Image evaluation for morphological characteristics

On MRC, an AG was defined as a localized outward protrusion of the dura mater with an intensity similar to CSF. On a PACS viewer (RapideyeCore; Canon Medical Systems, Tochigi, Japan), two diagnostic radiologists (R.N. and T.T.) quantified the numbers of BVs with subarachnoid cysts (Fig. 2a), with AGs protruding into the SSS (Fig. 2b), and with AGs protruding into the skull (Fig. 2c), near the SSS confluence, on MRC images in slices above the superior margin of the lateral ventricles. The number of BVs with stenosis (Fig. 2d), including peripheral cortical veins, was also quantified, and the perivascular space dilation was assessed. Multiplanar reconstruction was employed to confirm the positional relationship between the brain parenchyma, blood vessels, and skull. Any discrepancies between the authors were resolved through discussion until a consensus was reached.

Morphological findings of magnetic resonance cisternography. a Cystic structures in the subarachnoid space in contact with the vein within 1 cm of the confluence. b An arachnoid granulation protruding into the superior sagittal sinus within 1 cm of the confluence. c An arachnoid granulation protruding into the skull within 1 cm of the confluence. d A vein (enclosed by the dotted lines) with stenosis (arrow)

The inclusion criteria for each structure were as follows:

BVs ≥ 3 mm in diameter in confluence with the SSS;

BVs with a cystic structure in the subarachnoid space in contact with the BV or peripheral cortical vein within 1 cm of the confluence (BV-cyst);

BVs with AGs protruding into the SSS within 1 cm of the confluence (BV-AG-SSS);

BVs with AGs protruding into the skull within 1 cm of the confluence (BV-AG-skull);

BVs including any of these three factors (BV-incl);

BVs with stenosis, including peripheral cortical veins.

The perivascular space dilation in the cerebral white matter was classified into three levels: (1) no perivascular space dilation, (2) perivascular space dilation < 2 mm, and (3) perivascular space dilation ≥ 2 mm.