Diagnostic criteria for the MR imaging shrimp sign of cerebellar PML
| Core Inclusion Criteria of the Shrimp Sign | Core Exclusion Criteria of the Shrimp Sign |
|---|---|
| White matter lesion Well-defined lesion in the cerebellar white matter The lesion is hyperintense on T2-weighted and FLAIR imaging The lesion is hypointense on T1-weighted imaging The lesion abuts and sharply demarcates the dentate nucleus and outlines the dentate nucleus in horizontal, parasagittal, and/or coronal views The lesion must encompass at least 50% of the dentate nucleus (partial shrimp); if there are multiple lesions adjacent to the dentate, they do not need to be contiguous | White matter lesion Is not hypointense on T1-weighted imaging Is hazy and ill-defined on T2-weighted or FLAIR imaging Has cavitation within the substance of the lesion Demonstrates prominent focal, diffuse, or ring enhancement Dentate nucleus Is invaded by the white matter lesion Is displaced by the white matter lesion Shows enhancement of the nucleus itself (specifically excluding the hilum) Is severely atrophic early in the course of the disease |
| Other features compatible with PML | Permissible atypical featuresa |
| There may be a mottled appearance of the white matter lesion on T2-weighted imaging The white matter hilum of the dentate nucleus may be involved The lesion may occur together with, or independent of, cerebral hemisphere and brainstem PML lesions | Minimal enlargement of the MC P (up to 2–3 mm) Minimal mass effect on the fourth ventricle Faint enhancement of the white matter lesion or the hilum of the dentate nucleus Olivopontocerebellar atrophy in late-stage PML Bilateral, usually asymmetric white matter lesions |
Note:—MCP indicates middle cerebellar peduncle.
↵a In the right clinical and imaging context and when all core inclusion and exclusion criteria are met.