Spontaneously occurring ectopic thymus in a 10 week-old Wistar rat

A spontaneously occurring ectopic thymus in a 10-week-old male Wistar rat was observed in this study. At necropsy, the rat showed no lesions except the thymus was missing in its original location. Microscopical examination of all organs revealed no abnormal findings except the presence of ectopic thymus on the thyroid and parathyroid. Thymus contained densely packed various sized lymphocytes and scanty population of epithelial cells. Nuclei were hyperchromatic and oval to spherical in shape. No histomorphological alterations were found in the thymus, thyroid and parathyroid.