,1=trace/poor, 2=fair, 3=good or normal); the score is expressed as a percentage of the maximum score of 30.Prognostic significance is as follows:

A patient with a score of 60% or more has a good chance for community ambulation with no more than oneknee-ankle-foot orthosis (KAFO)A patient with a score of 79% or higher may not need an orthosisA patient with a score of 40% or less may require 2 KAFOs for community ambulation

Patient Education

Patient education needs will vary with the type and severity of persistent deficits, and may include the following:

Training in self-catheterization and finger fecal disimpaction, if requiredUse of measures to prevent pressure ulcers, such as skin inspection/care, positioning, turning andtransferring tactics, use of skin protectors, or pressure-reducing support surfacesMaintenance of endurance and strength-training exercisesRegular follow-up by the consulting teams who treated the patient in the hospitalInstructions on how and when medications should be taken and when follow-up laboratory tests should beperformed

For patient education information, see the Erectile Dysfunction Center and Brain and Nervous System Center, aswell as Impotence/Erectile Dysfunction, Erectile Dysfunction FAQs, and Cauda Equina Syndrome.

Contributor Information and DisclosuresAuthorSegun T Dawodu, MD, JD, MBA, LLM, FAAPMR, FAANEM Associate Professor of Rehabilitation Medicineand Interventional Pain Medicine, Albany Medical College

Segun T Dawodu, MD, JD, MBA, LLM, FAAPMR, FAANEM is a member of the following medical societies:American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular andElectrodiagnostic Medicine, American College of Sports Medicine, American Medical Association, AmericanMedical Informatics Association, Association of Academic Physiatrists, International Society of Physical andRehabilitation Medicine, and Royal College of Surgeons of England

Disclosure: Nothing to disclose.

Coauthor(s)Kirsten A Bechtel, MD Associate Professor, Department of Pediatrics, Yale University School of Medicine;

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Attending Physician, Department of Pediatric Emergency Medicine, Yale-New Haven Children's Hospital

Kirsten A Bechtel, MD is a member of the following medical societies: American Academy of Pediatrics

Disclosure: Nothing to disclose.

Michael S Beeson, MD, MBA, FACEP Professor of Emergency Medicine, Northeastern Ohio UniversitiesCollege of Medicine and Pharmacy; Attending Faculty, Akron General Medical Center

Michael S Beeson, MD, MBA, FACEP is a member of the following medical societies: American College ofEmergency Physicians, Council of Emergency Medicine Residency Directors, National Association of EMSPhysicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Scott D Hodges, DO Consulting Surgeon, Department of Orthopedic Surgery, Center for Sports Medicine andOrthopedics

Scott D Hodges, DO is a member of the following medical societies: American Academy of DisabilityEvaluating Physicians, American Medical Association, American Osteopathic Association, American SpinalInjury Association, North American Spine Society, Southern Medical Association, Southern OrthopaedicAssociation, and Tennessee Medical Association

Disclosure: Medtronic Royalty Consulting; Biomet Spine Royalty Consulting

S Craig Humphreys, MD Orthopedic Spine Surgeon, Department of Orthopedic Surgery, Center for SportsMedicine and Orthopedics

S Craig Humphreys, MD is a member of the following medical societies: Alpha Omega Alpha, AmericanAcademy of Orthopaedic Surgeons, American Medical Association, American Spinal Injury Association, NorthAmerican Spine Society, Southern Medical Association, Southern Orthopaedic Association, and TennesseeMedical Association

Disclosure: Nothing to disclose.

James F Kellam, MD Vice-Chair, Department of Orthopedic Surgery, Director of Orthopedic Trauma andEducation, Carolinas Medical Center

James F Kellam, MD is a member of the following medical societies: American Academy of OrthopaedicSurgeons, Orthopaedic Trauma Association, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Specialty Editor BoardMilind J Kothari, DO Professor, Department of Neurology, Pennsylvania State University College of Medicine;Consulting Staff, Department of Neurology, Penn State Milton S Hershey Medical Center

Milind J Kothari, DO is a member of the following medical societies: American Academy of Neurology,American Association of Neuromuscular and Electrodiagnostic Medicine, and American NeurologicalAssociation

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical CenterCollege of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

J Stephen Huff, MD Associate Professor of Emergency Medicine and Neurology, Department of Emergency

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Medicine, University of Virginia School of Medicine

J Stephen Huff, MD is a member of the following medical societies: American Academy of EmergencyMedicine, American Academy of Neurology, American College of Emergency Physicians, and Society forAcademic Emergency Medicine

Disclosure: Nothing to disclose.

Chief EditorNicholas Lorenzo, MD, CPE Chairman and CEO, Neurology Specialists and Consultants; Senior VicePresident, Founding Executive Director, Continuing Medical Education, Gannett Education (Division GannettHealthcare Group)

Nicholas Lorenzo, MD, CPE is a member of the following medical societies: Alpha Omega Alpha, AmericanAcademy of Neurology, and American College of Physician Executives

Disclosure: Nothing to disclose.

Additional ContributorsThe authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authorJason C Eck, DO, MS,to the development and writing of a source article.

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