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A probability of occurrence of a shunt malfunction of 81% at 12 years of follow-up has been reported in multicentric studies (75). A complication in a patient with a shunt may have clinical, psychological, and economic consequences.
- Risk factors for shunt infections: Risk factors include a young age (immaturity of immune system, vulnerability of thin skin), poor condition of the skin (malnourishment, dermatitis), intercurrent systemic infections, prior CNS infections, repeated procedures (multiple revisions), and the surgeon’s experience, among others.
- Incidence: A general shunt infection rate of less than 5% is reported by many centers. The aim is to reach a shunt infection rate below 1%.
- Time of occurrence: Most shunt infections occur within 2 months of surgery, including revisions, although delayed infections are possible.
- Etiology: In most of the infections, the organism is spread to the surgical wound either directly from the adjacent skin or by contamination of gloves or instruments with the patient’s flora.
- Organisms in acute infections: The primary bacteria infecting CSF shunts are staphylococci (40% S. epidermidis and 20% S. aureus). The organisms responsible for the remaining 40% include coryneforms (Propionibacterium), streptococci, enterococci, aerobic Gram-negative rods, and yeasts.
- Organisms in late infections: In late infections, a Gram-negative bacillus infection must be suspected, and a primary cause (i.e., abdominal) should always be ruled out and treated.
Types of infection and diagnosis
- Wound infection: Incision or shunt track with signs of inflammation, purulent discharge, with or without fever or leukocytosis, and organisms seen on Gram stain or culture.
- Meningitis/ventriculitis: Fever, meningismus, lethargy or decreased level of consciousness, CSF leukocytosis, and organisms seen on Gram stain or culture.
- Peritonitis: Fever, abdominal tenderness, and organisms seen on Gram stain or culture. Abdominal pseudocyst and abdominal abscess may present with mass, with or without fever. Abdominal ultrasound is useful for diagnosis.
- Ventriculoatrial shunt infection: Fever, leukocytosis, positive blood culture, with or without evidence of shunt nephritis or cor pulmonale.
- Infected shunt apparatus: Minimal signs of CSF contamination with bacteria recovered from purulent exudate in or on shunt material, Gram stain of CSF withdrawn from the shunt under sterile conditions.
- Antibiotic choice: If infection is suspected or confirmed, the appropriate IV antibiotic regimen should be started. Consider ceftriaxone + vancomycin as empiric treatment until cultures are obtained, then reassess. Consider Infectious Diseases team consultation.
- Infected hardware must be removed (19, 84, 87), and an EVD (usually, ±5 cm-tunneled exiting the scalp) should be placed until antibiotic treatment is completed and sterility of CSF is confirmed with at least three negative CSF cultures, taken every 3 days from EVD insertion. Externalization of the distal tubing at torso is an alternative in cases with an infection restricted to the distal shunt (84).
- Management of patients with small ventricles: In patients with slit ventricles, insertion of an EVD may be difficult. Consider externalization of peritoneal catheter as an interim step.
- Use of intraventricular antibiotics: Consider intraventricular antibiotics in the presence of Gram negative infections or to treat organisms sensitive to antibiotics that have poor CSF penetration.
- Timing for placement of new shunt: Once the infection has been treated and the CSF is sterile (documented by three negative CSF cultures taken 3 days apart), a new shunt can be placed in a different surgical site. Precautions to avoid new infections should be taken. If there is a high risk of new infection (e.g. immune deficiency, recurrent infections) or institutional infection rates are greater than 5%, consider using antibiotic-impregnated shunt catheters.
- Antibiotics alone, without shunt apparatus removal, can be considered in cases of infection by organisms that cause meningitis in the general population, infect patients with shunts or cause hydrocephalus, and are discovered at the time of shunt insertion (e.g., H. influenzae, meningococcal and gonococcal meningitis). Failure to clear CSF within 48–72 hours should prompt removal of the shunt equipment (19).
Shunt occlusion represents about half of shunt complications in pediatric series (75). Occlusion can occur at three different levels: proximal catheter, valve system, or distal catheter.
- Risk factors: The risk for occlusion is higher during the immediate postoperative period (due to debris, clots, or misplacement of catheters) than during the next months and decreases progressively with time to a steady rate of 0.5% per month (19). Ingrowth of the choroid plexus into the shunt’s inlets, ependymal reaction, and immune reaction predominate as causative agents in delayed occlusions.
- Presentation: The clinical picture includes irritability, lethargy, bulging fontanelle, sunset eyes, and increasing head circumference in newborns and infants, whereas headaches, nausea and vomiting, papilledema, increased frequency of seizures (if previously present), or decreased level of consciousness are found in older children with occluded shunts.
- Diagnosis: The diagnosis is confirmed by an increased ventricular size on CT scan compared with baseline scans. It is important, however, not to assume that because the ventricles are small, the shunt is not blocked. Patients can have a shunt obstruction with normal-sized ventricles, they may just be larger than their usual slit ventricles or they may not expand their ventricles with shunt occlusion. ICP monitoring can be helpful in cases where a diagnosis of occlusion is not clear. Shunt series (skull, chest, and abdomen x-rays) can show some causes of occlusion such as disconnection/fracture, migration, or misplacement of catheters.
- Treatment: Shunt revision is the treatment for shunt occlusions. Unless there is preoperative evidence of distal obstruction, the proximal end and valve should be revised first. Partial or total replacement of the shunt is often required.
Disconnection and fracture
Shunt disconnection or fracture constitutes the second most frequent cause of mechanical shunt malfunction. Disconnection is defined as a loss of continuity of the shunt at connecting points between catheters, valves, and/or connectors, whereas fracture is an actual breakage of the catheter with separation between the segments.
- Risk factors: Associated, but not necessarily causative factors for broken shunts are growth spurt; aging, brittle, partially calcified shunt; multiple proximal revisions; local trauma over shunt; sports activity without evident trauma; trunk elongation post-scoliosis correction; and shunt design (multiple-piece shunts have more risk of disconnection than one-piece shunts).
- Location: The most common place for breakage is the neck, followed by the scalp, either proximal or distal to the valve or connecting devices.
- Presentation: Patients with broken shunts may present with headaches, irritability, nausea and vomiting, lethargy, papilledema, oculoparesis, pain, or fluid collections along the shunt tract and a palpable gap. Asymptomatic patients are usually diagnosed during routine follow-up imaging in outpatient clinic or as an incidental radiological finding.
- Diagnosis: Disconnection or fracture is confirmed on plain x-rays (shunt series). CT scan can show increase in ventricular size or no change at all.
- Treatment of symptomatic patients: Shunt revision is required as soon as possible. Partial or total replacement is required, although sometimes reconnection is feasible.
- Treatment of asymptomatic patients: Patients may remain stable for years, due to patent fibrous tracts (demonstrated by nuclear medicine studies or contrast shuntogram), and develop symptoms in a delayed fashion. If the patient is shunt dependent, revision should be performed as soon as possible. If shunt independence is suspected, appropriate investigations including nuclear medicine scans, contrast shuntogram, ICP monitoring, and careful review of the patient’s history (etiology of hydrocephalus, previous revisions) should be conducted to prove it, Only then can a decision be made to observe the patient or correct the malfunction.
To migrate, a shunt needs to be pulled and be able to move into the subcutaneous tissue. Loose or improper connection will allow catheters to get disconnected from a valve or other segment of the shunt and migrate. Overdissection of the subcutaneous tissue also predisposes to migration.
- Risk factors: Valves not fixed in the subcutaneous tissue by ligature or inherent valve shape have a high risk to migrate into the distal site or, in a retrograde fashion, into the ventricles. Cylindrical valves, unless properly secured, are very prone to migration.
- Timing of migration: Migration may occur early after shunting or with time.
- Presentation: Patients present a clinical picture very similar to that for disconnection and fracture.
- Diagnosis: Shunt migration is diagnosed by brain CT scan and shunt series.
- Treatment: Replace the proximal catheter into the ventricle and anchor its connection to the valve to the pericranium.
The shunt can be improperly placed at the level of the ventricles or at the level of the drainage cavity.
- Risk factors: Inadequate technique is the main risk factor for improper placement of the shunt.
- Presentation: Signs and symptoms of improper placement are similar to those for shunt occlusion and appear in the early postoperative period.
- Diagnosis: Once suspected, shunt series and head CT scan are used to confirm diagnosis. A lateral abdominal film may be necessary to detect a pre-peritoneal distal catheter.
- Treatment: Once diagnosed, shunt revision and proper placement are indicated. If ventricular size or shape offers a technical challenge, image guidance or endoscopic assistance may be helpful. At the level the of drainage cavity: fluoroscopic guidance is indicated in the case of technical difficulties to access the atrium in VA shunts; consider laparoscopic assistance in case of peritoneal adherences or abdominal abnormalities.
Overdrainage is caused by an increase of the differential pressure applied to the shunt system that exceeds the sum of the opening pressure of the valve plus the pressure of the drainage cavity (1). This can happen normally with postural changes, REM sleep, straining, etc. Overdrainage can cause symptomatic orthostatic hypotension, subdural CSF collections, slit ventricle syndrome, craniosynostosis, and loculation of the ventricles. The risk of overdrainage can be minimized by increasing the opening pressure of the valve (programmable valves), adding a siphon-resistive device to the system, or using a flow-regulating device (Orbis-Sigma valves).
The risk of subdural collection (hematoma, hygroma), caused by disruption of the arachnoid or the stretched subarachnoid vessels, is related to the drainage capacity of the shunt, the size of the ventricles, and the compliance of the brain.
- Risk factors: Prevention of subdural collections can be achieved by avoiding a shunt in the presence of a valid alternative (e.g., ETV) or by the use of overdrainage-limiting devices.
- Presentation: These collections can be asymptomatic, but in some patients they can cause focal motor deficits, seizures, or deterioration of the level of consciousness.
- Diagnosis: A subdural collection is diagnosed by head CT scan or, less commonly, MRI of the brain.
- Treatment: Not all subdural collections require treatment, since some of them can resolve spontaneously. In other cases, drainage limitation by upgrading the valve pressure or use of a flow-rate-limiting system may be successful. In some instances, a subduro-peritoneal shunt (without a valve or with a lower pressure than the ventricular one) is required to restore a pressure gradient between the ventricles and the subarachnoid spaces.
Slit ventricle syndrome
Slit ventricle syndrome is a complex complication of shunts defined as severe, life-modifying headaches in patients with shunts and normal or smaller-than-normal ventricles. Five different pathophysiological processes have been involved (79): 1) severe intracranial hypotension analogous to spinal headaches, 2) intermittent obstruction of the ventricular catheter, 3) intracranial hypertension with small ventricles and a failed shunt (normal volume hydrocephalus), 4) intracranial hypertension with a working shunt (cephalocranial hypertension), and 5) shunt-related migraine.
- Risk factors: Age at shunt insertion, etiology of hydrocephalus, and valve type appear to be risk factors for developing slit ventricles (80).
- Presentation: Headache is the most common symptom. Some patients can present with nausea/vomiting, visual alterations, or decreased level of consciousness.
- Diagnosis: CT scan shows normal, small, or very small ventricles. ICP monitoring may be required to confirm diagnosis and aid the decision-making process.
- Treatment: Slow-draining valves and delayed shunt insertion might be used to decrease the incidence of slit-like ventricles and slit ventricle syndrome (80). Overdrainage limitation and/or skull expansion are strategies to solve this complex problem.
Acquired post-shunt craniosynostosis is a relatively common complication, but in most cases, is mild.
- Risk factors: Overdrainage in young or premature infants with open fontanelles is the main risk factor.
- Presentation: There may be a decrease in head circumference, cranial sutures overlapping, and, in severe cases, craniocephalic disproportion.
- Diagnosis: Clinical features and head circumference measurements are the key to diagnose craniostenosis as a complication of shunts. A CT scan with 3D reconstruction may complete the study of this condition.
- Treatment: Rarely, post-shunting craniostenosis requires reoperation of the shunt system or cranioplasty. Cases of true craniocephalic disproportion require conventional cranioplasty interventions (strip craniectomy, cranial vault reconstruction).
Although they are most commonly seen in inflammatory or infectious processes, loculated ventricles can be caused by overdrainage.
- Cause: The condition is usually due to an obstruction of the foramen of Monro or aqueduct of Sylvius secondary to asymmetric drainage of one ventricle.
- Presentation: Symptoms and signs of intracranial hypertension and, in some cases, focal deficit may configure the clinical picture of this condition.
- Diagnosis: A plain CT scan or MRI and ultrasound for infants with patent fontanelles will show the loculated ventricles.
- Treatment: When possible, the most satisfactory solution is to reestablish communication between the ventricles by neuroendoscopic procedures. Loculated ventricles may require two or more drainage systems connected to the same valve by means of a Y-connector or a two-way connector.
- Risk factors: Orthostatic hypotension frequently occurs after a shunt insertion in older patients.
- Presentation: Clinical symptoms of orthostatic hypotension include headaches, nausea, or dizziness.
- Diagnosis: Differential blood pressure in decubitus and sitting positions will make the diagnosis of orthostatic hypotension. Tilt test table is usually not indicated but might help in doubtful cases.
- Treatment: Usually these symptoms disappear after a short period of time as patients adapt to the new hydrodynamic conditions. In some cases, it is necessary to upgrade the opening pressure of the valve or to use a shunt with an antisiphon device.
- Pleural effusions are the most common complication of this type of shunt. They are usually minor and do not require treatment. If restrictive pulmonary problems are diagnosed, a thoracentesis can be considered. In some cases, a different drainage cavity must be found.
- Pleural empyemas are uncommon. If present, the shunt must be removed, an external CSF drain placed, and proper antibiotic treatment and surgical drainage established.
- Improper placement is one of the most common problems of a ventriculoatrial shunt. Fluoroscopy is generally used to correctly localize the tip of the catheter in the right atrium.
- Bacterial endocarditis is the most important infectious complication of these shunts. Echocardiogram is the indicated diagnostic test, and treatment includes shunt removal associated with the proper antibiotic regimen.
- Nephritis has also been reported as a complication of ventriculoatrial shunts. Treatment often requires changing the shunt type.
- Acquired Chiari malformation: Acquired Chiari malformation with tonsillar herniation has been described with lumboperitoneal shunts, especially when used without a valve system (82, 83).
- Other complications: Scoliosis and hyperlordosis, limited spinal flexion, transient back pain, sciatica, transient neck pain, lower limb neurological changes, arachnoiditis, and rarely, migration of the shunt may occur.
- Recommendations: Use lumboperitoneal shunts as second-line shunts to the more conventional ventricular shunts. Consider its use, with a valve system, in cases of pseudotumor cerebri or exceptional cases of communicating hydrocephalus when a conventional ventriculoperitoneal shunt is not feasible.
- Unnecessary surgery: Minor symptoms such as subtle deterioration of intellectual function or episodic headaches without a strict demonstration of shunt malfunction can lead to surgery. In unclear cases, extensive preoperative investigation, including CSF flow measurement and ICP monitoring, is recommended to avoid the performance of unnecessary surgery (19).
- Shunt allergy: The presence of eosinophilia in the CSF has been associated with CSF shunt failure and may be related to shunt allergies. CSF sampling usually demonstrates persistent eosinophilia and negative cultures. Pathological examination of the ventricular catheter may show mechanical obstruction by inflammatory debris consisting largely of eosinophils and multinucleated giant cells. On the suspicion that the child might have some uncharacterized allergy to the shunt hardware, shunt replacement should be performed with use of an unpolymerized shunt system (85, 86).
Long-Term Complications of Treating Hydrocephalus
Follow linkage to chapter dedicated to the long-term outcome of patients with shunts.