The sciatic nerve is the largest and longest single nerve in the human body. The nerve originates at the junction of the fourth and fifth lumbar nerve roots and the first three sacral nerve roots at the lumbosacral plexus. It divides into two major branches, tibial and peroneal nerves, and innervates many muscle groups, including the hamstrings, distal adductor magnus, and all the muscles of the leg and foot. It also supplies sensation to the lateral and posterior leg and to the entire foot (Fig. 59).

1. I. Ventriculoperitoneal (VP) shunts are used primarily for the treatment of hydrocephalus. They are favored in infants and growing children because extra tubing can be left in the peritoneal cavity, allowing for growth and extending the time between shunt revisions.
   
2. II. Ventriculojugular (VJ) and ventriculoatrial shunts are also used for the treatment of hydrocephalus and may be used after major growth is completed. Complications (thrombi, endocarditis, septic or tubing emboli, and arrhythmias) are more frequent and serious than with VP shunts, and thus these shunts are less used.
   
3. III. Ventriculopleural (VPL) shunts are a second line option for treatment of adult hydrocephalus cases in which VPS are unsuitable or contraindicated. VPL shunts have high revision rate, and complications include pleural effusions, pneumothorax, empyema, and overdrainage.
   
4. IV. Endoscopic third ventriculostomy is a newer method of approaching noncommunicating hydrocephalus that affects the third ventricle, particularly in the treatment of colloid cysts. This procedure uses an endoscope from a frontal burr hole to traverse the lateral ventricle and foramen of Monro and then enter the third ventricle to create a fistula between the third ventricle and the subarachnoid space.
   
5. V. Lumboperitoneal shunts are useful in communicating hydrocephalus, particularly normal-pressure hydrocephalus. Similarly, a lumbar drain can be used for temporary, constant relief of cerebrospinal fluid (CSF) pressure for the treatment of acute surgical complications. An intrathecal pump, as in the chronic administration of baclofen, can be placed in the spinal canal for more direct and efficacious treatment of spasticity.
   
6. VI. External ventriculostomy (external ventricular drains [EVDs]) temporary shunts, placed in the lateral ventricles, are useful immediately after cranial surgical procedures when CSF protein level is very high. They are also used to measure and control intracranial pressure (ICP) in traumas or acute intracranial hemorrhage (ICH) when there is debris in the CSF.
   
7. VII. Ventricular access devices (Ommaya reservoir) are also available to monitor ICP, provide central nervous system (CNS) antimicrobial treatment access, and treat CNS cancers with chemotherapy. They directly access the lateral ventricle from a frontal burr hole.

Shunt Malfunction

Classic symptoms of shunt dysfunction in older children and adults are headache, lethargy, nausea, and vomiting. Gradual shunt malfunction may come to medical attention as impaired school performance, irritability, or personality change. Infants may have irritability, poor feeding, vomiting, and an abnormal shrill cry. Children with repeated episodes of shunt malfunction generally come to medical attention in a similar manner with each episode.

1. I. Mechanical malfunction can be due to disconnection, breakage, or obstruction, including a ventricular catheter plugged with glia or choroid plexus, a valve plugged with high-protein CSF or debris, or a distal catheter plugged with thrombus (VJ) or omentum (VP).

Evaluation includes several steps: (1) Pump the valve. Difficulty with compression of the valve (“pumps hard”) suggests distal obstruction; slow refill suggests proximal obstruction or slit ventricles. Even if the shunt pumps, it may not be working properly. (2) Palpate the shunt tubing for any interruption. (3) Obtain a shunt series. Obtain plain x-rays of the entire shunt system (reservoirs and pumps may be radiolucent) to look for interruption and a noncontrasted head computed tomography (CT) scan to assess ventricular size (old films are invaluable for comparing ventricular size). (4) Tap the shunt (Huber needle only) for CSF pressure (if obstructed proximal to reservoir, measured pressure will not be elevated) and CSF examination. More than 90% of shunt failures occur in the first 3 months. In uncomplicated shunt placements, 6- to 12-month postoperative CT should be scheduled.

1. II. Shunt infection: A shunt tap is not always necessary when a fever develops in a child with a shunt. Upper respiratory infection, otitis media, pharyngitis, urinary tract infection, and gastroenteritis are frequent causes of febrile illness in any child, including those with shunts. A tap should be performed if the child is lethargic, unusually irritable, photophobic, or has neck stiffness. A shunt tap should also be considered if there is a history of similar presentation with a previous shunt infection or if there is unexplained fever or leukocytosis. Staphylococcus epidermidis and Staphylococcus aureus are the two most common types of infective agents. Although intrathecal antibiotics may be successful, removal of an infected shunt is usually necessary for effective treatment.
   
2. III. Other CNS complications of shunts include meningitis, seizures, hematomas, and hygromas. Asymptomatic bilateral subdural effusions are common (30%) in VP shunts and can occur secondary to a siphoning effect of the shunt, causing excess CSF to be drained. Programmable valves lessen this complication. Peritoneal complications include ascites and cyst formation, perforation of viscus or abdominal wall, infection with obstruction of the distal end of the catheter, and peritoneal metastases from CNS tumors (e.g., medulloblastoma). Other complications include soft tissue infection along the shunt tract and pressure necrosis of the skin.

Fig. 60 shows the major components of typical shunt systems.

Sickle cell disease (SCD) is a group of inherited red blood cell disorders characterized by the presence of two beta-globin gene mutations, at least one of which being a sickle mutation. The most common forms of SCD are sickle cell anemia (SCA) (homozygous sickle mutation; HbSS), sickle beta thalassemia (HbS/B-Th), and hemoglobin SC disease (HbSC). Conversely, sickle cell trait is defined as a carrier condition in which one beta-globin allele carries the sickle mutation and the other allele is completely normal (HbAS). In general, sickle cell trait is not symptomatic.

Sickle hemoglobin tends to polymerize when deoxygenated, resulting in damage of the red blood cells (RBC); this ultimately leads to hemolytic anemia and vascular obstruction/vasoocclusion. Virtually every organ can be affected; therefore SCD is considered a multisystem disorder. The neurologic complications of SCD include stroke (ischemic and hemorrhagic), posterior reversible encephalopathy syndrome (PRES), seizures, meningitis, headache, intracranial aneurysm, moyamoya syndrome, neurocognitive dysfunction, retinal detachment, and proliferative retinopathy.

1. 1. Stroke (ischemic and hemorrhagic):
   
   
   
   1. a. Patients with SCD are at high risk for stroke (ischemic and hemorrhagic), especially those with SCA (HbSS) and HbS/beta⁰-thalassemia.
      
   2. b. The prevalence of stroke (ischemic and hemorrhagic) in SCA is estimated as 11% by age 20, 15% by age 30, and 24% by age 45.
      
   3. c. The overall incidence is approximately 0.5 per 100 patient-years. The incidence of ischemic stroke in SCA is higher in children, adolescents, and elderly patients. Conversely, the incidence of hemorrhagic stroke is highest in individuals aged 20 to 29 years.
      
   4. d. Hemorrhagic stroke accounts for one-third of SCD-related strokes and is associated with a 25% mortality rate.
      
   5. e. The most common risk factors for ischemic stroke comprise prior transient ischemic attack (TIA), rate of and recent acute chest syndrome, high SBP, low steady state hemoglobin level, silent infarct, and high mean velocity (> 200 cm/s) on transcranial Doppler (TCD).
      
   6. f. The most common risk factors for hemorrhagic stroke comprise high steady state white blood cells (WBC) and low steady state hemoglobin levels, as well as presence of aneurysm. Other suggested risk factors include recent blood transfusion and treatment with steroids or nonsteroidal anti-inflammatory drugs (NSAIDs).
      
   7. g. Most ischemic strokes are secondary to large vessel vasculopathy involving the supraclinoid internal carotid artery (ICA) and proximal middle and anterior cerebral arteries. The most common topography for cerebral infarctions includes large vessel territory, borderzone regions, and punctate lesions in the deep white matter. Silent infarcts, found in approximately one-fifth of these patients, are usually located within deep white matter.
      
   8. h. Most intracranial hemorrhages (ICHs) (intraparenchymal, subarachnoid hemorrhage (SAH), intraventricular, or a combination) do not have an identified etiology. However, when the etiology is known, it is usually SAH—often secondary to intracranial aneurysm. Other causes include hemorrhagic transformation of an ischemic infarct, cerebral venous thrombosis, and moyamoya syndrome. Importantly, the presence of ICH does not exclude the possibility of a concurrent stroke.
      
   9. i. Acute management of ischemic stroke in patients with SCD should include optimal hydration, correction of hypoxemia, correction of systemic hypotension, and blood exchange to reduce the percentage of HbS levels to less than 30% with a target hemoglobin of approximately 10g/dL. Intravenous recombinant tissue plasminogen activator (IV r-TPA) for patients with known SCD (children and adults) and an acute ischemic stroke is not well established.
      
   10. j. Acute management of ICH in patients with SCD does not differ from ICH in the general population—because there is a lack of formal evidence on the treatment of ICH in SCD.
       
   11. k. Work-up should include neurovascular imaging to look for large vessel disease, aneurysm, and moyamoya syndrome. In the case of ICH, angiography should be performed if initial vascular imaging (magnetic resonance angiography/computed tomography angiography [MRA/CTA]) is unrevealing. Importantly, the use of contrast may increase the risk of stroke. Magnetic resonance venography (MRV) should be obtained if cerebral venous thrombosis (CVT) is suspected. In addition to standard stroke labs, complete blood count (CBC), reticulocyte count, percent hemoglobin S, and type and crossmatch should also be obtained. These patients should concurrently undergo thorough investigation for other possible causes of stroke (such as cardiac arrhythmia and hypercoagulability).
       
   12. I. Primary and secondary ischemic stroke prevention in children with SCD involves chronic transfusion therapy. Children with SCD and high TCD velocity (> 200 cm/sec) should receive chronic transfusions with a goal of reducing HbS to less than 30%. Similarly, children with SCD who have had an ischemic stroke should receive chronic transfusion therapy; these patients should also be evaluated for hematopoietic stem cell transplantation and/or hydroxyurea. Primary and secondary ischemic stroke prevention in adults has been understudied. Secondary ICH prevention relies on identifying and treating underlying causes—such as aneurysm. Cerebral revascularization may decrease the risk of recurrent stroke in patients with moyamoya syndrome.
   
   
2. 2. PRES
   
   
   
   1. a. PRES is characterized by confusion, headaches, visual symptoms, and seizures. Neuroimaging shows white matter changes predominantly in the posterior topography (occipital and parietal regions; frontal lesions may occur). This syndrome is associated with multiple conditions such as hypertension and immunosuppressive therapy, as well as SCD. Importantly, PRES can mimic stroke; differentiating these two entities is paramount and may be assisted by diffusion-weighted imaging.
   
   
3. 3. Seizures
   
   
   
   1. a. Seizures and epilepsy are 2 to 3 times more common in patients with SCD compared with nonsickle populations. Male gender and history of dactylitis are associated with a higher risk of developing epilepsy. (Dactylitis is characterized by sudden onset of severe pain associated with warmth and edema affecting the hands and/or feet. It is caused by bone marrow infarction of the carpal/tarsal bones and phalanges secondary to vascular blockage, and it is often the initial presentation in infants. An episode may last 1 to 4 weeks.) Seizures in SCD are believed to be secondary to a combination of factors including stroke/ICH and infection of the CNS, as well as other SCD-related mechanisms that potentially lead to (focal) cerebral hypoperfusion. If antiseizure medications are started, folic acid supplementation should be optimized.
   
   
4. 4. Meningitis
   
   
   
   1. a. Patients with SCD are more susceptible to infections, especially from encapsulated bacteria—such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis—mainly due to functional asplenia caused by splenic infarction. These infections include life-threatening bacterial meningitis. Patients with SCD and suspected meningitis should undergo lumbar puncture, blood cultures should be drawn, and broad-spectrum antibiotics should be started. The latter are generally a combination of a third-generation cephalosporin and vancomycin, as well as ampicillin (if > 50 years of age).
   
   
5. 5. Headache
   
   
   
   1. a. Headache in SCD may be secondary to a variety of severe conditions including stroke, ICH, CVT, and meningitis. Headache may also be due to pain crisis or rebound cephalgia (because chronic pain medication use is common). Therefore, although benign causes of headache predominate, these patients should undergo thorough evaluation.

The seven major categories of sleep disorders are insomnia, sleep-related breathing disorders, central disorders of hypersomnolence, circadian rhythm sleep-wake disorders, parasomnias, sleep-related movement disorders, and other sleep disorders.

• I. Insomnia is the most common sleep disorder and comes in three distinct types.
  
  
  
  • • Short-term insomnia: This is a problem related to sleep initiation or sleep maintenance (despite adequate opportunity and circumstances for sleep) and daytime sleepiness, lasting less than 3 months. It is often associated with a stressor, and can resolve when the stressor is removed and/or adequate coping develops.
    
  • • Chronic insomnia: This is a problem with sleep initiation or maintenance (despite adequate opportunity and circumstances for sleep) and daytime sleepiness occurring 3 times a week for 3 months or more.
    
  • • Other insomnia: These are insomnia that do not meet the criteria of the first two.
    
  • • Dyssomnia: This is a disorder of initiating and maintaining sleep. It is characterized by insomnia, excessive sleepiness, or abnormal circadian cycle.
  
  
• II. Sleep-Related Breathing Disorders: These are abnormal respirations that occur during sleep in adults or children. They comprise four types.
  
  
  
  • • Central Sleep Apnea: This comprises: (1) with Cheyne-Stokes breathing, (2) without Cheyne-Stokes breathing, (3) high altitude periodic breathing due to medication or substance use, and (4) primary central sleep apnea.
    
  • • Obstructive Sleep Apnea (OSA): This is defined as having 15 or more respiratory events per hour, even in the absence of an associated symptom or comorbid disorders. In adults with comorbid conditions such as hypertension, coronary artery disease, atrial fibrillation, congestive heart failure, stroke, diabetes, cognitive and mood disorders; or if there are signs or symptoms including excessive sleepiness, fatigue, and/or insomnia, the diagnosis of OSA is made when there are five or more predominant obstructive respiratory events per hour.
    
  • • Sleep-related hypoventilation: Defined as elevated arterial partial pressure of carbon dioxide (PaCO2). The criteria for diagnosis is PaCO2 > 45 mm Hg. Examples include obesity hypoventilation, congenital central alveolar hypoventilation, late onset central hypoventilation with hypothalamic dysfunction, idiopathic, due to medication or substances, or due to a medical disorder.
  
  
• III. Central Disorders of Hypersomnolence: These conditions have a primary complaint of daytime excessive sleepiness not due to another sleep disorder. Excessive sleepiness in this case is defined as daily episodes of irrepressible need to sleep or daytime lapse into sleep.
  
  
  
  • • Narcolepsy type 1: Described as having cataplexy with or without hypocretin-1 deficiency, although cerebrospinal fluid (CSF) hypocretin-1 < 110 pg/mL is diagnostic; or a mean sleep latency of ≤8 minutes and two sleep onset rapid eye movement periods (SOREMP) within 15 minutes of sleep onset on an MSLT (and/or the overnight polysomnogram).
    
  • • Narcolepsy type 2: Meeting the criteria of narcolepsy type 1 except for the absence of CSF hypocretin-1 level and cataplexy.
    
  • • Idiopathic hypersomnia: this is a subjective sleepiness with an MSLT <8 min and less than 2 SOREMPs, without cataplexy and without hypocretin 1 deficiency.
    
  • Other Central Disorders of Hypersomnolence
    
  • – Kleine-Levin Syndrome
    
  • – Hypersomnia due to medical disorder
    
  • – Hypersomnia due to medication or substance use
    
  • – Hypersomnia associated with psychiatric disorder
    
  • – Insufficient sleep syndrome
  
  
• IV. Circadian Rhythm Sleep-Wake Disorders: This is a group of chronic or recurrent sleep disturbances due to altered circadian system. There is a misalignment between the environmental cues and the individual sleep wake cycle. They are a common cause of excessive daytime sleepiness.
  
  
  
  • – Time zone change (also known as “jet lag”)
    
  • – Shift work syndromes
    
  • – Delayed/advanced sleep phase syndromes
    
  • – Non-24 hour sleep wake rhythm disorder with fluctuating periods of insomnia and/or excessive sleepiness: caused by intrinsic circadian pacemaker out of sync with 24 hour day cycle.
    
  • – Circadian rhythm disorders due to medical, psychiatric or neurologic disorders
    
  • – Irregular sleep wake rhythm disorders
  
  
• V. Parasomnias are abnormal undesired physiologic or behavioral events occurring at initiation of sleep, during sleep, or during arousal from sleep.
  
  
  
  • • Non-Rapid Eye Movement (NREM)-related parasomnias: NREM-related parasomnias are arousal disorders that include sleepwalking, confusional arousals, and sleep terrors, in contrast to nightmares, which occur during rapid eye movement (REM) sleep. These episodes are recurrent, and include (1) incomplete awakening, (2) absent or inappropriate responsiveness, (3) limited or no cognition of a dream, and (4) partial or complete amnesia to the episode.
    
  • • Rapid Eye Movement (REM) associated Parasomnias: These are associated with REM sleep and include nightmares, sleep paralysis, REM sleep behavior disorder, and sleep related painful erections.
    
  • • Other Parasomnias:
    
    
    
    • – sleep enuresis and bruxism
      
    • – nocturnal paroxysmal dystonia
      
    • – primary snoring
      
    • – benign neonatal myoclonus
      
    • – sleep-related abnormal swallowing
      
    • – sleep enuresis
      
    • – exploding head syndrome
      
    • – parasomnia associated with medical disorders
      
    • – parasomnia due to a medication or substance
  
  
• VI. Sleep-related movement disorders: These are described as simple, stereotypic movements that disturb sleep. Dysesthesia during wakefulness is a primary symptom.
  
  
  
  • • Restless Leg Syndrome (Willis-Ekbom Disease)—primary description is an urge to move the legs and/or presence of discomfort at rest, that is relieved with movement. There is an associated circadian component as it primarily occurs at night or in the evening, causing distress and impairment of sleep.
    
  • • Periodic Limb Movement Disorder—diagnosed by polysomnography which notes frequent limb movements of more than 15 times per hour in adults and more than 5 in children.
    
  • • Other sleep related movement disorders include:
    
    
    
    • • Sleep-related cramps
      
    • • Sleep-related bruxism (teeth grinding)
      
    • • Sleep-related rhythmic movement disorder
      
    • • Benign sleep myoclonus of infancy
      
    • • Propriospinal myoclonus at sleep onset
      
    • • Sleep-related movement disorder due to a medical disorder
      
    • • Sleep-related movement disorder due to medication or substance
  
  
• Treatment of Sleep Related Disorders:
  
  
  
  • – Associated medical or psychiatric conditions should be treated.
    
  • – General management of insomnia includes optimizing the patient’s “sleep hygiene” as follows:
    
    
    
    • • Behavioral therapies:
      
      
      
      1. (1) Sleep hygiene and stimulus control
         
      2. (2) Wake and sleep at the same time each day (including weekends)
         
      3. (3) Use the bed only for sleep and sex
         
      4. (4) Leave the bed if not asleep within 10 minutes of lying down in bed
         
      5. (5) Avoid heavy exercise or large meals just before bedtime
         
      6. (6) Avoid daytime napping (sleep restriction)
         
      7. (7) Make sure the bedroom is not too warm or cold
         
      8. (8) Exercise regularly, and
         
      9. (9) discontinue alcohol, caffeine, cigarettes, and psychoactive drugs.
      
      
    • • Other treatments include: biofeedback, sleep restriction therapy, and cognitive behavioral therapy.
      
    • • Approved medications include:
      
      
      
      • – Short-acting benzodiazepines that may offer temporary adjunctive benefit, but their long-term use is not recommended.
        
      • – Other sedatives, including melatonin agonists ramelteon, suvorexant (orexin agonist), zalephon, zolpidem, eszopiclone and diphenhydramine, may be used judiciously.
        
      • – Antidepressants such as doxepin, amitriptyline, trazodone can be used.
        
      • – Management of parasomnias and abnormal movements are complex and have an overarching goal to keep patient safe.
      
      
    • • Work-up includes: polysomnography.
      
    • • In Restless Leg Syndrome, labs for iron deficiency should be checked.