Control of drop attacks with selective posterior callosotomy: Anatomical and prognostic data*

Objective: In a previous proof of concept study, selective posterior callosotomy achieved similar degree of control of drop attacks as total callosotomy, while sparing prefrontal interconnectivity. The present study aims to confirm this finding in a larger cohort and to provide anatomical and prognostic data. Methods: Fifty-one patients with refractory drop attacks had selective posterior callosotomy and prospective follow up for a mean of 6.4 years. Twenty-seven patients had post-operative magnetic resonance imaging (MRI) and 18 had tractography (DTI) of remaining callosal fibers. Pre and postoperative falls were quantified and correlated with demographic, clinical and imaging data. Results: Mean monthly frequency of drop attacks had a 95 % reduction, from 297 before to 16 after the procedure. Forty-one patients (80 %) had either complete or greater than 90 % control of the epileptic falls. Age and duration of epilepsy at surgery correlated with outcome (p values, respectively, 0.042 and 0.005). Mean index of callosal section along the posterior-to-anterior axis was 53.5 %. Extending the posterior section anterior to the midbody of the corpus callosum did not correlate with seizure control (p 0.91), providing fibers interconnecting the primary motor (M1) and caudal supplementary motor areas (SMA) were sectioned. Only one patient had a notable surgical complication which resolved in two days. Conclusions: This level III cohort study with objective outcome assessment confirms that selective posterior callosotomy is safe and effective to control epileptic falls. Younger patients with smaller duration of epilepsy have better results. A posterior section contemplating the splenium, isthmus and posterior half of the body (posterior midbody) seems sufficient to achieve complete or almost complete control of drop attacks.