Programmable CSF Shunt Valves: Radiographic Identification and Interpretation

Abstract

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.ABBREVIATIONS: H ϭ high; L ϭ low; M ϭ medium; NPH ϭ normal pressure hydrocephalus; P/L ϭ performance levels H ydrocephalus affects between 1% and 2% of the population.1 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.2 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.3 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. 4 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 w...

Congenital Hydrocephalus

“…Most valves are compatible with MRI machines up to 3 T; however, evaluation after imaging and readjustment of the settings may be needed to ensure that correct opening pressure is maintained. 23,24 …”

Optimization of Codman® Hakim® adjustable valve radiography

“…[1][2][3] The abnormal intracranial pressure is handled (or treated) using a shunt system with an implanted valve, which is either adjustable or non-adjustable. 4,5 The valve helps drain excess CSF from the cerebral ventricular system to the atrial-(VA shunt) or peritoneal (VP shunt) space through a catheter. 6 Patients are at all ages; however, the majority are rather young.…”

“…Adjustable valves are sensitive to magnetic fields. 4,11 Therefore, radiography is important to control the settings before and after magnetic resonance imaging (MRI).…”

Shunt Overdrainage Caused by Displacement of the Pressure Control Cam after Pressure Adjustment

“…Salomon and Hakim during the late 1980s, and it has been one of most popular shunt systems used in the clinical practice for the treatment of hydrocephalus 7). It allows for a precise control of the cerebrospinal fluid (CSF) drainage by noninvasive adjustments using magnetic impulses into one of 18 different pressure settings within a range of 30 to 200 mmH 2 O 2367)…”