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- Predictors of Seizure Recurrence
Purpose: To investigate the longitudinal seizure outcome and identify potential prognostic indicators following posterior cortex epilepsy (PCE) surgery.
Methods: We reviewed patients who underwent a parietal, occipital, or parietooccipital resections between 1994 and 2006, using survival analysis and multivariate regression with Cox proportional hazard modeling. A favorable outcome was defined as Engel Class I at last follow-up.
Results: Fifty-seven patients were identified with a mean follow-up of 3.3 years (range 1–12 years). The estimated chance of seizure freedom (SF) was 73.1% at 6 postoperative months, 68.5% at 1 year, 65.8% at between 2 and 5 years, and 54.8% at 6 years and beyond. Most recurrences (75%) occurred within the first 6 postoperative months. Parietal resections had a worse outcome than occipital or parietooccipital resections (52% SF vs. 89% and 93%, respectively, at 5 years). Independent predictors of recurrence included an epilepsy etiology other than tumor or dysplasia [risk ratio (RR) 2.29], limiting resection to a lesionectomy (RR 2.10), having ipsilateral temporal spiking on preoperative scalp electroencephalography (EEG) (RR 2.06), or any ipsilateral spiking on postoperative EEG (RR 2.70) (Log likelihood-ratio test p < 0.0001). Only 40–50% of patients with a poor outcome predictor were SF at 5 postoperative years as opposed to about 80% otherwise. In surgical failures, recurrent seizure frequency was related directly to baseline seizure frequency and to the presence of ipsilateral spiking on postoperative EEG.
Discussion: These data highlight favorable long-term outcomes following PCE surgery. Limited surgical resection and diffuse baseline epileptogenicity may be important predictors of seizure recurrence.
Despite major advances in diagnostic and surgical techniques, parietooccipital resections still represent <10% of all epilepsy surgeries (Barba et al., 2005; Blume et al., 2005; Dalmagro et al., 2005). Reported success rates vary from 25–90% (Blume et al., 1991; Salanova et al., 1992, 1995a,b; Williamson et al., 1992a,b; Cascino et al., 1993; Aykut-Bingol et al., 1998; Bautista et al., 1999; Boesebeck et al., 2002; Barba et al., 2005), leaving this patient category in an undefined “outcome group” between the traditionally considered more “favorable” prospects of anterior temporal lobectomy (Yoon et al., 2003; McIntosh et al., 2004; Jeha et al., 2006) and the frontal lobe surgeries with a relatively poor prognosis (Janszky et al., 2000; Jeha et al., 2007).
Many prior studies were descriptive, reporting on rates of seizure freedom (SF) following parietal (Williamson et al., 1992a; Cascino et al., 1993; Salanova et al., 1995a, 1995b) or occipital lobe resections (Williamson et al., 1992b; Kuzniecky et al., 1997) without identifying specific prognostic outcome indicators. Considering well-described difficulties in drawing anatomic and neurophysiologic distinctions between the occipital and parietal lobes (Sveinbjornsdottir & Duncan, 1993), other studies analyzed a single group of “posterior cortex” surgery limiting the ability to distinguish variations in surgical outcome and its predictors in cases with well-defined pathology in either lobe (Bautista et al., 1999; Boesebeck et al., 2002; Dalmagro et al., 2005). All previous reports were cross-sectional. Therefore, none evaluated longitudinal aspects of recurrence, or investigated potential prognostic predictors using modern statistical techniques designed for time-dependent outcomes.
Our goal is to describe the long-term seizure outcome and its predictors following parietal, occipital, and multilobar resections in the posterior cortex. We use the statistical methods of survival analysis and proportional hazard modeling to evaluate rate, stability, and predictors of SF while accounting for variation in the duration of follow-up among patients. In addition, we will briefly address the issue of postoperative complications.