A common neurosurgical operation involves the diversion of excess cerebrospinal fluid (CSF) from the brain. Most commonly, a tube called a 'shunt' is tunneled under the skin from the brain to the abdomen. This implantable device generally stays in place for life. Problems with the shunt - including infection, obstruction, or disruption of the tubing - are occasionally encountered. Workup for a shunt problem may include a CT scan of the head, a 'shunt series', a 'shuntogram', a shunt tap, or some combination of these studies. A CT scan will give information regarding the amount of CSF in the brain. It will generally need to be compared to previous CT scans. Excessive CSF can mean that the shunt is not working properly. A 'shunt series' is a simple set of X-rays (skull, chest, and abdomen) that can reveal a break in the tubing. A 'shuntogram' is a more sophisticated study that involves placing a radioactive isotope in the shunt reservoir in the head and measuring the speed with which it moves to the abdomen. Delayed movement of CSF to the abdomen may imply a problem with the shunt. Lastly, a shunt infection may be assessed by sterilely removing some spinal fluid from the shunt reservoir and sending it to the microbiology lab for culture.