Protective Effect of Indocyanine Green Fluorescence Imaging Technology on Parathyroid Glands During Total Thyroidectomy

Postoperative hypoparathyroidism or hypocalcemia is the most frequent complication after total thyroidectomy (TT) . The median incidence of transient and permanent postoperative hypoparathyroidism is 27% (19%-38%) and 1% (0-3%), respectively. Transient hypoparathyroidism can increase the length of hospital stay and the costs of hospitalization for patients. Permanent hypoparathyroidism leads to lifelong medication use, which may severely impair the quality of life of patients. Therefore, identifying the parathyroid glands (PGs) and preserving those with adequate blood perfusion intraoperatively has always been a crucial procedure during thyroidectomy.

Conventional means of identification and assessment of PGs are mainly based on surgeon-dependent identification of their anatomical location and appearance (color, shape, etc.) by the naked eye. However, this visual inspection is often influenced by the experience of the surgeon, intraoperative hemorrhage, ectopic PGs and so on, which makes it difficult to fully protect the PGs.

Currently, there has been an emergence of near-infrared fluorescence imaging (NIFI) that can be applied during thyroid or parathyroid surgery for the evaluation and identification of PGs. This technique mainly exploits the autofluorescence (AF) of PGs and indocyanine green fluorescence (ICGF ) imaging.PGs could exhibit stronger AF than the surrounding tissue under near-infrared light, which can be exploited to accurately identify PGs in real time. Subsequent studies have demonstrated that AF can not only detect PGs intraoperatively in real time and improve the intraoperative identification of PGs but also reduce the incidence of postoperative hypoparathyroidism. However, AF cannot assess the status of PG blood perfusion and consequently is not useful when determining whether PGs need to be autotransplanted.

Indocyanine green (ICG) fluorescence imaging may be a great solution to this problem. ICG is a safe fluorescent dye with fast metabolism and few adverse effects that can quickly combine with plasma proteins after intravenous injection and is widely used in angiography in multiple surgical disciplines. In recent years, several studies have shown that ICGF may be superior in evaluating blood perfusion and predicting the function of PGs in situ, subsequently guiding their autotransplantation. However, ICGF may not be very suitable for the identification of PGs before dissection, as the thyroid gland would also emit intense fluorescence after the injection of ICG, which may lead to difficulties in distinguishing them. Thus, AF and ICGF have their own advantages and disadvantages in the identification and evaluation of PGs, respectively. These two methods can be considered complementary.

In the present study, the investigators used AF in combination with ICGF imaging by one fluorescence imaging system during different steps of the surgical procedure. At the beginning of the operation, AF was used to identify the PGs before any dissection. Then, after the thyroid gland was removed, AF was used again to locate the PGs in situ. Finally, ICGF was applied to evaluate the blood perfusion of the PGs in situ and guide their autotransplantation. The aim of this randomized controlled trial was to assess whether this strategy could reduce the incidence of postoperative hypoparathyroidism and benefit the identification and evaluation of PGs during total thyroidectomy.