Objective      To explore the application of intracranial electroencephalogram (iEEG) monitoring in intractable infantile spasm (IIS).       Methods      Long-term video-iEEG monitoring with subdural electrodes was applied to determine the epileptogenic zones and EEG characteristics of 18 patients with IIS whose epileptogenic zone could not be located by MRI

and 14 of the 18 patients were given video-scale electroencephalogram (sEEG) monitoring at the same time. The accuracy of epileptogenic zone localization by iEGG monitoring was evaluated based on postoperative pathological examination and clinical follow-up

and was also compared with that by sEGG monitoring.       Results      Hypsarrhythmia or variant hypsarrhythmia were shown in 7 patients by both iEEG and sEEG monitoring

while 11 patients displayed abnormalities in posterior hemisphere or focal unilateral discharge rather than hypsarrhythmia. The iEEG monitoring results showed focal unilateral epileptogenesis in 9 patients

bilateral epileptogenesis with lateralization in 5 patients

and undetermined localization in 4 patients. Fourteen patients were given corpus callosotomy. The postoperative follow-up for 1-3 years showed Engel Class Ⅰ and Class Ⅱ outcomes in 11 patients (11/14

78.6%)

and no severe complication occurred.       Conclusion      The epileptogenic zone of 14 IIS patients that can not be located by MRI can be determined by iEEG

and the identification ratio is 77.8%. The hypsarrhythmia shown by sEEG is not a real generalized discharge

and focal abnormalities in cortex observed by iEGG during  epileptic seizure indicate symptomatic IIS or cryptogenic IIS. Intracranial electroencephalogram is an approach to recognize and treat IIS in future.