[Craniotomy for lesions in the cerebral convexity; how to precisely localize the lesions with conventional CT slices]

A simple direct precise localization with a CT scan for convexity lesions is presented. The shape of the normal calvarium was analyzed and a characteristic pattern was obtained, that is, one spherical surface in the frontal area and 6 flat planes in the temporal, parietal and occipital areas. The temporal plane is perpendicular to the orbito-meatal line (OML), while the parietal plane declined 29 degrees in the A-P view, and the occipital plane declined 60 degrees in the lateral view. A summit of these three planes forming the parietal tubercle, and the crest following the tubercle between the parietal and occipital planes were detected either by CT scan, or by palpating the skull. Conventional methods of preoperative localization include measurement and calculation from the base line such as OML, or obtaining a CT scan with a marker on the scalp. The former might have an error that will be amplified in the parietal region that would not be negligible. The latter is a rather troublesome method demanding that the CT scan be taken after shaving the hair. Landmarks utilized for the localization should be identified both on the CT scan and on the scalp or skull. These involved OML, coronal suture, parietal tubercle, inion, pineal body, midline and so on. Of these, the coronal suture runs almost perpendicular to the OML and would be the best landmark for the localization in the parietal area.(ABSTRACT TRUNCATED AT 250 WORDS)