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A. Cortical gray matter shows hypoechogenicity (arrows) as compared to subcortical white matter on ultrasonography (US). Anechoic intraventricular cerebrospinal fluid (asterisk) is a useful landmark for intraoperative US neuronavigation. B. Color Doppler US can differentiate subdural fluid collection (asterisk) from subarachnoid fluid collection. Note the thin echogenic line suggesting the arachnoid membrane (arrowheads).
