Right frontal lobe extra-axial lesion measures 50 x 16 x 44 mm (AP x RL x CC) and demonstrates CSF signal on all sequences with no evidence of diffusion restriction. The right frontal bone is remodelled with thinning of the cortex. Mass effect present with effacement of adjacent sulci but no evidence of midline shift or hydrocephalus.
Conclusion: Right frontal extra-axial lesion demonstrates features characteristic of an arachnoid cyst.