This CT scan of the brain is from a 35 y/o male patient who presented with seizures. It demonstrates a relatively well circumscribed region of low attenuation centred immediately deep to the anterior part of the right insular cortex. There is no evidence of hemorrhage and no contrast enhancement. Despite its large size the tumor exerts little mass effect. The rest of the brain is unremarkable. The diagnosis was low-grade astrocytoma. Many low grade astrocytomas are strikingly hypo-attenuating and can appear very large with relatively little mass effect on account of their infiltrative nature and slow growth. Case produced with permission, courtesy of Dr. Frank Gaillard. Radiopaedia. Complete case is here.