Introduction: Accurate diagnosis of prolactinomas and non-functioning adenomas (NFA) can be challenging given that radiographic and biochemical testing is often equivocal. This study aims to better correlate prolactinoma size with serum prolactin levels to help guide surgical and medical decision making.
Methods: Retrospective review of patients undergoing transphenoidal surgery (TSS) from 2008 – 2018 was performed. Patients undergoing first-time surgical intervention for histologically confirmed prolactinoma and NFA were included. Pre-treatment MRI scans were reviewed and maximum diameter in orthogonal planes was measured. Radiographic cystic appearance was also noted. Tumors were grouped based on size as follows: <10mm, 11-20mm, and >20mm.
Results: Seventy-seven prolactinoma patients (28 cystic lesions and 49 non-cystic) and 217 NFA patients (34 cystic lesions and 183 non-cystic) were included in this study. Statistically significant differences (p<0.01) were detected between serum prolactin levels in patients with prolactinomas (mean 731.6ng/dl, range: 7.4ng/dl – 13,579.9ng/dl) compared to patients with NFAs (25.52ng/dl, range 0.25ng/dl – 148ng/dl). Comparison between cystic prolactinomas and NFAs, as well as non-cystic lesions, revealed statistical significance in tumors between 11-20mm (cystic mean: 133.37ng/dl vs. 23.38ng/dl, non-cystic means: 370.20ng/dl vs. 26.60ng/dl) and >20mm (cystic means: 2,394.42ng/dl vs. 28.42ng/dl, non-cystic means: 1,526.40ng/dl vs. 24.76ng/dl). In comparing serum prolactin levels in cystic to non-cystic prolactinomas, there was a statistically significant decrease in serum prolactin comparing across all sizes (means: 613.77ng/dl vs. 937.92ng/dl); however, no differences were found when categorized by size. Analysis was limited by the number of NFA microadenomas in this cohort.
Conclusions: Prolactinoma size and absence of cyst significantly influence serum prolactin levels. Additional characterization of these tumors, in larger cohorts will improve knowledge of their biochemical effects in the setting of equivocal diagnostic work-up. Furthermore, this study strengthens the classical teaching that serum prolactin levels below 150ng/dl may represent “stalk effect” as opposed to a functional adenoma.
Patient Care: Improve diagnostic accuracy for differentiating prolactinomas between non-functioning adenomas to guide surgical decision making
Learning Objectives: 1) Improve surgical decisions making with microadenomas
2) Correlate prolactinoma size with serum prolactin levels