Fig. 16.

Hemispheric pilocytic astrocytomas in a 26-year-old man. a An axial T2-weighted image shows a temporally located, lobular mass that is very hyperintense (arrows) without vasogenic oedema. b On this T1-weighted image, the lesion is hypointense compared with grey matter (arrows). c The lesion exhibits low signal on diffusion-weighted imaging, with high signal intensity on an ADC map (d). e On this post-contrast, T1-weighted image, nodular (arrow) and peripheral rim enhancements (arrowheads) are visible. f, g MRS with TE 144 ms revealed an elevated choline peak without reduction of the NAA peak. h Perfusion MRI reveals low rCBV in the solid (enhanced) part of the tumour