MR imaging features of epileptogenic focal cortical dysplasia and optimization of scanning protocols

Objective To analyze the MR imaging features of epileptogenic focal cortical dysplasia (FCD)and to optimize the scanning protocols by correlating MRI appearance with pathological findings.Methods MRI findings and the relative scanning protocols in 36 patients with surgically and pathologically proved 40 lesions of FCD were retrospectively analyzed. According to Palmini classification system,all 40 lesions were pathologically categorized as FCD type Ⅰ (including FCD Ⅰ A and FCD Ⅰ B) and FCD type Ⅱ (including FCD Ⅱ A and FCD ⅡB ). The distribution of cerebral or dual lesions accompanied hippocampal sclerosis were observed.Differences of the distribution of cerebral in FCD type Ⅰ and FCD type Ⅱ were compared by using Fisher exact probabilities. MR scans in all patients consisted of routine and optimized protocols.Axial FSE T2WI,axial SET1WI and axial FLAIR were recognized as routine scanning protocols,while adding oblique coronal FSE T2WI and FLAIR were recognized as optimization scanning protocols.Both routine and optimization scanning protocols were performed in all patients.The conspicuity of main findings of FCD on different imaging plane and sequences of each protocol were assessed.The detection of cerebral or dual lesion and the accompanied hippocampal sclerosis were compared between the routine protocol and the optimized protocol by using McNemar test.Results Forty lesions were found in 36 cases with FCD,29 had temporal lobe lesion (72.5％ ),9 had frontal lobe lesion(22.5％ ) and 2 had parietal lobe lesion (5.0％).According to Palmini classification system,29 lesions in 27 patients (72.5％ ) were FCD type Ⅰ,11 lesions in 10 patients (27.5％) were FCD type Ⅱ lesions.There were 25 temporal lobe lesions in FCD type Ⅰ,while 4 in FCD type Ⅱ.There were statistically significant differences between FCD type Ⅰ group and FCD type Ⅱ group in the distribution of cerebral (P =0.002 ).Fourteen cases were found to have hippocampal sclerosis simultaneously,with 13 cases found in FCD type Ⅰ patients and 1 case in type Ⅱ patients.The detection rate of temporal lobe lesion was 65.5 ％ (19/29) and 44.8 ％ ( 13/29 ) respectively on optimized protocol and routine protocol.There was statistically significant difference ( x2 =4.167,P =0.031 ).The detection rate of hippocampal sclerosis was 85.7％ (12/14) and 42.9％ (6/14) respectively on optimized protocol and routine protocol respectively.There was statistically significant difference ( x2 =4.167,P =0.031 ).The detection rate of frontal lobe lesion showed no statistically significant difference between optimized protocols and routine protocols (x2 =0.304,P =1.000 ).Conclusions FCD was frequently involved the temporal lobe,followed by the frontal lobe.FCD type Ⅰ lesion was frequently found in the temporal lobe,with a higher incidence of concomitant hippocampal sclerosis. The optimized whole temporal lobe scanning with imaging plane perpendicular to the hippocampus long axis was a highly desired scanning protocol specifically for FCD,which is helpful for the detection of the FCD lesions. Key words: Cerebral cortex;  Nervous system abnormalities;  Magnetic resonance imaging