Tumor shrinkage after transsphenoidal surgery for nonfunctioning pituitary adenoma

Object. Volume reduction of nonfunctioning pituitary adenomas has been described, for example, after radiotherapy and pituitary tumor apoplexy. Even when considerable remnants remain after surgery, spontaneous shrinkage and relief of mass lesion symptoms can sometimes occur. The aim of this study was to assess shrinkage of tumor residues after transsphenoidal surgery and to identify predictors of tumor shrinkage. Methods. A total of 140 patients with postoperative remnants of nonfunctioning pituitary adenomas treated at the Department of Neurosurgery, University Hospital Erlangen, Erlangen, Germany, were included in this study. All patients underwent transsphenoidal procedures with guidance by 1.5-T intraoperative MRI. The intraoperative images of remnants were compared with images taken at 3 months and at 1 year after surgery. The possible predictors analyzed were age; sex; preoperative and intraoperative tumor dimensions; tumor growth pattern; endocrinological, ophthalmological, and histological characteristics; and history of previous pituitary surgery. For statistical analyses, the Fisher's exact test, Mann-Whitney U-test, and multivariate regression table analysis were used. Results. Follow-up imaging 3 months after surgery showed tumor remnant shrinkage of 0.5 +/- 0.6 cm(3) for 70 (50%) patients. This reduction was 89% +/- 20% of the residual volume depicted by intraoperative MRI. In 45 (64%) patients, the remnants disappeared completely. Age, sex, and preoperative tumor volume did not significantly differ between the shrinkage and no-shrinkage groups. Positive predictors for postoperative shrinkage were cystic tumor growth (p = 0.02), additional resection of tumor remnants guided by intraoperative MRI (p = 0.04), smaller tumor volume (p = 0.04), and smaller craniocaudal tumor diameter of remnants (p = 0.0014). Negative predictors were growth into the cavernous sinus (p = 0.009), history of previous pituitary surgery (p = 0.0006) and tumor recurrence (p = 0.04), and preoperative panhypopituitarism (p = 0.04). Multivariate regression analysis indicated a positive correlation between tumor shrinkage and smaller tumor remnants (p <0.0001) and no history of previous pituitary surgery (p = 0.003). No spontaneous change in tumor remnant volume was detected between 3 months and 1 year postoperatively. During a mean follow-up time of 2.7 years, 1 (2%) patient with postoperative tumor shrinkage had to undergo another operation because of tumor progression. Conclusions. Spontaneous volume reduction of nonfunctioning pituitary adenoma remnants can occur within 3 months after surgery. Predictors of shrinkage are smaller tumor remnant volume and no history of previous pituitary surgery.