Morphometry, Topography and Arterial Supply of the Thyroid Gland in Brazilian Shorthair Cats

Abstract

Background: Thyroid gland diseases are the most common endocrinopathies in feline practice. Diagnosis and surgical treatment must base on solid anatomical knowledge about the gland size, localization, and blood supply. However, some textbooks provide a general anatomical description of the thyroid gland of domestic carnivores. Thus, specific details of the feline gland are missing. The present study aimed to investigate the dimensions, topography, and arterial supply of the thyroid gland in Brazilian shorthair cats and, therefore, provide additional data to diagnose and treat feline thyroid diseases.Materials, Methods & Results: Thirty Brazilian shorthair cats formalin-fixed cadavers (15 male and 15 female) were injected with red-stained latex solution by a canula in the thoracic aorta. The necropsy unit of the Rural Federal University of Rio de Janeiro donated the specimens. The study included only adult animals with no history of thyroid disease. After the fixation period, the cadavers were dissected to investigate the measurements (length, width at cranial and caudal poles, and thickness), topography, and in situ arterial supply of the thyroid lobes. The mean measurements of the length, cranial pole width, caudal pole width, and thickness in the right lobe were 19.39 ± 3.10 mm, 5.36 ± 1.40 mm, 3.67 ± 0.93 mm, and 1.30 ± 0.29 mm, respectively; and 20.29 ± 3.35 mm, 4.85 ± 1.58 mm, 3.88 ± 0.91 mm, 1.64 ± 0.65 mm in the left lobe, respectively. There were no statistical differences (P > 0.05) in the comparison of the measures between sexes or antimers (sides). Pearson's linear correlation detected a positive, moderate (r = 0.55), and significant (P < 0.05) correlation between the right and left lobe lengths. In 70% of the cats, both left and right lobes had the cranial poles located at the same level. Typically, the lobes extended between the first to the eighth tracheal ring. However, the cranial pole of some lobes located as cranially as the cricoid cartilage level, and the caudal pole as caudally as the 12th tracheal ring. Fifty-six percent of the cats had a ventrally located isthmus. In all the sampling, one single thyroid artery emerged as a branch of the common carotid artery and provided branches directly to the thyroid lobe, isthmus and the adjacent muscles and esophagus.Discussion: Besides establishing average dimensions of normal thyroid lobes in Brazilian shorthair cats, this study detected no significant difference between the average measurements of right and left lobes. Also, a positive linear correlation between the length and width of the right and left lobes became evident. Therefore, the practitioner must consider suspicious any length asymmetry between right and left thyroid lobes until further endocrine test proves otherwise. Most of the cats had the right and left thyroid lobe positioned at the same transversal level; however, positional asymmetries are not uncommon. Unlike dogs, Brazilian shorthair cats have only a single artery to supply each lobe: the thyroid artery. In a feline thyroidectomy, the surgeon must avoid blindly ligating the thyroid artery since this vessel also provided numerous branches to adjacent muscles and esophagus. In a bilateral thyroidectomy, the ventral region between lobes should be thoroughly inspected for the common presence of an isthmus. Sometimes, the surgeon may need to extend the incision caudally beyond the 12th tracheal ring level to visualize the gland tissue entirely.Keywords: endocrinology, feline anatomy, morphometrics, thyroidectomy.

Morphometry, topography and arterial supply of the thyroid gland in rhesus monkeys (Macaca mulatta Zimmermann, 1780)

“…Limited data regarding the morphometry, topography, and vascularization of the thyroid gland in primates are available. This study found no differences between the left and right lobes of the thyroid gland in rhesus monkeys, consistent with previous studies on other mammal species such as Santa Inês sheep (Lima et al, 2009), domestic dogs (Rodrigues et al, 2016), and Brazilian Shorthair Cats (Stocco et al, 2021). However, Novo et al (2009) reported larger measurements for the left lobe than the right lobe in dogs using ultrasonographic examination.…”

“…The thyroid gland in rhesus monkeys was located ventrolateral to the trachea, similar to many other domestic and wild mammals (Akudu et al, 2018;Borges et al, 2019;Carvalho et al, 2003;König and Liebich, 2016;Policeni et al, 2012;Rodrigues et al, 2016;Silva et al, 2019;Stocco et al, 2021;Yamasaki, 1990Yamasaki, , 1996Yamasaki, , 2016. However, koalas arranged it laterally to the trachea at the clavicle level (Yamasaki, 1993).…”

“…The topography of the thyroid lobes in New Zealand rabbits varied, with the cranial extremity typically at the level of the cricoid cartilage and the caudal end showing more variability, ranging from the third to the tenth tracheal ring (Silva et al, 2019). In Brazilian Shorthair Cats (Stocco et al, 2021), most lobes had their cranial pole at the level of the first tracheal ring and the caudal lobe at the eighth tracheal ring. However, some lobes had their cranial pole located as cranially as the level of the cricoid cartilage and the caudal pole as caudally as the 12th tracheal ring.…”