Abstract
ObjectiveFocal cortical dysplasia (FCD) represents a heterogeneous group of disorders of the cortical formation and is one of the most common causes of epilepsy. Magnetic resonance imaging (MRI) is the modality of choice for detecting structural lesions, and the surgical prognosis in patients with MR lesions is favorable. However, the surgical prognosis of patients with MR-negative FCD is unknown. We aimed to evaluate the long-term surgical outcomes and prognostic factors in MR-negative FCD patients through comprehensive presurgical data.MethodsWe retrospectively reviewed data from 719 drug-resistant epilepsy patients who underwent resective surgery and selected cases in which surgical specimens were pathologically confirmed as FCD Type I or II. If the epileptogenic focus and surgical specimens were obtained from brain areas with a normal MRI appearance, they were classified as MR-negative FCD. Surgical outcomes were evaluated at 2 and 5 years, and clinical, neurophysiological, and neuroimaging data of MR-negative FCD were compared to those of MR-positive FCD.ResultsFinally, 47 MR-negative and 34 MR-positive FCD patients were enrolled in the study. The seizure-free rate after surgery (Engel classification I) at postoperative 2 year was 59.5% and 64.7% in the MR-negative and positive FCD groups, respectively (p = 0.81). This rate decreased to 57.5% and 44.4% in the MR-negative and positive FCD groups (p = 0.43) at postoperative 5 years. MR-negative FCD showed a higher proportion of FCD type I (87.2% vs. 50.0%, p = 0.001) than MR-positive FCD. Unilobar cerebral perfusion distribution (odds ratio, OR 5.41) and concordance of interictal epileptiform discharges (OR 5.10) were significantly associated with good surgical outcomes in MR-negative FCD.ConclusionIn this study, MR-negative and positive FCD patients had a comparable surgical prognosis, suggesting that comprehensive presurgical evaluations, including multimodal neuroimaging studies, are crucial for obtaining excellent surgical outcomes even in epilepsy patients with MR-negative FCD.
Highlights
One-third of patients considering surgical treatment for drug-resistant epilepsy show a normal magnetic resonance imaging (MRI) appearance, that is called MR-negative epilepsy
47 MR-negative and 34 MR-positive Focal cortical dysplasia (FCD) patients were enrolled in the study
The seizure-free rate after surgery (Engel classification I) at postoperative 2 year was 59.5% and 64.7% in the MR-negative and positive FCD groups, respectively (p = 0.81). This rate decreased to 57.5% and 44.4% in the MR-negative and positive FCD groups (p = 0.43) at postoperative 5 years
Summary
One-third of patients considering surgical treatment for drug-resistant epilepsy show a normal magnetic resonance imaging (MRI) appearance, that is called MR-negative epilepsy. Physicians are reluctant to decide on conducting an epilepsy surgery even in intractable epilepsy patients with normal MRI. Focal cortical dysplasia (FCD) is the most common etiology of drug-resistant MR-negative epilepsy. FCD is a subgroup of cortical malformations characterized by an aberrant cortical organization resulting from abnormal neuronal migration and differentiation [5]. It includes pathologic features such as neuronal heterotopias, dyslamination, and a combination of bizarre pyramidal neurons of the cerebral cortex and white matter and the presence of balloon cells [6]. FCD accounts for 20–25% of focal epilepsy [7,8], and 25–40% of childhood drugresistant epilepsy cases are FCD [9]
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