The prevalence of obesity and the number of obese patients scheduled for surgical operation is alarming increasing. It has been previously reported that obesity may negatively influence the rate of surgical complications [5]. Several studies documented a higher complications rate in obese patients compared to non-obese [6,7,8]; nonetheless, an unanimous opinion is still lacking [9, 10].

Endocrine surgeons are increasingly faced with patients with elevated BMI. Obese patients usually presented a short and large neck with limited possibility of hyperextension, leading to reduced operatory space and consequently hard surgery [11, 12]. Some surgeons considered these features as related to a higher complications rate and longer operative time. We aim to assess the impact of obesity on thyroidectomy outcomes, in particular on postoperative complications.

Our study demonstrated that post-surgical complications of obese patients are comparable to those of non-obese: no statistically significant differences in terms of transient and definitive hypocalcemia, transient and definitive RLN palsy, hematoma, bleeding that requires reoperation and wound complications (infection and cheloid formation) were documented. These findings were confirmed even comparing non-obese patients with those with BMI ≥ 35 kg/m2 (obesity grade II and III).

Buerba et al. [13] in 2011 published a multi-institutional study in order to assess the 30-day clinical and economic outcomes of patients scheduled for endocrine neck surgery on the basis of BMI. The authors enrolled 18,825 patients from the American College of Surgeons National Surgery Quality Improvement Program database and documented that obese patients were associated to a higher rate of overall and wound complications. Moreover, obese patients were associated to longer operative time. However, the authors did not assess the rate of endocrine-specific complications, such as RLN palsy and hypocalcemia, limiting the power of the study [13].

Tresallet et al. [14] performed a retrospective study focusing on 1216 papillary thyroid carcinoma patients who underwent thyroid surgery. The authors found an association between recurrent/residual thyroid cancer and BMI, suggesting that obese patients may correlate with more difficult operation. Furthermore, although no significant differences were documented in terms of overall rate of complications, the rate of RLN palsy was higher in the obese group.

Recently, Jin et al. [11] assessed the impact of BMI on complication rate in patients with papillary thyroid cancer and lateral neck metastasis. The authors found that obesity was associated to a higher risk of postoperative bleeding, accessory nerve injury, infection and longer operative time. Nonetheless, the BMI cut-off considered to define obesity was 28.0 kg/m2, rather than 30.0 kg/m2. Similarly, a previous study on 2678 patients found obesity as a factor which significantly increase the risk of neck hematoma [15].

Notwithstanding, the issue of obesity is debated and several studies reported no significant influence on postoperative outcomes. Farag et al. [16] in a retrospective 3-year study reported no statistically significant differences in terms of postoperative complications, operative time and hospital length of stay between obese and non-obese patients.

Similarly, Canu et al. [17] recently published a large retrospective study on 813 patients (135 of whom were obese) and documented no statistically significant differences regarding postoperative complications and length of hospital stay; nonetheless, the authors reported a significant longer operative time in patients with BMI ≥ 30.0 kg/m2. Other studies [12, 18] reported superimposable findings regarding overweight and non-overweight patients (BMI < or ≥ 25.0 kg/m2).

Our study mirrors these reports, claiming thyroidectomy in obese patients as a safe and effective procedure regardless the obesity grade. Nonetheless, the lack of statistically significant differences in terms of surgical outcomes (postsurgical complications, operative time, use of energy devices) for obese patients may be due to the large number of patients with high BMI operated every year at our Institution, which made surgeons skilled in this cohort of patients.

On the other hand, as previously reported by Harari et al. [19], we documented a longer length of hospital stay in obese patients. This finding may be attributed to the fact that obese patients are often affected by several comorbidities (such as cardiovascular diseases, respiratory diseases, diabetes mellitus) which require post-operative monitoring in the intensive care unit, prolonging the length of the hospital stay and consequently influencing the hospital resources. Thyroidectomy is an operation which usually requires a short postoperative course which may significantly increase in case of extension of 1 or 2 days.

The obese body habitus was initially seen with great concern when a minimally-invasive or remote-access thyroidectomy was scheduled [20, 21]. Nonetheless, several studies reported no statistically significant differences in terms of surgical complications in case of minimally-invasive video-assisted thyroidectomy (MIVAT), robotic bilateral axillo-breast approach thyroidectomy and robotic transoral thyroidectomy, claiming these approaches as safe and effective in patients with elevated BMI [22,23,24]. However, it is noteworthy to underline that some case series took into account a limited number of obese patients.

In a recent study, Yap et al. assess the impact of BMI on robotic transaxillary thyroidectomy [25]. Overall, the authors enrolled 3697 patients, 559 of whom were overweight and 76 of whom were obese. After multivariate analysis, the authors found that seroma formation, transient voice hoarseness and operative time were related to increasing BMI [25]. These findings suggest that, although obesity should not be considered a contraindication to robotic transaxillary thyroidectomy, this cohort of patients require an elevated expertise in the field of robotic and endocrine surgery.

Our study harbors several limitations. First of all, the retrospective nature of the paper. Moreover, the enrolled patients underwent different surgical procedures (total thyroidectomy, thyroid lobectomy, total thyroidectomy and central neck dissection, total thyroidectomy and lateral neck dissection) which may have introduced some potential bias. However, in order to attenuate these limitations, we use a case–control matching methods to make the compared groups homogenous in terms of surgical intervention, as well as age, sex, preoperative diagnosis and nodule size. This approach leads to the creation of two comparable groups, minimizing the risk of potential bias. In addition, although the sample size is greater than the major part of previously published papers, because of the low rate of post-operative complications, some outcomes may not have reached the adequate statistical power to highlight significant differences. Moreover, these data come from a high-volume Institutions and may not be reproducible in all centers.

In conclusion, in high-volume Institutions, thyroid surgery in obese patients is safe and not associated to worse postoperative outcomes. It correlates to longer postoperative hospital stay which is mainly related to the immediately postoperative course in intensive care unit due to comorbidities. Future multicentric studies on larger cohorts are required to confirm these findings.