SUBDURAL GRID IMPLANTATION FOR INTRACRANIAL EEG RECORDING - CT AND MRAPPEARANCE

PURPOSE: Subdural grid arrays are used when seizure activity cannot be located by ictal scalp recordings and when functional cortical mappin g is required before surgery, This study was performed to determine an d compare the CT and MR imaging appearance of subdural EEG grids and t o identify the types and frequency of associated complications. METHOD S: We retrospectively reviewed the medical records and imaging studies of 51 consecutive patients who underwent 54 craniotomies for subdural EEG grid implantation with either stainless steel or platinum alloy c ontacts between June 1988 and September 1993, Twenty-two patients had both CT and MR examinations, 27 patients had CT only, and five patient s had MR imaging only, All studies were assessed for image quality and degradation by the implanted EEG grids, for intra- and extraaxial col lections, and for mass effect, with differences of opinion resolved by consensus. RESULTS: Subdural EEG grids caused extensive streak artifa cts on all CT scans (corresponding directly to grid composition) and m ild to moderate magnetic susceptibility artifacts on MR images. Sixtee n associated complications were detected among the 54 patients imaged, including four significant extraaxial hematomas, four subfalcine or t ranstentorial herniations, two tension pneumocephali, two extraaxial C SF collections, two intraparenchymal hemorrhages, and one case each of cerebritis and brain abscess,In all but four cases, the detected comp lications were not clinically apparent and did not require specific tr eatment. There were no residual sequelae, CONCLUSION: Because of exten sive streak artifacts, CT showed only gross complications, such as her niation and grid displacement by extraaxial collections. MR imaging ar tifacts were more localized, allowing superior evaluation of subdural EEG grid placement and associated complications.