Approach Considerations
The diagnosis of cauda equina syndrome generally is possible on the basis of medical history and physical examination findings. Radiologic and laboratory studies are used to confirm the diagnosis and for localizing the site of the pathology and the underlying cause.
Myelography, [79] computed tomography, [80] and MRI are each used in specific cases with good degrees of accuracy. Each test can be used to determine the level of pathology and aid in the determination of the cause of the syndrome. Bone scan may detect malignant tumor or metastases and inflammatory conditions affecting the vertebrae.
Due to its ability to depict the soft tissues, MRI generally has been the favored imaging study for assisting the physician in the diagnosis of cauda equina syndrome. [81, 82, 83] Urgent MRI is recommended for all patients who have new-onset urinary symptoms with associated back pain or sciatica.
Nevertheless, the superiority of MRI over CT is only suggested by case reports. Early consultation with the appropriate subspecialty is encouraged to guide imaging studies. [24]
Depending on the findings from the history and physical examination, laboratory studies can include basic blood tests, chemistries, fasting blood sugar, sedimentation rate, and syphilis and Lyme serologies. CSF examination should also be included if signs of meningitis are present. [84]
Alteration in bladder function may be assessed empirically by obtaining urine via catheterization. A significant volume with little or no urge to void, or as a post-void residual, may indicate bladder dysfunction. Bedside ultrasonography may be also used to estimate or measure post-void residual bladder volume.
Urodynamic studies are useful to evaluate the degree and cause of sphincter dysfunction, as well as to monitor recovery of bladder function following decompression surgery. Intraoperative monitoring of somatosensory and motor evoked potentials allows for evaluation of radiculopathy and neuropathy.
Blood Studies
The following studies may help to define possible causes and any associated pathology, especially other causes of lesions in the lower spinal cord or cauda equina:
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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
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Erythrocyte sedimentation rate (ESR) – Elevation may point to an inflammatory pathology
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Syphilis serology to rule out meningovascular syphilis
Radiography
Plain radiography is unlikely to be helpful in cauda equina syndrome but may be performed in cases of traumatic injury or in search of destructive changes, disk-space narrowing, or spondylolysis. For example, plain radiographs of the lumbosacral spine 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.
Magnetic Resonance Imaging
MRI with gadolinium contrast of the lumbosacral area is the diagnostic test of choice to define pathology in the areas of the conus medullaris and cauda equina (see the images below). It provides a more complete radiographic assessment of the spine than other tests; plain x-rays and CT scan may be normal. [85, 82] . Gadolinium contrast MRI 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.
Conus/epiconus infarction in the setting of sickle cell crisis. Image courtesy of Matthew J. Baker, MD.
Conus/epiconus infarction in the setting of sickle cell crisis in the same patient shown in the above image. Image courtesy of Matthew J. Baker, MD.
Conus/epiconus infarction in the setting of sickle cell crisis in the same patient shown in the images above. Image courtesy of Matthew J. Baker, MD.
Schwannomas are visible using myelography, but MRI is the criterion standard. Schwannomas are isointense on T1 images, hyperintense on T2 images, and enhanced with gadolinium contrast. With infectious conditions, MRI can display the abnormal appearance of the nerve roots being forced to one side of the dural sac.
Other Tests and Procedures
Needle electromyography (EMG) [86] 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, [12] especially of the pudendal nerve, may rule out more distal peripheral nerve lesions.
Somatosensory evoked potentials (SSEPs) [12] could be done as part of the workup to rule out multiple sclerosis, which could present initially as a lower spinal cord syndrome.
Duplex ultrasound of peripheral vessels may rule out compromised vasculature as a possible cause of associated claudication.
Lumbar puncture should be performed to examine the CSF to rule out inflammatory disease of the meninges or spinal cord.
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Muscle groups, surface anatomy, peripheral sensory innervation, and dermatomes of the anterior lower limb. This image should be correlated with Tables 1 and 2 in the text. Image courtesy of Nicholas Y. Lorenzo, MD.
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Muscle groups, surface anatomy, peripheral sensory innervation, and dermatomes of the posterior lower limb. This image should be correlated with Tables 1 and 2 in the text. Image courtesy of Nicholas Y. Lorenzo, MD.
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Conus/epiconus infarction in the setting of sickle cell crisis. Image courtesy of Matthew J. Baker, MD.
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Conus/epiconus infarction in the setting of sickle cell crisis in the same patient shown in the above image. Image courtesy of Matthew J. Baker, MD.
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Conus/epiconus infarction in the setting of sickle cell crisis in the same patient shown in the images above. Image courtesy of Matthew J. Baker, MD.
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Illustration demonstrating the relevant anatomy of the cauda equina region.
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Illustration demonstrating an example of cauda equina syndrome secondary to a spinal neoplasm.
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Sagittal MRI of a patient with cauda equina syndrome secondary to a large lumbar disk herniation.
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Epidural abscess with effacement of thecal sac in a 56-year-old man.
Tables
|
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 |
Radicular pain |
Less severe |
More severe |
Low back pain |
More |
Less |
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 |
Motor strength |
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 |
Impotence |
Frequent |
Less frequent; 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 |
Sphincter dysfunction |
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 |
Nerve Root |
Pain |
Sensory Deficit |
Motor Deficit |
Reflex Deficit |
L2 |
Anterior medial thigh |
Upper thigh |
Slight quadriceps weakness; hip flexion; thigh adduction |
Slightly diminished suprapatellar |
L3 |
Anterior lateral thigh |
Lower thigh |
Quadriceps weakness; knee extension; thigh adduction |
Patellar or suprapatellar |
L4 |
Posterolateral thigh, anterior tibia |
Medial leg |
Knee and foot extension |
Patellar |
L5 |
Dorsum of foot |
Dorsum of foot |
Dorsiflexion of foot and toes |
Hamstrings |
S1-2 |
Lateral foot |
Lateral foot |
Plantar flexion of foot and toes |
Achilles |
S3-5 |
Perineum |
Saddle |
Sphincters |
Bulbocavernosus; anal |
Muscle |
Nerve |
Root |
Iliopsoas |
Femoral |
L2, 3, 4 |
Adductor longus |
Obturator |
L2, 3, 4 |
Gracilis |
Obturator |
L2, 3, 4 |
Quadriceps femoris |
Femoral |
L2, 3, 4 |
Anterior tibial |
Deep peroneal |
L4, 5 |
Extensor hallucis longus |
Deep peroneal |
L4, 5 |
Extensor digitorum longus |
Deep peroneal |
L4,5 |
Extensor digitorum brevis |
Deep peroneal |
L4, 5, S1 |
Peroneus longus |
Superficial peroneal |
L5, S1 |
Internal hamstrings |
Sciatic |
L4, 5, S1 |
External hamstrings |
Sciatic |
L5, S1 |
Gluteus medius |
Superior gluteal |
L4, 5, S1 |
Gluteus maximus |
Inferior gluteal |
L5, S1, 2 |
Posterior tibial |
Tibial |
L5, S1 |
Flexor digitorum longus |
Tibial |
L5, S1 |
Abductor hallucis brevis |
Tibial (medial plantar) |
L5, S1, 2 |
Abductor digiti quinti pedis |
Tibial (lateral plantar) |
S1, 2 |
Gastrocnemius lateral |
Tibial |
L5, S1, 2 |
Gastrocnemius medial |
Tibial |
S1, 2 |
Soleus |
Tibial |
S1, 2 |
Features |
Cauda Equina Syndrome |
Conus Medullaris |
Vertebral level |
L2-sacrum |
L1-L2 |
Spinal level |
Injury to the lumbosacral nerve roots |
Injury of the sacral cord segment (conus and epiconus) and roots |
Severity of symptoms and signs |
Usually severe |
Usually not severe |
Symmetry of symptoms and signs |
Usually asymmetric |
Usually symmetric |
Pain |
Prominent, asymmetric, and radicular |
Usually bilateral and in the perineal area |
Motor |
Weakness to flaccid paralysis |
Normal motor function to mild or moderate weakness |
Sensory |
Saddle anesthesia, may be asymmetric |
Symmetric saddle distribution, sensory loss of pin prick, and temperature sensations (Tactile sensation is spared.) |
Reflexes |
Areflexic lower extremities; bulbocavernosus reflex is absent in low CE (sacral) lesions |
Areflexic lower extremities (If the epiconus is involved, patellar reflex may be absent, whereas bulbocavernosus reflex may be spared.) |
Sphincter and sexual function |
Usually late and of lesser magnitude; lower sacral roots involvement can cause bladder, bowel, and sexual dysfunction |
Early and severe bowel, bladder, and sexual dysfunction that results in a reflexic bowel and bladder with impaired erection in males |
EMG |
Multiple root level involvement; sphincters may also be involved |
Mostly normal lower extremity with external anal sphincter involvement |
Outcome |
May be favorable compared with conus medullaris syndrome |
The outcome may be less favorable than in patients with CES |
