Figure 11a. Hypothalamic-chiasmatic glioma in a 4-year-old boy with NF-1. Sagittal T1-weighted (a) and axial T2-weighted (b) MR images show an irregular hypothalamic mass (arrow in a) that involves the optic chiasm and extends to the right optic nerve (arrowheads in b). The mass has heterogeneous low signal intensity on the T1-weighted image and high signal intensity on the T2-weighted image, findings that are typical for this lesion. The diagnosis (hypothalamic-chiasmatic glioma) was confirmed at surgery.