A radionuclide cisternogram is a radiological procedure where a lumbar puncture is used to inject a radioactive substances into the patient's cerebro-spinal fluid. The flow of the substance can then be tracked through the body to determine if the flow of CSF is abnormal or it is leaking. In a normal procedure, the patient is scanned immediately after injection, then six hours later, then 24 hour after injection. Where necessary, the patient may be called in for further scans at 48 hours and 72 hours.