Thyroidectomy in dogs with thyroid tumors: Survival analysis in 144 cases (1994-2018).

BACKGROUND: Few studies have assessed predictors of outcome in dogs with thyroid tumors undergoing thyroidectomy. OBJECTIVE: To estimate the survival and identify prognostic factors in dogs with thyroid tumors treated by thyroidectomy. ANIMALS: A total of 144 client-owned dogs with thyroid neoplasia that underwent thyroidectomy. METHODS: Retrospective study. Data for analysis included hospital attended and year of surgery, signalment, thyroxine concentration, thyroid tumor features (lobe involvement, size, invasiveness, histopathological type), thrombosis, metastasis, additional surgery and therapy, administration of adjuvant chemotherapy. The association of predictors with survival (time from surgery to death) were assessed by calculating cause-specific hazard ratios (HRcs ) and 95% confidence intervals (CI). Causes of death were classified as thyroid-related or because of other cause. RESULTS: Overall median survival time was 802 days (CI95% = 723-1015 days); 89 dogs (77.4%) survived >500 days. Metastases were identified at admission in 12 (8.3%) dogs and were associated with higher thyroid cancer-related fatality (HR = 5.83, CI95% = 1.56-21.78; P = .009). Thrombosis occurred in 40 dogs and was associated with increased risk of death because of other cause (HR = 2.73, CI95% = 1.18-6.35; P = .019). Nonfollicular carcinoma (HR = 4.17, CI95% = 1.27-13.69; P = .018) and administration of chemotherapy (HR = 3.45, CI95% = 1.35-8.82; P = .01) were associated with higher risk of thyroid cancer-related death. CONCLUSIONS AND CLINICAL IMPORTANCE: Dogs with thyroid tumors undergoing thyroidectomy have a long life expectancy. Despite the rare presence of nonfollicular carcinoma and metastases, thyroidectomy should still be considered in some of these dogs.

Multiorgan metastases with massive bone involvement of a medullary thyroid carcinoma in a dog.

A 10-year-old mixed-breed male dog was referred for a subcutaneous mass on the ventral neck. Based on total-body computed tomography (TBCT), the mass was located in the left thyroid lobe. Further alterations included enlargement of the ipsilateral mandibular and prescapular lymph nodes (LNs). Surgical excision of the mass and enlarged LNs was performed. Histopathology and immunohistochemistry were consistent with a medullary (C-cell) thyroid carcinoma, with no evidence of nodal metastases. Surgery was considered curative, and no medical treatment was provided. Periodic follow-up rechecks were unremarkable. After 18 months, the dog exhibited lethargy, vomiting, anorexia, and hind leg stiffness. TBCT revealed polyostotic osteopathy, and cytology suggested a metastatic endocrine carcinoma. Due to the dog's poor clinical condition and prognosis, the owner elected euthanasia, and a necropsy was performed. Based on gross pathology, histopathology, and immunohistochemistry, multiple metastases of the previous thyroid carcinoma were diagnosed, involving the occipital bone, multiple vertebrae, left sacral wing, fourth right rib, left scapula, left humerus, intrathoracic LNs, lung, spleen, and adrenal glands. This report describes a case of medullary thyroid carcinoma with distant multiorgan metastases and massive bone involvement after a disease-free interval of 18 months.

Clinical outcomes of thyroid tumours with concurrent epithelial and mesenchymal components in 14 dogs (2006-2020).

BACKGROUND: While rare, multiple individual case reports have described mixed thyroid tumours in dogs containing both epithelial and mesenchymal neoplastic components. OBJECTIVES: In this retrospective case series, we describe the clinical presentation, treatment and outcome of 14 dogs of canine thyroid tumours with concurrent mesenchymal and epithelial neoplastic populations. METHODS: Fourteen cases were retrospectively abstracted from nine institutions. Histopathologic samples and reports were collected from 10/14 dogs and reviewed by a single board-certified anatomic pathologist. RESULTS: All 14 dogs had curative-intent surgery to remove the thyroid neoplasm. The most common surgery performed was a unilateral thyroidectomy (10/14 dogs). Postoperatively, systemic therapy was administered in eight dogs. Six dogs developed local recurrence with a median time to loco-regional recurrence of 53 days. Ten dogs developed metastatic disease with the most common metastatic site being the lungs (6/10 dogs), with a median time to metastasis of 93 days. Ten dogs were euthanised due to locoregional or distant progression of their mixed thyroid neoplasm. The overall median survival time was 156 days (95%CI: 49-244). The median survival time for dogs treated with adjuvant therapy was 189 days (95%CI: 24-244), whereas dogs without adjuvant therapy had a median survival time of 156 days (95%CI: 35-upper limit could not be calculated; p = 0.62). CONCLUSION: The thyroid tumours with both mesenchymal and epithelial components in this small sample set were associated with a poor prognosis after surgical excision with or without adjunctive therapy.

Outcome and postoperative complications in 73 dogs with thyroid carcinoma with gross vascular invasion managed with thyroidectomy.

Excellent outcomes have been reported following thyroidectomy for thyroid carcinoma in dogs, but outcomes for thyroid carcinomas with gross vascular invasion are poorly described. This study describes the clinical outcomes and complications in dogs with thyroid carcinomas with gross vascular invasion undergoing thyroidectomy. Medical records of dogs that underwent thyroidectomy between January 1st 2010 and December 31st 2019 were reviewed at 10 hospitals. Signalment, diagnostic data, primary and adjuvant treatments performed, and outcome were abstracted. Survival was calculated using Kaplan-Meier analysis. Multiple logistic regression was used to identify variables associated with disease-specific survival. Seventy-three dogs were included, of which 58 underwent unilateral thyroidectomy and 15 underwent bilateral thyroidectomy. Complications were reported in five dogs (three major, two minor; 6.8%) intraoperatively and 12 dogs (two major leading to death, 10 minor; 16.4%) postoperatively. Seven (9.6%) dogs developed locoregional recurrence at a median of 238 days postoperatively (range: 15-730 days). Distant metastasis was suspected or confirmed in nine dogs (12.3%) at a median of 375 days postoperatively (range: 50-890 days). Twenty-seven dogs (37%) received adjuvant therapy (chemotherapy: n = 21; radiotherapy: n = 6). Thirty-nine dogs were euthanized or died, with 20 deaths related to disease (n = 10) or of unknown cause (n = 10), 19 due to unrelated causes, and nine lost to follow-up. Median overall and disease-specific survival were 621 days and not reached respectively. One-year disease-specific survival rate was 82.5%. No variables were associated with disease-specific survival in our dataset. Surgery may be considered for loco-regional therapy in dogs with thyroid carcinoma with gross vascular invasion.

The outcome for feline non-hypersecretory thyroid carcinoma after thyroidectomy.

A 14-year-old neutered male cat was presented because of a left ventral cervical mass. Based on imaging, the mass was suspected to have a thyroid origin. There was no evidence of gross metastatic disease or hyperthyroidism. Left thyroidectomy alone was the treatment for this patient and a thyroid carcinoma was diagnosed on histopathology. At last follow-up, 831 days after surgery, there was suspicion of metastasis to the lungs and the cat had developed a right thyroid mass and hyperthyroidism. Key clinical message: This case report identifies a non-hypersecretory thyroid carcinoma. This is a rare diagnosis. The outcome with surgery alone was comparable to that reported for treatment with iodine131.

Issue à la suite d'une thyroïdectomie pour un carcinome thyroïdien non-hypersecréteur félin. Un chat mâle castré âgé de 14 ans fut présenté concernant une masse ventro-cervicale gauche. Basé sur l'imagerie, la masse était suspectée être d'origine thyroïdienne. Il n'y avait pas d'évidence macroscopique de métastases ou d'hyperthyroïdisme. Une thyroïdectomie gauche fut l'unique traitement pour ce patient et un carcinome thyroïdien fut diagnostiqué lors de l'examen histopathologique. Lors de la dernière visite de suivi, 831 jours après la chirurgie, il y avait un doute de métastases aux poumons et le chat avait développé une masse thyroïdienne droite et de l'hyperthyroïdisme.Message clinique clé :Ce rapport de cas identifie un carcinome thyroïdien non-hypersecrétoire. Il s'agit d'une condition rarement diagnostiquée. L'issue à la suite de seulement une chirurgie était comparable à ce qui est rapporté pour un traitement avec de l'iode131.(Traduit par Dr Serge Messier).

Hyperthyroidism in Cats: Considering the Impact of Treatment Modality on Quality of Life for Cats and Their Owners.

In cats, hyperthyroidism can be treated in 4 ways: medical management with methimazole or carbimazole, nutritional management (low-iodine diet), surgical thyroidectomy, and radioactive iodine (131I). Each form of treatment has advantages and disadvantages that should be considered when formulating a treatment plan for the individual hyperthyroid cat. Medical and nutritional managements are considered "reversible" or palliative treatments, whereas surgical thyroidectomy and 131I are "permanent" or curative treatments. The author discusses how each treatment modality could be the optimal choice for a specific cat-owner combination and reviews the advantages and disadvantages of each treatment option.

Updates on Thyroid Disease in Rabbits and Guinea Pigs.

Hyperthyroidism seems to be a rare, but likely underdiagnosed disease of guinea pigs (Cavia porcellus) and rabbits (Oryctolagus cuniculus). Diagnosis is confounded by nonspecific clinical signs, lack of validated assays, and species-specific reference intervals. With increasing English-language publications on the topic, naturally occurring thyroid disease is likely to be increasingly diagnosed in exotic small mammals. The most consistently observed clinical signs include weight loss with or without a change in appetite and a palpable cervical mass. Diagnosis is supported by elevated blood thyroxine concentrations. Treatment may include thyreostatic agents, radioactive iodine, or surgical thyroidectomy.

Complications and outcomes associated with unilateral thyroidectomy in dogs with naturally occurring thyroid tumors: 156 cases (2003-2015).

OBJECTIVE: To describe complications and outcomes of dogs undergoing unilateral thyroidectomy for the treatment of thyroid tumors. ANIMALS: 156 dogs undergoing unilateral thyroidectomy for a naturally occurring thyroid tumor. PROCEDURES: Dogs that underwent a unilateral thyroidectomy in 2003 through 2015 were included in a multi-institutional retrospective study. For each dog, information gathered through evaluation of electronic and paper records included perioperative complications, short-term outcome (survival to discharge from the hospital vs nonsurvival), and long-term outcome (survival time). RESULTS: In the perioperative period, complications occurred in 31 of the 156 (19.9%) dogs; hemorrhage was the most common intraoperative complication (12 [7.7%] dogs). Five of 156 (3.2%) dogs received a blood transfusion; these 5 dogs were among the 12 dogs that had hemorrhage listed as an intraoperative complication. Immediately after surgery, the most common complication was aspiration pneumonia (5 [3.2%] dogs). One hundred fifty-three of 156 (98.1%) dogs that underwent unilateral thyroidectomy survived to discharge from the hospital. One hundred-thirteen dogs were lost to follow-up; from the available data, the median survival time was 911 days (95% confidence interval, 704 to 1,466 days). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that unilateral thyroidectomy in dogs with a naturally occurring thyroid tumor was associated with a perioperative mortality rate of 1.9% and a complication rate of 19.9% and that hemorrhage and aspiration pneumonia were the most common complications. Long-term survival of dogs undergoing unilateral thyroidectomy for the treatment of thyroid tumors was not uncommon.

Primary hyperparathyroidism due to a cystic parathyroid adenoma in a cat.

A 15-year-old neutered female domestic shorthair cat was presented for weight loss, polydipsia/polyuria, and lethargy. A large fluctuant mass was palpated in the ventral right cervical region. Biochemistry results were consistent with primary hyperparathyroidism. Parathyroid hormone level in the fluid was higher to that observed in the plasma, consistent with a cystic parathyroid lesion. Right parathyroidectomy and thyroidectomy were performed without complications. Ionized calcium normalized within a few hours. Histopathology yielded a diagnosis of cystic parathyroid adenoma. Follow-up showed complete recovery of clinical signs and normalization of ionized calcium. This case shows an uncommon presentation of feline primary hyperparathyroidism secondary to a cystic parathyroid adenoma and is, to our knowledge, the first case presented with a large palpable mass in which parathyroid hormone concentration was measured. This report highlights the value of selective hormonal analyses of the cystic fluid to confirm the origin of the cystic lesion pre-operatively.

Use of a vessel-sealing device versus conventional hemostatic techniques in dogs undergoing thyroidectomy because of suspected thyroid carcinoma.

OBJECTIVE: To compare use of a vessel-sealing device (VSD) versus conventional hemostatic techniques in dogs undergoing thyroidectomy because of suspected thyroid carcinoma. DESIGN: Retrospective cohort study. ANIMALS: 42 client-owned dogs undergoing thyroidectomy because of suspected thyroid carcinoma. PROCEDURES: Medical records of dogs treated at 4 referral centers from 2010 through 2016 were reviewed, and information was obtained on patient signalment, surgical technique, tumor-specific factors, and operative duration. Postoperative hospitalization time and complications were compared between dogs grouped on the basis of hemostatic technique. RESULTS: Thyroidectomy was performed with a VSD in 23 dogs and with conventional hemostatic techniques (ie, ligatures, hemoclips, or electrocautery) in 19 dogs. Hemostatic technique (ie, use of a VSD vs conventional hemostatic techniques) was the only factor significantly associated with operative duration (median time, 28 vs 41 minutes). Postoperative hospitalization times and complication rates did not differ between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that use of a VSD, rather than conventional hemostatic techniques, in dogs undergoing thyroidectomy because of suspected thyroid carcinoma resulted in shorter operative times without significantly affecting complication rates or postoperative hospitalization times.

Changes in thyroid and renal function after bilateral thyroidectomy in cats.

BACKGROUND: Iatrogenic hypothyroidism might worsen the prognosis of cats with azotemic CKD after thyroidectomy. Varying thyroxine concentrations influence utility of creatinine in assessing renal function. Symmetric dimethylarginine (SDMA) has limited studies in cats with changing thyroid status. OBJECTIVES: Thyroid status is stable 6 months post-thyroidectomy. Symmetric dimethylarginine and creatinine are linearly associated without influence from total thyroxine concentration (tT4). ANIMALS: Electronic records of 2 first opinion practices were searched using the term "thyroidectomy" to include 81 client-owned cats that had undergone bilateral thyroidectomy. METHODS: Retrospective cross-sectional study assessing thyroid hormone concentrations of 68 cats within 6 months of surgery. A longitudinal study of thyroid status in 23 cats with >18 months follow-up post-thyroidectomy. A generalized estimating equation assessed the associations of bodyweight, tT4 and creatinine concentrations on SDMA concentration. RESULTS: Sixty-eight cats had follow-up within 6 months. Fifteen cats (22%) had persistent, or recurrent, hyperthyroidism and 33 cats (49%) were hypothyroid. Twenty-three of the euthyroid/hypothyroid cats had long-term follow-up (595-1955 days); 4 cats (17%) remained hypothyroid, 19 cats (83%) were euthyroid (often transiently), and 9 of 23 cats (44%) developed recurrent hyperthyroidism. Symmetric dimethylarginine and creatinine were linearly associated, but hyperthyroid cats had higher SDMA concentrations, relative to creatinine (P = .003). CONCLUSIONS AND CLINICAL IMPORTANCE: Cats have changes in thyroid function for years after bilateral thyroidectomy, with a high incidence of recurrent hyperthyroidism. Both SDMA and creatinine are affected by thyroxine concentrations, and the effect is greater in hyperthyroid cats.

Clinicopathological features and comorbidities of cats with mild, moderate or severe hyperthyroidism: a radioiodine referral population.

OBJECTIVES: This study sought to explore the clinicopathological features and comorbidities of cats with mild, moderate and severe hyperthyroidism in a radioiodine referral population. METHODS: Medical records were reviewed, along with results of serum biochemistry, urinalysis, systolic blood pressure and diagnostic imaging performed at the time of radioiodine referral. Cats were grouped by total thyroxine (TT4) levels as mildly (TT4 60.1-124.9 nmol/l), moderately (TT4 125-250 nmol/l) or severely (TT4 >250 nmol/l) hyperthyroid at the time of diagnosis and referral. RESULTS: Thirty percent (42/140) of the cats were <10 years old at diagnosis. In 24.3% (34/140), hyperthyroidism was diagnosed incidentally. The time between diagnosis and referral for radioiodine was significantly longer in cats with severe hyperthyroidism at the time of referral ( P = 0.004). An increase in severity group between the time of diagnosis and referral occurred in 38.6% (54/140) of cats. At referral, 54.3% (25/46) of cats with mild, 66.7% (42/63) with moderate and 80.6% (25/31) with severe hyperthyroidism were unstable despite ongoing medical or dietary management. The prevalence of cardiac abnormalities was significantly increased in cats with severe hyperthyroidism ( P = 0.014) compared with those with mild or moderate hyperthyroidism. There was no significant difference in the likelihood of renal disease ( P = 0.708) or hypertension ( P = 0.328) between the groups. CONCLUSIONS AND RELEVANCE: Incidental diagnosis of hyperthyroidism occurs commonly, potentially owing to increased disease screening. Cats with severe hyperthyroidism at referral were more likely to be chronically hyperthyroid with a history of poor stabilisation. This subset of patients was significantly more likely to have cardiac abnormalities. Thyrotoxic cardiomyopathy may ultimately affect patient suitability for curative treatments (radioiodine or thyroidectomy) owing to higher anaesthetic risks and potential for decompensation into congestive heart failure with the stress of travel and hospitalisation. Curative therapy should be considered before the development of severe hyperthyroidism.

Standing thyroidectomy in 10 horses.

OBJECTIVE: To describe a surgical technique for thyroidectomy in horses with thyroid neoplasia under standing sedation and local anesthesia. STUDY DESIGN: Retrospective study. ANIMALS: Client-owned horses (n = 10). METHODS: Medical records of horses with a history of thyroid enlargement were included in the study if thyroid gland enlargement was treated surgically via hemi- or bilateral thyroidectomy, with the horse standing and sedated. Data derived from follow-up clinical examination, performance level, recurrence, and cosmetic outcome were evaluated. RESULTS: Thyroid enlargement was unilateral in 8 and bilateral in 2 horses. Histopathological findings included adenomas (5/10), adenocarcinomas (2/10), cystic hyperplasia (2/10), and C-cell adenoma (1/10). No major complications were encountered during or after surgery. All horses resumed their previous level of exercise within 6 weeks. Recurrence was diagnosed in 1 horse, 7 months after excision, and a second surgery was required. Recurrent laryngeal nerve neuropathy and seroma formation subsequent to surgery were not recorded in any of the cases. CONCLUSION: Thyroidectomy can safely be performed with the horse standing and sedated with local anesthesia. CLINICAL RELEVANCE: Performing standing thyroidectomy does not increase intraoperative or postoperative complications and could be considered for horses with thyroid enlargement amenable to surgery.

Management and monitoring of hyperthyroid cats: a survey of Australian veterinarians.

Objectives This study sought to evaluate how Australian veterinarians approach management and monitoring of feline hyperthyroidism and compare these results with a similar survey recently performed in the UK. Methods An invitation to complete an online survey was sent to veterinarians in all states and territories of Australia. The survey comprised questions relating to management of hyperthyroidism, use of antithyroid drugs vs radioiodine treatment vs surgical thyroidectomy, in addition to demographic information for respondents. Results A total of 546 clinicians completed the survey. The most commonly preferred treatments for long-term management of feline hyperthyroidism were antithyroid medications (305/546; 56%) and radioiodine (210/546; 38%), with substantially more respondents selecting radioiodine when cost was removed as a consideration (425/546; 78%). However, most respondents had treated or referred few cases for radioiodine (median 2). Most veterinarians (500/546; 92%) used antithyroid medications either long term or prior to definitive treatment of hyperthyroidism. For medical management, 45% (244/546) of veterinarians used twice-daily carbimazole. Half of respondents (274/546) aimed to maintain the total thyroxine concentration anywhere within the laboratory reference interval in hyperthyroid cats without chronic kidney disease. Blood pressure monitoring was uncommon. Surgical thyroidectomy was rarely performed. Conclusions and relevance Radioiodine was more frequently preferred by Australian veterinarians compared with those in the UK, likely associated with greater availability, reduced cost and shorter hospitalisation times in this jurisdiction, although antithyroid medications were the most frequently used treatment modality. Barriers remain to its utilisation, however, including perceived cost, misconceptions with regard to expected success rate and accessibility. Recent changes to recommendations on the management and monitoring of hyperthyroid cats do not appear to have been widely adopted by veterinarians at this time.

Retrospective Evaluation of Hemithyroidectomy in 14 Horses.

OBJECTIVE: To describe the presentation, presurgical diagnostic findings, treatment, and outcome of horses with histologically confirmed, unilateral thyroid neoplasia. The complications, particularly laryngeal hemiplegia, were investigated. STUDY DESIGN: Retrospective case series. ANIMALS: Client-owned horses (n=14). METHODS: Medical records of horses presenting with a unilateral thyroid mass due to neoplasia from 2003-2015 were reviewed. Horses must have undergone preoperative clinical evaluations that included ultrasound examination of the mass and upper airway endoscopy. Short-term follow-up at 2 weeks after surgery and owner questionnaire for long-term follow-up at >6 months were completed. RESULTS: Fourteen horses aged 6-21 years were included. The majority of tumors were adenocarcinomas (11/14), mainly diagnosed in mares (9/14). Intraoperative complications included hemorrhage (1/14) and postoperative complications included seroma formation (4/14). No horse developed postoperative laryngeal hemiplegia. No horses developed clinical signs of metastases or a thyroid disorder long term (mean follow-up 4.9 years). All owners reported a successful long-term outcome. CONCLUSION: The clinical findings of thyroid neoplasia in horses are not associated with the diagnosis of malignancy. Complete surgical resection of the abnormal lobe prevents local recurrence of neoplastic thyroid tissue. The modified hemithyroidectomy technique preserves the function of the recurrent laryngeal nerve.

A rabbit model of fatal hypothyroidism mimicking "myxedema coma" established by microscopic total thyroidectomy.

Myxedema coma (MC) is a life-threatening endocrine crisis caused by severe hypothyroidism. However, validated diagnostic criteria and treatment guidelines for MC have not been established owing to its rarity. Therefore, a valid animal model is required to investigate the pathologic and therapeutic aspects of MC. The aim of the present study was to establish an animal model of MC induced by total thyroidectomy. We utilized 14 male New Zealand White rabbits anesthetized via intramuscular ketamine and xylazine administration. A total of 7 rabbits were completely thyroidectomized under a surgical microscope (thyroidectomized group) and the remainder underwent sham operations (control group). The animals in both groups were monitored without thyroid hormone replacement for 15 weeks. Pulse rate, blood pressure, body temperature, and electrocardiograms (ECG) were recorded and blood samples were taken from the jugular vein immediately prior to the thyroidectomy and 2 and 4 weeks after surgery. The thyroidectomized rabbits showed a marked reduction of serum thyroxine levels at 4 weeks after the surgical procedure vs. controls (0.50±0.10 vs. 3.32±0.68 µg/dL, p<0.001). Additionally, thyroidectomized rabbits exhibited several signs of hypothyroidism such as hypothermia, systolic hypotension, bradycardia, and low voltage on ECGs, compared with controls. Of the 7 rabbits with severe hypothyroidism, 6 died from 4 to 14 weeks after the thyroidectomy possibly owing to heart failure, because histopathologic examinations revealed a myxedema heart. In summary, we have established a rabbit model of fatal hypothyroidism mimicking MC, which may facilitate pathophysiological and molecular investigations of MC and evaluations of new therapeutic interventions.

Effects of feline hyperthyroidism on kidney function: a review.

Chronic kidney disease and hyperthyroidism are two commonly diagnosed conditions in the geriatric feline population, and are often seen concurrently. Management of both diseases is recommended; however, the physiologic implications of both diseases must be understood to ensure the most favorable outcome for each patient. This report reviews the complex interplay between hyperthyroidism and kidney function, as well as the effects of hyperthyroid therapy on kidney function.

Reptile Soft Tissue Surgery.

The surgical approach to reptiles can be challenging. Reptiles have unique physiologic, anatomic, and pathologic differences. This may result in frustrating surgical experiences. However, recent investigations provided novel, less invasive, surgical techniques. The purpose of this review was to describe the technical aspects behind soft tissue surgical techniques that have been used in reptiles, so as to provide a general guideline for veterinarians working with reptiles.

Identification and preservation of the parathyroid gland during total thyroidectomy in dogs with bilateral thyroid carcinoma: a report of six cases.

Simultaneous removal of bilateral thyroid tumors was performed while preserving the parathyroid gland in six dogs. At least one external parathyroid gland was identified in all dogs. In five cases, the external parathyroid gland and its blood supply were preserved intact. In one dog, the vessels supplying the external parathyroid gland had been invaded by the tumor, and the gland was thus removed and reimplanted into the sternohyoid muscle. That dog required postoperative treatment with oral calcium gluconate and vitamin D3. Local tumor recurrence was not observed in any of the cases. The mean survival time was 920 days. We found that the external parathyroid gland could be identified and preserved in most dogs undergoing total thyroidectomy.