From the Guidelines
MRI sequences reveal characteristic changes in brain lesions over time, with the most recent and highest quality study 1 indicating that lesions appear hyperintense on T2-weighted and FLAIR images, isointense to hypointense on T1-weighted images, with restricted diffusion on DWI and low ADC values in the acute phase. In the acute phase (0-7 days), lesions appear hyperintense on T2-weighted and FLAIR images, isointense to hypointense on T1-weighted images, with restricted diffusion on DWI and low ADC values. During the subacute phase (1-3 weeks), lesions remain hyperintense on T2/FLAIR but may show contrast enhancement as the blood-brain barrier breaks down. T1 signals gradually change from hypointense to hyperintense in hemorrhagic lesions due to methemoglobin formation. In the chronic phase (beyond 3 weeks), lesions typically show persistent T2/FLAIR hyperintensity but with normalization of diffusion restriction. T1 signals become permanently hypointense in areas of tissue loss, and volume loss or encephalomalacia may develop.
Key Characteristics of Cerebral Lesions on MRI
- Hyperintensity on T2-weighted and FLAIR images in the acute phase
- Isointensity to hypointensity on T1-weighted images in the acute phase
- Restricted diffusion on DWI and low ADC values in the acute phase
- Contrast enhancement in the subacute phase
- Persistent T2/FLAIR hyperintensity in the chronic phase
- Permanent hypointensity on T1-weighted images in areas of tissue loss
Importance of Understanding Temporal Changes
Understanding these temporal changes helps differentiate between acute and chronic injuries and assists in determining the timing of brain damage, which is crucial for treatment decisions and prognosis assessment, as supported by studies such as 1 and 1.
Variability by Pathology
Specific patterns vary by pathology - ischemic strokes follow a predictable evolution while inflammatory, traumatic, or neoplastic lesions have distinct temporal signatures, as noted in studies such as 1, 1, and 1.
From the Research
Characteristics of Cerebral Lesions on MRI Scans
- The characteristics of cerebral lesions on MRI scans can vary depending on the type and severity of the injury or condition 2, 3, 4, 5.
- In cases of traumatic brain injury (TBI), MRI scans have shown that lesion volume and apparent diffusion coefficient (ADC) values can change over time 2, 4.
- Hyperbaric oxygen therapy (HBO) has been shown to reduce lesion volume and improve ADC values in TBI patients 2, 4.
- In newborn infants with hypoglycemic brain damage, MRI scans have shown hyperintensive signals indicating cytotoxic edema in the occipital cortex and white matter 5.
- The use of diffusion-weighted imaging (DWI) has been shown to be effective in detecting early changes in cerebral lesions, particularly in cases of hypoglycemic brain damage 5.
Changes in Lesion Characteristics Over Time
- In TBI patients, lesion volume has been shown to decrease over time with HBO treatment 2, 4.
- ADC values have also been shown to change over time, with decreases in ADC values indicating improved outcomes 2, 4.
- In newborn infants with hypoglycemic brain damage, follow-up MRI scans have shown changes in lesion characteristics, including decreased hyperintensity on DWI and delayed myelination 5.