Ultrasound in Neurologic Diagnosis

Ultrasound echoing using a pulse transmitted transversely across the head can determine quickly and safely the symmetry of position of the brain within the cranial cavity. A brief pulse at about 2 Mc is transmitted into the head, and the reflections from the walls of the third ventricle and the septum pellucidum are picked up by the transducer which serves alternately as transmitter and receiver. Although most of the incident energy is reflected by skull, a sufficient portion of the pulse enters the head to be detected after reflection by smooth internal discontinuities properly oriented to reflect the pulse back to the transducer. Positioning of the transducer is highly critical and requires some practice. The lateral displacement of the third ventricle and septum pellucidum generally is a sensitive indicator of an increase of volume of the contents of one half of the cranial cavity relative to the other. These structures lie within the opening in the falx cerebri through which brain tissue must herniate when displaced from one compartment to the other. The technique is totally atraumatic and in most cases easily performed.