Enhancing outcomes of endoscopic vertical approach hemispherotomy: understanding the role of "temporal stem" residual connections causing recurrence of seizures.

Abstract

The authors sought to analyze the residual connections formed by the temporal stem as a cause for seizure recurrence following endoscopic vertical interhemispheric hemispherotomy and to review and compare lateral approach (perisylvian) with vertical approach surgical techniques to highlight the anatomical factors responsible for residual connections. This study was a retrospective analysis of patients who underwent endoscopic hemispherotomy for drug-resistant epilepsy. Postoperative MR images were analyzed. Specific attention was given to anatomical 3D-acquired thin-section T1 images to assess the extent of disconnection, which was confirmed with a diffusion tensor imaging sequence. Cadaver brain dissection was done to analyze the anatomical factors responsible for persistent connections. Of 39 patients who underwent surgery, 80% (31/39) were seizure free (follow-up of 23.61 ± 8.25 months) following the first surgery. Thirty patients underwent postoperative MRI studies, which revealed persistent connections in 14 patients (11 temporal stem only; 3 temporal stem + amygdala + splenium). Eight of these 14 patients had persistent seizures. In 4 of these 8 patients, investigations revealed good concordance with the affected hemisphere, and repeat endoscopic disconnection of the residual connection was performed. Two of the 8 patients were lost to follow-up, and 2 had bihemispheric seizure onset. The 4 patients who underwent repeat endoscopic disconnection had seizure-free outcomes following the second surgery, increasing the good outcome total among all patients to 90% (35/39). Cadaveric brain dissection analysis revealed the anatomical factors responsible for the persistence of residual connections. In endoscopic vertical approach interhemispheric hemispherotomy (and also vertical approach parasagittal hemispherotomy) the temporal stem, which lies deep and parallel to the plane of disconnection, is prone to be missed, which might lead to persistent or recurrent seizures. The recognition of this limitation can lead to improved seizure outcome. The amygdala and splenium are areas less commonly prone to be missed during surgery.