SUMMARY: The programmable CSF shunt valve has become an important tool in hydrocephalus treatment, particularly in the NPH population and in pediatric patients with complex hydrocephalus. The purpose of this study is to provide a single reference for the identification of programmable shunt valves and the interpretation of programmable shunt valve settings. Four major manufacturers of programmable shunts agreed to participate in this study. Each provided radiographic images and legends for their appropriate interpretation. Issues of MR imaging compatibility for each valve are also discussed.
AbbreviationsH high L low M medium NPH normal pressure hydrocephalus P/L performance levels
Hydrocephalus affects between 1% and 2% of the population. It accounts for 70,000 hospital admissions annually and the placement of between 18,000 and 33,000 CSF shunts in the United States each year. Because one-third of all shunts fail within 1 year of placement and the manifestations of shunt failure are protean, patients with shunts frequently undergo radiographic evaluation. These evaluations include not only cross-sectional imaging with CT and MR imaging but also plain radiographs of the shunt system.
Most CSF shunts consist of 3 components: a ventricular catheter, a valve, and a distal catheter. A shunt is a completely internalized system, as opposed to an external ventricular drain in which a ventricular catheter drains to a collection system at the bedside. The catheter components of a shunt are made from Silastic (Dow Corning, Midland, Michigan), a form of rubber tubing resistant to breakdown in the body. They are frequently impregnated with radiopaque material to aid in their radiographic visualization. The ventricular catheter sits within 1 of the ventricular spaces in the brain, most commonly the right lateral ventricle. The ventricular catheter is connected to a valve that regulates flow. To counter a siphoning effect associated with upright posture, many shunt systems also include an antisiphon device; this reduces overdrainage when the patient is standing.
Historically, shunt valves permitted a fixed amount of CSF drainage. This required the surgeon to select a specific valve for implantation, and if overdrainage or underdrainage resulted, a second operation was required to change the valve. The programmable valve is an important advancement in shunt technology. It provides the option of changing the opening pressure of the valve transcutaneously, most commonly with a device using a coded magnetic field. Although most valves placed in the United States are still fixed-pressure valves, the programmable valve has become an important tool in hydrocephalus treatment, particularly in the NPH population and in pediatric patients with complex hydrocephalus.
Patients with NPH often require multiple adjustments of opening pressure to optimize cognitive function and gait stability, while avoiding overdrainage and the secondary subdural effusion. Other patients with hydrocephalus have a very narrow therapeutic window between symptomatic overdrainage and symptomatic underdrainage. Because programmable valves allow noninvasive fine tuning of the opening pressure in these difficult patient populations, their use is increasing. While the dependability and relatively low cost of fixed-pressure valves will likely ensure their continued use, the programmable valve is now an important established tool in the treatment of hydrocephalus. It is important to be aware of the impact of the programmable valve on patient management and, specifically, of the altered significance of ventricular size change in these patients.
The purpose of this study was to provide a single reference containing radiographic depictions of the major programmable shunt valves in current use as well as information for accurate reporting of shunt valve settings. This will assist radiologists and other physicians in the complete assessment of skull radiographs in patients with shunts. We have also consolidated the current recommendations of the manufacturers regarding MR imaging compatibility of these valves.
Materials and Methods
Major shunt manufacturers were contacted and asked to participate in this study. Four companies currently producing ≥1 programmable shunt valve agreed to participate: Aesculap (Tuttlingen, Germany), Codman/Johnson & Johnson (Raynham, Massachusetts), Medtronic (Minneapolis, Minnesota), and Sophysa (Orsay, France). The manufacturers provided photographs and plain radiographs of programmable shunt valves in current production as well as the appropriate legends describing the appearance of the valves at various settings. As of this date, these are the most commonly used programmable shunt valves in the United States. Each participating manufacturer provided written permission to publish the images herein.