Table 4.

Overview publications regarding volume and outcome in thyroid surgery

Reference	Date of publication	Main outcomes
Sosa [4] et al.	1998	Statewide cross-sectional analysis including 5860 patients. Individual surgeons categorized according to the total 6-year volume (1–9 vs. 10–29 vs. 30–100 vs. > 100 thyroidectomies). Similarly, total hospital volume was categorized in 4 categories (1–99, 100–199, 200–300, > 300). Highest-volume surgeons had the shortest length of stay and the lowest complication rate. Hospital volume had no consistent association with outcomes.
Thomusch [5] et al.	2000	Prospective multicentric study including 7266 patients who underwent thyroid resection for benign diseases along 1 year (01/01/1998–31/12/1998). Hospitals were categorized as low-, intermediate-, and high-volume (< 50, 50–150, and > 150 procedures, respectively). No significant difference was found among hospital groups with regard to post-thyroidectomy morbidity and mortality rate.
Gourin [6] et al.	2010	Statewide cross-sectional analysis including 21,270 patients. Individual surgeons categorized according to the annual volume in low-, intermediate-, and high-volume (≤ 3, 4–24, > 24 thyroidectomies/year). Similarly, hospital volume was categorized in 3 categories (≤ 22, 23–100, > 100). Multiple logistic regression analysis of variables associated with thyroid surgery-specific complications revealed an association with surgeon but not with hospital volume. High-volume surgeons had a lower incidence of laryngeal nerve injury (OR 0.46, p < 0.01) and hypocalcaemia (OR 0.49, p < 0.01).
Loyo [7] et al.	2013	Nationwide cross-sectional analysis (Nationwide Inpatient Sample) including 871,644 patients. Individual surgeons categorized according to the annual volume in very low-, low-, intermediate-, and high-volume (≤ 3, 4–9, 9–23, and > 24 thyroidectomies/year). Similarly, hospital volume was categorized in 4 categories (≤ 25, 26–42, 43–76, and > 76). Multiple logistic regression analysis of variables associated with thyroid surgery-specific complications demonstrated that recurrent laryngeal nerve palsy and hypocalcemia were significantly less likely for high-volume surgeons (OR 0.71, CI 0.53–0.95, p = 0.24 and OR 0.7, CI 0.57–0.88, p = 0.002, respectively). After adjusting for surgeons’ volume, hospital volume was not associated with complication rate.
González-Sánchez [8] et al.	2013	Single-institution prospective cohort study including 225 patients and 8 surgeons (2 endocrine surgery specialized with a case load > 40 procedures/year and 6 endocrine non-specialized general surgeons with a case load < 5 procedures/year). Permanent recurrent laryngeal nerve palsy and hypocalcemia were significantly reduced for specialized high-volume surgeons (1/325 vs. 2/46 p = 0.04 and 3/130 vs. 3/16 p = 0.028, respectively).
Kandil [9] et al.	2013	Nationwide cross-sectional analysis (Health Care Utilization Project National Inpatient Sample datasets - HCUP-NIS) including 46,261 patients. Individual surgeons were categorized according to the volume of procedures performed over the 10-year study period (low-, intermediate-, and high-volume < 10, 10–99, ≥ 100 procedures, respectively). High-volume hospitals were considered those above the 75th percentile with regard to year case load. High-volume surgeons had a significantly lower rate of complications. Hospital volume had an inconsistent and marginal protective effect on postoperative outcomes.
Al-Qurayshi [10] et al.	2016	Nationwide cross-sectional analysis using the National Inpatient Sample datasets, including 77,863 patients. Surgeons were categorized based on the annual case load (low-, intermediate-, and high-volume 1–3, 4–29, ≥ 30 thyroidectomies/year, respectively). Procedures performed by low-volume surgeons were associated with a higher risk of postoperative complications compared with high-volume surgeons (15.8% vs. 7.7%, OR 1.55, CI 1.19–2.03, p = 0.01). A surgeon’s expertise (measured by surgical volume of procedures per year) is associated with favorable clinical and financial outcomes.
Adam [11] et al.	2016	Nationwide cross-sectional analysis (Health Care Utilization Project National Inpatient Sample datasets - HCUP-NIS) including 16,954 patients. Surgeons categorized in low-volume (≤ 25 procedures/year) and high-volume (> 25 procedures/year). Patients undergoing thyroidectomy by low-volume surgeon were more likely to have any complication (OR 1.52, CI 1.16–1.97, p = 0.002) and a longer hospital stay (+ 12%, p = 0.006).
Liang [12] et al.	2016	Nationwide cross-sectional analysis of data of 125,037 patients obtained by the Taiwan Bureau of National Health Insurance and systematic review and meta-analysis of the literature. Surgeons were categorized in low- and high-volume (1–70 and > 70 thyroidectomies/year, respectively) as well as hospitals (1–200 and > 200 thyroidectomies/year, respectively). Patients who received thyroidectomies performed by high-volume hospitals and surgeons had shorter length of stay and lower costs compared with those treated by low-volume hospitals and surgeons.
Nouraei [13] et al.	2017	Nationwide cross-sectional analysis using record of 72,594 patients obtained from the Hospital Episode Statistics (HES) dataset. High-volume surgeons achieve lower complication rates, including lower vocal palsy rates, and length of stay.
Duclos [14] et al.	2012	Prospective cross-sectional multicentric study from five academic French hospitals, including 28 surgeons and 3574 thyroid procedures, 20 years or more of practice was associated with increased probability of both, recurrent laryngeal nerve palsy (odds ratio 3.06 (1.07 to 8.80), p = 0.04) and permanent hypoparathyroidism (7.56 (1.79 to 31.99), p = 0.01). Surgeons’ performance had a concave association with their length of experience (p = 0.036) and age (p = 0.035); surgeons aged 35–50 years had better outcomes than their younger and older colleagues.
Mitchell [15] et al.	2008	Single-institution retrospective analysis on 335 thyroid and parathyroid reoperations. Many thyroid and parathyroid reoperations are avoidable. Most originate from low-volume centers. In addition to decreasing complication rates, thyroid and parathyroid surgery performed high-volume centers would decrease the need for patients to undergo reoperations.