Enhancing Thyroidectomy Safety with Intraoperative Methylene Blue

Abstract

Background: Thyroidectomy requires meticulous identification and preservation of the parathyroid glands and recurrent laryngeal nerves (RLNs). Their small size, variable anatomy and close relationship to the thyroid make intraoperative identification challenging. This study evaluated topical methylene blue spraying as a simple adjunct for visualization of these critical structures and assessed postoperative calcium and vocal cord outcomes.

Methods: A prospective observational study included 50 patients undergoing open total thyroidectomy at K R Hospital, Mysore Medical College and Research Institute, over an 18-month period. One millilitre (10 mg) of 1% methylene blue was sprayed over the thyroid lobe and perilobar area before inferior pole ligation. Differential staining was assessed after 5 minutes. Primary outcomes were parathyroid and bilateral RLN identification. Secondary outcomes included serum calcium, postoperative hypocalcemia, vocal cord function and complications. Continuous variables were compared using a paired t-test and categorical variables using chi-square or Fisher's exact test; p<0.05 was considered significant.

Results: Mean age was 45.50±11.38 years and 90% of participants were female. At least one parathyroid gland per side was identified in 47 patients (94%), with bilateral identification in 45 (90%); the mean number identified was 2.54±1.02. Bilateral RLN identification was achieved in all 50 patients (100%), with adequate visual contrast in 48 (96%). Mean serum calcium decreased from 9.18±0.56 to 8.64±0.63 mg/dL (mean difference 0.54±0.30 mg/dL; t=12.79; p<0.001). Biochemical postoperative hypocalcemia (<8.0 mg/dL) occurred in 7 patients (14%), all reported as transient. No permanent hypocalcemia or postoperative vocal cord dysfunction was recorded. Preoperative calcium <8.5 mg/dL was strongly associated with postoperative hypocalcemia (85.7% vs 3.8%; RR 22.29; p<0.001). Hypocalcemia was also associated with age <40 years (30.0% vs 0% in 40–50 years and 7.1% in >50 years; p=0.025).

Conclusion: Topical methylene blue spraying provided high rates of parathyroid and RLN visualization in this cohort and was not associated with documented dye-related adverse events. The observed hypocalcemia was transient, while low preoperative calcium and younger age were associated with increased risk. Larger controlled studies are required before the technique can be considered superior to standard thyroidectomy or established fluorescence and neuromonitoring technologies.