Morphometry, topography and arterial supply of the thyroid gland in brazilian shorthair cat

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. 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. 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.(AU)

Morfometría y vascularización de la glándula tiroides en conejo (Oryctolagus cuniculus) / Morphometry and vascularization of the thyroid glands in rabbits (Oryctolagus cuniculus)

Las glándulas tiroides consisten en dos partes denominadas lobos que se encuentran en ambos lados de la laringe. El objetivo de este estudio fue caracterizar las medidas, topografía y vascularización de la glándula tiroides de conejos Nueva Zelanda. Las disecciones anatómicas se realizaron en 36 cadáveres adultos, 17 machos y 19 hembras, con masa corporal media de 2,5 kg y longitud cara-sacral media de 40 cm. Los cadáveres fueron obtenidos del sector de necropsia de la Universidad. Los especímenes tuvieron la arteria aorta torácica canalada, por la cual se inyectó solución de formaldehído al 10 %, seguida de látex coloreado. En los machos, el lobo izquierdo de la glándula tiroidea midió 1,40 x 0,40 x 0,01 cm y el derecho 1,36 x 0,56 x 0,01 cm; en las hembras, el lobo izquierdo midió 1,50 x 0,49 x 0,01 cm y el derecho 1,37 x 0,48 x 0,01cm. No hubo diferencia significativa (p> 0,05) entre las medias de las medidas entre machos y hembras, pero la extensión del lóbulo izquierdo de las hembras y la anchura del lóbulo derecho de los machos fueran significativamente mayores (p <0,05). La extremidad craneal de los lobos tiroideos se encontraba al nivel del cartílago cricoide en casi todos los especímenes. El extremo caudal presentó topografía más variable, desde el tercer hasta el décimo anillo traqueal, habiendo predominado al nivel del quinto anillo. Invariablemente, la irrigación arterial fue determinada por las arterias tiroideas izquierda y derecha, originadas de la arteria carótida común. Las anastomosis entre las arterias tiroideas fueron comunes. La constancia en las dimensiones y irrigación de la glándula tiroidea puede ser ventajosa en la elección del Coelho como modelo experimental para el estudio de esta glándula.

The thyroid glands consist of two parts called lobes located on both sides of the larynx. The aim of this study was to characterize the measures, topography and arterial irrigation of New Zealand´s rabbits thyroid glands. The anatomical dissections were performed in 36 adult cadavers, 17 males and 19 females, with a mean body mass of 2.5 kg and a mean cranium-sacral length of 40 cm. The specimens were obtained from the necropsy unit of the University. The cadavers had the thoracic aorta artery cannulated, through which 10 % formaldehyde solution was injected, followed by injection colored latex. In males, the left lobe of the thyroid gland measured 1.40x0.40x0.01cm and the right 1.36x0.56x0.01cm; in females, the left lobe measured 1.50x0.49x0.01cm and the right one was 1.37x0.48x0.01cm. There was no significant difference (p> 0.05) between the means of the measurements between males and females, but the left lobe length of the females and the right lobe width of the males were significantly higher (p <0.05). The cranial extremity of the thyroid lobes was at the level of the cricoid cartilage in almost all specimens. The caudal end showed more variable topography, from the third to the tenth tracheal ring in few specimens, but predominated at the level of the fifth ring. Invariably, arterial irrigation was determined by the left and right thyroid arteries, originating from the common carotid artery. Anastomoses between the thyroid arteries were common. The constancy in dimensions and irrigation of the thyroid gland may be advantageous in choosing the rabbit as an experimental model for the study of this gland.