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Background: Thyroid neoplasia is a common endocrine neoplasm in dogs. The boxer is one of the reported breeds predisposed to malignant thyroid neoplasia. However, the association between thyroid neoplasia, malignancy and breed should be considered with caution., Cases Presentation: This article describes the presentation, clinical pathological findings, computed tomographic (CT) imaging findings and histopathological features of benign cystic thyroid tumour (cystadenoma) diagnosed in three boxers. These three dogs were presented for investigation of unilateral (n = 2) or bilateral (n = 1) cervical masses with no associated clinical signs of thyroid dysfunction. In each case, post-contrast CT scan identified a large, lateralised, non-invasive, well-defined homogeneous cystic structure with a hyperattenuating contrast-enhancing capsule of suspected thyroid origin displacing the surrounding cervical tissues. Ultrasound-guided fine needle aspiration of the cysts yielded fluid with a high thyroxine concentration in each case. Histopathology was consistent with thyroid cystadenoma in all cases. One dog was concurrently diagnosed with oral melanoma and euthanased. Two dogs underwent surgical excision with one lost to follow-up after 36 months and the other euthanased after 16 months following diagnosis of mast cell tumour., Conclusions: To the authors' knowledge, this is the first detailed report of non-functional benign thyroid cystadenoma in dogs and provides relevant information about case management for this type of tumour. The presence of a large cystic structure associated with benign non-functional thyroid neoplasia may be a condition to which boxer dogs are predisposed.

Background: Thyroid cysts are rare in cats and poorly documented., Objectives: To report distinguishing clinical features and treatment responses of cats with thyroid cysts., Animals: Forty client-owned cats., Methods: Retrospective review of medical records for cats with thyroid cysts confirmed by scintigraphy, ultrasound, magnetic resonance imaging, or necropsy at 4 referral centers between 2005 and 2016. Signalment, clinical findings, diagnostic testing, treatment, and outcome were recorded., Results: Cats ranged in age from 8 to 20 years with no apparent breed or sex predilection. 37 of 40 (93%) cats were hyperthyroid (duration, 1-96 months). Clinical findings included palpable neck mass (40/40, 100%), weight loss (15/40, 38%), dysphagia (8/40, 20%), decreased appetite (5/40, 13%), and dyspnea (4/40, 10%). Cysts were classified as small (≤8 cm 3 ) in 16 (40%) and large (>8 cm 3 ) in 24 (60%) cats. Of 25 cats treated with radioiodine, hyperthyroidism resolved in 23 (92%), whereas thyroid cysts resolved in 12 (50%). Radioiodine treatment resolved small cysts in 8 of 13 (62%) cats and large cysts in 4 of 11 (36%) cats. Eight cats, including 2 euthyroid cats, underwent thyroid-cystectomy; 3 with bilateral thyroid involvement were euthanized postoperatively for hypocalcemia. Excised cystic thyroid masses were identified as cystadenoma (4) and carcinoma (4)., Conclusions and Clinical Importance: Thyroid cysts are encountered in hyperthyroid and euthyroid cats with benign and malignant thyroid tumors. Radioiodine treatment alone inconsistently resolved thyroid cysts. Thyroid-cystectomy could be considered in cats with unilateral thyroid disease or when symptomatic cysts persist despite successful radioiodine treatment of hyperthyroidism., (Copyright © 2017 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

A 178-kg, 14-yr-old captive female American black bear (Ursus americanus) was examined because of lethargy, inappetance, obesity, and alopecia. Serum chemistry and complete blood count values were within normal limits. Based on serum levels for total thyroxine (T4), free T4 by equilibrium dialysis (fT4ED), and canine thyroid-stimulating hormone concentrations, using assays validated for domestic dogs, hypothyroidism was diagnosed presumptively, and therapy with levothyroxine sodium (0.022 mg/kg p.o. b.i.d.) was initiated. Haircoat, body weight, appetite, and activity level improved within 30 days. The levothyroxine dose was decreased twice (to 0.018 mg/kg p.o. b.i.d. and then to 0.011 mg/kg p.o. b.i.d.) during the course of treatment based on monitoring of serum T4 and fT4ED concentrations. After euthanasia for severe refractory lameness, postmortem examination revealed bilateral thyroid lobe enlargement and a fluid-filled cyst within the right lobe. Histologically, colloid goiter was present in both lobes, and a follicular cystadenoma had replaced one third of the cranial pole of the right lobe. The goiter and cystadenoma likely contributed to the hypothyroid condition in this bear and fT4ED was a more sensitive indicator of hypothyroidism than was T4. The recommended canine dosage of levothyroxine may be too high for the treatment of hypothyroidism in American black bears; 0.011 mg/kg p.o. b.i.d. may be a more appropriate dosage.

A 9-year-old cat with hyperthyroidism was referred for radioactive iodine treatment. The cat also had a ventral cervical mass that the owners reported had been present for several years and had increased in size during the past few weeks. On physical examination, the mass was found to have caused lateral displacement of the trachea, esophagus, jugular vein, and common carotid artery. The mass was aspirated and was determined to be cystic in nature. Concentrations of thyroid hormones in the cystic fluid were similar to serum concentrations, and nuclear scintigraphy revealed thyroactive tissue lining the cyst wall. Magnetic resonance imaging suggested that the cyst originated from the right lobe of the thyroid gland. The cat was treated with sodium iodide I 131 but died 4 days later, presumably as a result of aspiration of gastric or esophageal contents. A necropsy was not performed, but histologic examination of a biopsy specimen of the mass indicated that it was a cystic thyroid adenoma.

The incidence and morphology of thyroid neoplasms in different strains and stocks of rats are reported. The frequency of thyroid tumours varied to a great extent between different strains of rats. Low incidences were observed in DA/Han (0.85 per cent) and BDII/Han rats (1.25 per cent), while somewhat higher incidences occurred in Han:WIST rats (7.3 per cent). The highest number of thyroid tumour-bearing rats was found in the Han:SPRD stock (55.5 per cent). Thyroid neoplasms were classified histologically as polymorphofollicular adenomas, papillary adenomas, cystadenomas, polymorphofollicular carcinomas, papillary carcinomas, C-cell adenomas and C-cell carcinomas (medullary carcinomas). C-cell neoplasms were predominant in Han:SPRD rats (93.0 per cent), while the majority of tumour-bearing Han:WIST rats (61.4 per cent) had follicular tumours.

From 1964 to 1973, 370 tumors were collected from cows of unknown age. Ten (2.7%) of these were primary thyroid tumors. Three were malignant. The benign tumors were solitary encapsulated adenomas in the parenchyma with more or less defined trabeculae, tubular, and microfollicular pattern. One of the malignant tumors was a cystic papillary adenocarcinoma, and two were small cell carcinomas consisting of small, sometimes binuclear, pleomorphic cells.