Cerebral Edema Patterns

Normal State

In the normal state, water freely diffuses in and around the cells/neurons including both the gray and white matter

In this schematic- the Cell Bodies are depicted as lighter gray to follow the density of the gray matter on CT. The white matter/axons are darker gray as this structure is lower in density due to the fat from the myelin sheaths which surrounds the axons

Vasogenic Edema

What happens if you have a brain tumor that results in leaky capillaries?

Leaky capillaries leads to increase in amount of water in the interstitial space.
Cells remain the same size, but water accumulates in between cells.
Because the edema/water follows the path of least resistance, there is more space in between axons and no space in between cell bodies, you can see that the edema preferentially occurs within the white matter.

This edema pattern occurs in any scenario that results in leaky capillaries-- often seen in the setting of tumor, infection, hemorrhage etc.

Cytotoxic Edema

What happens if you block the flow of blood, O₂ & ATP to a region of the brain?

Na+/K+ ATPase pump dies
Intracellular Na+ accumulates
H20 Follow Na+
Cellular swelling leads to apoptosis
Because the entire cell is involved in this process- both the gray and white matter are affected. This results in loss of gray white matter differentiation, which is normally seen on routine head CT examinations.

This edema pattern occurs in the setting of stroke

Normal: Functional ATP pump

Normally, ATP fuels the Na/K pump to pump sodium out of the cell into the extracellular space and potassium into the intracellular space.

Abnormal: Non functional ATP pump

In the setting of a stroke, oxygen and ATP can no longer fuel the Na/K pumps. Sodium accumulates within the intracellular space and water follows sodium which results in cellular swelling and apoptosis.

Cytotoxic Edema

This patient presented with acute onset left sided weakness 1 day prior. He was found to have a right middle cerebral artery large vessel occlusion. Notice how in this example there is blurring of the gray-whiter matter differentiation. This pattern of edema is referred to as cytotoxic edema, which is typically seen in the setting of stroke.

Vasogenic Edema

This patient presented with acute onset of visual disturbance and was found on exam to have left homonymous hemianopsia. This patient was initially clinically thought to have a stroke, but on imaging we see that the edema pattern preferentially involves the white matter with relative sparing of the gray matter. This pattern of edema is called vasogenic edema, which is typically seen as a response to tumor, infection, hemorrhage etc. This patient was found go have a brain tumor which was appreciated on MRI.

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