Near-infrared Imaging Techniques for Identifying and Preserving Viable Parathyroid Glands During Thyroidectomy

Hypoparathyroidism Postprocedural

Near-infrared fluorescence

The parathyroid glands and their blood vessels are notoriously difficult to visualize and may therefore be unintentionally and irrevocably damaged during thyroid surgery. This project investigates new surgeon-performed imaging techniques that visualize the parathyroid glands and their vessels in real-time during thyroid surgery. The purpose is to examine, in a matched cohort study, whether the implementation of near-infrared-induced autofluorescence for identification of the parathyroid glands, combined with indocyanine green near-infrared angiography of the parathyroid feeding vessels, can reduce the incidence of postoperative hypocalcaemia in patients undergoing total and completion thyroidectomy at Odense University Hospital.

The most common complication after thyroidectomy is postoperative hypoparathyroidism due to unintentional intraoperative injury, excision, or devascularisation of the parathyroid glands. This complication can be either transient (≤6 months), or permanent (\> 6 months). The pooled results from four recent studies from three different Danish university hospitals show that 117/945 patients (12.4%) suffered from permanent hypoparathyroidism after total and completion thyroidectomy. This is a very high percentage, considering that the consequences of hypoparathyroidism and its treatment may be severe and include prolonged hospitalization, neuromuscular symptoms, nephrocalcinosis, nephrolithiasis, premature cataracts, seizures, basal ganglia calcification, and increased mortality. To minimize the risk of postoperative hypoparathyroidism, the standard approach to thyroidectomy is to keep dissection as close to the thyroid capsule as possible while visually scrutinizing the surgical field for the parathyroid glands and their delicate feeding vessels. In spite of these measures, the reported incidences of transient and permanent hypocalcaemia clearly demonstrate a need to further decrease the risk of inadvertent injury to the parathyroid glands and their vessels during thyroid surgery. To achieve this goal, surgeons need a reliable intraoperative aid that can 1) help them identify the parathyroid glands in vivo and 2) locate their feeding vessels and evaluate their perfusion in real-time during thyroid surgery. Recently, two near-infrared fluorescence techniques have emerged, that could potentially meet the requirement of identifying the parathyroid glands and assessing their vasculature using the same piece of technical equipment. The techniques are: near-infrared-induced autofluorescence of the parathyroid glands (NIRAF) for parathyroid identification, and indocyanine green near-infrared angiography (ICGA) for the assessment of parathyroid vascularization. A recent systematic review concluded that these most reported-on optical tools for parathyroid identification and perfusion assessment are favourable for clinical application in terms of being real-time and non-invasive, having a high sensitivity, an excellent safety profile, and involving no exposure to ionizing radiation. Prior to a broader implementation, commercially unaffiliated investigator-initiated studies are needed to evaluate the clinical effect of the bimodal application of NIRAF and ICGA on the incidence of postoperative hypoparathyroidism after total and completion thyroidectomy. This study intends to address this need. The hypothesis of the study is that near-infrared-induced autofluorescence (NIRAF) combined with indocyanine green near-infrared angiography (ICGA) of the parathyroid glands can reduce the incidence of permanent hypoparathyroidism after total and completion thyroidectomy to 1/3 or less of the incidence in a matched retrospective control group.

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