In February 2013, a 23-year-old man was admitted to the hospital with headache. Cranial magnetic resonance imaging (MRI) showed a homogeneous, well-demarcated, hyperintense mass on T2-weighted imaging and peritumoral hyperintensity due to edema. The mass showed no enhancement on T1-weighted imaging with contrast (Figure 1A). Surgical resection was recommended. However, the patient rejected surgery. In 2016, he presented again with severe headache. MRI showed hemorrhage and herniation (Figure 1B). The patient underwent emergency surgery, but the mass could not be completely excised.

Morphologically, this hypercellular neoplasm exhibited the following features. There were perivascular pseudorosettes with short, thickened cytoplasmic processes extending from cell bodies to vessel adventitia. In addition, there was vascular hyalinization with little fibrillar background, tumor necrosis with pseudopalisading, and high mitotic activity (Figure 1I). Immunohistochemically, glial fibrillary acidic protein (GFAP) was diffusely present in the epithelioid cells, mostly around the perivascular areas. The tumor cells showed diffuse positivity for S-100 and vimentin and focal positivity for epithelial membrane antigen (EMA). The Ki-67 proliferation index was calculated as 60% (Figure 1J). In light of these findings, the patient was diagnosed with a malignant astroblastoma.

On postoperative MRI, the residual tumor was evident behind the resection cavity (Figure 1C). Radiotherapy (RT) and concomitant temozolomide (TMZ) were started immediately after surgery. Six months after RT, a contrast-enhancing lesion was noticed, which was considered to be radiation necrosis (Figure 1D). A new, ringenhancing focus was apparent...