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Objective:
The purpose of this study is to define the incidence and degree of valve setting changes experienced in patients with ventriculoperitoneal (VP) shunts who underwent magnetic resonance imaging (MRI) examinations at our institution, to determine the vendor shunt models that were most susceptible to setting changes, and to characterize the short-term clinical consequences of setting changes due to MRI.

Materials and Methods:
In this institutional review board approved retrospective study, we reviewed pre- and postMRI skull radiographs in patients with VP shunts at our institution over an 18-year period. The following information for each patient was collected: gender, age and relevant diagnoses, the date of each MRI study conducted, presence of pre- and postMRI skull radiographs for each MRI examination, the shunt valve type, including vendor and model, the documented shunt settings before and after each MRI examination measured radiographically, any documented clinical consequences and follow up immediately following the MRI examination.

Results:
We identified 217 patients having undergone a total of 574 MRI examinations. Among these, 265 MRI examinations (46%) led to a radiographically evident change in shunt valve setting. Of the most common shunt valve types imaged, patients with the Medtronic Strata valve experienced a change in setting 65.5% of the time, those with the Codman Hakim programmable valve experienced a change in setting 60.0% of the time, and patients with the Codman CERTAS shunt valve experienced a change in setting 13.8% of the time. Of all MRI examinations, 29 (5%) led to short-term clinical changes that were temporally related to the MRI examination and 18 of these (3.1% of total) were also associated with documented changes in shunt setting. Common clinical changes included dizziness, somnolence, headache and weakness.

Conclusion:
VP shunt valve setting change immediately following MRI examinations is common, occurring in 46% of our patient cohort. We found a wide variance in rates of change between different vendor models. The most common type of VP shunt to show a setting change following an MRI examination was the Medtronic Strata valve. Short-term clinical changes were uncommon in our cohort, occurring in only 5% of patients. Of patients with these clinical changes, 62% also had radiographically identifiable VP shunt valve changes. Overall, VP shunt valve changes following an MRI examination are common in clinical practice. Fortunately, associated short-term clinical changes are uncommon. Organizations offering MRI examinations for patients with VP shunts should be aware of these findings and follow VP shunt vendor instructions to safely image this special patient population.