Pathology of Shunt Infections in Children

Pathophysiology

• Source of infection uncertain: Although pathogens associated with CSF shunt infection are in most cases normal skin flora, less than 50% of the organisms cultured from infected shunts can be traced back to the patient or the operative field at the time of shunt insertion (20).
• Patient factors: The skin of a premature child has a thickness of a few millimeters and is prone to breakdown due to pressure from the profile of the underlying shunt. A tear in or injury to the skin during the passing of the distal shunt catheter can lead to an infection.
• Environmental factors: The use of laminar flow ventilation and reducing the time between the removal of the shunt from its packaging and its insertion are two measures that have been suggested for minimizing the risk of wound infection by bacteria normally found in the operating room environment. However, recent studies have raised questions about the the efficacy of laminar flow in preventing surgical site infections (57, 99).
• CSF constitutes an excellent bacterial growth culture: Under normal conditions CSF is an isotonic, ionically balanced glucose solution free of leukocytes and antibodies. If this fluid is encased within a CSF shunt system, the host responses are isolated (124).
• Surgical preparation factors: There is insufficient evidence to state whether removing hair impacts surgical site infection or when the best time to remove hair may be. Skin flora can rapidly recolonize the surgical field after completion of the surgical prep (150, 151).
• Distal “retrograde” infection: Distal catheters can slowly erode their way into a hollow viscus, thereby leading to retrograde spread of microorganisms. Whenever there is more than one biological agent, e.g., gram-positive and gram-negative bacteria, a bowel perforation should be suspected (136).
• Hematogenous spread: Debilitated children (e.g., premature infants, neonates with sepsis, children on hemodialysis) or those with indwelling central venous catheters are prone to experiencing bacteremia with potential contamination of foreign materials, including CSF shunts.
• No increased risk associated with shunt tap: The real risk of contaminating a shunt while performing a “shunt tap” appears to be extremely low, and therefore the clinician must not hesitate to perform this procedure whenever a shunt infection is suspected.

Micropathology

• Majority skin flora: The majority of isolated organisms in cultured CSF from infected shunts reflect the skin flora at the implant sites. In older individuals these tend to be gram-positive staphylococcal organisms, whereas in infants gram- negative fecal organisms are more common.