[A rare renal tumour : Ectopic thyroid tissue in the kidney].

During a nephrectomy of a nonfunctioning, tumour-bearing kidney we found ectopic thyroid tissue in the kidney. This location of ectopic thyroid tissue has not been described before. In general, ectopic thyroid tissue is uncommon and rather found in the cervical region or upper mediastinum. A 131-iodine whole-body scan is the most precise method to detect the presence of ectopic thyroid tissue. It is often difficult to distinguish between benign and differentiated malignant thyroid tissue.