Intraoperative Indocyanine Green Fluorescence for Assessment of Suspected Venous Invasion in a Dog With Thyroid Carcinoma

ABSTRACT Accurate intraoperative assessment of vascular involvement in canine thyroid carcinoma remains challenging when preoperative imaging findings are equivocal. This case describes the use of intraoperative indocyanine green fluorescence imaging to assist real‐time assessment of suspected venous involvement during canine thyroidectomy. A 5‐year‐old spayed female Maltese dog was presented with a cervical mass and clinicopathological findings consistent with hypothyroidism. Contrast‐enhanced computed tomography identified a left thyroid mass with suspected external jugular vein compression but no definitive evidence of vascular invasion. During left thyroidectomy, dilation and distal tapering of the thyroid veins raised concern for venous involvement. Indocyanine green (0.5 mg/dog) was administered intravenously for intraoperative near‐infrared fluorescence imaging. Diffuse fluorescence of the thyroid mass and segmental intraluminal fluorescence within the dilated thyroid vein were observed, with signal loss at the tapering point. Based on these findings, en bloc resection including a short segment of the involved vein was performed. Histopathology confirmed thyroid carcinoma without evidence of regional lymph node metastasis. This case illustrates that intraoperative indocyanine green fluorescence imaging may provide adjunctive real‐time information for assessing suspected venous involvement during canine thyroid carcinoma surgery and may complement preoperative imaging when vascular invasion is uncertain.