Neurosurgical shunts and their complications

Arthur E Marlin MD (Dr. Marlin of the University of South Florida has no relevant financial relationships to disclose.)
Sarah J Gaskill MD (Dr. Gaskill of the University of South Florida has no relevant financial relationships to disclose.)
Matthew Lorincz MD PhD, editor. (Dr. Lorincz of the University of Michigan receives salary support from Wilson Therapeutics AB for performing UWDRS examinations in a clinical trial.)
Originally released August 16, 1999; last updated May 19, 2016; expires May 19, 2019

Overview

The mainstay treatment for hydrocephalus remains the placement of a ventricular shunt with a terminus most commonly in the peritoneum, atrium, or pleural cavity. Although this is an effective treatment, there are numerous complications that can occur in the operative placement and management of neurosurgical shunts. The latest thoughts on the placement and management of shunts are highlighted in this overview. The importance of minimizing radiation exposure in the evaluation of the shunted patient is discussed, including the use of rapid sequence MRI scans for surveillance and emergent evaluation. The potential impact of tablet computers on programmable shunts is also reviewed.

Key points

 

• Shunt malfunction is a life-threatening condition and must be treated urgently.

 

• It is imperative when evaluating for a potential shunt malfunction, the “baseline” image is known to have been taken at a time of shunt function to avoid the misinterpretation of “no change” as the incorrect conclusion of “no evidence of shunt malfunction.”

 

• Image gently in shunted patients as their lifetime exposure to unnecessary radiation puts them at increased risk of developing leukemia, brain tumors, and other cancers.

 

• Attention to detail in the operating room (reduced traffic, preoperative antibiotics, patient preparation, and efficient operating) is key to reducing shunt infections.

Historical note and terminology

Hydrocephalus is one of the most commonly encountered pediatric neurosurgical diseases.

Image: Shunt malfunction (CT)
The first implantable shunt was placed in 1952 by Nulsen and Spitz (Nulsen and Spitz 1951), and since then shunt placement has remained the most common treatment of hydrocephalus. The peritoneum is the most common location for placement of the distal catheter; however, the distal end can also be placed in the right atrium, pleural cavity, or gallbladder. Since the 1960s, the use of modern shunts has become commonplace. As a mechanical device, a shunt can be expected to fail at a rate of approximately 10% a year. Shunt malfunction is a life-threatening condition, and any neurosurgical center serving a large population performs a significant number of ventriculoperitoneal shunt revisions, the procedure most frequently performed in children by neurosurgeons (Sainte-Rose et al 1991; Piatt and Carlson 1993; Lazareff et al 1998). More importantly, the possibility of malfunction impacts significantly on the quality of life of patients with shunted hydrocephalus (Iskandar et al 1998b). This article concentrates on the nature of shunt malfunction, its diagnosis, and management.

Shunt malfunctions.

Image: Shunt malfunction (rsMRI)
When assessing shunt malfunctions, it is critical that the comparison images are known to have been taken in the setting of a functioning shunt. If the comparison image is from a time of shunt malfunction, the interpretation may be that there is no change in the ventricular size and, therefore, no shunt malfunction. Shunt failures can occur due to obstruction, disconnection, migration, fracture, ascites, abdominal pseudocyst, infections, and even constipation (Kariyattil et al 2007; Martínez-Lage et al 2008). The most common type of mechanical obstruction is blockage of the ventricular catheter, usually by the growth of choroid plexus into the ventricular catheter. Occlusion of the ventricular catheter is the cause of nearly two thirds of mechanical obstruction of shunts. This particular problem increases the risk of hemorrhage during a shunt revision as the removal of the ventricular catheter can cause bleeding from the highly vascular choroid plexus, resulting in intraventricular and parenchymal hemorrhage. This hemorrhage increases the risk of subsequent shunt malfunction and can also result in more severe neurologic injury. The shunt system can occlude anywhere along its course, including the proximal catheter, reservoirs, the valve, and the distal tubing.

Disconnection of a shunt rarely occurs shortly after placement of a new shunt unless there was a technical error, such as not attaching the catheter effectively. In some shunt systems, the ventricular catheter snaps on to a reservoir, and if this is not done adequately the ventricular catheter can disconnect from the reservoir, resulting in malfunction.

Image: Shunt disconnection
Late fractures often result from chronic mechanical stress associated with patient growth and movement. Using spectroscopy, conventional histology, and scanning electron microscope, Yamamoto and colleagues found that mineral deposits in degraded shunt tubing consisted of hydroxyapatite (Yamamoto et al 2002). The most extensive calcification was seen in the neck, presumably due to the increased mechanical stress in this region.
Image: Disrupted shunt with calcification in the neck
Most surgeons will revise a shunt when a fracture or disconnection is demonstrated because the fibrous tract along a fractured shunt can drain CSF for an indeterminate length of time but ultimately fail (Kazan et al 2000). Deposition of sodium chloride and other crystals involving the valve has also been demonstrated as a contributing factor in shunt malfunction (Sgouros 2004).

Distal obstruction is far less common than proximal obstruction. In particular, premature infants with a high protein count in their CSF may present with a distal obstruction without infection. In premature infants with certain types of shunts, the obstruction can often be cleared by irrigating the shunt, obviating the need for an operation. Distal obstructions can be associated with an infection. When distal obstruction is suspected, an abdominal ultrasound study can be useful to look for a pseudocyst, ascites, or constipation. CSF ascites can be due to infection, shunt disseminated metastases, or poor absorption of CSF into the peritoneum. Infection must be ruled out in cases of ascites. Abdominal pseudocysts are infected in 17% to 80% of cases (Mobley et al 2005). It is more common for a small pseudocyst to be infected than a large one (Gaskill and Marlin 1989).

The evaluation of a shunt malfunction is first and foremost a complete history and physical examination including a funduscopic examination. The Image Gently campaign has emphasized the importance of reconsidering the need for radiation as well as altering the type of radiation performed, particularly in children (Goske et al 2008). Children with ventriculoperitoneal shunts are at risk of developing malignancies at a later date if the exposure to diagnostic radiation is not carefully considered with every evaluation (Smyth et al 2008; Pearce et al 2012). There are studies to support not performing a routine shunt series in every child with a possible shunt malfunction unless there is clinical evidence to suggest a break, an x-ray may not even be necessary (Blumstein and Schardt 2009). If available, rapid sequence MRI can be used to assess the ventricular size. The advantage of rsMRI is that there is no radiation and it does not require sedation as it can be performed in less than 1 minute (Wait et al 2012). If that modality is not available, consideration of a low-dose CT would be another option for minimizing radiation exposure (Udayasankar et al 2008). In the child with an open fontanelle, ultrasound is effective. In any event, careful consideration should be given to ordering diagnostic radiation in these patients. The routine of ordering a shunt series and a CT scan on all cases, often even prior to notifying the neurosurgeon, must be stopped.

One publication describes the use of cerebral regional oxygen saturation monitoring in the assessment of pediatric shunt patients (Abramo et al 2013). This technology has been used most commonly for the intraoperative monitoring of children undergoing repair of congenital heart disease. The advantage is that it is a noninvasive, easy-to-apply technology that gives instantaneous readings. The researchers found that in the setting of malfunctioning shunts, there was an asymmetrical hemispheric cerebral regional oxygen saturation. Although this methodology requires more study, it potentially provides another noninvasive and safe technique for the evaluation of shunt malfunction.

In shunted adult patients with a diagnosis of normal pressure hydrocephalus, a technique of using noninvasive auditory tests (as currently used for universal neonatal hearing screenings) for the diagnosis of cerebrospinal fluid shunt malfunction was described by Sakka and colleagues (Sakka et al 2015).

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