Predictive value of serum prolactin levels measured immediately after transsphenoidal surgery

Object. Prolactin-secreting pituitary adenomas may be managed by surgery, medication, radiotherapy, or observation. The authors reviewed a consecutive series of patients who were followed for at least 5 years after surgery to assess the prognostic significance of preoperative factors (tumor size and prolactin level) and an immediate postoperative factor (prolactin level obtained the morning after surgery) on long-term hormonal outcome, thereby clarifying the indications for surgical removal of tumor, the definition of successful treatment outcomes, and the nature of "recurrent" tumors. Methods. Between 1979 and 1991, 241 patients with prolactinomas underwent transsphenoidal resection. Nineteen patients were lost to follow-up review, whereas the remaining 222 patients underwent measurement of their prolactin levels on postoperative Day 1 (POD 1), at 6 and 12 weeks, and every 6 months thereafter for a minimum of 5 years. On POD 1, prolactin levels in 133 patients (Group 1) were lower than 10 ng/ml, in 43 patients (Group 2) between 10 and 20 ng/ml, and in 46 patients (Group 3) higher than 20 ng/ml. At 6 and 12 weeks, normal prolactin levels (≤ 20 ng/ml) were measured in 132 (99%) of the 133 patients in Group 1 but only in 32 (74%) of the 43 patients in Group 2. By 5 years postoperatively, normal levels of prolactin were still measured in 130 patients (98%) in Group 1 compared with only five patients (12%) in Group 2. No patient with a prolactin level lower than 3 ng/ml on POD 1 was found to have an elevated hormone level at 5 years. The likelihood of a long-term chemical cure was greater for patients with microadenomas (91% cure rate) than for those with macroadenomas (33%). Preoperative prolactin levels also correlated with hormonal outcome. Conclusions. Prolactin levels lower than 10 ng/ml on POD 1 predict a long-term chemical cure in patients with microadenomas (100% cure rate) and those with macroadenomas (93% cure rate). In contrast, a cure is not likely to be obtained in patients with normal levels ranging between 10 and 20 ng/ml on POD 1 if they harbor macroadenomas (0% cure rate). A recurrence reported several years after surgery probably represents the presence of persistent tumor that was not originally removed. If the initial operation was performed by an experienced surgeon, however, reoperation is not likely to yield a chemical cure.