Interdisciplinary Neurosurgery (Dec 2021)
Category-2 shunt valve marketed as MRI-Conditional malfunction following routine 3 T magnetic resonance imaging
Abstract
Background: CSF diversion techniques have been in use for decades, with the first plastic-based ventricular shunt designs originating in the 1960 s. The first generation of valves, termed fixed differential pressure (DP) valves, have a fixed flow rate (low, medium, or high) and require surgical replacement of the valve in order to alter CSF flow dynamics. Second-generation valves, including GAV, dual switch, Delta, Orbis-Sigma, and Sophysa/Siphon X, incorporate an antisiphon mechanism to avoid over drainage. Other second-generation valves are programmable differential pressure valves, and include the Sophy, SPV, CHPV, and Strata NCS. MRI conditional programmable shunts has become a feature of newer models and generations of shunt valves. The benefit of MRI conditionality is considerable, as it diminishes concern for valve setting changes due to MRI magnetism and hence theoretically eliminates the need for post-MRI setting verification. Here we present the case of a patient with a category-2 shunt valve marketed as MRI-conditional placed in 2018 with subsequent valve setting change following MRI and inability to perform external shunt valve setting adjustment following MRI. Case Description:: The patient is a 35 year-old woman with a history of posterior fossa medulloblastoma, who underwent surgical resection of this tumor in 2017. Following tumor resection, she developed hydrocephalus, for which she underwent ventriculoperitoneal shunt (VPS) placement with the category-2 shunt valve marketed as MRI-conditional. She underwent follow-up brain MRI that was performed at 1.5 Tesla, and in accordance with valve manufacturer guidelines. The following morning, her mental status declined and EEG demonstrated left-hemisphere rhythmic delta activity, for which she was loaded with antiepileptic medications. Head CT (Fig. 2) demonstrated evidence of hydrocephalus with transependymal CSF flow. VPS series showed the category-2 shunt valve marketed as MRI-conditional (Certas Plus) at a setting of 7.0, in contrast to her prior setting of 4.0. An emergent VPS revision was performed, at which time the valve was replaced. Conclusions: In this case, we present a patient with a shunt valve that is marketed as designed to minimize the unintended setting changes from magnetic interference 3 T MRI, which demonstrated evidence of unexpected setting change with inability to externally adjust following routine MRI. Within 48 h of MRI, she had developed symptoms of elevated intracranial pressure for which she required emergent surgical shunt revision. This case demonstrates the necessity of constant vigilance of possible valve complications, regardless of reported product features. Monitoring valve function closely can avoid potentially fatal malfunctions when detected early.
