Aliasing artefact causing a spurious cerebellar lesion
Recent onset of ataxia with signs suggestive of a cerebellar lesion
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Focus of apparent T2 brightening on the coronal 3D FLAIR sequence involving the right cerebellar tonsil without abnormality on the axial T2 and routine FLAIR sequences. Shown to be due to "wrap around" of the nose superimposed on the cerebellar tonsil on the sagittal sequence
Aliasing artefact must be recognized in order to avoid error in lesion detection. It comes about by way of a selected scan FOV being smaller than the anatomical part leading to displaying of the anatomical information outside the scan FOV over or on top of anatomical information inside the scan FOV. It is generally a clinical interpretation problem in the phase encoding direction of the image acquisition (as in this case).