Supplementary Material for: Abnormal T<sub>2</sub>-Weighted MRI Signal Surrounding Leads in a Subset of Deep Brain Stimulation Patients

<i>Background:</i> Deep brain stimulation (DBS) surgery is a common treatment option for numerous neurological disorders. However, it is not without potential complications, such as hemorrhage and infection. Interestingly, we have observed several instances of abnormal T<sub>2</sub>-weighted signal hyperintensity surrounding DBS leads on postoperative MRI that are not associated with hemorrhage or infection. <i>Methods:</i> To better characterize the incidence and timing associated with this finding, we retrospectively reviewed postoperative imaging for all DBS implants performed over 9 years at one institution. <i>Results and Conclusions:</i> Fifteen instances of T<sub>2</sub> signal hyperintensity surrounding DBS leads on postoperative MRI scans were observed across 239 implants (6.3% incidence) in 133 patients. The signal characteristics were most consistent with vasogenic edema, possibly representing an inflammatory response. The finding was typically unilateral, even in patients with simultaneous bilateral lead implants. Most affected patients were asymptomatic, although 3 were symptomatic and 1 experienced marked gait instability that was treated with steroids. T<sub>2</sub> signal abnormality was seen more commonly in scans obtained 3 or more days after surgery than in those collected immediately postoperatively. No differences in age, anatomical target, diagnosis, or number of microelectrode passes were noted between patients with or without T<sub>2</sub> signal. Further research will be needed to explain this curious neuroimaging finding, and to rule out cause for clinical concern.