Long-term octreotide therapy in growth hormone-secreting pituitary adenomas: evaluation with serial MR.

PURPOSE To compare the changes in tumor volume with length of octreotide treatment in patients with acromegaly, to analyze signal alterations of the pituitary mass during treatment, and to determine an optimal MR imaging protocol. METHODS Eighteen patients with growth hormone (GH)-secreting pituitary adenomas were studied with MR imaging before and during octreotide treatment. The length of follow-up was 9 to 70 months. Tumor volume, extension, and signal characteristics were evaluated. RESULTS The total pituitary volume decreased in 16 patients by a mean of 37%. In 11 patients the tumor could be demarcated from the normal gland, and mean tumor reduction was 51%. Most of the tumor reduction took place within the first year, but an additional effect was noted in four patients during the following 3 years. Tumor reexpansion, hemorrhage, or necrosis did not occur. Serum GH levels were effectively lowered within the first year, with slight additional reductions thereafter. CONCLUSION In long-term octreotide treatment of GH-secreting pituitary adenomas, tumor shrinkage occurs primarily during the first year, but effects are noted up to 4 years. The treatment may be considered an alternative to surgery in the select group of patients in whom the peripheral effects of chronic GH elevation, as determined by serum insulinlike growth factor I (IGF-I), are controlled. We suggest MR imaging with T1-weighted coronal and sagittal images at baseline and after 3 and 12 months, with additional MR imaging if GH or IGF-I levels rise during treatment. At baseline, both noncontrast and contrast-enhanced images should be obtained. Unenhanced images may be sufficient during follow-up unless tumor reexpansion occurs or surgery is anticipated.