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Cerebral abscesses: investigation using apparent diffusion coefficient maps
A C Guo1, J M Provenzale, L C Cruz
1Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA. acquo@yahoo.com
Abstract:
The combination of high signal and reduced apparent diffusion coefficients (ADC) within abscesses on diffusion-weighted MRI (DWI) has been reported as characteristic of abscesses, and useful for distinguishing them from cystic or necrotic neoplasms. To assess whether these are consistent findings in abscesses, we used DWI-derived ADC to investigate changes in water diffusibility in cerebral abscesses. We reviewed the MRI studies and clinical records of five patients with brain abscesses, who underwent DWI. Regions of interest were drawn within the abscesses on ADC maps, to obtain the ADC. The center of all five abscesses gave signal higher than that of white matter on DWI. The three largest also appeared bright on ADC maps, i. e., showed ADC substantially lower than those of normal white matter, consistent with restricted diffusion. However, the two smaller abscesses were not visible on ADC maps because their ADC were essentially the same as that of white matter; they did not show restricted diffusion. The absence of restricted diffusion within small abscesses may be related to intrinsic differences in molecular microenvironment between small and large abscesses, or to greater influence of volume averaging with surrounding edema on the ADC in smaller abscesses.
Insights
High signal on diffusion-weighted MRI (DWI) is typical for brain abscesses. However, reduced apparent diffusion coefficients (ADC) indicating restricted diffusion are only consistently seen in larger abscesses, not smaller ones.
Area of Science:
- Neuroradiology
- Neuroimaging
- Diffusion-Weighted MRI
Background:
- Diffusion-weighted MRI (DWI) with apparent diffusion coefficients (ADC) is used to differentiate brain abscesses from neoplasms.
- High signal on DWI and low ADC values are considered characteristic findings for abscesses.
Purpose of the Study:
- To evaluate the consistency of restricted diffusion findings in cerebral abscesses using DWI-derived ADC.
- To investigate potential factors influencing ADC values in brain abscesses.
Main Methods:
- Retrospective review of five patients with brain abscesses who underwent DWI MRI.
- Analysis of ADC values by drawing regions of interest within the abscesses on ADC maps.
- Comparison of ADC values with normal white matter.
Main Results:
- All five abscesses showed high signal on DWI compared to white matter.
- Three larger abscesses exhibited restricted diffusion (low ADC values).
- Two smaller abscesses did not show restricted diffusion; their ADC values were similar to white matter.
Conclusions:
- Restricted diffusion is not a universal finding in all brain abscesses, particularly smaller ones.
- Absence of restricted diffusion in small abscesses may be due to microenvironmental differences or volume averaging effects.
- DWI-ADC findings in brain abscesses can vary based on abscess size.