Lumbar puncture or spinal tap. This test allows an estimation of CSF pressure and analysis of the fluid. Under local anesthetic, a thin needle is passed into the spinal fluid space of the lower back. As much as 50 cc of CSF may be removed to determine if symptoms are temporally relieved.
Lumbar catheter insertion. This test is a variation of the lumbar puncture. A spinal needle is inserted in the spinal fluid space of the lower back. Then a thin, flexible tube is passed into the spinal fluid and the needle is removed. The lumbar catheter allows continuous recording of spinal fluid pressure or continuous removal of spinal fluid as needed over several days to imitate the effect that a shunt would have. Patients who respond dramatically to such spinal fluid drainage are likely to respond well to shunt surgery.
Intracranial pressure (ICP) monitoring. ICP monitoring requires admission to the hospital. A small pressure monitor is inserted through the skull into the brain or ventricles to measure ICP. The pressure is not always high, and pressure monitoring (either by lumbar catheter or the intracranial method) can detect an abnormal pattern of pressure waves.
Measuring CSF outflow resistance. This test requires admission to the hospital. The test assesses the degree of blockage to CSF absorption back into the bloodstream. It requires the simultaneous infusion of artificial spinal fluid and measurement of CSF pressure. If the calculated resistance value is abnormally high, then the patient has a good chance of improving with shunt surgery.
Isotopic cisternography. In this procedure a radioactive isotope is injected into the lumbar subarachnoid space (lower back) through a spinal tap. The absorption of CSF can then be evaluated over time by periodic scanning, which shows whether the isotope is being absorbed over the surface of the brain or whether it remains trapped inside the ventricles. Isotopic cisternography involves spinal puncture and is considerably more involved than either CT or MRI. This test has become less popular because a positive cisternogram does not reliably predict whether a patient will respond to shunt surgery.
