MKI67 and pleomorphic xanthoastrocytoma: However, we considered that the diagnosis of GBM is incorrect in our case for the following reasons: (i) the features identified on MRI, in particular the multiple cystic lesions with little intervening parenchyma and minimal invasion to the basal ganglia, are not typical of GBM and (ii) histological examination of autopsy specimens demonstrated typical PXA with well-defined boundaries between the tumor and the surrounding normal brain tissue and the highest Ki-67 index was 1 %.