Serum Prolactin Level to Tumor Size Ratio as a Potential Parameter for Preoperative Differentiation of Prolactinomas from Non-Functional Pituitary Adenomas

Abstract

INTRODUCTIONPreoperative diagnosis of prolactinomas is critical because dopamine agonists have been regarded as a primary treatment modality. However, serum prolactin level alone is suboptimal for differentiating between prolactinomas and hyperprolactinemia-causing non-functioning pituitary adenomas (NFPAs). The authors investigated more effective parameter for differentiating prolactinomas and NFPAs by using the adenoma size. METHODS We performed a retrospective review of patients who underwent trans-sphenoidal surgery for pituitary lesions in a single institute between January 2015 and May 2021. Using the receiver operating curve (ROC) analyses, we compared performances of serum prolactin levels (PRL), a ratio of serum PRL levels to maximal tumor diameter (MD) (PRL/MD; PDR1), and MD squared (PRL/(MD)2; PDR2) in preoperative diagnosis of prolactinomas. RESULTS 223 patients with NFPAs (n=175) and prolactinomas (n=48) were included in the analysis. The prolactinoma group showed higher serum prolactin (258.6 ㎍/L) and smaller MD (16.6 mm) than those in the NFPA group (44.4 ㎍/L and 23.9 mm; both p-values < 0.001). Among diagnostic parameters, PDR2 exhibited the optimal diagnostic performance with the cutoff value of 0.83 [㎍/L]/mm2 (area under the curve [AUC] = 0.945), compared to the PDR1 (8.93 [㎍/L]/mm with AUC 0.938) and PRL (99.4 ㎍/L with AUC 0.910). PDR2 still maintained superior performance in the validation study than PDR1 and PRL (Accuracy of 94.8%, 91.8%, and 75.8%, respectively).CONCLUSIONS PDR2 provided the best performance of three parameters in preoperative discrimination of prolactinomas from NFPAs with hyperprolactinemia, and could contribute to select patients who benefit from medical treatment primarily.