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Zofia Czosnyka, John D. Pickard, and Marek Czosnyka

Object

Independent testing of hydrocephalus shunts provides information about the quality of CSF drainage after shunt implantation. Moreover, hydrodynamic parameters of a valve assessed in the laboratory create a comparative pattern for testing of shunt performance in vivo. This study sought to assess the hydrodynamic parameters of the Certas valve, a new model of a hydrocephalus shunt.

Methods

The Certas valve is an adjustable ball-on-spring hydrocephalus valve. It can be adjusted magnetically in vivo in 7 steps, equally distributed within the therapeutic limit for hydrocephalus, and the eighth step at high pressures intended to block CSF drainage. The magnetically adjustable rotor is designed to prevent accidental readjustment of the valve in a magnetic field, including clinical MRI.

Results

The pressure-flow performance curves, as well as the operating, opening, and closing pressures, were stable, fell within the specified limits, and changed according to the adjusted performance levels. The valve at settings 1–7 demonstrated low hydrodynamic resistance of 1.4 mm Hg/ml/min, increasing to 5.1 mm Hg/ml/min after connection of a distal drain provided by the manufacturer. At performance Level 8 the hydrodynamic resistance was greater than 20 mm Hg/ml/min. External programming of the valve proved to be easy and reliable. The valve is safe in 3-T MRI and the performance level of the valve is unlikely to be changed. However, with the valve implanted, distortion of the image is substantial. Integration of the valve with the SiphonGuard limits the drainage rate.

Conclusions

In the laboratory the Certas valve appears to be a reliable differential-pressure adjustable valve. Laboratory evaluation should be supplemented by results of a clinical audit in the future.

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Hugh K. Richards, Helen M. Seeley, and John D. Pickard

Object

In recent years CSF shunt catheters impregnated with rifampicin and clindamycin have been introduced to the United Kingdom (UK) market. These catheters have been shown to be effective in vitro against cultures of Staphylococcus epidermidis. The authors used data collected by the UK Shunt Registry to assess the efficacy of antibiotic-impregnated catheters (AICs) against shunt infection by using a matched-pair study design.

Methods

The UK Shunt Registry contains data on nearly 33,000 CSF shunt-related procedures. The authors identified 1139 procedures in which impregnated catheters had been used, and accurate information was known about diagnosis, number of revisions, sex, and age in these cases. The database was ordered chronologically and searched forward and backward for cases with these same characteristics but involving conventional catheters. Matches were found for 994 procedures.

Results

Among the 994 procedures in which AICs had been used, 30 shunts were subsequently revised because of shunt infection. Among the 994 controls, 47 were subsequently revised for infection (p = 0.048, chi-square test).

Conclusions

The UK Shunt Registry does not collect data on causative organisms, and the surgeon is relied on entirely for the diagnosis of infection. However, with the large number of matched pairs evaluated, the authors attempted to reduce bias to a minimum. Their data suggest that AICs have the potential to significantly reduce shunt infections.

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Letter to the Editor

Shunt catheters

Michael Kiefer and Regina Eymann

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Andrea Lavinio, Sally Harding, Floor Van Der Boogaard, Marek Czosnyka, Peter Smielewski, Hugh K. Richards, John D. Pickard, and Zofia H. Czosnyka

Object

Exposing patients with ventricular shunts to magnetic fields and MR imaging procedures poses a significant risk of unintentional changes in shunt settings. Shunt valves can also generate considerable imaging artifacts. The purpose of this study was to determine the magnetic field safety and MR imaging compatibility of 5 adjustable models of hydrocephalus shunts.

Methods

The Codman Hakim (regular and with SiphonGuard), Miethke ProGAV, Medtronic Strata, Sophysa Sophy and Polaris programmable valves were tested in a low-intensity magnetic field, and then translational attraction (TA), magnetic torque (MT), and volume of artifacts on T1-weighted spin echo (SE) and gradient echo (GE) pulse sequences in a 3-T MR imaging unit were measured.

Results

The ProGAV and Polaris valves were immune to unintentional reprogramming by magnetic fields up to 3 T. Other valves randomly changed settings, starting from the intensity of field: Sophy valve 24 mT, Strata valve 30 mT, and both Codman Hakim programmable valves from 42 mT. Shunt performances in the 3-T MR imaging unit are reported in the order of compatibility: 1) Codman Hakim regular, TA = 0.005 N, MT = 0.000 Nm, GE = 30 cm3, SE = 2 cm3; 2) Miethke ProGAV, TA = 0.001 N, MT = 1.4 × 10−3 Nm, GE = 231 cm3, SE = 13 cm3; 3) Codman Hakim with SiphonGuard, TA = 0.005 N, MT = 2.3 × 10−3 Nm, GE = 233 cm3, SE = 19 cm3; 4) Medtronic Strata, TA = 0.27 N, MT = 18.0 × 10−3 Nm, GE = 484 cm3, SE = 86 cm3; 5) Sophysa Sophy, TA = 0.82 N, MT = 38.9 × 10−3 Nm, GE = 758 cm3, SE = 72 cm3; and 6) Sophysa Polaris, TA = 0.80 N, MT = 39.6 × 10−3 Nm, GE = 954 cm3, SE = 100 cm3.

Conclusions

All valves, with the exception of the Polaris and ProGAV models, are prone to unintentional reprogramming when exposed to heterogeneous magnetic fields stronger than 40 mT. All tested valves can be considered safe for 3-T MR imaging. All valves generated a distortion of the MR image, especially the GE sequences.