Arnold-Chiari II malformation: intraoperative real-time US.

Nineteen cases in which high-resolution, intraoperative, real-time sonography was performed during decompression of an Arnold-Chiari II malformation were reviewed. The variations of the often complicated hindbrain anatomic features, well known from autopsy series, were shown in detail with intraoperative sonography. The extent of herniation of the cerebellar vermis, the medulla, and the fourth ventricle into the cervical spinal canal, as well as fourth ventricular dilatation, arachnoid cysts, and cervical hydromyelia, were also demonstrated sonographically. Real-time imaging was useful in guiding the neurosurgeon in decompression of the hindbrain, especially the fourth ventricle, in an anatomic area often obscured visually by intense fibrovascular adhesions.