Sonography of the adult brain through surgical defects.

Echoencephalographic examinations of the brain, first reported by Leksell [1] in 1956, were initially limited to A-mode determinations of midline shifts. In 1963, de Vlieger et al. [2] introduced bistable, two-dimensional imag ing 8-mode. With the advent of modern gray-scale techniques, the quality of sonographic scans improved markedly, and 8-scan imaging of the intrac ranial contents, performed either through the unossified skull or through calvarial defects, now provides informative images in planes similar to computed tomography (CT) scans. Sonographic evaluation of the newborn infant's head has proved to be a valuable neuroradiologic screening examination in the high-risk infant, in many instances obviating ionizing radiation techniques or expensive CT scans. Realtime sonography can be performed in the newborn nursery without removing the baby from the incubator. It provides accurate neuroanatomic information and is useful in the diagnosis of intraventricular or subependymal hemorrhage, the discrimination between cystic and solid lesions, and the assessment and followup of early hydrocephalus [3-9]. As the calvarium ossifies, the attenuating bone creates increasing impedance to the transmission of the sonographic signal. Consequently, the applications of sonography in the management of adult neurosurgical patients have been limited , and the potential of the procedure has been largely overlooked . Attempts to overcome this limitation by using very low-frequency transducers have resulted in images of poor resolution [10]. However, a craniotomy or burr holes provide openings that can function as acoustic windows to the adjacent intracranial contents . In 1965, Tanaka et al. [11], using A-mode technique, demonstrated the value of sonography in the localization and characterization of brain tumors during craniotomy. In 1975, Hoffman and Landau [12] reported 8-scan imaging of an intracranial lesion through a postoperative bone-flap defect. We examined eight adults with postoperative calvarial defects and found c linical applications of greater variety than those reported previously .