Scintigraphy as an ancillary examination in determination of death by neurologic criteria: Update and future perspectives.

The concept of death by neurologic criteria (DNC), a medicolegal construct also known as "brain death", is over 50 years old. Ancillary examinations have a well-defined role in this diagnosis, principally when the clinical examination cannot be completely or safely performed. Radionuclide studies, which provide a combination of ease of performance and high accuracy, remain amongst the most recommended ancillary studies in current clinical guidelines. There are in fact 2 discrete categories of radionuclide studies, using hydrophilic or lipophilic radiopharmaceuticals (RPs), which have overlapping but discrete features, described in this review. Lipophilic RPs that provide both flow and parenchymal imaging are superior to hydrophilic RPs that provide only flow imaging. Various signs have been described in regard to interpretation of the radionuclide study and serve to encapsulate findings in a concise and clearly understood manner. The trident and empty skull signs, relevant to flow and parenchymal phases of radionuclide examinations, respectively, remain the key elements of interpretation and are both necessary and sufficient to make the diagnosis of DNC. The hot nose sign and the sagittal sinus sign are not sufficiently specific for this diagnosis, and do not have a place in the interpretation of DNC examinations. Because it operates in the medicolegal realm and requires rapid and definitive reporting, the nuclear medicine physician must be particularly familiar with methods and interpretation of scintigraphy as an ancillary examination in determination of death by neurologic criteria.