Objective To investigate the clinical pathologic features of a distinct variant of focal cortical dysplasia (FCD) characterized by neuronal loss of layer four.Methods Between 2005 and 2017,approximately 3 000 surgeries were performed for the treatment of intractable epilepsy at Xuanwu Hospital,Capital Medical University and Yuquan Hospital,Tsinghua University.Retrospective analysis of clinic-pathological data of patients with epilepsy surgery was made and histological manifestations of neuronal loss of cortical layer four were included in this study.Results In this cohort,25 patients (22 males and three females) were identified with early onset pharmaco-resistant epilepsy and regionally circumscribed neuronal loss of cortical layer four in surgical specimens from the occipital lobe.Histologically,except for neuronal loss in cortical layer four in all cases,glial scar lesions were found in some patients.Thus the histology of those cases can be subdivided into two groups:group A (13 cases):neuronal loss of cortical layer four without glial scar lesions;and group B (12 cases):neuronal loss of cortical layer four with glial scar lesions.Due to the prominent horizontal disorganization of cortical layering and lack of any other microscopically visible principle lesion,group A should be classified hitherto as FCD International League Against Epilepsy (ILAE) type Ⅰ b,however,group B with scar lesions and cortical dysplasia around the main leision,should be classified as FCD ILAE type Ⅲd.This retrospective analysis of clinical histories revealed a perinatal distress in 20 patients (80％),suggesting an acquired pathomechanism.Magnetic resonance imaging revealed abnormal signals in the occipital lobe in all patients,and signal changes suggestive of encephalomalacia were found in 18 patients.Surgical treatment achieved favorable seizure control (Engel class Ⅰ and Ⅱ) in 18 patients (75％ among 24 available follow up).Comparion of the two groups with age at epilepsy onset (group A:5.00±2.76,group B:5.01±3.78),the proportion of perinatal distress (group A:11/13,group B:9/12) and the follow-up results (favorable seizure control of the two groups was 9/13,9/11 respectively) showed that there was no statistically significant difference between the two groups.Conculsion Neuronal loss of cortical layer four in the occipital lobe should be classified as a distinct variant of FCD ILAE type Ⅲd.