NEW TECHNIQUE FOR QUANTITATION OF PITUITARY-ADENOMA SIZE - USE IN EVALUATING TREATMENT OF GONADOTROPH ADENOMAS WITH A GONADOTROPIN-RELEASING-HORMONE ANTAGONIST

Because administration for 1 week of the GnRH antagonist Nal-Glu GnRH had been shown to decrease FSH secretion from supranormal to normal in men with gonadotroph adenomas, we investigated the effect of prolonge d administration of Nal-Glu on the size of gonadotroph adenomas. To qu antitate the effect of Nal-Glu GnRH on gonadotroph adenoma size, we fi rst developed a technique for calculating adenoma volume. The techniqu e involved collecting magnetic resonance (MR) imaging data from each a denoma at 1-mm slice intervals in the coronal, axial, and sagittal vie ws and using the Softvu computer program to calculate adenoma volume f rom the MR data. The precision of this technique, as judged by the coe fficients of variation of the calculations of the same view of the sam e study three times, was 1.7%, 1.0%, and 1.0% for each of three studie s. When Nal-Glu GnRH (5 mg, sc, every 12 h) was self-administered for 3-12 months to five men with gonadotroph adenomas and supra-normal ser um FSH concentrations, the serum FSH concentrations decreased to norma l or below normal for the entire treatment period. Adenoma size, howev er, did not change during treatment in any of the five men. We conclud e that calculating pituitary adenoma volume from MR data using the Sof tvu computer program is a highly reproducible technique, but that Nal- Glu GnRH is not an effective treatment for reducing gonadotroph adenom a size. The failure of Nal-Glu to reduce adenoma size despite its succ ess in reducing FSH secretion suggests that FSH secretion from gonadot roph adenomas is dependent on endogenous GnRH, but growth of gonadotro ph adenomas is not.