Neocortical epilepsy is a type of seizure disorder that can be either partial (focal) or generalized, in which the seizures originate in the neocortex, part of the external surface layer of the brain. Neocortical epilepsy differs from other kinds of epilepsy because often there is no clearly defined area from which the seizures originate.
Neocortical epilepsy may be caused by a lesion, such as a tumor or vascular malformation; an injury to the brain, such as a traumatic injury or an infection; or abnormal brain development before birth. In this condition, the morphology, or structure, of the neurons changes so that the region is more easily excitable and more prone to seizures. Neocortical epilepsy involves both ictal (during seizure) and interictal (between seizures) neuronal activity.
Like other forms of epilepsy, the seizures associated with neocortical epilepsy can cause a variety of symptoms such as strange sensations, changes in behavior or emotions, muscle spasms, convulsions, and a sudden loss of awareness or consciousness.
Diagnostic techniques, such an encephalograms (EEGs), video-EEG telemetry, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and functional MRI, are used to assess epilepsy and determine a course of treatment. For neocortical epilepsy, careful analysis of these studies may suggest that a particular patient’s seizures have onset in a single brain region. Specific diagnosis often requires surgery to implant electrodes directly on or in the brain, to permit monitoring for seizures to localize the region of onset.
Seizures caused by neocortical epilepsy do not respond well to medication. Surgery for neocortical epilepsy must be done carefully and may not have the same success rates as surgery for other kinds of epilepsy. In patients with other forms of epilepsy, such as mesial temporal lobe epilepsy, in which the lesion that causes the seizure is clearly defined, surgery can provide seizure freedom in 70 to 80 percent of cases. Patients with neocortical epilepsy see lower success rates. This is because it may be difficult to isolate the region that is causing the seizures, there may be multiple initiation points, or the initiation points may be related to important functional sites in the brain. In addition, the portions of the brain involved in both ictal and abnormal interictal activity must be identified and removed. Because of the complications, patients with neocortical epilepsy often need individually tailored surgeries. The seizure-free outcome rates for surgery in patients with neocortical epilepsy drop to between 20 and 40 percent; an additional significant percentage (20 to 40 percent) may experience an 80 percent reduction in seizure frequency.
In addition to surgical resection of portions of the brain, multiple subpial resection can be used for patients with neocortical epilepsy. Multiple subpial transection is a surgical technique that limits seizures by severing the nerve pathways along which they propagate. Functional nerve cells in the neocortex tend to be arranged in vertical columns. To stop seizure propagation without compromising brain function, surgeons can make subpial transections, cuts that sever the horizontal connections that appear to help seizures spread, while preserving the vertical connections that are important for cortical function.