Group II tumors - pilocytic astrocytoma with focal gangliocytic differentiation. The classic pathologic features of a posterior fossa pilocytic astrocytoma (a) combines focally with collections of dysmorphic ganglion cells (b). The edge of a gangliocytic nodule is highlighted by immunoreactivity for synaptophysin (c). An admixed GFAP-positive pilocytic and fibrillary astrocytic component surrounds a few dysmorphic ganglion cells (d). All images, x200.