Focal cortical dysplasia

Clinical History

The patient presented with complaints of refractory focal seizures, delayed speech development and was apparently ambidextrous. On EEG, the focus was localised to left frontal and temporal lobe.

Imaging Findings

MRI of brain showed asymmetry in the gyral pattern in both frontal lobes with prominent CSF spaces surrounding left frontal lobe near the posterior aspect of superior frontal gyrus and middle frontal gyrus . In this region the sulci appeared abnormally deep with increased cortical thickness . On T2 and FLAIR images, grey white matter junction in this region was slightly blurred. No evidence of any T2, FLAIR subcortical whitematter signal. Hippocampal and parahippocampal regions were normal. There were no other abnormalities in the brain. Imaging findings were suggestive of focal cortical dysplasia (closely related to Taylor type IIa). But, the diagnosis was confirmed to be Taylor type IIb. This is a case of Atypical Taylor type IIb Focal cortical dysplasia.

Discussion

Focal cortical dysplasia (FCD) is a cerebral cortical developmental malformation which is now recognized as a common cause for medically refractory seizures in paediatric population as well as for intractable seizures in adult population [1]. There are three types of FCD recognized [1]. Type I FCD commonly seen in adult patients who mostly present with mild symptoms [1].Brain MRI features of Type I FCD are focal brain hypoplasia, white matter atrophy and white matter signal alterations [2]. Patients with Type II FCD present with severe clinical symptoms and usually affects paediatric population [1]. Brain MRI shows increased focal cortical thickness, abnormal gyral & sulcal patterns, marked blurring of grey-white matter junction and high T2, FLAIR subcortical whitematter signal gradually tapering towards the ventricle (The Transmantle sign) [3].Type I FCD commonly affects temporal lobes whereas Type II FCD commonly affects frontal lobes [1].
An ad hoc ILAE Task Force proposed a new clinico-pathological classification for FCD [4].FCD with abnormal cortical lamination either radial or tangential or both are classified as Type I (Ia, Ib and Ic) [4].FCD with dysmorphic neurons are classified as Type IIa and FCD with both dysmorphic neurons and balloon cells are classified as Type IIb [4]. FCD with cortical lamination abnormalities associated with a principal lesion (Hippocampal sclerosis, tumours, vascular malformations and others) adjacent to or affecting same cortical defect are classified as Type III (IIIa, IIIb, IIIc and IIId) [4].Cortical dysplasia with balloon cells (Taylor Type IIb) is classified under malformation due to abnormal neuronal cell proliferation and cortical dysplasia without balloon cells are classified under malformation due to abnormal cortical organisation [5]. MRI brain features of Transmantle sign and bottom of sulcus dysplasia are pathologically associated with Type IIb FCD [3]. Bottom of sulcus dysplasia is characterized by focal cortical thickening at the bottom of a sulcus with blurring of grey-white matter junction [3]. MR spectroscopy show decrease NAA:Cr due to impaired neuronal migration , low choline to creatine ratio due to diffuse hypomyelination and increased mI [3, 6]. MR perfusion may be normal or shows reduced rCBV [6]. On contrast enhanced T1, FCD type IIb doesnot enhance [6]. On DTI, it shows increased diffusivity and decreased fractional anisotropy [6]. Medically refractory epilepsy secondary to FCD is treated with surgery [6].

Differential Diagnosis List

Final Diagnosis

Atypical Taylor Type IIb Focal Cortical Dysplasia

URL:	https://www.eurorad.org/case/13396
DOI:	10.1594/EURORAD/CASE.13396
ISSN:	1563-4086