Unilateral Approach for Bilateral Posterior Cingulate Coverage in Stereoelectroencephalography: A Technical Note and Case Series

BACKGROUND AND OBJECTIVES: Posterior cingulate cortex (PCC) epilepsy is a rare focal epilepsy variant, recognized as a propagation zone for commonly encountered types of epilepsy. Stereoelectroencephalography (SEEG) is the preferred method for identifying the seizure-onset zone (SOZ) and propagation zone in patients with complex epilepsy. Previous studies document the use of transhemispheric anterior and mid-cingulate electrodes. However, to our knowledge, bilateral coverage of the PCC has not been reported. Physical impediments, including the falx cerebri and proximity to deep cerebral veins, have limited consideration. This study assesses the feasibility and efficacy of unilateral transhemispheric SEEG placement for investigating bilateral PCC. METHODS: We describe the operative technique for 12 patients who underwent bilateral PCC coverage using transhemispheric electrodes. Outcomes from implantation and accuracy were computed to assess the safety of these trajectories. A nonenhancing falx and absence of falcine calcification were considered as radiologic indicators that unilateral placement was feasible. RESULTS: All transhemispheric leads were placed without any complications with all but one requiring a transfalcine approach. Postoperative error analysis showed a median Euclidean entry error of 0.75 mm (IQR: 0.52-1.15), median radial entry error of 0.75 mm (IQR: 0.52-1.00), median Euclidean target error of 1.53 mm (IQR: 1.06-2.36), and median radial target error of 1.24 mm (0.91-1.76). Eleven patients demonstrated the PCC to be involved in the propagation zone, but none were the SOZ. CONCLUSION: We have shown that the unilateral transhemispheric approach for bilateral PCC SEEG is feasible to sample both sides. Importantly, the transfalcine approach used, and previously considered a relative contraindication, was performed safely and accurately in our series. We demonstrated the utility of sampling both ipsilateral and contralateral PCC to identify the epilepsy network. Thus, unilateral SEEG for bilateral coverage, including transfalcine, provides an approach to consider, when exploring the PCC and other midline cortical regions.