CSF Shunts: A Primer

1. CSF Shunts:A Primer Tamara Simon, M.D. July 2004

2. Purpose • CSF flow: • produced in choroid plexus of ventricles • Flows through lateral ventricles, through foramen of Monro, to third ventricle • Flows through aqueduct of Sylvius to fourth ventricle • Flows through foramina of Lushka and Magendie to subarachnoid space • Reabsorbed by arachnoid villi and arachnoid granulations into the venous sinuses • Hydrocephalus develops when there is an increase in CSF production, decrease in CSF absorption, or (most commonly) obstruction to flow

3. Procedure • Allows for relief of hydrocephalus • Allows for prevention of increased ICP • Tumors • Congenital anomalies • Posttraumatic hemorrhage • Intraventricular hemorrhage • Postinfectious obstruction • Other causes

4. Types of Shunts • Named for position of proximal and distal catheters • Most commonly, ventriculoperitoneal shunts are placed • Proximal catheters are in lateral, third, or fourth ventricles or in intracranial cyst • Distal catheters can be in peritoneal space, right atrium, pleural space, gallbladder, ureter, urinary bladder, bone marrow, mastoid, thoracic duct, fallopian tube, and other locations

5. Anatomy of a CSF shunt • Proximal catheter • Placed in ventricle • Exits skull through burr hole • One way valve system • Allows one-way drainage of CSF at predetermined pressure differential • May be integrated into distal catheter or separate • On exterior of skull

6. Anatomy of a CSF shunt (cont) • Distal catheter • Tunneled under skin to final destination • Other components: • On-off valves • Used for intermittent shunting • Can be used to assess shunt function • Antisiphon devices • Prevents overdrainage of CSF • Reservoirs (single or double chamber) • Allows withdrawal of CSF or drug infusion • On exterior of skull proximal to one way valve

7. Sample CSF Shunts • Rickham reservoir with antisiphon device (left) • Single chamber reservoir (middle) • Rickham reservoir with double chamber reservoir/valve system (right)

8. Temporary Shunts • In patients who have rapidly progressive ventriculomegaly or progressive or symptomatic ventriculomegaly, patients • can be quite small • have persistently proteinaceous and cellular CSF • be at high risk for shunt obstruction and infection • Some preterm infants will not evolve to permanent, shunt-dependent hydrocephalus by term, so a temporary technique is at times expeditious • Several studies cite 25% of patients with posthemorrhagic hydrocephalus ultimately recover

9. Temporary Shunts (continued) • Surgeons believe that wound dehiscence and skin breakdown over shunt hardware are less frequent in larger infants as well • Clinical endpoint: • infant reaches term and • weight of 2 kg.

10. Temporary Shunt: EVD • External ventricular drainage • Drain placed into CSF space and drained directly externally. • Pros: Attain temporary drainage • Cons: • drain interferes with nursing care • drain is easily dislodged • drain obstruction is frequent because of low CSF flow volumes • formidable risk of infection with prolonged drainage

11. Temporary Shunt: Subgaleal Ventricular Reservoir/ Shunt Reservoir and outlet of the shunt sit in the subgaleal space CSF drains into a subgaleal pocket Plug is removed if the surgeon intends to use the device as a shunt Plug can be left in place, and the device can be used as a simple ventricular reservoir

12. Temporary Shunt: Subgaleal Ventricular Reservoir • Also called ventricular access device • Small, flat-bottomed reservoir attached to a ventricular catheter • reservoir sits on the surface of the skull under the galea of the scalp • percutaneous puncture of the reservoir with aspiration of CSF on a daily or every-other-day schedule serves to keep the ventricular system decompressed. • Clinical endpoints are arrest of ventricular dilatation, control of head growth, and elimination of symptoms and signs of elevated ICP.

13. Temporary Shunt: Subgaleal Shunt • Ventricular access device with an outlet • Reservoir with outlet is placed in a large subgaleal pocket on the surface (hemicranium) of the skull • CSF decompression occurs by draining through the reservoir, out the outlet, into the subgaleal pocket • subgaleal space probably has some absorptive capacity • pocket also serves a simple mechanical function as a high-compliance receptacle for ventricular CSF • over weeks, scarring of scalp to periosteum obliterates the pocket, and periodic needle aspiration of the shunt reservoir can be initiated • Some believe that subgaleal shunts control ventricular volume more consistently

14. Complication: Shunt Malfunction • Most common complication, seen in 30-40% of shunt procedures and 67% of patients with shunts • Usually caused by simple obstruction • Debris, fibrosis, choroid plexus, or parenchymal occlusion of proximal catheter (first 2 years after placement in general) • Kinking, knotting, breaking, obstruction, migration of distal catheter (after 2 years after placement) • Also caused by infection, disconnection of shunt components, catheter migration, inadequate drainage, overdrainage

15. Complication: Shunt Malfunction • Varied signs and symptoms • Swelling or erythema around shunt tract - Lethargy • Bulging or full fontanel - Ataxia • Increased head circumference - Neck pain • Headache - Back pain • Irritability - Blurred vision • Increased seizures - Sun setting eyes • Vomiting - Behavioral changes • Papilledema - Not acting right • Most predictive? • Vomiting, lack of fever, parental suspicion

16. Complication: Infection • Second most common complication, seen in 2-30% of shunt procedures • Increased risk in children under 1 year of age, a short duration from shunt procedure • Most common organisms: • Coagulase-negative Staph species • Staph epidermidis • Staph aureus • Gram negative rods (6-20%) • Pathogens that cause meningitis (more remote)

17. Complication: Infection • Vague signs and symptoms • Swelling, erythema, cellulitis, or wound infection around shunt tract • Fever - Shunt malfunction • Nausea - Vomiting • Lethargy - Irritability • Headache -Change in sensorium • Feeding problems • When VP shunt is present, additionally: • Abdominal pain • Diarrhea • Peritonitis

18. Complication: Slit Ventricle Syndrome • Found in 50-60% of patients, only symptomatic in 11-37%, require treatment in 6-7% • Overdrainage of CSF leads to collapse of ventricles, blocking fenestrations in proximal catheter, leading to increased ICP • Symptoms similar to shunt malfunction until ICP rises and ventricles re-expand • Some patients are position-sensitive and lying down increases ICP • Diagnosed when head CT shows small- to normal-sized ventricles

19. Complication: Proximal Catheter Obstruction • Medical signs of increased ICP • Hyperventilation • Diuretics (acetazolamide, mannitol) • Elevate head of bed • Ventricular puncture through burr hole or open fontanel

20. Complication: VP Shunts • Inguinal hernia • Increased abdominal fluid increases intra-abdominal pressure, converting potential in clinical hernia • Perforation of hollow viscus • Bladder, stomach, small intestine, colon, gallbladder, vagina, anus, and mouth have been reported • Bowel perforation can present with peritonitis, meningitis, ventriculitis; with signs of shunt infection • Abdominal pseudocyst (0.8-10%) • Decreased appetite, abdominal pain, tenderness, distention, mass, and guarding; increased ICP and shunt malfunction • Foreign body reaction with chronic granulomatous inflammation • Migration of distal catheter tip • Through abdominal incision, through neck incision, into mediastinum, throacic cavity, umbilicus

21. Complications: Other Rare Ones • Intussusception • Intractable hiccup • Omental cyst torsion • Volvulus around catheter

22. Radiographic studies • Shunt series • Plain radiographs of skull, neck, chest, abdomen • Used to detect disconnections, kinks, and migration of catheters • Proximal and distal catheters are radiopaque, reservoirs are radiolucent • Head CT • Demonstrates location of proximal catheter tip and size of ventricles • Comparison to prior study is critical • Ultrasound • For children with open fontanel • Radionucleotide clearance study • Radionucleotide is injected into shunt reservoir and observed as it flows proximally and distally

23. Further Diagnostic Studies • Pumping the shunt reservoir • Assesses proximal and distal shunt function • Pitfall abound, experience is needed- consult Neurosurgery • Tapping the shunt • Assess shunt function and diagnoses shunt infection • Consult Neurosurgery • Reservoir is cleaned, 23 gauge butterfly needle +/- manometer is inserted into reservoir • Opening pressure, rate of flow, closing pressure, and CSF sample is obtained • CSF should be sent for culture, Gram stain, protein, glucose, and cell count

24. References • Teoh DL. Tricks of the Trade: Assessment of High-Tech Gear in Special Needs Children. Clinical Pediatric Emergency Medicine. 3(1), March 2002. • Baddour LM, Flynn PM, Fekete T. Infection of central nervous system shunts and other devices. Up To Date. April 30, 2004. • Garton HJ, Piatt JH. Hydrocephalus. Pediatric Clinics of North America, 51(2), April 2004.