Parenchymal imaging in movement disorders

The use of B-mode sonography in neurological diagnosis was once considered of limited importance due to the barrier of the skull. However, modern ultrasound systems allow visualization of the brain parenchyma with a high degree of accuracy. Transcranial sonography (TCS) can offer unique information on brain tissue pathology, as it uses different physical principles for imaging acquisition than do other neuroimaging techniques. The method is harmless, is quick to perform at low cost and demands no sedation. The main limitations of this technique are dependence on the quality of the individual bone window and on proper operator training. A huge body of research has shown that patients with Parkinson's disease (PD) display an enlarged hyperechogenic substantia nigra by TCS with a positive predictive value of 92.9%. Healthy individuals (8-15%) may show the same marker, in some cases correlating with decreased striatal dopamine uptake, motor slowing and prodromal markers of PD, indicating that this ultrasound sign may constitute a risk marker for PD. Other movement disorder diagnoses, although less extensively studied for TCS, may benefit from using this method as a supplementary diagnostic tool. This review provides a summary of the typical TCS findings and their value in the differential diagnosis of some movement disorders.