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Evaluation of structural and ultrastructural changes in thyroid and parathyroid glands after near infrared irradiation: study on an animal model.

ABSTRACT: Intraoperative identification of parathyroid glands is a tough task for surgeons performing thyroid or parathyroid surgery, because the small size, color and shape of these glands hinder their discrimination from other cervical tissues. In 2011, Paras described the autofluorescence of parathyroid glands, a property that could facilitate their intraoperative identification. Parathyroid glands submitted to a 785 nm laser beam emit fluorescence in the near infrared range, with a peak at 822 nm. As the intrinsic properties of secretory tissues may be affected by the exposure to the near infrared light, a situation that could preclude their intraoperative utilization, the authors compared the structural and ultra-structural patterns of rat's thyroid and parathyroid glands submitted to irradiation replicating the conditions that allow their intraoperative identification, with those of non irradiated animals. Twenty-four Wistar rats were divided into six groups: animals of Groups 1, 3 and 5 were submitted under general anesthesia to direct irradiation of the cervical area with a 780 nm LED light for 3 minutes through a cervical incision, and animals of Groups 2, 4 and 6 were submitted to cervical dissection without irradiation. Animals of were euthanized immediately (Groups 1 and 2), at Day 30 (Groups 3 and 4) at and at Day 60 (Groups 5 and 6) and thyroid and parathyroid glands were removed: one lobe was prepared for conventional pathological examination and the other lobe for electron microscopy observed by three experienced pathological experts. Twenty-four samples were prepared for conventional histology and there were no alterations reported in any group. Due to technical problems, only 21 samples were observed by electron microscopy and there were no differences in the ultrastructure of parathyroid and thyroid glands, namely the nuclear pattern, mitochondria, endoplasmic reticulum or secretory granules, in any of the groups. These results confirm the innocuity of near infrared irradiation', allowing its intraoperative utilization.

SUBMITTER: Serra C

PROVIDER: S-EPMC8349517 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description: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.

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Evaluation of structural and ultrastructural changes in thyroid and parathyroid glands after near infrared irradiation: study on an animal model.

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