Today I want to share with you all some basic ideas related to CT Brain. How can we identify what problem a patient has? As a technician, you should know what happened to the patient because wherever you work, the advising doctor may ask you what it is. You should also know because sometimes in some hospitals there is no radiologist available, so you may have to decide yourself whether contrast should be given or not.
In CT Brain scan, we can detect trauma and abnormal soft tissue like tumors or abscesses. We can also identify mass effect, such as excessive bleeding or increased pressure due to excess fluid around a tumor. CT Brain is also done to detect bleeding.
To define different brain problems, there are terms like hypodense and hyperdense. Hypodense means dark areas on CT Brain. Lower-grade tumors, edema, and infarcts appear hypodense. Wherever brightness is reduced, it is called hypodense because its density is less than normal brain tissue.
Areas that are brighter are called hyperdense. For example, this bright area is a bleed area, so it is hyperdense. Radiation absorption is higher there, and its Hounsfield Unit is higher. Bleeding usually has an HU value around 50, so it appears hyperdense.
Low-density lesions are called hypodense lesions. Many tumors appear hypodense. MRI can detect lesions with lower density more clearly. Lower-grade tumors are often detected this way.
Now in CT Brain, when we see bleeding, I want to show some images. This is ICH – Intracranial Hemorrhage. When bleeding occurs in the brain tissue like this, it is called ICH.
Next, look here inside the ventricles. These are ventricles where CSF is present. When bleeding occurs inside the ventricles, it is called Intraventricular Hemorrhage (IVH).
Then there are EDH and SDH. They look similar. EDH means Epidural Hematoma. EDH slightly bulges inward. Sometimes it appears as a small lens-shaped collection. SDH appears like a crescent shape along the side and spreads more widely. EDH comes inward, while SDH spreads along the side.
SDH can involve multiple regions such as temporal and occipital lobes, causing bleeding in many areas.
Ischemic infarct occurs where blood supply is blocked. If an artery supplying a region of the brain is blocked, then after a few days that area becomes dark because the cells die and fluid accumulates. Usually, this becomes visible on CT after 3–4 days. Early infarcts are better detected on MRI.
This is a normal brain scan. A healthy brain appears symmetrical without abnormalities.
Interparenchymal hemorrhage means bleeding inside the brain tissue itself. SDH appears along the side like a crescent, while EDH appears more lens-shaped.
To assess bleeding severity, we look at midline shift. A line is drawn through the middle of the brain. If the brain tissue shifts significantly to one side, it means pressure inside the brain is high and the situation is more serious.
If skull bones fracture after injury, air may enter the brain. Air appears as black sharp-edged dots because air has no proper shape and remains distinct from tissues. This is called pneumocephalus or intracranial air.
Mass effect means how much the bleeding or lesion is pushing the brain tissue. Greater shift indicates more dangerous pressure effects.
Contusions occur after injury when brain tissue and blood vessels are damaged, causing bleeding in irregular round shapes in different brain areas.
By seeing many cases and correlating with reports, you will gradually understand what is bleeding, calcification, tumor, or contrast enhancement.
Some tumors enhance after contrast. For example:
• Glioma
• Meningioma
• Lipoma
• Polycystic astrocytoma
• Lymphoma
• Medulloblastoma (common in children)
Hypodense tumors appear darker, while highly cellular tumors or calcified tumors may appear hyperdense.
Sometimes tumors also bleed, so you must differentiate between normal hemorrhage and tumor-related hemorrhage. Tumors usually show abnormal soft tissue or mass effect around them.
When tumors are present, surrounding edema or fluid collection is also seen. Contrast helps tumors appear more clearly because abnormal cells absorb contrast differently compared to normal tissue.
Old and new hemorrhages can also be differentiated. Old hemorrhage usually has sharper margins and surrounding fluid collection. Chronic untreated bleeding may show edema around it. Fresh bleeding appears brighter and more acute.
Metastatic brain tumors mean cancer cells have spread from another part of the body to the brain. These tumors may appear in multiple areas rather than one isolated location.
Toward the end, a few example cases were shown. In one brain image, a hypodense area suggested an old infarct or cell death. Another image showed associated bleeding.
By seeing more CT Brain cases regularly and correlating them with reports, you will gradually learn to identi
fy different pathologies and abnormalities confidently.
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