A cisternogram is a specialized diagnostic imaging test that allows medical professionals to observe the movement of cerebrospinal fluid (CSF) around the brain and spinal cord. This procedure helps in understanding the dynamics of CSF circulation within the central nervous system. By evaluating how this fluid flows, doctors can gain insights into conditions that might affect its normal pathways.
What a Cisternogram Is
A cisternogram involves the injection of a small amount of a radioactive substance, known as a tracer, into the cerebrospinal fluid (CSF) space. This injection typically occurs in the subarachnoid space, which surrounds the spinal cord and brain. The tracer, often Indium-111 DTPA, then mixes with the CSF and begins to circulate.
Following the injection, a series of imaging scans are performed over several hours to days using specialized equipment like a gamma camera or SPECT scanner. These scans visualize the pathways and dynamics of CSF flow within the central nervous system. This process allows doctors to track how CSF moves, delivering nutrients, removing waste, and cushioning the brain.
Reasons for the Procedure
Medical professionals may recommend a cisternogram to assess conditions affecting the flow of cerebrospinal fluid. One common reason is to evaluate for Normal Pressure Hydrocephalus (NPH), which is identified by the ICD-10 code G91.2. In NPH, the cisternogram can reveal abnormal reflux of the tracer into the brain’s ventricles and a reduced presence of the tracer over the brain’s convexities.
Another significant application is in the detection of cerebrospinal fluid (CSF) leaks, identified by the ICD-10 code G96.0. This test helps pinpoint the precise location of a leak, which can be crucial for treatment planning. Additionally, a cisternogram can be used to assess the function of shunting procedures, coded as Z98.89, to determine if a CSF shunt is blocked or functioning correctly.
How the Procedure is Performed
Preparation for a cisternogram is generally minimal, though specific instructions may be provided by the healthcare team. Patients might be advised about eating or drinking restrictions, or adjustments to certain medications like blood thinners. It is important to inform the medical staff about any possibility of pregnancy or allergies.
The core of the procedure involves a lumbar puncture, commonly known as a spinal tap. A specialist, such as a radiologist or neurologist, performs this step. The area in the lower back is numbed with a local anesthetic before a thin needle is inserted into the subarachnoid space to inject the radioactive tracer. X-ray or fluoroscopy guidance often assists in precise needle placement.
After the tracer injection, the patient typically lies flat for about one to two hours to allow the substance to distribute properly within the CSF. Initial imaging scans are then taken, usually within one to six hours post-injection. Subsequent scans are performed at specific intervals, commonly at 24, 48, and sometimes 72 hours later. These scans are non-invasive, requiring the patient to lie still on a table while images are captured.
After the Cisternogram
Following the tracer injection, patients are generally advised to lie flat for a period, often one to two hours or more, which helps to minimize the risk of a post-lumbar puncture headache. Staying well-hydrated is also encouraged during this time. Any discomfort at the injection site is usually monitored, and driving is restricted for the remainder of the day.
Because the procedure involves multiple imaging sessions over several days, the full results are not available immediately. A radiologist interprets the images obtained from each scan. They meticulously assess the tracer’s distribution, its clearance over time, and look for any abnormal pooling, such as in the brain’s ventricles which might suggest Normal Pressure Hydrocephalus. The radiologist also identifies any blockages or extravasation of the tracer that would indicate a CSF leak. Normally, the tracer should circulate, indicating healthy CSF flow.
Understanding Potential Risks
Like any medical procedure, a cisternogram carries certain potential risks, though serious complications are rare. The most common side effect is a post-lumbar puncture headache, which can range from mild to intense and may last for several hours to a few days. Discomfort or mild pain at the injection site in the lower back is also frequently reported.
Less common risks include infection at the injection site, bleeding into the spinal canal, or an allergic reaction to the radioactive tracer used. Very rarely, nerve damage or more severe conditions like meningitis or brainstem herniation could occur. These serious complications are infrequent, and the procedure is generally considered safe when performed by experienced teams. The radioactive dose used is small and leaves the body within a few days.