Clinical and Pathological Features of Canine Metastatic Adrenocortical Carcinoma

Background: Adrenocortical carcinomas (ACC) are uncommon in dogs. ACC often invade the posterior vena cava wall and the advential layer of the abdominal aorta; however, metastases to distant organs are rare. Most dogs with ACC show clinical signs of Cushing`s syndrome in a similar way with signs reported in humans. The aim of this study is to report three cases of metastatic ACC in dogs and their clinical and pathological features.Cases: This report describes three cases of metastatic adrenocortical carcinoma (ACC) in dogs diagnosed post mortem through histopathological examination. The animals presented no signs of adrenal hormones overproduction. Case 1. A 13-year-old intact, mixed breed female dog was presented with a history of progressive hepatomegaly during the last four months. The animal was submitted to an exploratory laparotomy, but due to anesthetic complications no tissue specimen was sampled and after one week, the animal died. The necropsy examination showed an increased left adrenal (3 cm in diameter), multiple yellow to whitish nodules measuring 1 to 2 cm of diameter in the lung and severe hepatomegaly. The histopathological diagnosis was established as ACC with pulmonary metastasis. A severe and diffuse accumulation of gly­cogen in hepatocytes was also observed in Periodic acid-Schiff (PAS) staining. Case 2. A 9-year-old female intact, mixed breed dog was presented showing ataxia, left head-tilt and dyspnoea. The clinical signs progressed and the dog died after four days. The gross examination showed a diffuse increase of the left adrenal gland (2 cm of diameter) accompanied by a yellowish colour at cut surface; diffuse bronchopneumonia and cerebral and renal discrete congestion. The microscopi­cal diagnosis was ACC with kidney and CNS metastasis. Case 3. A 16-year-old male, intact, Poodle dog was presented with apathy, anorexia, vomiting and diarrhoea in the last two days. The animal was submitted to treatment, but the clinical signs progressed and the dog died. In the necropsy exam an increased right adrenal gland was observed (5 cm of diameter) showing multiple yellowish nodules when sectioned. The lung showed multiple whitish nodules mainly in pleural region. In the histopathological examination, the definitive diagnosis was ACC with pulmonary metastasis.Discussion: Most of adrenocortical tumours in dogs are functional and secrete excessive amounts of cortisol; therefore commonly animals show clinical signs of Cushing`s syndrome. In the present cases, the animals showed no clinical evidence of hormonal changes. Well-differentiated neoplastic cells were observed in cases 1 and 2, whereas in case 3 tumorous cells showed marked features of malignancy as cellular pleomorphism, binucleation, high mitotic index and atypical mitosis. Despite mild anaplastic features observed on cases 1 and 2, animals showed focus of metastases in lung, kidney and CNS. Apparently features of malignancy in ACC were not associated to the risk of metastasis development, indicating that even well-differentiated ACC may metastasize to distant organs. Metastases of ACC to distant sites are rare in dogs and there was no previous report of metastasis to CNS as observed in case 2. Canine ACC are considered uncommon tumours, how­ever, they should be included in the differential diagnosis of mass in the abdominal cavity since the animals may show no clinical signs of adrenocortical hormones overproduction.Keywords: adrenal tumours, adrenocortical hormones, metastases, dog