Near-infrared autofluorescence in thyroid and parathyroid surgery

Contrast-free autofluorescence (AF) of the parathyroid glands (PTGs) and thyroid tissue occurs in the near-infrared (NIR) spectrum on excitation by light in the upper range of the visible spectrum or lower NIR spectrum. In vivo, PTGs autofluoresce more brightly than thyroid (by a factor of 2-20 times) and appear as a bright spot against surrounding thyroid, muscle or fat on a processed image which is generated in real-time. NIR-AF of PTGs was first described in 2009 although NIR-AF had previously been used in several other clinical applications. Since then there has been a great amount of interest in the use of NIR-AF in thyroid and parathyroid surgery with over 25 published reports of the utilisation of both self-built and proprietary NIR-AF devices in neck endocrine surgery. All of these reports have confirmed the feasibility of NIR-AF intraoperatively and its ability to detect PTGs, although the reported accuracy varies from 90-100%. Reports of the effect of NIR-AF on relevant clinical endpoints i.e., post-operative hypoparathyroidism in thyroidectomy and persistent disease in parathyroidectomy are however scant. There has been one multicentre clinical trial of NIR-AF in thyroidectomy but this did not report clinical outcomes and two single-centre, non-randomised studies which did report post-operative hypoparathyroidism but with differing results: one showing no benefit in 106 NIR-AF vs. 163 controls and one, a reduction of early hypocalcaemia from 20% to 5% in 93 NIR-AF patients vs. 420 controls. There were only 2 cases of permanent hypoparathyroidism across both studies and therefore no significant observable difference in this key outcome variable. In parathyroidectomy, possible variability of the AF signal due to composition of a PTG adenoma, secondary/tertiary disease and MEN1 as well as depth-penetration preventing detection of sub-surface PTGs would imply that NIR-AF in its current form is not well-placed to improve cure-rates in hyperparathyroidism, which may already be as high as 98%. Thus far, no study has addressed this. Despite the promising results of NIR-AF, the absence of data demonstrating an improvement in outcomes and the cost of its use currently limit its use in routine clinical practice, especially in a publicly funded healthcare system with budgetary constraints. However, it can be utilised in research settings and this should be undertaken within the context of well-designed and conducted randomised, multi-centre, appropriately powered studies, which will assist in establishing its role in neck endocrine surgery.

Total thyroidectomy with intraoperative neural monitoring and near-infrared fluorescence imaging

PURPOSE

To describe our personal experience during aclassic complete thyroidectomy adopting both intraoperative neural monitoringand near-infrared autofluorescence.

METHODS

In October 2021, 20 patients underwent totalthyroidectomy for benign and malignant conditions: 13 patients were affected bymultinodular goiter, 2 by Graves' disease, and 5 by indeterminate lesions (3Tir-3B and 2 Tir-3A). For each patient, intraoperative neural monitoring of therecurrent laryngeal nerve and near-infrared autofluorescence were used.

RESULTS

Overall, 76/80 (95.0%) parathyroid glands weredetected: 34/76 (44.7%) were identified by the surgeon during the dissection,while 42/76 (55.3%) were detected by the near-infrared camera before thesurgeon saw them with naked eye. Indocyanine green angiography was adopted inall the patients, and in 2 cases, parathyroid gland autotransplantation wasperformed since 2 parathyroid glands resulted devascularized after dissection.Operative time ranged from 113 to 201 min (mean 156 min).

CONCLUSION

Together with intraoperative neural monitoring,near-infrared autofluorescence is a reliable device in thyroid surgery. Furtherprospective studies are necessary to establish if the adoption ofautofluorescence may result in long-term benefit in terms of calcemia.