Table 2

Rules for defining cortical lesions on PSIR

Inclusion	Lesions are hypointense relative to surrounding normal cortex
Inclusion	They must involve the cortex in part or whole a. A lesion confined to the cortex is called intracortical (IC) (figure 1) b. A lesion that involves both cortex and juxtacortical white matter is called leucocortical (LC) (figure 1)
Caution	If small or ill-defined on a single slice, they must be visible on at least one other contiguous slice
Caution	Equivocal lesions must be confirmed by retrospective detection of signal abnormality compatible with a lesion at the same location on the corresponding T2-weighted and/or FLAIR images
Exclusion	Adjacent cerebrospinal fluid (partial volume effect), determined after reviewing adjacent PSIR slices and corresponding T2-weighted and FLAIR scans; especially likely in sulcal regions, at the temporal poles and near the vertex
	Artifacts, sometimes recognised by their symmetrical appearance (as also seen in DIR images)1
	Vessels, which form very thin linear hypo-intensities, especially those that do not follow the direction of the cortical ribbon (cortical lesions may have a curvilinear or linear appearance, but they are less thin and invariably follow the direction of the cortical ribbon (supplementary figure 1))
	Virchow-Robin spaces, which are prone to manifest in certain cortical regions27 28 (in particular, the insula and temporal poles), especially if linear and multiple, forming mesh-like or bundle-like appearances (these were seen in patients and controls (figure 1))