Figure 5. 2-year-old boy with neurofibromatosis type 1. (a) Axial T₁ weighted image. Normal appearance to the intracranial optic nerves and chiasma. Enlargement of the right intraorbital optic nerve. (b) Axial CT after contrast infusion, 18 months later, demonstrates a large solid tumour of the chiasma; the left cystic component could either be tumour or an entrapment arachnoidal cyst.