Heterotopic thyroid tissue at the porta hepatis in a fetus with trisomy 18

Heterotopic thyroid tissue at the porta hepatis in a fetus with trisomy 18 is described. The fetus had an eutopic thyroid gland without any abnormalities. The heterotopic thyroid was found at the porta hepatis and showed histological features similar to the eutopic thyroid. Immunohistochemically, the heterotopic follicles were positive for thyroglobulin, but no calcitonin-positive cells were found. Intra-abdominal heterotopic thyroid is exceedingly rare in locations other than the ovary, and to our knowledge, this is the first report of a fetal case. The present case provides clear evidence that abdominal heterotopic thyroid can occur as a congenital anomaly. Migration abnormality of the median anlage of the thyroid is the most likely histogenesis of heterotopic thyroid at the porta hepatis.