Pathophysiology of transcranial sonography signal changes in the human substantia nigra

The characteristic change in ultrasound signal seen in the substantia nigra in Parkinson's disease and related disorders is known as hyperechogenicity and is suggested to be a risk or state marker for these disorders. The underlying cellular basis of this change, however, is unknown. Imaging studies on Parkinson's disease patients, experimental studies on animal models, and human postmortem studies support the hypotheses that an alteration in regional iron and/or change in regional cell composition within the substantia nigra underlie this echo feature. Future quantitative postmortem studies incorporating cellular and metal analyses of the substantia nigra, in Parkinson's disease patients and healthy controls of known echogenic status during life, will be important to clarify the cellular basis of this change.