What Is Focal Cortical Dysplasia?
Focal cortical dysplasia is an abnormal formation of cortical development (the process by which the cerebral cortex forms in mammals). Brain cells (neurons) are organized in layers to form the outermost part of the brain, known as the cortex. In focal cortical dysplasia, disorganization of the brain cells in a specific region poses the risk of seizures. In addition, neurons (brain cells) of the affected area behave abnormally, disrupting brain functions generated from that particular area. Focal cortical dysplasia is the most common cause of refractory (drug-resistant) epilepsy in the pediatric population (children) and the second or third most common cause of intractable epilepsy (epilepsy that cannot be controlled by drugs) in adults.
What Are the Types of Focal Cortical Dysplasia?
The various types of focal cortical dysplasia are based on the microscopic appearance and the multiple changes associated with brain function.
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Focal Cortical Dysplasia Type 1 - It has late onset. The neurons are abnormally organized both horizontally and vertically in the cortex. The patient expresses mild symptoms. It is seen more in adults, and the changes are mainly associated with the temporal lobe. It is primarily identified based on the clinical history of the patient’s seizures. The seizures are usually drug-resistant (do not respond to the antiseizure medication). MRI (magnetic resonance imaging) rarely detects focal cortical dysplasia. EEG (electroencephalogram measures brain activities) findings help confirm the focal seizure (beginning in one area and do not spread to other regions) onset. Other diagnostic tools like PET (positron emission tomography), MEG (magnetoencephalography measures the magnetic field produced by the brain's electrical activities), and SPECT (single photon emission computerized tomography) should be used before planning surgery.
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Focal Cortical Dysplasia Type 2 - In this type, the neurons (brain cells) are organized abnormally in the cortex. The presence of dysmorphic neurons (larger than usual neurons) or balloon cells is reported. It has more severe clinical symptoms than type 1. Changes outside the temporal lobe with a preference for the frontal lobe are noted. It is mainly seen in children and is evident on MRI (magnetic resonance imaging).
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Focal Cortical Dysplasia Type 3 - In addition to focal cortical dysplasia type 1 or type 2, other associated abnormalities like tumors, vascular malformation (abnormal development of blood vessels), brain damage, and hippocampal atrophy (shrinkage of the hippocampus) are noted.
What Are the Symptoms of Focal Cortical Dysplasia?
The lesions in the focal cortical dysplasia are multifocal (present at more than one location) and vary in size. It can affect any part of the brain with a predilection for the temporal lobe (seen in type 1) and frontal lobe (seen in type 2). It can occur at any age; however, it is commonly seen in children. Drug-resistant epilepsy is the main symptom of focal cortical dysplasia. Other symptoms are mental retardation with early seizure onset. Even though lesions occupy a large brain area, major neurological defects are not observed.
What Are the Types of Seizures Seen in Focal Cortical Dysplasia?
Seizures associated with focal cortical dysplasia depend on the patient's age and the location of the brain's abnormal brain cells (neurons). The most common seizure is the focal-onset seizure (seizures that begin in one area of the brain) which progresses to the generalized tonic-clonic seizures (stiffness and twitching or jerking muscles). The initial symptoms of the seizure indicate the brain region that is affected by focal cortical dysplasia. Infantile spasms are often present in very young children.
What Is the Treatment of Focal Cortical Dysplasia?
Treatment of focal cortical dysplasia depends on epilepsy severity and its response to anti-seizure medication.
1. Antiseizure Medication - It is the drug of choice; however, most patients with focal cortical dysplasia are drug resistant. The seizures do not respond to the drug treatment. Surgery should be considered if more than two antiseizure medications fail to control seizures.
2. Surgery - Itis considered if focal cortical dysplasia is localized in a region from where the brain can be resected without causing any impairment to brain activities. The surgical outcome is better for focal cortical dysplasia type 2 than for type 1. However, the seizure-free result is challenging if the surgical resection is incomplete. Incomplete surgical resection occurs if focal cortical dysplasia involves brain regions that serve essential functions like movement, memory, and coordination.
3. Neuromodulation - It is the alteration in nerve activity via targeted stimulus delivery such as electrical stimulation which is opted for cases where most of the brain region is involved in focal cortical dysplasia, and surgical removal is not feasible. In this technique, devices like RNS (responsive neurostimulation), DBS (deep brain stimulation), and VNS (vagus nerve stimulation) are implanted in the patient. These devices reduce seizures but do not make a patient seizure-free.
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Responsive Neurostimulation (RNS) - Doctors implant a neurostimulator device over the patient’s skull. It is connected to the area of seizure origin by thin wires called leads. The device continuously records the brain activities, and when an action that leads to a seizure is detected, it passes electrical stimulation through the leads to stop the episode. A neurosurgeon can remove this device anytime from the patient’s body.
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Deep Brain Stimulation (DBS) - Neurosurgeon implants one or more wires called leads in the patient’s skull. These wires are attached to a generator-like device called the neurostimulator implanted in the patient’s collarbone. These wires produce continuous electrical impulses and regulate abnormal impulses, thus reducing seizures.
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Vagus Nerve Stimulation (VNS) - It uses a device to send mild electrical impulses to the brain via the vagus nerve (10th cranial nerve that coordinates brain and other internal organs activities). The device is placed under the skin and below the collarbone in the chest. The wires, called the leads, are connected to the left vagus nerve. The right vagus nerve is not used as it supplies to the heart. Electrical impulses are then transmitted to the brain via the vagus nerve, stopping seizure attacks and frequency. The noninvasive vagus nerve stimulation technique has been approved for treating epilepsy in Europe recently, which does not require any surgical implantation.
Conclusion:
Focal cortical dysplasia is not life-threatening but becomes a matter of concern if the seizures last too long or occur too often. A life with focal cortical dysplasia is challenging, but an early diagnosis and getting treatment help to gain control over the seizures. The prognosis is good with medications, resective epileptic surgeries, and neurostimulators.
