Endoscopic Transsphenoidal Prolactinoma Surgery: Immediate Postoperative Serum Prolactin Threshold Levels Are Predictive for Hormonal Remission

Background Prolactinomas are the most common functional pituitary adenoma. Although prolactinomas are often treated medically, a fair amount of these tumors require surgical resection. Successful long-term prolactin hormone remission following transsphenoidal prolactinoma surgery is difficult to determine and often requires life-long follow-up for prolactin levels. This study statistically evaluates a cohort of patients who underwent a prolactinoma resection via an endoscopic transsphenoidal approach to determine immediate postoperative serum prolactin threshold levels that are prognostically significant at predicting a successful long-term hormonal remission.

Methods This is a single-center, retrospective study of 25 patients with a prolactinoma who underwent endoscopic transsphenoidal surgery. Surgical outcomes are presented and postoperative day 1 (POD1) and inpatient nadir serum prolactin (the lowest serum prolactin level obtained during the inpatient stay following surgery) levels are assessed. Prolactin levels were statistically evaluated using logistic regression, area under the curve(AUC) values, and receiver-operating characteristics (ROC) curves to assess predictive threshold values for remission. Prolactinoma tumor volume was volumetrically calculated using the OsiriX software.

Results: Twenty-two patients (88%) were found to be in remission, or have a hormonal cure, over a 10-year follow-up. Fasting POD1 prolactin serum level, the inpatient nadir prolactin level, and preoperative tumor volume were found to be significant predictors of hormonal cure ([Table 1]). Optimal threshold levels for predicting long-term hormonal cure was fasting POD1 serum prolactin less than 8.3 ng/mL(sensitivity 88%, specificity 83%; Fig. 1), and inpatient nadir serum prolactin less than 3.8 ng/mL (sensitivity 100%, specificity 71%, Fig. 2).

Table 1 Predictors for hormonal cure

Variables	Odds ratio	p-Value
POD1 prolactin serum level	0.807	0.030
Inpatient nadir prolactin serum level	0.753	0.049
Preoperative tumor volume	0.204	0.023
Maximal diameter	0.178	0.027
Macroadenoma	0.095	0.012
Knosp 0	8.50	0.020
Age	0.955	0.175
Gender	0.211	0.063
Preoperative prolactin level	0.997	0.163
Knosp 4	0.727	0.805

Conclusion We present the first statistically based evaluation of postoperative serum prolactin levels to determine serum thresholds that successfully predict long-term hormonal remission following prolactinoma surgery. We find that preoperative tumor volume, POD1 serum prolactin level, and inpatient nadir serum prolactin level were found to be significant predictors for hormonal cure. We also purport that a POD1 serum prolactin level of <8.3 ng/mL or an inpatient nadir serum prolactin of <3.8 ng/mL are good predictors of hormonal remission with good sensitivity and specificity, and may be useful for neurosurgeons to use for prognostic purposes when counseling postoperative prolactinoma patients.

Fig. 1 ROC curve for postoperative day 1 serum prolactin.

Fig. 2 ROC curve for postoperative inpatient nadir serum prolactin.

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