MR findings of subarachnoid dissemination of a pituitary adenoma.

Although pituitary adenoma is a benign tumour, subarachnoid dissemination occurs rarely. We describe a case of pituitary adenoma with subarachnoid dissemination. After the third operation for pituitary adenoma, an extraaxial mass was demonstrated on MR images. On T1 and T2 weighted images, the signal intensities of the extraaxial mass were similar to those of the primary pituitary adenoma. On dynamic contrast T1 weighted images, the time-intensity curve of the extraaxial mass, which showed early and persistent signal intensity, was also similar to that of the primary pituitary adenoma. These MR findings are considered to reflect the similar vascularity and stroma of the extraaxial mass and the primary pituitary adenoma.