Preoperative serum prolactin as a predictor of endocrine outcomes in nonfunctioning pituitary adenoma surgery: revisiting the "stalk effect"

OBJECTIVE: Nonfunctioning pituitary adenomas (NFPAs) often present with associated mild hyperprolactinemia, described in literature as "stalk effect." The presence of preoperative hyperprolactinemia caused by tumor compression of the pituitary stalk and endocrinological outcomes has been noted; however, a detailed investigation on the impact on perioperative endocrinological outcome is lacking. The authors aimed to determine whether elevated preoperative serum prolactin concentrations are associated with increased risk of perioperative pituitary dysfunction in patients with NFPAs undergoing endonasal transsphenoidal surgery (ETS). METHODS: The authors conducted a single-center retrospective cohort study of patients who underwent ETS for NFPAs between January 2013 and April 2023. Patients were divided into two groups based on preoperative prolactin concentrations: normal or hyperprolactinemic (prolactin values above upper limit of reference range, adjusted for sex). Outcomes included perioperative endocrinological function and surgical outcomes. Multivariable analysis was conducted to identify factors associated with perioperative endocrinological function outcomes. RESULTS: Of 244 patients (140 [57%] males; median age 59 years) with a median follow-up of 65 months, 131 (54%) had hyperprolactinemia. Compared with patients with normal preoperative prolactin levels (n = 113), the hyperprolactinemia group had similar tumor size (median diameter 2.5 cm vs 2.3 cm, p = 0.102) but higher rates of cavernous sinus invasion (99% vs 91%, p = 0.035), pituitary stalk deviation (95% vs 74%, p = 0.001), stalk bending (14% vs 1%, p = 0.001), preoperative secondary hypothyroidism (39% vs 22%, p = 0.005), and adrenal insufficiency (AI; 34% vs 22%, p = 0.048). Postoperatively, the hyperprolactinemia group showed higher rates of new secondary hypothyroidism (16% vs 7%, p = 0.048) and new permanent AI (16% vs 6%, p = 0.046). Multivariable analysis revealed preoperative high prolactin as an independent predictor of preoperative secondary hypothyroidism (OR 1.83, 95% CI 1.17-3.44; p = 0.046) and its postoperative deterioration (OR 2.65, 95% CI 1.02-7.69; p = 0.042). Maximum tumor diameter was also a significant predictor of various endocrinological dysfunctions both pre- and postoperatively. CONCLUSIONS: Preoperative hyperprolactinemia in patients with NFPA is associated with higher risks of specific perioperative endocrinological dysfunction and pronounced pituitary stalk deviation. These findings highlight the utility of preoperative prolactin levels as a biomarker for predicting postoperative endocrinological outcomes, potentially enhancing risk assessment and guiding personalized perioperative management.