The herniating lobe compresses the following structures: Ipsilateral 3rd cranial nerve (often first) and posterior cerebral artery As herniation progresses, the ipsilateral cerebral peduncle In about 5% of patients, the contralateral 3rd cranial nerve and cerebral peduncle Eventually, the upper brain stem and the area in or around the thalamus Subfalcine herniation The cingulate gyrus is pushed under the falx cerebri by an expanding mass high in a cerebral hemisphere.