The small abnormal parathyroid gland is increasingly common and heralds operative complexity.

Background: Over decades, improvements in presymptomatic screening and awareness of surgical benefits have changed the presentation and management of primary hyperparathyroidism (PHPT). Unrecognized multiglandular disease (MGD) remains a major cause of operative failure. We hypothesized that during parathyroid surgery the initial finding of a mildly enlarged gland is now frequent and predicts both MGD and failure.

Methods: A prospective database was queried to examine the outcomes of initial exploration for sporadic PHPT using intraoperative PTH monitoring (IOPTH) over 15 years. All patients had follow-up ≥6 months (mean = 1.8 years). Cure was defined by normocalcemia at 6 months and microadenoma by resected weight of <200 mg.

Results: Of the 1,150 patients, 98.9 % were cured and 15 % had MGD. The highest preoperative calcium level decreased over time (p < 0.001) and varied directly with adenoma weight (p < 0.001). Over time, single adenoma weight dropped by half (p = 0.002) and microadenoma was increasingly common (p < 0.01). MGD risk varied inversely with weight of first resected abnormal gland. Microadenoma required bilateral exploration more often than macroadenoma (48 vs. 18 %, p < 0.01). When at exploration the first resected gland was <200 mg, the rates of MGD (40 vs. 11 %, p = 0.001), inadequate initial IOPTH drop (67 vs. 79 %, p = 0.002), operative failure (6.6 vs. 0.7 %, p < 0.001), and long-term recurrence (1.6 vs. 0.3 %, p = 0.007) were higher.

Conclusions: Single parathyroid adenomas are smaller than in the past and require more complex pre- and intraoperative management. During exploration for sporadic PHPT, a first abnormal gland <200 mg should heighten suspicion of MGD and presages a tenfold higher failure rate.