NIMG-78. FIRST TIME CORRELATION OF FET PET, MRI AND POST-MORTEM WHOLE-BRAIN HISTOPATHOLOGY IN A PROGRESSIVE GLIOBLASTOMA

BACKGROUND Amino acid PET using O-(2-[18F]fluoroethyl)-L-tyrosine (FET) provides important additional information on the extent of viable tumor tissue of glioblastoma compared with MRI. Especially after radiochemotherapy, progression of contrast enhancement in MRI can be equivocal and may represent either true tumor progression or treatment-related changes. We present the first case comparing post-mortem whole-brain histopathology in progressive glioblastoma with dynamic in vivo FET PET and MRI.METHODSA 61-year-old glioblastoma patient underwent initially partial resection and died eleven weeks after completion of chemoradiation with concurrent temozolomide. Three days before the patient died, a follow-up FET PET and MRI scan indicated local tumor progression within the irradiation field. An autopsy was performed at 48 h hours after death and the tumor bearing brain was preserved. After fixation in formalin and paraffin embedding, the brain tissue was cut into 3500 coronal sections (20 micrometers). Representative sections were stained using GFAP and cresyl violet. An experienced neuropathologist identified areas of neoplastic tissue, astrogliosis and necrosis. In vivo FET PET, MRI and histopathology were co-registered and compared by three experienced physicians.RESULTSIncreased FET uptake (tumor-to-brain ratio = 2.3) in the area of equivocal contrast enhancement on MRI correlated very well with vital tumor cells and showed tracer kinetics typical for malignant gliomas (early peak followed by constant descent). An area of reactive astrogliosis showed only moderate FET uptake (tumor-to-brain ratio = 1.5) and tracer kinetics usually observed in benign lesions (constantly increasing). Necrotic areas showed neither enhanced FET uptake nor contrast enhancement in MRI.CONCLUSIONSThis case report documents for the first time the correct imaging of a progressive glioblastoma by FET PET, thereby confirming findings from previous studies. FET PET significantly contributes to the correct identification of neoplastic tissue and, thus, to a better differentiation of tumor progression and treatment-related changes