Source of the midline echo and its implications in echoencephalography.

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Abstract
In determining the source of the midline echo in ultrasonic echoencephalography, clinic observations were correlated with anatomical experiments using post-mortem material. The reflected echo was constantly and most easily received when the transducer was positioned on the ear vertical in the temporal region. Examination of the 2 lateral walls of the cranial cavity revealed that at a point level with the ears, the 2 temporal bones were most nearly parallel. A coronal section of a fixed cadaver brain taken along a line from a point above each pinna was found to pass behind the third ventricle. In the midline was the base of the pineal body, the fibers of the posterior commissure, and the aqueduct of Sylvius. Localization of the dominant echo in a fixed brain was the pineal body. The echo was reflected from the pineal tissue[long dash]cerebrospinal fluid interface rather than from the pineal-calcium interface. A "stand off" attachment to the transducer would eliminate any skull curvature and allow routine examination to include scanning of the pineal body and the anterior and posterior parts of the 3rd ventricle. Therefore, previously concealed lesions of the fronto-temporal areas could be identified.