Proximal catheter obstruction is known to be the most common cause of malfunctioning of ventriculoperitoneal (VP) shunt followed by infection and disconnection14,17). The optimal position of the catheter tip was focused to reduce potential occlusion of proximal catheter by ventricular parenchyma or choroidal tissues1,4,12). Many studies including Tuli et al.22) have shown that a ventricular catheter tip surrounded by cerebrospinal fluid (CSF) could decrease the risk of shunt failure25).

Accurate placement of ventricular catheter is related with both proper insertion trajectory and proper catheter tip positioning. So recently, many studies have validated accuracy in VP shunt with the development of frameless neuronavigation in the field of neurosurgery2,25). However, it has not clearly proven that the role of the catheter position using navigation system on failure rates. The authors conducted a retrospective study of navigated shunt placement about real impact on clinical shunt failure rates, comparing with standard shunt placement.

A total of 72 patients were participated in this study, 27 with the EM navigated shunts and 45 with the standard shunts. Eleven patients were children (11% of in the EM group. as 17% of the standard group) and 61 patients were adults. Patients had numerous causes from congenital anomaly to spontaneous or traumatic intracranial hemorrhage. Time interval of follow-up period was various from a day to 20 months. The baseline characteristics of the study patients are shown in Table 1.

According to the results of the previous studies, various methods have been suggested to improve the accuracy of catheter tip position. Pang and Grabb15) described a method of calculating catheter length based on bony landmarks on skull radiographs and a shunt placement by free-hand passage using simple stereotactic guidance and palpable surface anatomy. Serlo et al.18) ascertained the catheter position using X-ray imaging by filling the catheter with contrast medium. Neuroendoscopic procedures have also been used effectively16,24). Kestle et al.13) compared the revision rates after endoscopically versus non-endoscopically placed ventricular catheter. Despite placement of catheter tip under direct vision, that study concluded no differences in failure rates between 2 cohorts because burr hole and catheter trajectory were still based on anatomical landmarks1,11).

Frameless stereotaxy has been shown to be helpful for precise location of catheter tip and avoiding unnecessary injury to brain tissue, leading to prevent repeated shunt revisions in children with slit ventricles8,9,18). This study has demonstrated that neuronavigation in the placement of ventricular catheters assures optimal catheter position within ventricles, reducing revision rate in not only special cases, but also general shunt surgeries.

VP shunts are still often complicated by malfunction, predominantly with proximal catheter obstruction despite improved surgical equipment and operative skill10,14,19,25). About 30% to 50% of shunts fail within the first year and only 30% to 37% of shunts survive for 10 years without revision3,21,22,25). Choroid plexus has generally been considered to be the most frequent cause of ventricular catheter obstruction4,12,14,17). It is well known that the ideal placement of the proximal catheter tip is the frontal horn away from the choroid plexus5,7). The obstruction of catheter tip is caused by connective tissue, inflammatory changes, and foreign bodies which are found frequently at the ventricular end. Astrocytes and fibroconnective tissues are especially capable of proliferation. They may fill the side holes in the 15 mm from their tip and the inside of the catheter, leading obstruction of catheters2). Choroid plexus and ependymal cells also have proliferative capability under some conditions. Collins et al.6) frequently found choroid plexus in catheter tips placed in behind the foramen of Monro, but ependyma predominated in catheters placed in front of it.

A ventricular catheter tip surrounded by CSF decreased the risk of shunt failure to one-fifth, whereas a catheter tip touching the brain decreased the risk to one-third, compared with a catheter tip surrounded by brain tissue21,25). The significant relationship of tip position and shunt failure rate has already reported in our study. There might be several other factors to affect shunt catheter obstruction like type of catheter.

Although it is already demonstrated that endoscopically guided catheter insertion could get intended position of the tip with controversy, image guidance like neuronavigation system may be helpful in determining the entry point and approach trajectory before and during the procedure17). The EM group of this study has been found more in grade I, representing the close relationship of navigation and catheter position. Therefore, the formula can be established that use of EM navigation lead an ultimate catheter placement, resulting decrease of shunt failure rate.

There are several disadvantages to frameless neuronavigation which include the prolongation of operation time and dependence on expensive technology8,23,25). More operation time can have risk to increase intraoperative infection rate. In fact, 5 to 10 minutes can be required to install and to register the navigation by skilled person11). Stieglitz et al.20) described that the additional time needed for preparations did not exceed 15 minutes with their experiences. The DRF can be placed while anesthesia personnel are obtaining intravenous access1). The other problem is that frameless stereotaxy is expensive program. It requires additional imaging to be used for navigation with additional radiation dosage11). It also adds cost to the procedure of neuronavigation and to the use of a navigation stylet. As a practice matter, average 40% of total sum of money was charged to operation fee at our institution with EM navigation shunts. But, revision surgery needs more cost added on the first surgery11). Hayhurst et al.11) measured that cost of a shunt revision was ten times greater than the cost of a using navigation in their own country. Furthermore, the time span between revisions shortens progressively after second revision, indicating that economical disadvantages can be replicated14). Therefore, the cost-benefit ratio must be carefully established to obviate its need.

Mechanical malfunction and infection are the most significant problems associated with shunts for the treatment of hydrocephalus. Above all, a significant proportion of shunt failures were due to obstruction of the ventricular catheter, and accurate placement of the shunt catheter is highly important to reduce the incidence of shunt malfunction.

In conclusion, the use of EM navigated system in routine shunt surgery can eliminate poor shunt placement resulting in a dramatic reduction in shunt revision rates.