Histology and Pathology of the Thyroid Gland in Bottlenose Dolphins from the Western Coast of the Gulf of Mexico
IAAAM Archive
Daniel F. Cowan
Department of Pathology, the University of Texas Medical Branch, Galveston, and the Texas Marine Mammal Stranding Network, Galveston, TX


Thyroid glands were recovered from preservation code 2 bottlenose dolphins (Tursiops truncatus) stranding along the Texas coast over a 10 year period, 1991-2000. 38 were found to be suitable for inclusion in this study. Organ weight ranged from 21 g in a 115 cm long neonate to 58 g in a large (249 cm) male. More typical weights were in the range of 25 to 45 g. Glands may be larger in pregnant females than in non-pregnant animals in the same size range. In infancy, the gland tends to be compact and relatively homogeneous, with sparse delicate internal fibrous septation, but with advancing age it tends to become lobular, defined by the occurrence of denser sub-dividing fibrous bands. In a few animals, the gland may occur in separate left and right lobes. In one older female (GLG 40, 233 cm length), the gland was represented by a cluster of lobules. Lobulation is not necessarily accompanied by enlargement by weight; i.e., it is not the same as hyperplasia. With age, variability of follicle size and colloid density tends to increase. We have an impression of seasonable variation, with follicles tending to be smaller in the cooler months (October-March), but owing to sample size and the age factor, this may not be physiologically or statistically significant.

Four animals (10%) had discrete nodules diagnosable as hyperplastic, a separate condition from lobulation. Four had grossly identifiable colloid-filled cysts (size range 1 to 4 mm). Five animals (13%) had squamous cysts in the thyroid, (size range 4 to 15 mm) which all contained a creamy white fluid material, easily recognizable on gross examination. Other abnormalities included patchy or greater diffuse interstitial fibrosis (5 cases) amyloidosis (2 cases) thyroiditis (1 case) and vasculitis (1 case). No neoplasms were found. Presumptive C cells were identified among follicle cells and in the interstitium using synaptophysin antibody.

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Daniel F. Cowan, MD, CM
Department of Pathology, University of Texas Medical Branch
Galveston, TX, USA
Texas Marine Mammal Stranding Network

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