Summary of Key Points
- •
For a diagnosis of cauda equina syndrome (CES), one or more of the following must be present: (1) bladder or bowel dysfunction, (2) reduced sensation in the saddle area, or (3) sexual dysfunction, with possible neurologic deficit in the lower limb (motor/sensory loss, reflex change).
- •
Mechanical or ischemic compromise of two or more spinal nerve roots below the conus medullaris generally leads to the clinical manifestations associated with CES.
- •
Acute/chronic CES is often challenging to diagnose: (1) CES may present as a combination of various nonspecific signs and symptoms and (2) side effects of certain medications (e.g., opioids promoting urinary retention or other nonspinal or nonurgent spinal pathologies) can manifest with similar clinical findings as CES.
- •
Although CES is an uncommon condition (7 per 100,000 individuals) most often resulting from a prolapsed herniated intervertebral lumbar disc (up to 6% of surgically treated prolapse discs), it is associated with a high likelihood of permanent neurologic sequelae, which may dreadfully impact quality of life.
- •
Patients with a clinical history and physical examination compatible with a diagnosis of CES should undergo lumbar magnetic resonance imaging, which is the radiologic imaging technique of choice.
- •
Correlation between preoperative clinical features, such as severity of somatic signs and symptoms, symptom duration before surgical decompression, the size and location of disc herniation, and postoperative outcomes (i.e., improvement of pain, motor, and sensory radiculopathy and autonomic functions), are variable.
- •
CES is associated with a disproportionately high medicolegal profile given its relatively low incidence.
- •
Physicians must maintain a high index of suspicion for the diagnosis of CES.
- •
Patients with suspected CES should be promptly managed by undergoing rapid radiologic evaluation; if CES is confirmed, surgical spinal decompression should be performed on an urgency basis.
Definition and Clinical Significance
Cauda equina syndrome (CES) results from a neuropathy of two or more nerve roots within the spinal canal below the conus medullaris and may present with the following typical red flags: unilateral/bilateral pain radiculopathy, saddle anesthesia ( Fig. 95-1 ) or genital sensory disturbance; bladder or bowel incontinence, and lower extremity weakness ( Table 95-1 ). However, CES is often challenging to diagnose. In fact, CES is associated with numerous traumatic and nontraumatic etiologies and conditions ( Table 95-2 ) that give rise to a plethora of nonspecific signs and symptoms and subtleties of clinical presentations that vary according to the anatomic location (lumbar, sacral, or coccygeal regions), rapidity, duration, specific combination of spinal nerve roots (L1 to S5) of the cauda equina affected, individual differences, and confounding factors related to medications, or other nonspinal or spinal pathologies. For instance, whereas motor weakness can involve L1 to S5 nerve roots, hypoesthesia or complete anesthesia is often present in the dermatomal distribution of L3 to Coc1, inclusive.
| Types of Cauda Equina Syndrome (CES) | Definition | Most Common Associated Clinical Features (seen in all 3 tpes) |
|---|---|---|
| Early CES (CESE) | Patient has unilateral/bilateral progressive motor/sensory radiculopathy in the lower extremities |
|
| Incomplete CES (CESI) | Patient has urinary difficulties:
| |
| Complete CES (CESR) | Painless urinary retention and overflow incontinence |
| Category | Examples |
|---|---|
| Vascular |
|
| Inflammatory |
|
| Neoplastic |
|
| Infectious |
|
| Congenital |
|
| Anatomic/degenerative |
|
| Trauma |
|
| Biochemical | Paget disease |
| Iatrogenic |
|
CES is rare: incidence rates ranging from 1 in 33,000 to 1 in 100,000 have been reported. In a retrospective study that involved one of the largest cohorts of patients studied to date, it was concluded that the overall incidence of CES was 7 per 100,000 individuals. However, the actual occurrence of CES is difficult to estimate partly due to the fact that there is not a single universally accepted clinical definition. In their literature review, Fraser and colleagues identified 17 distinct definitions for CES and thus proposed: “For a diagnosis of CES, one or more of the following must be present: (1) bladder or bowel dysfunction, (2) reduced sensation in the saddle area, or (3) sexual dysfunction, with possible neurologic deficit in the lower limb (motor/sensory loss, reflex change).” Prompt recognition and treatment of patients with CES is imperative to avoid both (1) permanent debilitating neurologic deficits, which is associated with considerable socioeconomic burden, and (2) medicolegal consequences related to delayed diagnosis and management.
Pathophysiology
Mechanical or ischemic compromise of the spinal nerve roots is thought to be responsible for the clinical manifestations characterizing CES. Spinal nerve root compression commonly occurs in conditions such as acute herniated disc, spinal stenosis, trauma (e.g., burst fractures), metastatic or primary tumors of the spine, or spinal infections (e.g., epidural abscess) (see Table 95-2 ). Acute CES most commonly presents secondary to lumbosacral intervertebral disc prolapse ( Fig. 95-2 ). Generally, mechanical compression physically deforms and or disturbs the microcirculation of the nerve fibers leading to ischemia and the formation of intraneural edema. However, the pathophysiology of the signs and symptoms related to spinal nerve root compression remains poorly defined.
Several experimental studies have assessed the pathophysiologic mechanisms of CES. Delamarter and associates developed an animal model of CES, subjecting 30 beagle dogs to L6-7 laminectomy and cauda equina compression. Neurologic recovery was assessed in animals undergoing 75% constriction of the cauda equina followed by immediate, early, or delayed decompression. The first group was constricted and immediately decompressed. The remaining groups were constricted for 1 hour, 6 hours, 24 hours, and 1 week, respectively, before being decompressed. Evoked potentials were measured before and after surgery, before and after decompression, and 6 weeks after decompression. Six weeks after decompression, all dogs were sacrificed, and the neural elements were analyzed histologically. After compression, all 30 dogs had significant lower extremity weakness, tail paralysis, and urinary incontinence. All dogs recovered significant motor function by 6 weeks after decompression. The dogs with immediate decompression typically recovered neurologic function within 2 to 5 days. The dogs receiving 1- and 6-hour compression recovered within 5 to 7 days. Dogs receiving 24 hours of compression remained paraparetic for 5 to 7 days, with bladder dysfunction persisting for 7 to 10 days and tail dysfunction for up to 4 weeks. The dogs with compression for 1 week were paraparetic and incontinent for the duration of cauda equina compression. They recovered the ability to walk by 1 week and regained bladder and tail control by the time of euthanasia. Delamarter and coworkers demonstrated axoplasmic flow blockade and Wallerian degeneration of the motor nerve roots distal to the constriction and of the sensory roots proximal to the site of constriction, as well as dorsal column degeneration. Severe arterial narrowing occurred at the level of the constriction with venous congestion of the roots and dorsal root ganglia of the seventh lumbar and first sacral nerves. Evoked potential monitoring was the most sensitive predictor of neural compression, revealing neurologic abnormalities before the appearance of neurologic signs and symptoms. Cystometrograms were not sensitive until severe compression was achieved. Bladder dysfunction was correlated with axoplasmic flow blockade and early sensory changes during neurovenous congestion.
Olmarker and colleagues developed an experimental model of acute, graded compression of the cauda equina in pigs that accurately mimics the neural and vascular anatomy of human cauda equina. There were structural and vascular differences between spinal nerve roots and peripheral nerves that could contribute to differences in compression susceptibility between these two parts of the nervous system. Pressure transmission from the balloon to the nerve roots permitted determination of occlusion pressures for the arterioles, capillaries, and venules of the cauda equina. Arteriolar blood flow ceased when the applied pressure approached the mean arterial blood pressure. Compression up to 200 mm Hg for 2 hours did not induce a no-reflow phenomenon upon compression release. However, transient hyperemia was noted at all pressure-time relations studied, indicating nutritional deficit in the compressed segment during compression. Signs of edema were observed in nerve roots exposed to compression for 2 hours at either 50 or 200 mm Hg. The nutritional supply to the cauda equina was impaired at low pressure levels (< 10 mm Hg). Thus, diffusion from adjacent tissues with a better nutritional supply, including cerebrospinal fluid, could not compensate completely for compression-induced effects on the transport of nutrients. A rapid compression rate resulted in more pronounced effects on the nutritional supply than did a slow compression rate. Nutritional impairment was observed both within and outside the compressed nerve segment. An increase in vascular permeability was induced by compression at 50 mm Hg for 2 minutes. The magnitude of this permeability increase was dependent on both the magnitude and the duration of compression. The permeability increase was more pronounced for the rapid compression onset rate than for the slow compression onset rate at all pressure-time relations studied. Overall, mechanical compression of the spinal nerve roots has been shown to impede nutrient delivery via decreased blood flow and nutrient diffusion from the cerebrospinal fluid.
Pedowitz and coworkers and Rydevik and associates presented an experimental model of compression-induced functional changes of the porcine cauda equina that permits electrophysiologic investigation of the neurophysiologic changes induced by nerve root deformation. In several studies, they compared the effects of various pressures and durations of acute compression on spinal nerve root conduction in the pig cauda equina. Changes in both afferent (compound nerve action potentials) and efferent (compound motor action potentials) conduction were induced at an acute pressure threshold of 50 to 75 mm Hg. Higher compression pressures produced a differential recovery in afferent and efferent conduction. Efferent conduction and afferent conduction were monitored during compression for 2 or 4 hours with compression pressures of 0 (sham treatment), 50, 100, or 200 mm Hg. Recovery was monitored for 1.5 hours. No significant deficits in spinal nerve root conduction were observed with 0 or 50 mm Hg compression, whereas significant deficits were induced by 100 and 200 mm Hg compression. Variance analysis demonstrated significant effects of compression pressure and duration on conduction, with a significant difference between efferent and afferent conduction at the end of the recovery period, suggesting a synergistic interaction between biomechanical and microvascular mechanisms in the production of nerve root conduction deficits.
Compression of the spinal nerve roots often occurs at multiple levels simultaneously; however, the basic pathophysiology of multilevel compression is poorly defined. Using a thermal diffusion technique, Takahashi and colleagues quantitated intraneural blood flow in the uncompressed segment between two compressive balloons in the porcine cauda equina. At 10 mm Hg compression, there was a 64% reduction of total blood flow in the uncompressed segment compared with precompression values. Total ischemia occurred at pressures 10 to 20 mm Hg less than the mean arterial blood pressure. After two-level compression at 200 mm Hg for 10 minutes, there was a gradual recovery of the intraneural blood flow to the baseline level. Recovery was less rapid and less complete after 2 hours of compression. Double-level compression of the cauda equina induced blood flow impairment, not only at the sites of compression but also in the intermediate nerve segments located between two compression sites, even at very low pressures.
Neurogenic Bladder
Urinary control is a complex process involving several lower motor neuron reflex arcs that become disrupted in CES, leading to neurogenic bladder dysfunction. Parasympathetic fibers of S2-S3-S4 nerve roots, the main excitatory input to the bladder, promote bladder emptying by contracting the smooth muscles of the detrusor urinae and relaxing the internal sphincter while the sympathetic fibers from the hypogastric plexus (T11-L3, specifically the hypogastric nerves arising from L1-L2-L3) have the opposite effect. In addition, the pudendal nerves (S2-S3-S4) innervate the skeletal striated muscles of the external sphincter of the urethra (sphincter urethrae) as well as of the anus (sphincter ani externus). These two muscles are in a baseline state of constant tonic contraction. Thus, their excitatory state resulting in muscle relaxation, hence promoting micturition/defecation, is under voluntary control of the somatic nervous system. Sensory information from tension receptors and nociceptors of the bladder wall travel to the sacral segments of the spinal cord via the parasympathetic nerves and are essential for initiating micturition ( Table 95-3 ). Consequently, patients with CES typically present with a decreased/absent ability to (1) contract the detrusor, (2) relax both internal and external sphincters, and (3) feel the degree of bladder fullness, resulting in urinary retention, bladder distention, incomplete emptying (i.e., postvoid residual), and overflow incontinence.
| Principal Associated Clinical Deficits | Type of Nerve Fibers (Action) | ||
|---|---|---|---|
| Nerve roots | Sensory/Dermatomal Area | Motor (Osteotendinous Reflex) | |
| L2 | Mid-anterior thigh | Knee extension | Autonomic fibers (L2): |
| |||
| L3 | Lower anterior thigh | Knee extension | Autonomic fibers (L3): |
| |||
| L4 | Medial part lower leg | Ankle dorsiflexion (patellar reflex) | |
| L5 | Lateral part lower leg |
| |
| S1 | Lateral foot, heel, sole, and calf area | Foot plantar flexion (Achilles reflex and bulbocavernosus reflex 1 ) | |
| S2 | Higher calf area, popliteal fossa, and posterior thigh, perineum | Contraction of anal external sphincter (anal wink 2 and bulbocavernosus reflex 1 ) | Autonomic fibers (S2):
Somatic fibers (pudendal nerves):
|
| S3 | Perineum | Contraction of anal external sphincter (anal wink 2 and bulbocavernosus reflex 1 ) | Autonomic fibers (S3):
Somatic fibers (pudendal nerves):
|
| S4 | Perianal region | Contraction of anal external sphincter (anal wink 2 ) | Autonomic fibers (S4):
Somatic fibers (pudendal nerves):
|
| S5 | Perianal region | ||
1 Bulbocavernosus reflex (S1-S2-S3): Reflexive contraction of the external anal sphincter upon applying pressure to the clitoris or glans of the penis or traction on the Foley catheter.
2 Anal wink (i.e., anocutaneous reflex) (S2-S3-S4): Reflexive contraction of the external anal sphincter upon stimulation of the skin of the perianal area.
3 Pudendal nerve fibers (somatic): Sphincter urethrae and sphincter ani externus, both external sphincter composed of skeletal striated muscle under voluntary control, whose excitatory state promote micturition and defecation, respectively.
Cauda Equina Syndrome Secondary to Disc Herniation
Epidemiology
Since Mixter and Barr first postulated the relationship between lumbar disc herniation and radiculopathy in 1934, CES secondary to a large central disc herniation is still a relatively uncommon entity. However, it has a clinical importance that far exceeds its rarity. CES secondary to lumbar disc herniation is an absolute indication for surgical intervention. The incidence of CES has been estimated to range from 1.2% to 6%. The highest prevalence of herniated disc is typically at L4-L5-S1, and a female predominance has been repeatedly cited in the literature regarding CES due to a herniated disc.
Clinical Syndrome
Cauda equina injuries result in lower motor neuron neurophysiologic signs and symptoms, including diverse degrees of lower extremity motor/sensory deficits or decreased/absent deep tendon (osteotendinous) reflexes. CES can mimic the typical presentation of lumbar intervertebral disc herniation with low back pain and unilateral radiculopathy. However, back pain often predominates, and radicular symptoms may be minimal. Severe back pain, often out of proportion with the radicular pain, should alert the physician to a possible CES lesion and mandates periodic evaluation to exclude a progressive neurologic deficit. Accurate diagnosis may be delayed if the lesion is incomplete or evolving. CES often presents with abnormal radicular signs and can present as a lower motor neuron lesion, but it is not associated with upper motor neuron signs, as seen in lesions involving the conus medullaris.
Clinical presentation varies depending on the level and location of the disc herniation, as well as individual patients characteristics. For example, a central disc herniation, which does not need to be particularly large in patients with narrow spinal canal (e.g., congenital spinal stenosis), can compress several or all of the traversing cauda equina roots. An L5-S1 disc may cause CES without motor or sensory loss in the lower extremities. This scenario happens when the herniation is focally central and compresses the lower centrally located sacral nerve roots, serving bowel and bladder function, but leaves the S1 roots unaffected. If slowly progressive, large central disc herniations can also mimic the presentation of an intraspinal tumor. When compromised, the centrally placed sacral fibers to the lower abdominal/pelvic viscera produce the symptoms characterizing cauda equina compression, such as perianal numbness, saddle dysesthesia or anesthesia, and a loss of the anal reflex or diminished rectal tone. Difficulty with urination can develop relatively early in the clinical course. The onset of bladder and rectal paralysis with saddle anesthesia should be viewed with a high index of suspicion in any patient with backache and sciatica. In men, impotence can occur. This should be specifically addressed when gathering the patient’s history and clarified as to whether the impotence is pain mediated or neurologically (unable to obtain an erection) mediated. Most authors agree that an element of bladder dysfunction is required for the diagnosis of CES. Table 95-3 presents the key clinical functions of the spinal nerve roots of the cauda equina.
Clinical Course
Tay and Chacha reported eight cases observed over a 5-year period that fell into three clinical groups. The first group of patients noted sudden onset of symptoms without previous back problems. The second group noted recurrent episodes of backache and sciatica, with the most recent episode resulting in cauda equina involvement. The final group of patients had slowly evolving backache and sciatica that progressed to cauda equina paralysis. Disc prolapse occurred between the L5 and S1 vertebrae in 50% of the patients, most of whom had no limitation in straight-leg raising. Urgent myelography and disc removal within 2 weeks of symptom onset resulted in substantial recovery of motor and bladder function within 5 months after surgery. Sensory and sexual function recovery was incomplete for as long as 4 years postoperatively. Patients at the preclinical and early stages have better functional recovery than patients in later stages after surgical decompression.
Lafuente and colleagues noted sacral sparing and preservation of sphincter control in 8 of 14 cases of cauda equina compression from central lumbar disc herniation and postulated that the triangular shape of the lumbar spinal canal may be one factor for this constellation of findings, because the increase in linear strain on the stretched roots of the cauda equina is least in the more centrally placed lower sacral roots. Kostuik and coworkers identified two distinct modes of presentation. The first was an acute mode (in 10 patients) in which there was an abrupt onset of severe symptoms and signs and a slightly poorer prognosis after decompression, especially for the return of bladder function. The second mode of presentation (in 21 patients) had a more protracted onset, characterized by prior symptoms for varying time intervals before the gradual onset of CES. The prognosis for return of motor function was good. Of 30 patients receiving surgery, 27 regained normal motor function. All patients reported preoperative urinary retention. Bladder function was the most seriously affected function preoperatively and remained so postoperatively. Korse and associates reported that at presentation, the mean prevalence of micturition disturbance was 88.9% and the corrected mean prevalence of persistent dysfunction at a mean minimal postoperative follow-up of 17 months was 45.1% (total of 409 patients).
Gleave and MacFarlane reviewed 932 patients who underwent surgery for prolapsed lumbar intervertebral disc and identified a group of 33 with acute urinary retention. No identifiable factor predisposed this group of patients to CES. The mean duration of bladder paralysis before operation was 3.6 days. Ultimately, 79% of patients claimed full recovery of bladder function, but only 22% were left without sensory deficits in the limbs or perineum. There was no correlation between recovery and the duration of bladder paralysis before surgery, except in three patients in whom there was no sciatica and in whom the correct diagnosis was delayed for many days. Retention developing less than 48 hours after acute prolapse was associated with a worse prognosis. Later Gleave and MacFarlane distinguished CES into two stages: incomplete CES (CESI) and CES with retention (CESR), and Sun and colleagues divided the progression of CES into three stages: early stage of CES (CESE), with bilateral peripheral nerve dysfunction characterized by progressive motor/sensory deficits in the lower extremities; CESI, with diminished sphincter functions; and CESR, with severe sphincter impairment (see Table 95-1 ).
Severe saddle anesthesia was indicative of a poor prognosis, particularly for return of bladder and bowel function. However, any correlation of factors such as severity of somatic signs and symptoms, symptom duration before surgical decompression, and the size and location of disc protrusion with recovery of bowel and bladder function is still unclear. In their systematic review, Fairbank and colleagues reported that back pain and bowel incontinence had high sensitivities but low specificities as opposed to bilateral pain radiculopathy and reduced anal tone, which had low sensitivities but high specificities. Bladder incontinence/retention, decreased urinary sensation, frequent urination, and saddle dysesthesia had varying sensitivities and specificities. All of the latter signs and symptoms had low likelihood ratios.
Diagnostic Imaging
Diagnosis and treatment are often delayed because of lack of recognition of the condition and failure to appreciate the surgical imperative for its treatment. Once cauda equina compression is recognized or suspected based on patient history and physical examination, magnetic resonance imaging (MRI) is the investigation method of choice. CES was confirmed by MRI study in 14% to 48% of patients with clinical suspicion of CES. If an MRI is contraindicated, of poor quality because of motion artifact (patients with CES are often in severe pain), or unavailable, computed tomography (CT) myelography is recommended. CT alone can be misleading in cases of complete canal occlusion (see Fig. 95-2 ).
Surgical Therapy
Urgent surgical intervention should commence after diagnosis. A routine microdiscectomy interlaminar approach necessitates retraction on already severely compromised nerve roots. Furthermore, because of the extent of compression, these roots often have no available canal space; thus, retraction not only increases traction but also may cause direct compression (against the disc or the overlying lamina). For the same reason, the use of large punches with a thick foot plate is also not recommended (compresses underlying roots against the herniated disc) ( Fig. 95-3 ). Consequently, the authors recommend a wide bilateral decompression (laminectomy and medial third facetectomy). To avoid iatrogenic compression of the cauda equina, the surgeon can perform the laminectomy using a high-speed bur to thin out the lamina and then curettes and small punches lateral to the area of maximal compression to release the medial portion of the lamina (see Fig. 95-3 ). Once the lamina is released, it can be safely lifted away from the cauda equina. The decompression should be sufficient to allow access lateral to the thecal sac and traversing roots at the level of the affected disc space or the sequestered fragment. The surgeon should carefully retrieve the herniated fragment to avoid creating further mass effect and therefore increased traction on the less mobile central sacral roots. This can be accomplished by performing a lateral annulotomy and discectomy and then pushing the central fragment back into the disc space with a reverse-angle curette. If the fragment is sequestered, it should be manipulated in a lateral direction using a nerve hook or angled curette and then retrieved. Before closure, the surgeon should confirm adequate decompression.
Related posts:
Anatomy of Nerve Root Compression, Nerve Root Tethering, and Spinal Instability
Ventral and Ventrolateral Subaxial Decompression
Diffuse Idiopathic Skeletal Hyperostosis
Timing of Surgery Following Spinal Cord Injury
Spinal Wound Closure
Explant Analysis of Wear, Degradation, and Fatigue in Motion Preserving Spinal Implants
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
