Diagnostic imaging and conservative management of an ultimobranchial thyroid cyst in an adult horse

Abstract

The equine thyroid gland is a bilobed organ, which is located in the dorsolateral aspect of the third to sixth tracheal ring (Viana et al., 2019). The embryonic ultimobranchial body is an outpocketing of the fourth pharyngeal pouch that fuses with the thyroid diverticulum, giving rise to calcitonin-producing C-cells (David et al., 2008;Saulez et al., 2012). Cysts or cyst-like lesions in adult equine thyroid glands are quite uncommon (Østergaard et al., 2014). Clinically, these cysts emerge as a well-defined, fluctuating mass in the perilaryngeal region. The masses are not painful at palpation and their appearance is often similar to branchial apparatus anomalies, like remnant cysts, sinuses and fistulae (Østergaard et al., 2014;Slovis et al., 2006).The differential diagnoses of thyroid cyst include thyroglossal duct cyst, branchial cyst, oesophageal and tracheal duplication cysts, and salivary mucocele (Kelmer et al., 2007). Consequently, the use of diagnostic imaging is crucial for an in-depth diagnosis and appropriate treatment. In the literature, pharyngeal endoscopy and ultrasound examination accompanied by plain or contrast radiography have been described in thyroid cystic masses in horses (Rinnovati et al., 2018). By using ultrasonography, a comparison of the size between the left and right thyroid lobe can be easily made (Viana et al., 2019). However, neither ultrasonography nor contrast radiography can identify the exact size of the cyst and more importantly, the relationship between the cyst and adjacent vital organs. For this reason, advanced imaging modalities are extremely useful in these cases, especially the use of standing computed tomography (Peters et al., 2003). Before surgical removal of one or both thyroid lobes, it is recommended to test the thyroid function. This can be achieved via measuring the serum thyroid hormone concentrations. However, the concentration of thyroid hormones have seasonal and diurnal variation, which may complicate the interpretation (Wallack et al., 2010). Technetium pertechnetate is an iodine analogue, so it is transported to the thyroid gland similarly to iodine (Iqbal & Rehman, 2020). That makes thyroid scintigraphy a suitable diagnostic method to assess the metabolic activity and the detection of functional disparity between the lobes of thyroid glands (Iqbal & Rehman, 2020). The presented report describes the diagnostic methodology of a thyroid cyst in a mature horse using ultrasonography, computed tomography (CT) and scintigraphy. The conservative management by sclerotherapy and positive long-term outcome 2 years' post treatment are reported.

Welfare considerations for management of horses on prolonged periods of box rest

“…Here Peeters et al. (2024) reflected, in hindsight, in‐hand walking could have been started earlier to stimulate remodelling at the fracture sight. Most equestrians will be familiar with the perils of turning horses out after a period of confinement and/or hand walking a horse on restricted exercise, where the motivation to run, rear and buck can overshadow the handler's cues.…”

“…Peeters et al. (2024) describe the presentation, diagnosis and successful management of an unusual fracture, of the femoral greater trochanter, in an 8‐year‐old Warmblood mare. Internal fixation was not considered feasible due to the high likelihood of implant failure at this location and financial constraints.…”