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|NI FEATURE: THE EDITORIAL DEBATE II-- PROS AND CONS
|Year : 2018 | Volume
| Issue : 6 | Page : 1601-1602
Focal cortical dysplasia
Varindera P Singh
Department of Neurosurgery, Medanta, The Medicity, Gurugram, Delhi National Capital Region, New Delhi, India
|Date of Web Publication||28-Nov-2018|
Dr. Varindera P Singh
Department of Neurosurgery, Medanta, The Medicity, Gurugram, Delhi National Capital Region, New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Singh VP. Focal cortical dysplasia. Neurol India 2018;66:1601-2
Focal cortical dysplasia (FCD) is an important cause of intractable epilepsy especially in children. This developmental disorder, involving abnormal migration of neurons and abnormal cortical assemblage, encompasses a wide range of pathologies. Consequently, the radiological abnormalities may be easily visible or may be extremely subtle bordering on the normal. Identification of focal cortical dysplasia is, therefore, not always easy. FCD is often the pathological substrate of MRI-negative extratemporal intractable epilepsy in children.
The paper on focal cortical dysplasias by Chaturvedi et al., in this issue of the journal is an important one. The authors present their vast experience of 52 patients in the Indian scenario and demonstrate that the diagnostic evaluation and surgery for these complex disorders is possible in economically restrained situations with good outcomes. It is also the first study from India detailing the quality of life outcomes pre- and postoperatively in these patients. This paper, I am sure, would inspire many more centres in India to focus on children with this difficult-to-treat epilepsy.
A number of techniques have evolved to increase the diagnostic yield of imaging. Quantitative volume based morphometry has been done to localise abnormal areas (either atrophic or hypertrophic) in which the FCD may reside. The radiologist could then focus on these areas and pick up more lesions. Hu et al., studied various image post-processing techniques to detect these MRI invisible lesions including morphometric analysis, statistical parametric mapping and MRI/PET co-registration – with the last one having the highest detection rate. A gray matter specific MR imaging sequence called FLAWS (fluid and white matter suppression imaging) and 3-D FLAIR (three-dimensional fluid attenuated inversion recovery) imaging were found useful to detect the blurred gray-white matter junction and the abnormal signal intensity of subcortical white matter seen in FCD.
The surgical strategy in these cases is more complex than a simple lesionectomy. It is known that the epileptogenic potential varies in different parts of the focal cortical dysplasia, and therefore, the epileptogenic zone may be much smaller than the size of the dysplasia. Therefore, functional information derived from stereo-electroencephalography (SEEG) or magnetic source imaging using magnetoencephalography (MEG) may be invaluable. SEEG is a minimally invasive technique which localises the epileptogenic zone precisely. The electrodes are inserted stereotactically using the Brainlab Vario guide or with the ROSA (robotic stereotactic assistance)robotic guidance. This is then co-registered on the MRI to get an accurate depiction of the epileptogenic zone. MEG is non-invasive with a high accuracy of source localisation even if the surface EEG is non-localising, as happens with a small dysplasia in the depth of a sulcus. The MEG localisation is often not in the centre of the dysplasia seen on MRI but on the edges. Co-registration of magnetic source imaging data with the structural data from magnetic resonance imaging leads to an appropriate surgical resection resulting in better seizure outcomes. Intraoperative ultrasound aids in the identification of dysplastic tissue during surgery and facilitates the completeness of its removal. This benefit is mainly seen in FCD type II as type I FCD is sonologically not so distinct. The minimally invasive technique of MR guided laser interstitial thermal therapy (LITT) has been applied to small focal cortical dysplasias. Using MR thermometry sequences, one can make a controlled thermocoagulation lesion in the epileptogenic zone using a laser probe. The long term effects of this technique still await validation.
The pathogenetic mechanisms underlying FCD are still unknown. There is increasing evidence of germline and somatic mutations in genes regulating the mTOR pathway resulting in the structural and electric changes in type II FCD. Recently, the human papilloma virus oncoprotein E6 has been isolated from FCD patients. The mTOR inhibitor, rapamycin, has been tried in animal models of FCD as well as in a few FCD patients with promising results. There is not much data on the pathogenesis of type I and III FCD. Further studies elucidating the pathogenetic mechanisms may result in some innovative solutions to this complex disorder.
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