The presenting symptomatology of shunt infection can vary depending on the age and weight of the patient and can range from subtle shunt malfunction (e.g., decreased school performance, loss of desire to play) to septic shock in very-low-weight preterm infants.
- Shunt malfunction most common: Presenting symptoms are those of shunt malfunction in up to 65% of patients. Infected shunts can present with evidence of distal catheter malfunction, with ventricular enlargement, and in many cases with fluid accumulation along the shunt tract as CSF tries to find a diversion path. During the early stages of this process, the CSF analysis and cultures from the shunt reservoir may remain normal. Gradually the distal slits, if present, become filled with protein exudate that tethers the catheter to the surrounding omentum. This can cause resistance when the catheter is pulled from the abdominal cavity.
- Systemic signs of infection: Systemic signs include irritability and fever.
- Cutaneous signs of shunt infection: Wound dehiscence and tenderness along the subcutaneous shunt tract are typical signs of a chronically infected shunt. Wounds may break down with exposure of shunt hardware and purulent discharge, and in some severe cases the skin flap over a valve may become necrotic.
- Abdominal pseudocyst: The formation of abdominal pseudocysts, which present with mass effect and abdominal distension, can be the presenting sign of a shunt infection.
- Acute abdomen: It is not infrequent to find that children with a shunt who were operated on because of the suspicion of acute abdominal pathology (e.g., appendicitis) actually have a shunt infection with bacteria-laden CSF draining into the peritoneum (127, 140).
- Spread of infection to CNS: The progression of an infected shunt system to serious meningitis/ventriculitis, brain abscess, and/or empyema is now rather rare, as awareness of these complications has led to earlier diagnosis (87).
Patterns of evolution
- Early infection after implantation: Wound dehiscence usually presents within 7–10 days after implantation of a shunt if it is to occur. It is not rare to find wound edges that open immediately after removal of suture material. In this case it is assumed that the shunt hardware became inoculated with skin bacteria (usually Staphylococci) at the time of insertion and that host mechanisms and prevention strategies failed to minimize bacterial growth.
- Intermediate infections after implantation: In this period, which can extend for 180 days after implantation, an infection will present with signs and symptoms of a shunt malfunction, evidence of wound and shunt tract tenderness, or only patient irritability associated with fever.
- Long delay after implantation: Shunts that have been implanted for years without previous evidence of infection can suddenly become infected. Reasons for this phenomenon may be an associated systemic infection that colonized the shunt via the bloodstream or a localized infection that spread to the shunt hardware (e.g., skin ulcers, tracheostomy and gastrostomy sites, skin cellulitis). In many cases, however, an associated infection is not demonstrated, leading to the hypothesis that microorganisms either found their way from the dermal layers to the shunt or inoculated the shunt materials at the time of insertion and lay dormant until the host defenses gave way to allow for increased bacterial activity.
Evaluation at Presentation
- See EVALUATION
When facing a patient with an infected CSF shunt device, the neurosurgeon should consider several factors to define the best sequence of steps in management:
- Raised ICP: Intracranial hypertension should always be a priority to rule out as shunt mechanism failure could be associated with infection. If this is the case, shunt removal and EVD placement should be performed at once.
- Complicated infection within intracranial space: Ventriculitis with formation of multiple septums and pockets of infected CSF, brain abscess, epyema, and dural sinus thrombosis can be terminal complications of an infected shunt and will require several different approaches in addition to removal of the infected device and placement of an EVD.
- Complicated infection distally: Distal catheter complications range from peritonitis resulting from bacteria-laden CSF draining into the abdominal cavity to bowel, cul de sac, or bladder perforation. When the distal catheter drains into alternate compartments, infected pleural effusions, bacteremia, and cholecystitis can occur (103). Catheter removal and antibiotic treatment may be sufficient in the case of a perforated viscus, thereby avoiding the need of a laparotomy.
- Systemic considerations: The medical history and workup should seek associated comorbidities that may prevent emergent surgery until the patient has been properly balanced for general anesthesia (e.g., severe electrolyte imbalance, coagulopathy, decompensated shock).
Preparation for definitive intervention, non-emergent
- Await culture results: Patients who have some evidence suggestive of CSF shunt infection but no positive gram stains on the initial stain can await definite culture results to confirm the diagnostic suspicion. When the definitive CSF culture results are known, the decision to extract the shunt and replace it with an EVD will follow other specific strategies.
- Externalize distal catheter: If there are no immediate threats to the patient’s health, the distal catheter can be exteriorized at clavicle level and attached to a sterile EVD drainage bag.
Preparation for definitive intervention, emergent
- Control ICP and infection: Two considerations dictate the initial intervention on an unstable child with a shunt infection. First, the ICP must be normalized by securing adequate CSF flow through the shunt or an EVD. Second, the systemic and CNS effects of the infection must be controlled with broad spectrum antibiotics that can later be tailored according to culture results. If present, septic shock, seizures, or metabolic imbalance should be corrected accordingly.
- EVD setup: Some centers have adopted the strategy of leaving a valve coupled to the distal end of the EVD catheter to maintain a constant ICP and avoid accidental overdrainage. This strategy has logistical advantages, but further studies are warranted to define its value in terms of cost and effectiveness. Since most patients will have an EVD that is not protected by a valve, mandatory bed rest is enforced to keep drainage at a constant level. The height of the drainage chamber of the EVD will depend on individual patient characteristics (age and height). The height will vary in accordance with the normal ICP valves for children of the same age.
- Antibiotics: Antibiotic treatment will be tailored to patient needs. Commonly a consultation is obtained from the Infectious Disease specialists for guidance in the selection of the antibiotics and their management.