A ring-enhancing lesion is an abnormal
radiologic sign
A radiologic sign is an objective indication of some medical fact (that is, a medical sign) that is detected by a physician during radiologic examination with medical imaging (for example, via an X-ray, CT scan, MRI scan, or sonographic scan).
...
on
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 ...
or
CT scan
A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...
s obtained using
radiocontrast
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 ...
. On the image, there is an area of decreased density (see
radiodensity
Radiodensity (or radiopacity) is opacity to the radio wave and X-ray portion of the electromagnetic spectrum: that is, the relative inability of those kinds of electromagnetic radiation to pass through a particular material. Radiolucency or hypod ...
) surrounded by a bright rim from concentration of the enhancing contrast dye. This enhancement may represent breakdown of the blood-brain barrier and the development of an inflammatory capsule. This can be a finding in numerous disease states. In the brain, it can occur with an early
brain abscess
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special sense ...
as well as in ''
Nocardia
''Nocardia'' is a genus of weakly staining Gram-positive, catalase, catalase-positive, rod-shaped bacteria. It forms partially acid-fast beaded branching filaments (appearing similar to fungi, but being truly bacteria). It contains a total of 8 ...
'' infections associated with lung cavitary lesions. In patients with HIV, the major differential is between
CNS lymphoma and CNS
toxoplasmosis
Toxoplasmosis is a parasitic disease caused by ''Toxoplasma gondii'', an apicomplexan. Infections with toxoplasmosis are associated with a variety of neuropsychiatric and behavioral conditions. Occasionally, people may have a few weeks or month ...
. CT imaging is the appropriate next step to differentiate between the two conditions.
[Fauci A. Harrison's Principles of Internal Medicine, New York, McGraw Hill Medical, 2008]
References
External links
Ring Enhancement: The Free Medical Dictionary
Neuroimaging
Radiologic signs
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