Identification of high-grade, unusual tumor type in a case with inconclusive histopathology. MRI of a 13-year-old girl revealed a supratentorial tumor of uncertain diagnosis. Although a definitive diagnosis was not made following biopsy, the lesion demonstrated histological features consistent with a low-grade tumor. MRS demonstrated high-grade features of high choline, low NAA, and lipids. This unusual MRS profile alerted clinicians to the possibility of rare tumor type and possible sampling error on biopsy, which was later confirmed. Close monitoring allowed early detection of rapid growth and metastatic spread. This tumor followed an aggressive course and was diagnosed as a probable astroblastoma following central review.