Focal cortical dysplasia is an anomaly of the structure of the cerebral cortex, affecting its limited area. Clinically manifested by focal motor epiprimes with loss of consciousness, but of short duration. It is diagnosed by a neurologist or epileptologist according to EEG data, specially conducted MR scanning, subdural electrocorticography, PET of the brain. As a rule, epilepsy in cortical dysplasia is resistant to antiepileptic therapy. An alternative method of treatment is neurosurgical resection of the dysplasia site.
General information
Focal cortical dysplasia (FCD) is a local disorder in the structure of the cerebral cortex that occurred during intrauterine development. It is the most frequent etiofactor of the development of epilepsy in children. According to the international ILAE study (2005), FCD was diagnosed in 31% of children with epilepsy. The 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, the effectiveness of neurosurgical methods of treatment.
Local dysplastic changes of the cortex are located mainly in the temporal and frontal lobes. They are barely noticeable at the macroscopic level, which makes it difficult to diagnose PFCDD even with the help of such modern neuroimaging methods as MRI. The problems of diagnosis of FCD are particularly relevant in practical neurology and pediatrics, since its identification as the cause of epileptic paroxysms is crucial for the choice of effective therapeutic tactics in relation to resistant forms of epilepsy.
Causes
FCD is caused by a violation of the final stages of the development of the cerebral cortex (corticogenesis) in the prenatal period. As a result of violations of migration and differentiation of cortical cells, an area with abnormal neurons, pathological thickening, flattened convolutions or altered architectonics (the appearance of cells typical of 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 cortex defects (for example, polymicrogyria, hemimegalencephaly) are associated with disorders of the end of the 2nd beginning of the 3rd trimester of pregnancy.
It is impossible to exclude the genetic nature of the failure in corticogenesis leading to FCD. Thus, many patients have changes in the TSC1 gene, which are also observed in tuberous sclerosis. Currently, international research is being conducted to find a genetic substrate for cortical dysplasia.
Classification
Until recently, there were 2 main types of focal cortical dysplasia. In 2011, a new classification was developed, which included type 3 associated with another major lesion of cerebral structures. According to this classification, there are:
- Type I — a local violation of the architectonics of the cortex: radial (IA), tangential (IB) or mixed (IC). It is detected in 1.7% of practically healthy people surveyed.
- Type II is a focal violation of cytoarchitectonics with the presence of abnormal neurons (IIA) and so—called balloon cells (IIB). As a rule, dysplasia affects the frontal lobes.
- Type III is a secondary violation of cortical architectonics caused by another pathology: mesial temporal sclerosis (IIIA), glial tumor (IIIB), malformation of cerebral vessels (IIIC) or other disorders (IIID) — Rasmussen encephalitis, neuroinfection, post-traumatic or post-ischemic changes, etc.
Symptoms
The leading clinical manifestation of focal cortical dysplasia is focal epilepsy. As a rule, it manifests in childhood. Epileptic paroxysms are characterized by their short duration — they last no more than a minute. Among them, complex (with a disorder of consciousness) focal motor attacks predominate, often with automatism in the initial period of paroxysm. Confusion of consciousness in the post-criminal period is expressed slightly. Motor phenomena and sudden falls are characteristic. Secondary generalization of epiprimes occurs noticeably faster than in temporal lobe epilepsy.
The age of onset of epilepsy and concomitant clinical symptoms depend on the type, severity and location of the focus of cortical dysplasia. Early manifestation of the anomaly is usually accompanied by a delay in the child’s mental development and cognitive impairment.
Type I FCD has a less severe course and is not always manifested by epiprimes. In a number of patients, it leads to difficulties in cognitive activity and learning problems. Type II FCD is accompanied by severe partial and secondary generalized epiprimes. Many patients have an epileptic status. The clinic and course of type III FCD depends on the nature of the underlying pathology.
Diagnostics
The main method of diagnosis of FCD is magnetic resonance imaging. It should be carried out according to a special protocol with a thickness of 1-2 mm slices. Only such a thorough scan can reveal minimal structural changes in the cerebral cortex. In the MRI diagnosis of cortical dysplasia, the experience and qualifications of a radiologist are important. Therefore, if necessary, the results of the study should be shown to a more experienced specialist in this matter.
MRI signs of FCD include: local hypoplasia or thickening of the cortex, “smearing” of the transition between white and gray matter, altered course of the gyrus, increased MR signal in a limited area of the cortex when examined in T2 and FLAIR modes. Each type of focal cortical dysplasia has its own features of the MRI picture.
Electroencephalography is performed on a mandatory basis for patients with FCD. In most cases, it reveals focal epileptic activity of the brain not only at the time of the attack, but also during the intercrime period. During the attack, there is increased excitability and activation of cortical areas adjacent to the focus of dysplasia visualized on MRI. This is due to the presence of abnormal cells outside the main area of cortical dysplasia, which is only the “tip of the iceberg”.
Identification of the zone of the onset of an epileptic seizure is possible with the help of PET combined with an MRI image. In this case, the radiopharmaceutical should be administered to the patient after the first paroxysmal discharge. Such a study is especially valuable in MRI-negative cases of FCD and in case of mismatch of the focus visualized on MRI with EEG data. To more accurately determine the location of the epileptogenic focus, invasive electrocorticography is performed with the installation of subdural electrodes, requiring a craniotomy.
Treatment
Therapy begins with the selection of an effective anticonvulsant drug and its dose. The patient is jointly supervised by an epileptologist and a neurologist. It is possible to use carbamazepine, valproic acid preparations, diazepam, levetiracetam, topiramate, etc. anticonvulsants. However, epilepsy in FCD often turns out to be resistant to anticonvulsant therapy. In such cases, the question of surgical treatment is raised and a neurosurgeon is consulted.
Since dysplastic changes are of a focal nature, surgical removal of the pathological focus is an effective way to treat FCD. At the beginning of the neurosurgical intervention, electrostimulation and individual intraoperative corticography are performed with mapping of functionally important areas of the cortex, which avoids their injury during the operation. Many neurosurgeons insist on the expediency of removing the dysplastic focus as radically as possible in order to achieve the best treatment results. The difficulty lies in the wide spread of the zone of point-located pathologically altered cells around the main focus and the impossibility of their complete removal. Common and bilateral epileptogenic lesions are a contraindication to surgical treatment.
Depending on the localization and prevalence of the focus, one of 3 types of surgical interventions is used: selective resection of the epileptogenic zone, standardized resection of the brain (lobectomy), taylor resection — “cutting out” the dysplasia zone determined during corticography. With type III FCD, removal of both dysplasia and the main lesion (tumor, sclerosis site, vascular malformation, etc.) is often required.
Forecast
The prognosis depends on the type of focal cortical dysplasia, the timeliness of the treatment, the radical removal of the cortical dysplasia site. Conservative therapy, as a rule, does not give the desired result. A long course of epilepsy in childhood is fraught with a violation of neuropsychiatric development with an outcome in oligophrenia.
Surgical treatment is most effective with a single well-localized lesion. According to some data, the complete absence of paroxysms or their significant reduction is observed in 60% of operated patients. However, after 10 years, only 32% have no seizures. Apparently, the recurrence of epilepsy in such cases is associated with incomplete removal of epileptogenic elements.
Persistent postoperative neurological disorders are noted in 2% of cases, with common lesions — in 6%. The risk of their development is increased during lobectomy and interventions near functionally significant areas of the cortex.