Radionuclide cisternogram; Intrathecal scan; RHISA scan; CSF flow scan; Cisternogram
A RHISA scan is a nuclear scan test using small amounts of radioactive material (radioisotope) injected into the cerebrospinal fluid (CSF) to detect disorders of CSF circulation.
How the test is performed
A RHISA scan is a type of nuclear scan. Small amounts of radioactive material are injected into the cerebrospinal fluid at the lower spine. The cerebrospinal fluid is allowed to circulate for a time. The scanner can detect the presence of radiation emitted by the materials, and images are taken to illustrate the flow of those radioactive materials through the cerebrospinal fluid circulation.
A lumbar puncture (spinal tap) is performed. A radiopharmaceutical (material tagged with a radioisotope; in this case, usually albumin mixed with indium 111) is injected into the lumbar subarachnoid space (the space where the cerebrospinal fluid flows through the spine). The cerebrospinal fluid is allowed to circulate for a time and the tracer travels with it.
You will be scanned 4-6 hours later. You are asked to lie flat on a table and are placed beneath the arm of the scanner (which resembles an X-ray machine). The scanner detects the presence of radiation from the radioisotope. There will be a series of scans, usually at 4-6 hours after injection, again at 24-hours after injection, and possibly again at 48 and 72 hours after injection.
How to prepare for the test
No preparation is usually necessary. However, if you are very anxious or agitated, sedation may be necessary. You must sign a consent form. You will wear a hospital gown (to make the spine more accessible). Remove jewelry or metallic objects before the scan.
For infants and children:
The preparation you can provide for this test depends on your child’s age and experience. For specific information regarding how you can prepare your child, see the following topics:
- toddler test or procedure preparation (1 to 3 years)
- preschooler test or procedure preparation (3 to 6 years)
- schoolage test or procedure preparation (6 to 12 years)
- adolescent test or procedure preparation (12 to 18 years)
How the test will feel
During lumbar puncture, the lower back over the spine is numbed with an anesthetic. However, many people find lumbar puncture somewhat uncomfortable, usually because of the pressure on the spine during insertion of the needle.
The scan is painless, although the table may be cold or hard. No discomfort is produced by the radioisotope or the scanner.
Why the test is performed
The test is performed to detect abnormalities of CSF circulation.
A normal value indicates normal circulation of CSF through all parts of the brain and spinal cord.
What abnormal results mean
An abnormal RHISA scan indicates disorders of CSF circulation, including:
- CSF leak
- normal pressure hydrocephalus (NPH)
- patency/obstruction of CSF shunts
What the risks are
There is some risk any time lumbar puncture is performed, particularly a risk of infection. Risks for RHISA scan are no greater than when lumbar puncture is performed for other reasons.
A very slight amount of radiation is produced by the radioisotope. The amount of radiation is very small and virtually all of the radiation is gone within a few days. There have been no documented cases of injury or damage caused by the radioisotope used with RHISA scan. However, as with any radiation exposure, caution is advised if you are pregnant or breastfeeding.
Extremely rarely, a person will develop an allergic reaction to the radioisotope used during the scan. This may include a serious anaphylactic reaction.
This procedure requires multiple scans, and the entire test may take 48 to 72 hours. You must be able to lie still during the scan.
by Simon D. Mitin, M.D.