Focal cortical epilepsy

Definition

Focal cortical epilepsy (dysplasia) is an abnormality of the structure of the cerebral cortex affecting a limited area of the brain. It is clinically manifested by focal motor epilepsies with loss of consciousness but of short duration. A neurologist or epileptologist diagnoses focal cortical epilepsy according to the EEG, specially performed MR scanning, subdural electrocorticography, and PET of the brain. As a rule, epilepsy in cortical dysplasia is resistant to current antiepileptic therapy. Neurosurgical resection of the area of dysplasia is an alternative method of treatment.

General information

Focal cortical dysplasia (FCD) is a localized disorder in the structure of the cerebral cortex that occurs during intrauterine development. It is the most frequent etiologic factor in the development of epilepsy in children. According to the ILAE international study (2005), FCD was diagnosed in 31% of children with epilepsy. Distinctive features of epileptic paroxysms in FCD are resistance to antiepileptic therapy, aggressive course with the development of mental retardation and epileptic encephalopathy in children, and the effectiveness of neurosurgical treatment options.

Local dysplastic cortical changes are located mainly in the temporal and frontal lobes. They are poorly visible at the macroscopic level, which makes it challenging to diagnose FCD even with the help of such modern neuroimaging methods as MRI. The problems of diagnostics of FCD are especially relevant in practical neurology and pediatrics since its identification as the cause of epileptic paroxysms is crucial for the choice of effective therapeutic tactics for resistant forms of epilepsy.

Causes

FCD is caused by disruption of the final stages of cerebral cortex development (corticogenesis) during the intrauterine period. As a result of disturbances in the migration and differentiation of cortical cells, an area with abnormal neurons, pathological thickening, flattening of the gyrus, or altered architectonics (appearance of cells typical for one layer in another layer of the cortex) is formed. The formation of focal cortical dysplasia occurs shortly before delivery – 4-6 weeks before the end of the period of intrauterine development. More severe forms of cerebral cortical malformations (e.g., polymicrogyria, hemimegalencephaly) are associated with disorders at the end of the 2nd and beginning of the 3rd trimester of pregnancy.

Classification

Until recently, two main types of FCD were distinguished. In 2011, a new classification was developed, which included a3rd type associated with another underlying lesion of cerebral structures. According to this classification, the following types are distinguished:

• Type I FCD is a local disorder of cortical architectonics: radial (IA), tangential (IB), or mixed (IC). It is detected in1.7% of examined practically healthy people.
• Type II FCD is a focal disorder of cytoarchitectonics characterized by abnormal neurons (IIA) and so-called balloon cells (IIB). The dysplasia generally affects the frontal lobes.
• Type III FCD is a secondary disorder of cortical architectonics caused by other pathology: mesial temporal sclerosis (IIIA), glial tumor (IIIB), cerebral vascular malformation (IIIC), or other disorders (IIID) – Rasmussen’s encephalitis, neuroinfection, post-traumatic or post-ischemic changes, etc.

Symptoms

The leading clinical manifestation of FCD is focal epilepsy. As a rule, it manifests in childhood. Epileptic paroxysms are characterized by their short duration, lasting no more than a minute. They are dominated by complex (with disturbance of consciousness) focal motor seizures, often with automatisms in the initial period of the paroxysm. Confusion of consciousness in the post-ictal period is insignificant. Motor phenomena and sudden falls are characteristic. Secondary generalization of seizures occurs much faster than in temporal lobe epilepsy.

The age of onset of epilepsy and the associated clinical symptoms depend on the type, severity, and location of the cortical dysplasia. Early manifestation of the abnormality is usually accompanied by mental retardation and cognitive impairment.

Type I FCD has a less severe course and is not always manifested by episodes. In some patients, it leads to cognitive difficulties and learning problems. Type II FCD is accompanied by severe partial and secondary generalized epilepsies. Many patients have status epilepticus. The clinic and course of type III FCD depend on the nature of the underlying pathology.

Diagnosis

The primary method of diagnosing FCD is magnetic resonance imaging (MRI). It should be performed according to a particular protocol with a 1-2 mm cross-section thickness. Only such a thorough scan can detect minimal structural changes in the cerebral cortex. The experience and qualification of the radiologist are important in MRI diagnosis of cortical dysplasia. Therefore, if necessary, the study results should be shown to a more experienced specialist.

MRI signs of FCD include local hypoplasia or thickening of the cortex, “blurring” of the transition between the white andgray matter, altered course of the gyrus, and increased MR signal in a limited cortex area when studied in T2 and FLAIR modes. Each type of FCD has its own specific MR imaging features.

Electroencephalography is mandatory in patients with FCD. In most cases, it reveals focal epileptic brain activity not only at the time of seizure but also during the interictal period. During the seizure, there is increased excitability and activation of cortical areas adjacent to the focal dysplasia visualized on MRI. This is due to abnormal cells outside the main area of cortical dysplasia, which is only the “tip of the iceberg.”

PET combined with MRI imaging can detect the epileptic seizure onset zone. The radiopharmaceutical should be administered to the patient after the first paroxysmal seizure. Such a study is especially valuable in MRI-negative cases of FCD and in cases of inconsistency of the focus visualized on MRI with EEG data. Invasive electrocorticography with placement of subdural electrodes, which requires craniotomy, is performed to determine the location of the epileptogenic focus more precisely.

Treatment of focal cortical dysplasia

Therapy begins with the selection of an effective anticonvulsant drug and its dose. An epileptologist and a neurologistsupervise the patient together. However, epilepsy in FCD is often resistant to anticonvulsant therapy. In such cases, the question of surgical treatment is raised, and a neurosurgeon is consulted.

Since dysplastic changes are focal, surgical removal of the pathologic focus effectively treats FCD. At the beginning of neurosurgical intervention, electrical stimulation and individual intraoperative corticography with mapping of functionally important cortical areas are performed to avoid their traumatization during surgery. Many neurosurgeons insist on the advisability of removing the dysplastic focus as radically as possible to achieve the best treatment results. The difficulty lies in the widespread distribution of a zone of punctuated pathologically altered cells around the main focus and the impossibility of their complete removal. Disseminated and bilateral epileptogenic lesions are contraindications to surgical treatment.

Depending on the localization and prevalence of the focus, one of three types of surgical interventions is used: selective resection of the epileptogenic zone, standardized resection of the brain (lobectomy), or focal resection—removal of the zone of dysplasia determined by cartography. In type III FCD, removing both the dysplasia and the underlying lesion (tumor, sclerosis, vascular malformation, etc.) is often necessary.

All these treatment options are available in more than 430 hospitals worldwide (https://doctor.global/results/diseases/focal-cortical-epilepsy). For example, Focal resection can be done in following countries:

Turkey – 5.9 K in 16 clinics

Israel – 8.9 K in 12 clinics

China – 18.7 K in 5 clinics

Germany – 21.9 K in 20 clinics

United States – 33.2 K in 15 clinics.

Prognosis

The prognosis depends on the type of FCD, the timeliness of treatment, and the radical removal of the cortical dysplasia site. Conservative therapy, as a rule, does not give the desired result. Prolonged epilepsy in childhood is fraught with impaired neuropsychiatric development with an outcome in oligophrenia.

Surgical treatment is most effective in a single well-localized focus. According to some data, 60% of operated patients have a complete absence of paroxysms or a significant reduction in them. However, after ten years, only 32% have no seizures. Recurrence of epilepsy in such cases is associated with incomplete removal of epileptogenic elements.

Persistent postoperative neurologic disorders are observed in 2% of cases and widespread lesions – in 6%—their development risk increases during lobectomy and interventions near functionally significant cortical areas.