20-Year MRI and CT Scan Follow-up of Pituitary Adenomas: Tumor Regression and the Implications for Radiotherapy

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Purpose/Objective: Pituitary adenomas are benign endocrine tumors that represent 10% of all intracranial neoplasms. These tumors have a variable growth rate and a variable response to hormonal manipulation, radiotherapy, or surgery. Surprisingly, very little information is available documenting regression of pituitary adenomas after surgery with serial imaging studies. To clearly define the postoperative regression rate of pituitary adenomas, we analyzed a group of 35 patients who had undergone surgery and pre- and postoperative imaging over a 20-year period. Materials and Methods: Between 1977 and 1997, 125 patients with pituitary macroadenomas were managed at our institution. Fourteen patients were observed without surgery or radiation. Follow-up MR and CT data were available for 73 patients; 38 patients received postoperative radiation; 38 patients were without adequate follow-up. The remaining 35 patients who underwent trans-sphenoidal hypophysectomy (TSH) alone comprise the cohort for analysis. To follow the changes in tumor size with time, individual measurements were obtained on all patients from CT and MR using standard response criteria, namely, the product of the two maximal orthogonal dimensions. Results: The mean follow-up period for all patients was 24.4 months. The age at diagnosis for all patients ranged from 20 to 78 years (mean 46.4 years). The mean initial and postoperative tumor maximal cross-sectional areas were 5.4 cm2 and 3.6 cm2, respectively. The mean time period to achieve a mean maximal decrease in postoperative tumor size of 2.9 cm2 was 3 months. Subsequently, at 6, 12, and 24 months, there was a 4%, 17%, and 21% respective increase in tumor size. Conclusion: Serial MRIs and CTs document that a significant decrease in tumor size is possible after TSH for pituitary macroadenomas. There appears, however, to be no benefit in observing patients beyond 3 months postoperatively as this is the nadir of tumor regression. Furthermore, tumor size appears to increase on 2-year follow-up. Since maximal tumor shrinkage is desired prior to XRT to reduce the RT dose received by the optic apparatus and normal brain tissues, these data may aid in determining when to administer postoperative radiation. Additional follow-up data on the value of observation and/or postoperative radiation may add to the current knowledge that is available on the natural history of treated or untreated pituitary macroadenomas.