Hyperdensity is a descriptive term sometimes used in radiology reports. This means that the abnormality is brighter than the surrounding brain. Many abnormalities are hyperdense but one of the most important ones is blood. Blood in the head needs to be treated promptly. Other abnormalities that are brighter than the brain can be tumors, calcifications and blood clots.
What can hyperdensity on a CT be?
One of the more important causes is blood. Brain bleeds can occur between the surface of the brain and the skull. These are called epidural or subdural bleeds. Subarachnoid bleeds occur between the meninges or coverings of the brain. Brain bleeds can also occur within the brain itself. These can be traumatic or because of underlying brain or blood vessel abnormalities. Brain bleeds are bright or hyperdense on CT.
Calcifications in the brain are hyperdense on head CT. Calcifications can be small or be large and sheet like. Many diseases can cause calcification. Infections like neurocysticercosis and toxoplasmosis. Previous insults to the brain like strokes, bleeds and abscesses. Neurodegenerstive diseases and radiation treatment are a few others. Certain tumors of the brain can also look hyperdense.
Blood vessels can be hyperdense on head CT. Normal veins along the brain periphery called venous sinuses can look hyperdense. These can be mistaken for bleeds to the untrained eye along the back part of the brain.
Crossing arteries can also cause an appearance of a hyperdense abnormality. It is important to look at all planes of the imaging to avoid this pitfall. Blood clots can look hyperdense. One example is when a major artery gets blocked and looks unusually bright because of clot. The clot can be confirmed with a test that looks at the blood vessels.
With all these possibilities for hyperdensity on head CT, how is it ever possible to tell anything apart? Radiologists undergo years of training which helps. But all of these abnormalities have characteristic appearances on head CT.
In cases when we are not sure, we provide a differential diagnosis which is a list of possibilities. Additional testing with MRI helps in many cases when we are not sure what we are dealing with but know something is abnormal. Correlating with the clinical history is also important when we see hyperdensity on head CT.