[Determination of approach angle to intra- and peri-ventricular lesions; ultrasonography with reference to MRI].

Ultrasonography using a 5-MHz sector-scanning probe was performed in 4 patients with intraventricular or periventricular lesions. All patients underwent craniotomy, and the lesions included an intraventricular cyst (Case 1, Fig. 1), a subependymoma (Case 2, Figs. 2 and 3), a hypothalamic glioma (Case 3, Fig. 4) and a periventricular cavernoma (Case 4, Fig. 5). The lesion was approached in the former 3 cases via the transcallosal route and in the last via the transcortical route. Preoperative MRI was performed in such a way that both the lesion and the anticipated operative route to it were shown on the image, so that the approach angle and surrounding structures could be assessed. During craniotomy, intraoperative ultrasonographic examination was performed while the dura was still closed. By frequently changing the probe direction, we were able to obtain an image similar to that shown on the preoperative MRI, and we then initiated intradural operative procedures at an angle parallel to the axis of the probe. Since MRI provides detailed anatomical information about the approach to the lesion and the tissue around it, it has become an indispensable tool in the planning of neurosurgical operations. Although ultrasonography generally provides poorer resolution than does MRI, especially for deep structures, it does provide convenient, real-time images of any slice. Because the interhemispheric fissure, lateral ventricle, and choroid plexus have distinctive shapes and echogenicity and, hence, can be readily recognized, we found that they can be good landmarks in the imaging of periventricular or intraventricular lesions.(ABSTRACT TRUNCATED AT 250 WORDS)