During a normal cisternographic study, radioactivity is not visualized in which of the following areas?

In a normal cisternographic study, radioactivity is typically not visualized in the lateral ventricles. This is due to the way cerebral spinal fluid (CSF) dynamics operate and how the radiopharmaceutical spreads in the central nervous system.

During a cisternogram, the radiopharmaceutical is injected into the subarachnoid space and should flow through the basal cisterns, around the cerebral convexities, and into the central canal. Basal cisterns are areas where CSF accumulates around the base of the brain, while the cerebral convexities refer to the outermost portions of the brain's surface where CSF would normally mix. The central canal, although less commonly evaluated in this context, would also appear due to the flow of CSF.

Conversely, the lateral ventricles are filled with CSF, but they are not directly accessed during the injection of the radiopharmaceutical in a typical cisternographic procedure. As such, the visualization of radioactivity in these ventricles does not occur in a normal cisternographic study, indicating that any radioactivity seen elsewhere (like in the basal cisterns or cerebral convexities) does not extend to the lateral ventricles under normal circumstances. This is essential for