LGGs are associated with a mixture of inflammatory and immune cells and, particularly for pilocytic astrocytoma, a macrophage population is dominant peri-vascularly.19 Gutmann et al.20–22 also reported that in neurofibromatosis 1 (NF1)-associated LGG, microglia were present in increased number and facilitated glial proliferation in the early phase of optic pathway glioma development. The gene discussed is NF1; the disease is optic pathway glioma.