兽研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.
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Introduction
Thyroid tumours account for approximately 1%–3.8% of all neoplasms in dogs, and up to 88% are carcinomas (Liptak 2007). Venous invasion is an important clinicopathological feature of canine thyroid carcinoma, reported in about one‐third of cases (Reagan et al. 2019) and recognised as a poor prognostic indicator that can markedly influence surgical planning when tumour thrombi are present (Brodey and Kelly 1968; Campos et al. 2014). Thyroidectomy remains the preferred treatment for thyroid tumours (Prastiti et al. 2018) and can be feasible in selected cases with vascular invasion (Latifi et al. 2021). Preoperative contrast‐enhanced computed tomography (CT) is primarily used to evaluate vascular invasion (Latifi et al. 2021).
Indocyanine green (ICG) is a near‐infrared fluorescent (NIRF) dye that rapidly binds plasma proteins after intravenous administration and distributes throughout the vascular system, emitting fluorescence at around 800 nm (Alander et al. 2012). These pharmacological properties enable its broad use for intraoperative fluorescence imaging in both human and veterinary surgery (Kim and Lee 2025; Majlesara et al. 2017). In tumours, ICG fluorescence may accumulate around the lesion due to the enhanced permeability and retention effect, aiding in the delineation of tumour margins (Egloff‐Juras et al. 2019). In both human and veterinary thyroid surgery, ICG has primarily been used to assess parathyroid perfusion (Solórzano et al. 2021) and to identify sentinel lymph nodes (Griffin et al. 2025).
This case describes the intraoperative use of intravenously administered ICG fluorescence as an adjunct to visual assessment during thyroidectomy in a dog with thyroid carcinoma, to aid evaluation of suspected venous involvement. Reports describing the intraoperative use of ICG fluorescence for tumour‐directed assessment in canine thyroid carcinoma are limited in the veterinary literature.
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Case Description
A 5‐year‐old, 4.35‐kg, spayed female Maltese was presented with a 1‐week history of hyporexia, hypoactivity and pelvic limb ataxia. The owner also mentioned that a firm cervical mass had been palpable for some time before presentation. On physical examination, the rectal temperature was 38.1°C, heart rate was 144 beats/min, respiratory rate was 36 breaths/min, and systolic blood pressure was 120 mmHg. The dog was estimated to be 6% dehydrated, and a grade III/VI left apical heart murmur was auscultated. A soft‐to‐firm, non‐painful mass measuring approximately 3 × 2 cm was palpated in the left cervical region. Bilateral prescapular lymph nodes were also palpable and were estimated on palpation to be approximately 0.5 cm in size. Haematology revealed a decreased PCV (31.3%; reference interval (RI), 37.3%–61.7%) and reticulocytopenia (5.5 × 103/µL; RI, 10.0–110.0 × 103/µL), consistent with non‐regenerative anaemia. Serum biochemistry showed marked hypercholesterolaemia (864 mg/dL; RI, 135–270 mg/dL) and hypertriglyceridaemia (1211 mg/dL; RI, 21–116 mg/dL). The dog had received no regular medications before presentation, including glucocorticoids. Thyroid function testing revealed decreased total thyroxine (T4) and free T4 concentrations (<0.5 µg/dL, RI 1.0–4.0 µg/dL; <0.3 ng/dL, RI 0.6–3.7 ng/dL, respectively), whereas thyroid‐stimulating hormone was increased (1.30 ng/mL; RI 0.05–0.42 ng/mL), confirming primary hypothyroidism.
To further characterise the cervical mass, CT was performed to delineate the cervical anatomy and evaluate possible vascular invasion. A contrast‐enhancing mass involving the left thyroid lobe was evident on CT (26 × 18 × 17 mm) (Figure 1). The contralateral thyroid lobe appeared atrophic (approximately 9 × 6 × 5 mm). Compression of the ipsilateral external jugular vein was suspected, but there was no definitive evidence of tumour extension into the vein. On the basis of these findings, a left extracapsular thyroidectomy was planned.
[图：Preoperative contrast‐enhanced computed tomography (CT) of the cervical region. (A) Transverse, (B) sagittal, and (C) co]
Premedication consisted of midazolam (0.2 mg/kg IV; Bukwang Midazolam; Bukwang Pharm). Anaesthesia was induced with propofol (6 mg/kg IV; Provive 1%; Myungmoon Pharm) and maintained with isoflurane (Terrell; Piramal Critical Care) in oxygen after endotracheal intubation. Analgesia was provided via a remifentanil constant rate infusion (1.1–3.4 µg/kg/h; Tivare; BCworld Pharm). With the dog positioned in dorsal recumbency and the neck extended, a midline incision from the larynx to the manubrium was made. After retraction of the sternohyoid and sternothyroid muscles with a Gelpi retractor, the left thyroid mass was exposed. The mass was firmly attached to the carotid sheath and adjacent soft tissues. Although no overt intravascular tumour thrombus was observed, both the cranial and caudal thyroid veins were visibly dilated with abrupt distal tapering (Figure 2A), raising suspicion of subtle vascular invasion.
[图：Intraoperative findings during left thyroidectomy with corresponding near‐infrared fluorescence (NIRF) images. (A) After]
To assess venous involvement intraoperatively, ICG (1 mg/mL; Cellbion) was administered intravenously. Fluorescence imaging was conducted using a NIRF system (Metagenie, MetapleBio, Korea). The dose of 0.5 mg/dog (0.115 mg/kg) was selected with reference to previously reported intravenous ICG use during thyroid and parathyroid surgery in dogs (Suh et al. 2015). After administration of 0.5 mg/dog, diffuse tumour fluorescence became visible within approximately 2 min (Figure 2B). Segmental intraluminal fluorescence appeared within the dilated thyroid vein, and the signal abruptly terminated at the point of tapering (Figure 2D). Based on the ICG findings, the resection plan was modified to extend slightly beyond the intraluminal fluorescence cut‐off, and a short segment of the thyroid vein was removed en bloc. The vessels were double‐ligated with 4‐0 silk and transected using a bipolar vessel‐sealing device. After adhesions were freed, the mass and ipsilateral cranial cervical lymph node were excised, and the wound was closed routinely.
The thyroid mass and the cranial cervical lymph node were submitted for histopathological examination (IDEXX Laboratories, ME, USA) (Figure 3). Histopathology confirmed a thyroid carcinoma replacing most of the thyroid parenchyma, with capsular extension. The mitotic count was 5 per 10 high‐power fields. Microscopic vascular invasion was not identified within the main tumour or capsule. The cranial cervical lymph node showed moderate reactive lymphoid hyperplasia without metastatic disease. These findings were consistent with a thyroid carcinoma confined to the thyroid region, with no histological evidence of vascular or nodal metastasis, although intraoperative findings suggested possible venous invasion.
[图：Gross specimen and histopathology of the resected left thyroid tumour. (A) En bloc specimen showing the thyroid tumour w]
Postoperatively, the dog remained hospitalised for three days. Vital parameters were stable, and no neurological deficits were noted. Mild hypocalcaemia was recorded on postoperative day (POD) 1 (8.7 mg/dL; RI, 9.0–11.3 mg/dL) and resolved spontaneously by POD 2. Over eight months of follow‐up, serum electrolytes stayed within RI, and there was no indication of postoperative hypoparathyroidism. Follow‐up imaging included thoracic radiography and cervical ultrasonography, with no evidence of local recurrence or metastasis.
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Discussion
ICG‐NIRF has been used in both human and veterinary surgery as a real‐time imaging adjunct during tumour resection (Choi and Lee 2024; Kim and Lee 2022; Yu and Lee 2024). However, its application to thyroid neoplasia has been considered limited because thyroid tissue exhibits strong background fluorescence and ICG distributes non‐specifically (Dip et al. 2022). Consequently, previous reports have focused largely on parathyroid identification rather than direct tumour visualisation. In the present case, ICG‐NIRF was applied intraoperatively to delineate the thyroid mass and to assess possible invasion into the adjacent thyroid vein.
Unlike conventional ICG‐NIRF use during thyroidectomy, which focuses on parathyroid preservation, the present case required enhanced tumour fluorescence to achieve complete excision (Liptak 2007). Consequently, previously reported low‐dose ICG protocols (0.018–0.025 mg/kg) for parathyroid preservation were not considered sufficient for delineating the tumour and assessing possible invasion into the adjacent thyroid vein (Ruffin et al. 2025; Suh et al. 2015). For this reason, a higher dose (0.5 mg/dog; 0.115 mg/kg) was selected with reference to a previous study in dogs demonstrating strong thyroid and parathyroid fluorescence at doses up to 0.1 mg/kg (Suh et al. 2015). With this dosing strategy, tumour fluorescence and intraluminal venous fluorescence were observed. However, no established dosing protocol exists for ICG use in thyroid tumours, and this single case cannot determine whether the chosen dose is broadly applicable. Further studies are required to define optimal administration strategies.
Canine thyroid carcinoma frequently invades regional cervical vessels, particularly the thyroid veins and the internal jugular vein (Liptak 2007; Prastiti et al. 2018), and this vascular invasion is an important prognostic factor linked to incomplete excision and distant metastasis. Accurate assessment of vascular invasion is therefore essential when planning a thyroidectomy, and when invasion is suspected, the principle of en bloc resection is recommended (Enache et al. 2023). Ultrasonography and CT are commonly used for preoperative evaluation, but a retrospective study in dogs reported that CT missed evidence of major vascular invasion in approximately half of the cases, suggesting potential underestimation of vascular involvement (Latifi et al. 2021). CT also cannot be used intraoperatively, which limits its value for real‐time surgical decision‐making. These limitations highlight the need for an adjunctive technique capable of assessing vascular invasion in real time during surgery.
In this case, ICG fluorescence served as a useful adjunct for intraoperative assessment of possible thyroid vein invasion, which was not clearly evident on the preoperative CT. Following ICG administration, fluorescence was observed within the thyroid mass and in a segmental pattern along the dilated thyroid vein, a finding interpreted as suggestive of possible intraluminal tumour extension (Figure 2). The fluorescence findings informed surgical decision‐making. Instead of ligating the vessel close to the tumour, the resection margin was extended to the point where fluorescence abruptly ceased, allowing en bloc removal of the tumour and the involved vein.
In conclusion, intraoperative ICG fluorescence provided functional information that was incorporated into intraoperative assessment and contributed to refinement of the resection extent when venous involvement was suspected. Rather than serving solely as a visual aid, ICG fluorescence complemented conventional anatomical assessment during surgery. This case suggests that ICG fluorescence may be a useful intraoperative adjunct in selected cases of thyroid tumour surgery where preoperative imaging does not clearly delineate vascular involvement .
Author Contributions
Mingyeong Kim: Conceptualisation (equal); data curation (equal); investigation (lead); writing – original draft preparation (lead); writing – review & editing (equal). Yujin Kim: data curation (equal); investigation (equal); writing – original draft preparation (equal); writing – review & editing (equal). Sungin Lee: Conceptualisation (equal); writing – review & editing (equal); validation (equal); supervision (lead).
Funding
This research was financially supported by the Ministry of Small and Medium‐sized Enterprises(SMEs) and Startups(MSS), Korea, under the ‘Supporting Project for boosting a Local Innovation Leading Company(R&D), (S3451530)’ supervised by the Korea Technology and Information Promotion Agency for SMEs(TIPA). Also, this work was supported by Chungbuk National University NUDP program (2025).
Consent
Informed consent was obtained from the dog's owner prior to all diagnostic and therapeutic procedures. The owner was fully informed about the clinical procedures and the use of clinical data and images for publication.
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
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