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K.Y. Lam, FRCPA, Department of Pathology, Queen Mary Hospital, Hong Kong (Hong Kong) Dear Sir, Although secondary tumors involving the kidneys are not uncommon, it is rare to find thyroid carcinoma giving rise to solitary renal metastasis. We describe such a case with atypical features. A 91-year-old Chinese woman presented with acute onset of epigastric pain and vomiting. She also suffered from parkinsonism, an old myocardial infarction and osteoar-thritis of the hip. Physical examination on admission showed features of dehydration and thyroid enlargement. Investigation indicated an increased white blood cell count (22.8 × 109/1), elevated urea (13.3mmol/l) and creatinine levels (174 μmol/l). The general condition of the patient deteriorated and she developed sudden cardiac arrest a few hours after admission. At autopsy, the cause of death was seen to be small bowel gangrene as a result of severe atherosclerosis of the superior mesen-teric artery. The thyroid was slightly enlarged and weighed 27 g. It had a multinodu-lar appearance. Besides, a 5-cm brown nodule was found incidentally in the middle pole of the left kidney (fig. 1). The nodule was well demarcated from the surrounding renal parenchyma. The cut surfaces were light brown, variegated and of a colloid-like substance. It had the gross appearance of tissue from the thyroid gland. Microscopic examination of both kidneys revealed senile nephrosclerosis with focal glomerulosclero-sis, tubular atrophy and retention cysts. Sections of the left kidney mass showed meta-static follicular carcinoma surrounded by a pseudocapsule. The thyroid gland showed a tiny focus of primary follicular carcinoma in the right lobe on reexamination. Both vascular and capsular invasion were present. Follicular carcinomas of the thyroid are known to have a high tendency to hematoge-nous spread. However, the authors could only find 10 cases in which renal metastases has been reported in follicular carcinomas of the thyroid [1-6]. The clinicopathological features were only available in 3 cases. The features of these cases and the present one are listed in table 1. All the patients were females. This is not surprising as follicular carcinomas were more commonly detected in women. It is also worth noting that there Fig. 1. A well-demarcated mass (arrows) was noted in the middle pole of the left kidney which has the gross appearance of thyroid tissue. Table 1. Renal metastases from thyroid follicular carcinoma Author Sex/age Presentation Years Site/size (diameter)