Two cases of thyroid neoplasia were diagnosed in privately owned raccoons. The first case involved a 9-year-old female spayed raccoon that presented with a palpable cervical mass. A complete blood count, biochemistries, chest radiographs, and total T-4 were within normal limits. A pertechnetate thyroid scan was consistent with non-functional thyroid neoplasia. A thyroidectomy was performed, and histopathology demonstrated follicular adenocarcinoma. The mass locally recurred twice after thyroidectomy, and currently there is evidence of pulmonary metastases.
The second case involved an 11-year-old female spayed raccoon. Ultrasound showed bilateral cystic masses in the area of the thyroids. Total T-4 was elevated, while clinical pathology and chest radiographs were unremarkable. A thyroid scan demonstrated bilateral infiltrative neoplasia. No evidence of renal insufficiency was seen after a 3-week trial of methimazole gel (0.1 ml of 25 mg/ml gel applied inside alternating ears BID). A right thyroidectomy and partial left thyroidectomy were performed, leaving a grossly normal portion of the left thyroid. Histopathology displayed bilateral cystic follicular adenomatous hyperplasia. At a recheck exam 4 weeks post-op, the total T-4 had increased; therefore, methimazole was reinitiated, decreasing the dose to once daily because the total T-4 the day of surgery was low.
Thyroid pathology has been documented in raccoons in Europe but is not reported in the United States.2 Thyroid neoplasia in raccoons can occur as a non-functional adenocarcinoma, as is commonly reported in dogs, or as a functional adenoma, as is commonly reported in cats.1 Raccoons with adenocarcinomas should be evaluated for pulmonary metastasis.
1. Ettinger, S.J. and E.C. Feldman (eds.). 2000. Textbook of Veterinary Internal Medicine, 5th ed. W. B. Saunders Co., Philadelphia, Pennsylvania.
2. Wisser, J. 1995. Zum vorkommen von thyreopathien bei waschbaeren (Procyon lotor). Verh. Erkrank. Zoo-Wildt. 37: 435–442.