The authors stress the difficulties of a precise topographical diagnosis of tumors in the region of the third ventricle and point out the recent advànces in this field. A case of a 36 year old man with a four months history characterized by severe signs of increased intracranial pressure, mild left hemiparesis and psychic disturbances is reported. The cerebrospinal fluid test revealed increased pressure, The electroencephalographic findings were: 1 - diffuse and bilateral abnormalities; 2 - repetitive bursts of bisynchronous theta waves from the central-parietal regions; 3 - focal delta waves with phase reversals from the right frontal region. Increased intracranial pressure and cerebral oedema were considered to be responsible for the first type of abnormality. The focal delta and theta waves were interpreted as being the manifestations of a deep seated midline tumor in the region of the third ventricle with secondary involvement of the right frontal lobe. The localization was confirmed by ventriculography. At operation it was found a cystic pediculated tumor coming from the sella turcica and invading the third ventricle and right frontal lobe.
