THE EARLY DEVELOPMENT OF NEUROSONOLOGY .1. ECHOENCEPHALOGRAPHY IN ADULTS

The discovery of Midline Echoencephalography is usually attributed to Leksell in 1956. While this was the first time that the examination had been used clinically, it had been preceded by work in England where the echo from the midline of the head appears first to have been demonstrated but its clinical usefulness not recognised. The clinical need for such an examination was so great that, until 1968, more papers were published about echoencephalography than any other medical ultrasonic technique. It only slowly became appreciated how subjective was the technique which, for highest accuracy, had to be performed by a skilled neurologist or neurosurgeon with an intimate knowledge of the patient's cerebral status. The development of more objective automatic techniques, which did not involve the expenditure of a skilled clinician's time, was vociferously opposed by established echoencephalographers who appeared to believe that the demonstration that the examination depended, for accuracy, upon clinical bias by both operator and interpreter, reflected upon their honesty. It was demonstrated that it was the gross attenuation of the acoustic beam by scattering while propagating through the diploic layer of the skull that was responsible for the very variable displays made by echoencephalography. It was for the same reason that two-dimensional B-mode examinations were equally unsatisfactory and none of the ingenious attempts to overcome the obscuring effect of the skull have, after 35 years, been successful. It is only when the skull is removed that the techniques of transdural and intracerebral ultrasonic encephalography can provide useful images from the brain within the skull. It was fortuitous that the realization that ultrasonic encephalography in adults was largely useless coincided with the development of more sophisticated radiological and magnetic techniques which were much more successful in imaging the brain.