RESUMEN
The authors report a case of interhemispherical fissure arachnoid cyst with agenesis of the corpus callosum who was 11-year-old child suffering from partial seizure. The interhemispheric area is a rather uncommon site for arachnoid cysts. Careful analysis of the anatomical and radiological features of this case seems to suggest that two morp-hologically distinct types of cysts occurred in the interhemispheric area; (1) Interhemispheric cyst associated with agenesis of the corpus callosum(2) parasagittal cyst, not associated with such an anomaly. The interhemispheric fissure arachnoid cyst occurs in the midline, straddling the falx, and extends about equally on either side, compressing the medial surface of both hemispheres. A coronal CT or MRI view shows a "batwing" appearance of the lateral horns and dorsal displacement of the third ventricle. It should be stressed that a histologically heterogenous group of cysts(ependymal, glial, choroid epithelial, and arachnoid) may give rise to this same morphologic appearance. The anterior interhemispheric approach was performed and removal of cystic membrane was achieved. Postoperatively, there was no focal neurological deficit.