Cortex, Subcortex, Vasogenic Edema, and Cytotoxic Edema

In a brain edema report, location and diffusion behavior provide more information than T2/FLAIR hyperintensity alone. Vasogenic edema often predominates in white matter and relatively spares cortex. Cytotoxic edema reflects cellular swelling, can affect gray and white matter, and shows restricted diffusion at the appropriate stage.

The distinction is not absolute. Tumor, posterior reversible encephalopathy, venous disease, infection, and trauma can produce mixed patterns. DWI hyperintensity should be confirmed by low ADC to exclude T2 shine-through.

Assessment framework

• Locate the center of abnormality in cortical ribbon, subcortical white matter, or deep structures.
• Read DWI and the ADC map together in the same region.
• Compare arterial territories, venous drainage areas, and peritumoral distribution.
• Assess enhancement, hemorrhage, and vascular findings separately from edema type.
• Measure sulcal effacement, ventricular compression, and midline shift.

What the report should contain

• State the side, lobe, and gray-white matter distribution.
• Name true restricted diffusion with its ADC correlate.
• Use probability language when the cause of a vasogenic pattern is not established.
• With cortical involvement, consider seizure, ischemia, encephalitis, and metabolic causes in context.
• Make mass effect visible in the impression regardless of edema type.

Common errors

• Calling every FLAIR hyperintensity edema.
• Diagnosing acute infarction from DWI brightness without ADC.
• Excluding tumor because abnormality is white-matter predominant.

Example report wording

Example impression: Extensive right parietal subcortical white-matter T2/FLAIR hyperintensity largely spares the cortical ribbon and has no low ADC. The distribution supports vasogenic edema. An adjacent 18 mm enhancing corticosubcortical lesion is the likely cause. Local sulcal effacement is present without midline shift.

When mass effect is substantial, use the cerebral herniation guide to assess cisterns and midline structures.

References

1. American College of Radiology. Practice Parameter for MRI of the Head and Neck. Source (opens in a new tab)
2. American College of Radiology. Practice Parameter for CT of the Head. Source (opens in a new tab)

Clinical note: This material is for radiology education. Do not generate an automatic diagnosis or management decision without checking guideline scope, patient factors, and local policy.