Pilocytic Astrocytoma (PA) characteristically exhibits biphasic morphology featuring densely fibrillar, compact regions alternating with loosely-cohesive microcystic or myxoid areas; the latter is pictured here.  Diagnosis can be difficult, especially on small biopsies, but molecular testing can help.  BRAF-KIAA1549 fusion occurs in about 70% of PAs, whereas BRAF V600E mutation occurs in about 5-10% of PAs.