Epilepsy is a neurological condition marked by recurrent, unprovoked seizures, which are sudden bursts of abnormal electrical activity in the brain. Structural epilepsy is a specific type of epilepsy caused by a visible abnormality or lesion within the brain. This identifiable physical change differentiates it from other forms of epilepsy where a clear structural cause may not be present.
Understanding Structural Epilepsy
Structural epilepsy involves a physical change in the brain that directly causes seizures, often visible with neuroimaging like MRI. Unlike genetic epilepsies or those of unknown origin, it has a tangible, observable source.
The presence of a structural abnormality disrupts the brain’s normal electrical signaling, leading to uncontrolled neuronal firing. The abnormality’s location and nature influence the type and presentation of seizures. For example, a temporal lobe abnormality might cause focal seizures with altered awareness, while a motor cortex lesion could result in focal seizures involving muscle jerking or stiffness.
Common Structural Causes
Common structural causes of epilepsy include:
- Brain tumors: These can alter brain tissue, causing seizures by compressing or irritating surrounding cells.
- Strokes: Both ischemic (blockage) and hemorrhagic (bleeding) strokes can damage brain tissue.
- Traumatic brain injuries: These can create scarred areas in the brain that lead to seizures.
- Congenital malformations of cortical development: Abnormalities like focal cortical dysplasia occur when brain cells don’t form or migrate correctly during development.
- Vascular malformations: Abnormal clusters of blood vessels, such as cavernous malformations, can cause seizures due to bleeding or irritation.
- Infections: Brain damage from infections like encephalitis (brain inflammation) or meningitis (inflammation of the membranes surrounding the brain and spinal cord) can leave structural changes.
- Mesial temporal sclerosis: Scarring in the hippocampus, often linked to prolonged febrile seizures in early life.
Diagnosing Structural Epilepsy
Diagnosing structural epilepsy begins with a thorough medical history and a detailed neurological examination. This initial assessment helps clinicians understand the seizure characteristics, frequency, and any associated symptoms, providing clues about the potential location of the brain abnormality. The medical history often includes questions about past head injuries, infections, or developmental milestones.
Neuroimaging plays a primary role in identifying structural lesions. Magnetic Resonance Imaging (MRI) of the brain is the preferred imaging modality due to its ability to visualize subtle structural abnormalities with high detail. Specialized MRI protocols, often referred to as “epilepsy-directed protocols,” are employed to enhance the detection of specific lesions like hippocampal sclerosis or focal cortical dysplasia. While MRI is highly sensitive, some subtle abnormalities might require advanced imaging techniques or higher-strength MRI machines for detection.
Electroencephalography (EEG) is another important diagnostic tool, recording the brain’s electrical activity through electrodes placed on the scalp. The EEG helps identify abnormal brainwave patterns associated with seizures, pinpointing the area of seizure onset. Although a normal EEG does not rule out epilepsy, an abnormal EEG can indicate an increased likelihood of seizures. Blood tests may also be conducted to exclude other potential causes of seizures, such as metabolic imbalances or infections not directly causing structural damage.
Managing Structural Epilepsy
The management of structural epilepsy primarily focuses on controlling seizures and improving the individual’s quality of life. Anti-seizure medications (ASMs) are typically the first line of treatment, working to stabilize electrical activity in the brain and reduce seizure frequency. There are various ASMs available, and the choice depends on the individual’s seizure type, age, and potential side effects. Many individuals find adequate seizure control with medication, but approximately 20% to 30% may experience drug-resistant epilepsy, where seizures persist despite trying two or more appropriate medication regimens.
For individuals whose seizures are not adequately controlled by medication and when the structural lesion is clearly identifiable and accessible, surgical intervention may be considered. Epilepsy surgery aims to remove the affected brain area (resective surgery) or disconnect it from other parts of the brain to prevent seizure spread. Successful surgical outcomes can lead to significant seizure reduction or even seizure freedom for some patients. Pre-surgical evaluation often involves comprehensive testing, including advanced neuroimaging and prolonged EEG monitoring, to precisely localize the seizure-generating area.
Other treatment approaches are available for individuals who are not candidates for surgery or whose seizures remain uncontrolled. Vagus nerve stimulation (VNS) involves implanting a device that sends electrical impulses to the vagus nerve, which can help reduce seizure frequency and severity. Dietary therapies, such as the ketogenic diet, a high-fat, low-carbohydrate diet, can also be effective, particularly in children and some adults with drug-resistant epilepsy, by altering brain metabolism to reduce seizure susceptibility. These alternative therapies are typically explored when conventional medications are insufficient.