Four patients with longstanding tectal tumors are included in this study. The tectal lesion in a neurofibromatosis type 1 (NF1) patient was due to a hamartoma, while others represented gliomas. On spectroscopy, decreased NAA peaks with resultant decreases in the NAA/Cho, and NAA/Cr ratios were observed in two patients. In three patients, on diffusion MRI the tectal tumors were hyperintense on b=1000 s/mm(2) (heavily diffusion-weighted) images. On apparent diffusion coefficient (ADC) maps, they had high signal, and high ADC values (mean=1.20 x 10(-3)mm(2)/s), compared to normal cerebral parenchyma. Diffusion MRI findings suggested that tectal tumors had a relatively high nuclear to cytoplasmic ratio (high-signal on b=1000 s/mm(2) images) in association with a relatively loose intercellular matrix (high ADC values).