Abstracts

RATIONALE: Focal cortical dysplasia of Taylor type (FCDTT) is a frequent pathological finding in pediatric epilepsy surgical resections. The clinical and MRI characteristics of children with FCDTT are reported in this large series.
METHODS: Entry criteria were children without clinical stigmata of tuberous sclerosis, who had surgical resection between 1990 and 2000 with FCDTT confirmed by light microscopy (LM) of original tissue sections. We defined FCDTT as per Taylor: a disruption of the horizontal cortical lamination with replacement of normal cells by masses of giant aberrant neurons (GN). Two radiologists reported the MRI features. Pathological features were correlated with the clinical features and MRI findings.
RESULTS: 35 children (17 male) had FCDTT from a cohort of over 300 cases. The median age of epilepsy onset was 2 months and median age at surgery of 4.5 years. Clinical characteristics included daily seizures in 84%, intellectual disability (ID) in 52% and hemiparesis in 63%. Focal resection was performed in 24, hemispherectomy in 11. Seizure free surgical outcome was obtained in 69% at 12 months. Radiological features present in greater than half, were focal cortical thickening, blurring of the grey white junction and white matter T2 hyperintensity. A subset of the patients (n=5) had features consistent with hemimegalencephaly. There was no significant predilection for lobar location. By LM, presence of GN was the predominant if not an exclusive feature in 20 cases (group 1), including most of those with hemimegalencephaly. In contrast, the remaining 15 cases (Gp 2), in addition to a varied number of GN, also had an abundance of ballooned cells, striking diffuse astrocytosis with occasional focal microcystic white matter degeneration and mineralization. Group 1 cases had statistically significant earlier age of onset, shorter time to surgery, and higher rate of ID and hemiparesis.
CONCLUSIONS: FCDTT is a common pathological finding in pediatric epilepsy surgical resections with distinct clinical and radiological findings. Associated morbidity is very common and highly characteristic; an extremely early age of onset, multiple daily seizures, hemiparesis and intellectual disability observed in the majority of cases. Certain MRI features had a high sensitivity for the diagnosis of FCDTT but specificity was not tested. The histological findings suggest that some changes in CDTT may be acquired during the course of intractable epilepsy, although genetic differences between the two morphological subtypes cannot be ruled out. Early recognition of children with FCDTT is essential as seizure free outcomes from surgical resection are obtainable in the majority of cases.