Summary Cauda equina syndrome (CES) is caused by severe compression of nerve roots in the thecal sac of the lumbar spine, most commonly due to an acute lumbar disc herniation Early diagnosis is critical and is made clinically by characteristic symptoms of saddle-like paresthesias combined with acute back and leg pain. The cause is confirmed by urgent MRI Treatment is prompt surgical decompression that should be performed within 24 hours, and absolutely within 48 hours ETIOLOGY Epidemiology incidence rare (annual incidence of 1.5-3.4 cases per million) estimated prevalence of ~1/65,000 ~1,000 new cases per year in the U.S. occurs with ~3% of all lumbar disc herniations demographics more common in males 4th decade (30s) of life is the most common age group location most commonly occurs at the L4-5 level Pathophysiology pathoanatomy massive space-occupying lesion within lumbosacral canal disc herniation (most common) spinal epidural hematoma may occur spontaneously with high-dose DVT prophylaxis neuraxial anesthesia (epidural) postoperative period with early DVT prophylaxis spinal cord tumors myxopapillary ependymoma schwannoma spinal meningioma synovial facet cyst spinal epidural abscess trauma (retropulsion of fracture fragment, dislocation, or collapse) lumbar burst fractures developmental spondylolisthesis pathobiology mechanical compression decreases nutrient delivery to the nerve root decreased blood flow decreased CSF diffusion intraneural compartment syndrome venous congestion and intraneural edema from hypoperfusion injury further decrease arterial perfusion pressure nerve root ischemia follows Associated conditions orthopedic conditions conus medullaris syndrome lumbar disc herniation spinal cord tumor spondylolisthesis lumbar burst fracture sacral fracture epidural hematoma medical conditions deep vein thrombosis (DVT) well-known complication after spinal trauma or spine surgery DVT prophylaxis is often held out of concern for epidural hematoma antiplatelet medications can be safely resumed ~48-72 hours postoperatively after spinal procedures Prognosis natural history delays in diagnosis and management can lead to devastating lifelong impairment progressive weakness of the lower extremities without surgery progressive loss of bowel and bladder function without surgery even with early surgery, neurologic recovery is variable long-term urinary dysfunction is common prognostic variables presence of saddle anesthesia or bladder dysfunction is associated with worse outcomes surgical decompression after 48 hours is associated with worse outcomes Anatomy Spinal cord conus medullaris tapered, terminal end of the spinal cord terminates at the T12 or L1 vertebral body filum terminale non-neural, fibrous extension of the conus medullaris that attaches to the coccyx cauda equina (horse's tail) collection of L1-S5 peripheral nerves within the lumbar canal compression is considered to cause lower motor neuron lesions roots are only covered with endoneurium therefore, are sensitive to compression Bladder receives innervation from parasympathetic nervous system (pelvic splanchnic nerves and the inferior hypogastric plexus) promotes urination contraction of the detrusor urinae muscle relaxation of the internal sphincter sympathetic plexus (hypogastric plexus) promotes urinary retention relaxation of the detrusor urinae muscle contraction of the internal sphincter external sphincter of the bladder is controlled by the pudendal nerve voluntary control lower motor neuron lesions of cauda equina can interrupt the nerves forming the bladder reflex arcs unable to sense bladder filling unable to initiate appropriate muscle contraction and relaxation Classification Bladder function classification incomplete loss of urgency or decreased urinary sensation, but no incontinence or retention complete clear urinary and/or bowel retention or incontinence Presentation History may have a history of lifting a heavy object with lumbar spine in a flexed position ask about use of anticoagulation (hematoma), recent invasive procedures (hematoma), and IV drug use (infection) Symptoms common back pain (most common) may be initial presenting symptom alone unilateral or bilateral leg pain (second most common) unilateral or bilateral sensory changes in legs unilateral or bilateral motor weakness in legs saddle anesthesia while less common, more specific for CES if present, initiate surgery emergency protocol bladder dysfunction disruption of bladder contraction and sensation leads to urinary retention, and eventually to overflow incontinence important to document presence of bladder dysfunction prior to surgery rare sexual dysfunction (impotence in men) bowel dysfunction Physical exam inspection patient in distress due to low back pain, leg pain, and weakness palpation low back pain/tenderness is not a distinguishing feature palpation of the bladder to assess for urinary retention neurologic motor bilateral or unilateral lower extremity weakness decreased rectal tone on voluntary contraction sensory reduced or absent sensation to pinprick in the perianal region (S2-S4 dermatomes), perineum, and posterior thigh must distinguish between pinprick and light-touch sensation bilateral or unilateral lower extremity sensory disturbances reflex decreased or absent lower extremity reflexes provocative tests diminished or absent bulbocavernosus reflex diminished or absent anal wink reflex reflex contraction of the external anal sphincter upon pinprick stimulation of skin around the anus Imaging Radiographs indications if high suspicion of CES, MRI is the study of choice radiographs can be obtained, but the process of obtaining an MRI should be initiated immediately recommended views AP and lateral findings usually normal (most common cause is lumbar disc herniation) may see other causes of spinal canal stenosis burst fractures high-grade developmental spondylolisthesis (intact lamina) MRI indications study of choice to evaluate neurologic compression must be performed emergently if cauda equina syndrome is suspected ideally obtained within 1-2 hours of presentation to ER findings often reveals large central disc herniation with complete spinal canal obliteration presence of spinal stenosis epidural hematoma epidural abscess CT myelography indications study of choice if patient is unable to undergo MRI (pacemaker, MRI-incompatible implants) findings sagittal and axial reconstructions can reveal space-occupying lesion partial or complete blockage of contrast Studies Laboratory CBC, ESR, and CRP concern for infectious etiology (epidural abscess) Urodynamic studies preoperative post-void residual volumes (PVR) recommended to be obtained prior to decompression, but not at the expense of delaying decompression normal post-void residual volume is <50-100 mL PVR values <200 mL have a 97% negative predictive value for cauda equina syndrome postoperative post-void residual volume assessment for return of bladder function DIAGNOSIS Key differential conus medullaris syndrome spinal cord infarct myelopathy Diagnosis diagnosis of cauda equina syndrome is made based on history, symptoms, and physical examination MRI imaging confirms the cause of the CES and is critical for surgical planning Treatment Operative emergent surgical decompression indications clinical symptoms of CES with imaging to support diagnosis timing as soon as safely possible within 24 hours preferable within 48 hours considered acceptable standard of care techniques microdiscectomy (unilateral laminotomy, medial facetectomy, and discectomy) laminectomy (bilateral laminectomy and medial facetectomy) laminectomy with fusion (rarely indicated) outcomes studies have shown improved outcomes in bowel and bladder function and resolution of motor and sensory deficits when decompression is performed within 48 hours of the onset of symptoms residual bladder deficits may persist despite successful decompression motor recovery may continue up to 1 year postoperatively bladder function may continue to improve up to 16 months postoperatively no comparison studies between microdiscectomy alone and wide decompression combined with microdiscectomy Techniques Microdiscectomy (unilateral laminotomy, medial facetectomy, and discectomy) indications massive soft disc herniation in a younger patient with minimal degenerative changes approach 2 cm midline (or slightly paramedian) incision is made on one side of pathology expose lamina from spinous process to facet joint laminotomy 5-10 mm laminotomy made over the area of disc herniation medial facetectomy minimal facetectomy made with Kerrison rongeur ligamentum flavum window cleft in ligamentum flavum made, and lateral section removed annulotomy dural retraction removal of herniated disc material micropituitary rongeur irrigation through a metal cannula ensure disc material is thoroughly removed Laminectomy (bilateral laminectomy and medial facetectomy) indications older patient with degenerative changes including hypertrophic ligamentum flavum and lateral recess stenosis approach preservation of spinous process and PLC can be performed with a PLC-preserving undercutting approach or spinous process resection comes with a risk of incomplete decompression spinous process (and PLC) resection traditional method of resection of spinous process with complete laminectomy may be preferred to ensure complete decompression technique bilateral laminectomy bilateral ligamentum flavum resection bilateral medial facetectomy unilateral discectomy advantages wide laminectomy performed decreases the amount of dural retraction greater degree of decompression better visualization of the dura removal of herniated disc fragment Laminectomy and fusion indications high-grade spondylolisthesis insidious-type cauda equina syndrome in the context of degenerative spondylolisthesis Complications Nonoperative sexual dysfunction risk factors delay in surgical decompression prognosis recovery may be prolonged over several years worse prognosis for recovery in older patients urinary dysfunction risk factors delay in surgical decompression treatment may require permanent catheterization chronic pain persistent leg weakness Operative dural tear incidence 1-4% of cases treatment primary repair of the dura with or without dural fat grafting prevents pseudomeningocele and durocutaneous fistula formation postoperative bedrest for 4-7 days may require a lumbar drain no difference in outcomes if adequately treated iatrogenic segmental instability occurs with overlying aggressive medial facetectomy epidural fibrosis (scarring) cause of postoperative back and leg pain presents about 3 months postoperatively treatment responds poorly to re-exploration evaluate with gadolinium-enhanced MRI differentiates from recurrent HNP wound infection incidence ~1% of cases risk factors diabetic patients vascular injury incidence rare risk factors perforation of the anterior longitudinal ligament (ALL) with curettes during disc removal treatment requires immediate resuscitation and intraoperative vascular consultation mortality up to 50%