To assess the ability of MRI to predict consistency of pituitary macroadenomas.

We prospectively studied the ability of magnetic resonance imaging (MRI) to predict the consistency of pituitary adenomas. The hypothesis was that firm, fibrous tumours would appear homogeneously hypointense on T2-weighted images. Eighty patients who underwent surgery for pituitary macroadenomas were studied. MR images were evaluated preoperatively by the radiologist. The tumour consistency was reported by the surgeon as soft or firm. There were 68 soft tumours and 12 firm tumours. Of the firm tumours, four (33%) were homogeneously isointense, one (8%) homogeneously hyperintense and seven (59%) were heterogeneous in appearance in T2-weighted images. We conclude that the consistency of pituitary macroadenomas cannot be accurately predicted based on MRI signal intensities.