Metrizamide is a
non-ionic
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
iodine-based
radiocontrast agent
Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically iod ...
. It is also a density gradient medium for the
centrifugation
Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...
of biological particles.
Historically metrizamide replaced
iofendylate
Iofendylate is a molecule that was used as a radiocontrast agent, typically for performing myelography studies. It was marketed under the trade names Pantopaque (in North America) and Myodil (rest of the world).
Iofendylate is a highly lipophilic ...
(trade names: Pantopaque, Myodil) as the
contrast agent
A contrast agent (or contrast medium) is a substance used to increase the contrast of structures or fluids within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasound, which is different from radiop ...
of choice for
myelography
Myelography is a type of radiographic examination that uses a contrast medium (e.g. iodised oil) to detect pathology of the spinal cord, including the location of a spinal cord injury, cysts, and tumors. Historically the procedure involved the inj ...
(an
X-ray study of the spine now largely replaced by
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...
). The radio opacity characteristics are such that finer detail is displayed with metrizamide, as well as the advantage of reabsorption from spinal fluid and excretion from the body – since unlike iofendylate, metrizamide is a water-soluble substance.
Both agents are administered by
lumbar puncture (also referred to as a spinal tap or cisternal puncture), at the cervicocranial junction. The human patient is rolled from the
lateral decubitus (lying on the side) to prone. Ankles are strapped to the end of a hard X-ray,
CT, or MRI table. To obtain images of the
cervical region the patient is then carefully tilted in the
Trendelenberg position (head down) so the contrast agent (particularly iofendylate) can enter the neck region. Care is given to prevent spilling dye into the
posterior cranial fossa
The posterior cranial fossa is the part of the cranial cavity located between the foramen magnum, and tentorium cerebelli. It is formed by the sphenoid bones, temporal bones, and occipital bone. It lodges the cerebellum, and parts of the brai ...
(back of the head) or to enter the cranial cavity in general. This speaks to the inability to remove the heavier or more viscous iofendylate without aspirating it with
spinal fluid
Cerebrospinal fluid (CSF) is a clear, colorless transcellular body fluid found within the meningeal tissue that surrounds the vertebrate brain and spinal cord, and in the ventricles of the brain.
CSF is mostly produced by specialized ependym ...
through a lumbar puncture needle in the low back (sticking up vertically) or back of the neck. Removal of iofendylate is necessary since it is not water-soluble. With metrizamide the issue is that if entering the
cranial cavity
The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull is also known as the cranium. The cranial cavity is formed by eight cranial bones known as the neurocranium that in human ...
and high dose exposure to the
blood brain barrier
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.
Blood is compo ...
, side effects are more likely encountered. Issues related to absorption into the general circulation are also encountered.
Side effects
* Headache
* Nausea
* Vomiting
*
Mass effect
''Mass Effect'' is a military science fiction media franchise created by Casey Hudson. The franchise depicts a distant future where humanity and several alien civilizations have colonized the galaxy using technology left behind by Elder race, a ...
,
herniation
A hernia (: hernias or herniae, from Latin, meaning 'rupture') is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. The term is also used for the normal development of the in ...
, and major central nervous system complications including spinal cord compression
*
Seizures
A seizure is a sudden, brief disruption of brain activity caused by abnormal, excessive, or synchronous neuronal firing. Depending on the regions of the brain involved, seizures can lead to changes in movement, sensation, behavior, awareness, o ...
* Muscle rigidity and
dystonic
Dystonia is a neurological hyperkinetic movement disorder in which sustained or repetitive muscle contractions occur involuntarily, resulting in twisting and repetitive movements or abnormal fixed postures. The movements may resemble a tremor. ...
reaction
*
Aphasia
Aphasia, also known as dysphasia, is an impairment in a person's ability to comprehend or formulate language because of dysfunction in specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine, but aph ...
* Adverse neurobehavioral reactions
History
Metrizamide was approved in the US in 1978. Its marketing is discontinued as of 2021.
References
Further reading
*
*
External links
*
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{{Contrast media
Radiocontrast agents
Iodobenzene derivatives
Acetanilides
Glucosides