Effects of excitation light intensity on parathyroid autofluorescence with a novel near-infrared fluorescence imaging system: two surgical case reports

The intraoperative identification and preservation of the parathyroid glands are vital techniques, which are largely dependent on a surgeon's experience. Therefore, a simple and reproducible technique to identify the parathyroid glands during surgery is needed. Parathyroid tissue shows near-infrared (NIR) autofluorescence, which enables the intraoperative identification of the parathyroid gland. We herein present two cases that underwent surgery on the parathyroid glands, which were observed using the NIR fluorescence imaging system LIGHTVISION (R) (Shimazu, Kyoto, Japan). In a case of papillary thyroid carcinoma, the system was adopted to preserve normal parathyroid glands during left hemithyroidectomy. The left lower parathyroid gland was identified using the imaging system under white light; however, its autofluorescence was visualized more dearly with the excitation light of NIR. In a case of primary hyperparathyroidism due to MEN1, the system was adopted to identify and remove all of the parathyroid glands during total parathyroidectomy. The autofluorescence of diseased glands was weaker than that of normal glands, even with the excitation light of NIR. When the parathyroid glands were irradiated with a red laser pointer, the intensity of autofluorescence significantly increased. However, the largest gland, which was pathologically proven to contain strongly proliferating chief cells, did not show autofluorescence. These results suggest that normal or less diseased parathyroid glands, which are generally small and difficult to identify during surgery, showed relatively strong autofluorescence. A stronger excitation light increases the autofluorescence of parathyroid glands, which enhances sensitivity for detecting parathyroid glands during surgery. In conclusion, LIGHTVISION (R) is a useful device to identify parathyroid glands and an additional excitation light of a red laser pointer increases the detection sensitivity.