Surgery for insular low-grade glioma: predictors of postoperative seizure outcome

Object. Although a number of recent studies on the surgical treatment of insular low-grade glioma (LOG) have demonstrated that aggressive resection leads to increased overall patient survival and decreased malignant progression, less attention has been given to the results with respect to tumor-related epilepsy. The aim of this investigation was to evaluate the impact of volumetric, histological, and intraoperative neurophysiological factors on seizure outcome in patients with insular LGG. Methods. The authors evaluated predictors of seizure outcome with special emphasis on both the extent of tumor resection (EOR) and the tumor's infiltrative pattern quantified by computing the difference between the preoperative T2- and Ti-weighted MR images (Delta VT2T1) in 52 patients with preoperative drug-resistant epilepsy. Results. The 12-month postoperative seizure outcome (Engel class) was as follows: seizure free (Class I), 67.31%; rare seizures (Class II), 7.69%; meaningful seizure improvement (Class III), 15.38%; and no improvement or worsening (Class IV), 9.62%. Poor seizure control was more common in patients with a longer preoperative seizure history (p < 0.002) and higher frequency of seizures (p = 0.008). Better seizure control was achieved in cases with EOR >= 90% (p < 0.001) and Delta VT2T1 < 30 cm(3) (p < 0.001). In the final model, Delta VT2T1 proved to be the strongest independent predictor of seizure outcome in insular LGG patients (p < 0.0001). Conclusions. No or little postoperative seizure improvement occurs mainly in cases with a prevalent infiltrative tumor growth pattern, expressed by high Delta VT2T1 values, which consequently reflects a smaller BOR.