Disorders of the Spinal Cord.docx
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Ch. 14: Disorders of the Spine and Spinal Cord Anatomy of the Vertebral Column and Spinal Cord Vertebral column 24 individual vertebrae 7 cervical, 12 thoracic, and 5 lumbar Sacrum & coccyx Anterior section of vertebrae consists of a body and adjacent vertebral bodies separated in interverte...
Ch. 14: Disorders of the Spine and Spinal Cord Anatomy of the Vertebral Column and Spinal Cord Vertebral column 24 individual vertebrae 7 cervical, 12 thoracic, and 5 lumbar Sacrum & coccyx Anterior section of vertebrae consists of a body and adjacent vertebral bodies separated in intervertebral disks Posterior vertebrae consist of 1 midline spinous process and 2 lateral transverse processes Lamina: region of bone btw spinous and transverse processes Pedicle: segment of bone connecting transverse processes w/ vertebral body Posteriorly, adjacent vertebrae articulate at facet joints SC is contained within bony confines of the central canal of the vertebral column SC extends from medulla oblongata of the brainstem → lumbar region of the vertebral column At each vertebral level, the SC gives off bilateral nerve roots Posterior nerve roots carry afferent info from the periphery to the spinal cord Deep touch and vibration sensation → carried by SC to the brain via posterior columns Pain and temp → carried to brain via the lateral spinothalamic tracts Corticospinal tract carries efferent info from the brain through the spinal cord, and this info leaves the anterior roots of the spinal cord Innervation of muscles by spinal roots Blood is supplied to SC by: 2 posterior spinal arteries that predominantly supply posterior spinal roots and posterior columns 1 anterior spinal artery that supplies remainder of the SC Spinal Cord Injury Acute Spinal Cord Injury Mobility of C spine → vulnerable to injury, esp. hyperextension injury Occurs a lot in major trauma victims Pts w/ traumatic head injury have a concurrent injury of the spine, typically occurring in upper C-spine (C1-3) Trauma can also injure the thoracic and lumbar spinal cord segments Clinical manifestations of acute spinal cord injury: Depend on both the extent and the site of injury Initially produces a state of spinal shock Characterized by flaccid muscle paralysis with loss of sensation below the level of injury Spinal shock: loss of neuro function following spinal cord injury Neurogenic shock: manifestations of ANS impairment that can result following central nervous system injury Extent of injury described in terms of the American Spinal Injury Association (ASIA) classification system (Table 14.2) Characterizes the injury in terms of both motor & sensory impairment Score of A → “complete” injury, all motor and sensory function is lost below the level of the lesion, including function at the lower sacral segments of S4 and S5 Lower sacral neuro function determined by rectal tone and sensation Scores of B-D → “incomplete” lesions, some degree of spinal cord integrity is maintained below the level of injury Score of E → indicates “normal” spinal cord function. Extent of physiologic effects from SCI depends on the level and extent of injury Most severe physiologic derangements occurring with complete injury to the cervical cord Lesser perturbations occurring with less complete injury and more caudal cord injuries Reductions in BP → common esp w/ C-spine injury Influenced by: (1) loss of SNS activity & decrease in SVR (2) bradycardia resulting from loss of the T1-T4 sympathetic innervation to the heart (i.e., loss of cardiac accelerator innervation). Hypotension can occur with thoracic and lumbar cord injuries, although typically it is less severe With cervical and upper thoracic cord injury, major cause of M&M → alveolar hypoventilation combined with an inability to clear bronchial secretions Respiratory muscles not affected with lumbar and low thoracic injuries, so minimal respiratory impairment Aspiration, pneumonia, and pulmonary embolism can occur C-spine radiographs obtained for pts who come for tx of various forms of trauma and are intended to identify both suspected and occult C-spine injuries Probability of C-spine injury → minimal in patients < 60 years who meet the following five criteria: (1) no midline cervical spine tenderness (2) no focal neurologic deficits (3) normal sensorium (4) no intoxication (5) no painful distracting injury Pts who meet these criteria do NOT require routine imaging studies to rule out occult cervical spine injury 2/3 of trauma pts have multiple injuries that interfere with C-spine eval Eval includes CT or MRI but imaging may not be practical in some cases because of the risk of transporting pts in an unstable condition For this reason, portable XR are frequently relied upon to evaluate for the presence of cervical spine injury and associated instability For C-spine imaging to have greatest utility, the entire cervical spine (including the body of the first thoracic vertebra) must be visible Images are analyzed for alignment of the vertebrae (lateral view) and presence of fractures (all views), and the disk and soft tissue spaces are evaluated The sensitivity of plain radiographs for detecting C-spine injury is <100%, so the likelihood of cervical spine injury must be interpreted in conjunction with other clinical signs, symptoms, and risk factors If there is any doubt, it is prudent to treat all acute cervical spine injuries as potentially unstable until proven otherwise Treatment Management of Anesthesia Chronic Spinal Cord Injury (SCI) Sequelae of chronic SCI: impaired alveolar ventilation, autonomic hyperreflexia, chronic pulmonary and GI tract infections, renal stones and possible renal dysfunction, anemia, and altered thermoregulation Injuries that occur more rostral along the SC have more significant systemic effects Chronic UTIs reflects inability to empty the bladder completely and predisposes to calculus formation As a result, renal failure may occur and is a common cause of death Prolonged immobility → osteoporosis, skeletal muscle atrophy, and decubitus ulcers Immobility predisposes pts to DVTs, so prophylactic measures (SCDs, low-dose anticoagulant therapy, and insertion of IVC filters) may be needed Pathologic fractures can occur when these pts are moved Pressure points should be well protected and padded → minimize trauma to skin and decubitus ulcers Chronic pain and depression → common following SCI Nerve root pain is localized at or near the level of injury Visceral pain produced by distention of the bladder or bowel Phantom pain occur in areas of complete sensory loss Loss of lifestyle and ability that frustrates and depresses many As a result, many pts on antidepressants & analgesics including opioids that require attention when anesthetic management is planned (e.g., avoidance of serotonin syndrome by judicious use of serotonergic agents such as ondansetron or fentanyl for pts on SSRIs or MAOIs) Several weeks after acute SCI, SC reflexes gradually return, and pts enter a more chronic stage Characterized by overactivity of the SNS and involuntary skeletal muscle spasms Baclofen, which potentiates the inhibitory effects of GABA → tx spasticity Abrupt cessation of baclofen → withdrawal S&S (seizures) May occur with hospitalization for an unrelated problem Diazepam and other benzos facilitate the inhibitory effects of GABA and may have utility in the management of a pt receiving baclofen Spasticity refractory to pharm suppression → require surgical tx via dorsal rhizotomy or myelotomy, but usually implant of a spinal cord stimulator or subarachnoid baclofen pump will be undertaken before rhizotomy is considered SCI at or above the C5 → result in apnea caused by denervation of the diaphragm (“C three, four, and five to keep the diaphragm alive”) With function of the diaphragm intact → Vt sufficient, but coughing and secretion clearance are impaired because of decreased expiratory reserve volumes from denervation of intercostal and abdominal muscles Acute SCI at the cervical level → marked decreases in VC Arterial hypoxemia → early finding following cervical SCI Tracheobronchial suctioning → a/w bradycardia and even cardiac arrest important to optimize arterial oxygenation before suctioning the airway Management Autonomic Hyperreflexia Appears following spinal shock and in a/w return of spinal cord reflexes This reflex response can be initiated by cutaneous or visceral stimulation below the level of SCI Surgery and distention of a hollow viscus (bladder, rectum) → common stimuli Stimulation below level of SCI → initiates afferent impulses that enter the spinal cord Because of reflexes entirely within the spinal cord itself, these impulses elicit an increase in SNS activity along the splanchnic outflow tract In neurologically intact pts, this outflow would be modulated by inhibitory impulses from higher centers in the CNS But in the presence of a spinal cord lesion, this outflow is isolated from inhibitory impulses from above, so generalized vasoconstriction occurs below the level of the SCI B/c of the intense vasoconstriction, reflex bradycardia and cutaneous vasodilation occur above the level of the SCI → which is often inadequate to overcome the increased BP Nasal stuffiness → reflects vasodilation Headaches and blurred vision → reflect severe HTN This increase in BP results in cerebral, retinal, or subarachnoid hemorrhage as well as increased operative blood loss Loss of consciousness, seizures, arrythmias often occur Pulmonary edema reflects acute left ventricular failure resulting from dramatically increased afterload Incidence of autonomic hyperreflexia depends on level of SCI Approx 85% of pts with lesions above T6 exhibit this reflex It is unlikely to be a/w spinal cord lesions below T10 Also, in pts with cervical or high thoracic spinal cord lesions → those with complete lesions are more likely to exhibit autonomic hyperreflexia v. incomplete Incidence and severity also diminish the further out from injury Management Elective Spine Surgery Indications and populations of pts requiring sx on the spine are very diverse and represent a variety of indications in a wide range of patient ages Some of the major indications for spine sx include: Disk disease, spinal stenosis, spondylolisthesis, scoliosis, spinal cord tumors Indications for Elective Spine Surgery Disk Disease Common cause of back and neck pain → intervertebral disk dz The intervertebral disk composed of a compressible nucleus pulposus surrounded by a fibrocartilaginous annulus fibrosis The disk acts as a shock absorber btwn vertebral bodies Trauma or degenerative processes → lead to changes in the disk Nerve root or spinal cord compression → results when the nucleus pulposus protrudes through the annulus fibrosis With compression of a single nerve root (a radiculopathy), pts complain of pain in a single dermatomal distribution or localized muscle weakness Spinal cord compression → lead to complex sensory, motor, and autonomic symptoms at and below the level of the insult CT or MRI confirms the dx and location of intervertebral disk herniation Tx: Initial treatment of cervical disk protrusion--conservative and includes rest, pain control, and possibly epidural admin of steroids Surgical decompression is necessary if symptoms do not abate with conservative tx or sig motor involvement Spondylosis and Spondylolisthesis Spondylosis Common acquired degenerative disorder → leads to osteophyte formation and degenerative disk disease The term spondylosis = spinal stenosis There is narrowing of the spinal canal and compression of the spinal cord by transverse osteophytes or nerve root compression by bony spurs in the intervertebral foramina Spinal cord dysfunction → reflect ischemia of the spinal cord caused by bony compression of the spinal arteries Symptoms: Develop insidiously; age >50 years With cervical spondylosis → neck pain and radicular pain in arms and shoulders are accompanied by sensory loss and skeletal muscle atrophy Later, sensory and motor signs may appear in the legs producing an unsteady gait With lumbar spondylosis → leads to radicular pain and muscle atrophy in the lower extremities Sphincter disturbances are uncommon regardless of the location of spondylosis Spine radiographs demonstrate osteoarthritic changes, but these changes correlate poorly with neurologic symptoms Surgery may be necessary to arrest progression of the symptoms, especially if there is evidence of motor loss Spondylolisthesis Refers to anterior subluxation of one vertebral body on another Most commonly occurs at lumbosacral junction Radicular symptoms involve the nerve root inferior to the pedicle of the anteriorly subluxed vertebra Tx: analgesics, anti-inflammatory meds, and PT if low back pain is the only symptom Surgery is reserved for pts who have myelopathy, radiculopathy, or neurogenic claudication Scoliosis Refers to the sideward bending or rotation of the vertebral column Scoliosis is an incidental finding and is asymptomatic A greater curvature can result in pain or physical deformity Severe cases impact chest wall dynamics during breathing In most circumstances, scoliosis is idiopathic with no attributable cause but is a/w family hx of scoliosis Idiopathic scoliosis presents before or during early adolescence with an equal rate among males & females However, mild asymptomatic scoliosis is approximately 10x more likely to increase in severity among females Other conditions a/w scoliosis: cerebral palsy, Marfan syndrome, muscular dystrophy, spinal muscular atrophy, Ehlers-Danlos, dwarfism, and prior vertebral column trauma Tx: Conservative for mild scoliosis → exercise and PT focused at strengthening the paraspinal musculature and bracing For progressive or severe cases → spinal fusion surgery Spinal Cord Tumors Divided into 2 broad categories: (1) Intramedullary tumors Located within the spinal cord Account for approx 10% of tumors affecting the spinal column Gliomas and ependymomas account for majority (2) Extramedullary tumors Can be either intradural or extradural Neurofibromas and meningiomas account for most of the intradural tumors Metastatic lesions, usually from lung, breast, or prostate cancer or myeloma → most common extradural lesions Other mass lesions of the spinal cord, including abscesses and hematomas, share many of the clinical S&S of tumors Symptoms Spinal cord tumors present with symptoms of cord compression Pain is common and usually aggravated by coughing or straining Spinal tenderness Motor symptoms and sphincter disturbances Dx based on symptoms and imaging of SC MRI is the technique of choice Tx and prognosis depend on the nature of the lesion Tx: corticosteroids, radiation, chemo, surgical decompression or excision Management of Anesthesia Congenital Anomalies and Degenerative Diseases of the Vertebral Column Spina Bifida Occulta Results from incomplete formation of a single lamina in the lumbosacral spine without other abnormalities It is a congenital defect Usually produces no symptoms and incidentally discovered Because there are no associated abnormalities, an increased risk with spinal anesthesia is not expected, and tolerate spinals safely Meningocele and Myelomeningocele During fetal development, closure of the neural tube is required for normal formation of the brain, spinal cord, and their enclosing structures: the cranium and vertebral canal Failure of the neural tube to appropriately close in the caudal segments → results in neural tube defects Herniation of contents of the spinal canal → meningocele and myelomeningocele if the herniated contents contain only meninges and CSF versus meninges, cerebrospinal fluid, and neural elements This is opposed to a pseudomeningocele → refers to a collection of CSF that does not contain meninges or neural elements and results from trauma or sx Meningocele: rare and a/w a lower incidence and severity of neuro deficits Myelomeningocele: most common severe congenital anomaly of the spine Although it usually occurs in the lumbosacral region, myelomeningocele can also occur in cervical or thoracic regions of vertebral column and cord Increased risk is a/w maternal folate deficiency Can occur w/ other congenital anomalies → trisomy 13 & 18, and type II Chiari malformations Hydrocephalus can occur, especially if a type II Chiari mal is present A myelomeningocele results in severe sensory and motor deficits Bowel and bladder dysfunction can occur Due to frequent and multiple exposures from a very early age to medical products containing latex, pts often develop latex sensitivity; avoid latex periop Perioperative management Avoid succinylcholine d/t increased risk for hyperkalemia in the setting of motor deficits Resistance to nondepolarizing NMBDs can occur in weak extremities, thus titration of muscle relaxant dose should NOT be based on monitoring of the lower extremities The clinician should also be aware of other neuro deficits that may be r/t hydrocephalus → presence of a CSF–diverting shunt or a Chiari malformation In utero surgical repair of a myelomeningocele → reduce the incidence of associated hydrocephalus and improve overall neuro function Tethered Spinal Cord Syndrome During fetal development, vertebral column develops and elongates at a rate greater than the spinal cord Abnormal attachments of the spinal cord to the vertebral column → result in stretching of the spinal cord → tethered spinal cord syndrome These abnormal attachments can occur in the setting of: Myelomeningocele, dermal sinus tracts, lipomatous tissue in the spinal canal, diastematomyelia (or a bifurcated spinal cord), or a filum terminale of reduced elasticity Also, trauma or injury to the SC and vertebral column can cause scar formation that can lead to cord tethering Spinal cord stretch leads to dysfunction Depending on the cause and severity, it can present at any stage of life, from early childhood through adulthood S&S: Many individuals with a tethered spinal cord have cutaneous manifestations overlying the anomaly → tufts of hair, hyperpigmented areas, cutaneous lipomas, and skin dimples Scoliosis and foot deformities (clubfoot) Spinal anesthesia in pts with tethered spinal cord → increase risk of cord injury Normally, conus medullaris lies at the level of L1-L2 in adults Pts with tethered spinal cord syndrome → conus medullaris lies lower than the L2 level, but the absence of a low-lying conus medullaris does not rule out the diagnosis This latter effect may be d/t stretch of the cord w/o associated lengthening of the cord or a functional cord stretch that may occur only with changes in position Patients may present with motor and sensory deficits with bladder and bowel incontinence Surgical management: Involves release of tethering if possible. Avoid spinals to reduce risk for exacerbation of neurologic deficits In patients with motor deficits avoid succinylcholine d/t risk of high K Resistance to nondepolarizing muscle relaxants can also occur Syringomyelia (Syrinx) Also known as syrinx Disorder in which there is cystic cavitation of the spinal cord Often congenital, but it can also occur following spinal cord trauma or in a/w various neoplastic conditions such as gliomas Rostral extension into the brainstem → syringobulbia 2 main forms of syringomyelia occur → depending on whether there is communication of the cystic regions with the subarachnoid space or central canal 1) Communicating syringomyelia Either there is only dilation of the central canal of the cord (known as hydromyelia) or there is communication btw the abnormal cystic lesions in the spinal cord proper and the CSF spaces A/w either a hx of basilar arachnoiditis or Chiari malformation 2) Noncommunication syringomyelia In contrast, the presence of cysts that have NO connection to the CSF spaces A/w a hx of trauma, neoplasms, or arachnoiditis S&S of congenital syringomyelia Begin during the third or fourth decade of life Early complaints are those of sensory impairment → pain and temp sensation in the upper extremities This reflects compromise of pain and temp neuronal pathways that cross within the spinal cord near the central canal As cavitation of the SC progresses → destruction of lower motor neurons ensues with the development of skeletal muscle weakness, wasting, loss of reflexes Thoracic scoliosis may result from weakness of paravertebral muscles Syringobulbia is characterized by paralysis of the palate, tongue, and vocal cords and loss of sensation over the face MRI → dx No known tx that is effective in stopping the progressive degeneration of the spinal cord or medulla Management of Anesthesia Amyotrophic Lateral Sclerosis (ALS) “Lou Gehrig” Degenerative disease involving: (1) the lower motor neurons in the anterior horn gray matter of the SC (2) the upper motor neurons of corticospinal tracts Therefore this disease process produces both upper and lower motor neuron degeneration Most commonly affects men 40 to 60 years When the degenerative process is limited to the motor cortex of the brain → disease is called primary lateral sclerosis Limitation to the brainstem nuclei → known as pseudo-bulbar palsy Werdnig-Hoffmann disease resembles ALS EXCEPT it occurs during 1st 3 years of Cause unknown & occasionally genetic pattern is present with defects in the gene for superoxide dismutase S&S: Reflect upper and lower motor neuron dysfunction Initial manifestations: skeletal muscle atrophy, weakness, and fasciculations, frequently beginning in intrinsic muscles of the hands With time, atrophy and weakness involve most of the skeletal muscles →including tongue, pharynx, larynx, and chest Early symptoms of bulbar involvement include fasciculations of the tongue plus dysphagia, which leads to pulmonary aspiration Ocular muscles are generally spared ANS dysfunction → orthostatic hypotension and resting tachycardia Complaints of cramping and aching sensations, particularly in legs Plasma creatine kinase concentrations → normal Distinguishes this dz from chronic polymyositis Lung carcinoma a/w ALS No known treatment, and death is likely within 6 years after onset → resp failure Management: GA in pts with ALS a/w exaggerated resp depression Minimization or narcotics and other resp depressants Avoid deep extubation ALS pts vulnerable to hyperkalemia following admin of succs as a result of lower motor neuron disease Prolonged responses to nondepolarizing muscle relaxants Bulbar involvement with dysfunction of pharyngeal muscles predispose to pulmonary aspiration No evidence that any specific anesthetic drug or combo of drugs is ideal Friedreich Ataxia An autosomal recessive condition Characterized by degeneration of the spinocerebellar and pyramidal tracts Cardiomyopathy present in 10-50% of pts Kyphoscoliosis, producing a progressive deterioration in pulm function → very common S&S: Ataxia → typical presenting symptom Dysarthria, nystagmus, skeletal muscle weakness and spasticity, DM Usually fatal by early adulthood d/t heart failure Management of anesthesia: Similar to that described for patients with ALS If cardiomyopathy is present → negative inotropic effects of anesthetic drugs must be considered when selecting a technique Kyphoscoliosis → difficult epidurals; spinals are fine The likelihood of postop vent failure → increased, esp. in the presence of kyphoscoliosis Key Points
