Objectives: You will learn
- Types of cerebral edema
- Image findings in cerebral edema
- Consequences of edema
Excess accumulation of water in brain.
- Intracellular edema: Cytotoxic. Blood brain barrier intact. Inadequate functioning of sodium and potassium pump.
- Early stroke is a good example.
- Extracellular edema: Loss of blood brain barrier. Commonly produced by intracerebral tumors.
What are the common reasons for brain edema due to loss of blood brain barrier?
- Diffuse cerebral edema: Common causes are head trauma, high altitude, malignant hypertension and anoxia.
- Localized cerebral edema: Occurs with any lesion of brain like tumor, infarct or injury. There is edema surrounding the lesion.
What imaging procedure is helpful in detecting brain edema?
- Both CT and MRI can demonstrate cerebral edema.
How does edema appear in CT and MRI?
- Edema is recognized as an area of lucency or hypodense or hypoattenuation by CT imaging.
- Edema is recognized in MRI as bright signal (T2 weighted or FLAIR pulse series).
- Diffusion weighted MRI sequence is most sensitive to detect intracellular cytotoxic edema with bright signal.
- Contrast helps delineate the lesion within the surrounding edema.
Consequences of edema:
- Swollen brain causing increased intracranial pressure.
- Compression of vasculature resulting in hypoperfusion of brain.
- Edema can cause significant mass effect producing either a midline shift (subfalcine herniation) or downward shift into foramen magnum (tonsillar herniation).
- Swollen gyri can efface sulci.
- Poor differentiation of white and gray matter.
Localized extracellular edema
81 year old male with few months of confusion, poor memory, getting lost, misplacing items; left homonymous hemianopsia noted on exam.
Figure 1: MR images
- FLAIR MR image shows a right parieto-occipital area of high signal from peritumoral edema (black arrow).
- Post-contrast axial MRI: Contrast study helps delineate the lesion causing edema. Edema
does not enhance with contrast (yellow arrow). Tumor enhances with contrast (black arrow).
Localized extracellular edema
Figure 2: Pre-contrast axial CT scan
60 year-old patient with melanoma. Hemorrhage is from metastatic tumor bleed.
- Pre-contrast axial CT: Acute intracerebral hematoma within the right temporal lobe (arrow) with surrounding
- Pre-contrast axial CT: Acute hematoma is seen by pre-contrast imaging as an area of high
attenuation (HU 68.6).
|What are the other associated imaging consequences of edema?
Mass effect producing compression of left lateral ventricles.
Figure 3: Pre-contrast axial CT scan
- MCA distribution infarct with edema is seen (hypodense or low attenuation).
- Mass effect on the body of left lateral ventricle (arrow).
Figure 4: Pre contrast axial CT scan
- Arrow points to subdural collection of blood (high density).
- Brain edema (hypoattenuation) with shift of right lateral ventricle across the midline (arrowhead) from subfalcine brain herniation.
Diffuse brain edema
30 year old patient with head trauma.
Figure 5: Pre-contrast axial CT
- Absence of sulcal markings and poor differentiation of white and gray matter from diffuse bilateral cerebral hemispheric edema..
Common causes are head trauma, anoxia, infections, syndrome of inappropriate antidiuretic hormone secretion (SIADH) and high altitude.
Intracellular cytotoxic edema
Acute one day old infarction involving the right middle cerebral
artery (MCA) territory.
Figure 6: MR images
- Diffusion wtd. image shows area of infarct as bright signal (arrow).
- Pre-contrast axial T1 wtd. MRI shows hypodense area in the corresponding site.