The relationship between Tc-99(m)-sestamibi uptake and ultrastructural cell types of thyroid tumours

Although several hypotheses have been suggested regarding the accumulation of Tc-99(m)-sestamibi in rumours, the exact uptake mechanism is still a mat ter of discussion. We investigated ultrastructural cell type of thyroid tum ours by electron microscopy (EM) and compared them with uptake of Tc-99(m)- sestamibi. Thyroid scintigraphy with Tc-99(m)-sestamibi was performed on 25 patients who displayed a cold nodule on previous pertechnetate scintigraph y. Tumour-to-thyroid (T/N) uptake ratio was measured semiquantitatively. Su rgery was performed in all patients and cytological evaluations were done b y EM. Histopathology revealed six papillary carcinomas, 16 follicular adeno mas and three Hurthle cell tumours. Thyroid cells were classified as A and B cells using EM. The cytoplasm of an A cell has the normal amount of mitoc hondria, whereas cytoplasm of a B cell (mitochondria-rich oxyphilic cell) c ontains abundant mitochondria. The median T/N ratio on the early scan for a n A-cell tumour was 1.21 (range, 0.74-3.2), late T/N ratio was 1.25 (range, 0.72-3.85). The T/N ratio for the B-cell tumours was 1.42 (range, 0.6-3.6) on the early scan and 1.18 (range, 0.64-5.58) on the late scan. There was no statistically significant difference between T/N ratios of A- and B-cell tumour groups. A significant difference was also not seen between early an d late T/N ratios. According to our findings, Tc-99(m)-sestamibi accumulate s in thyroid rumours with both A and B cells, therefore these results sugge st that the mitochondrial content of tumours is not only responsible for se stamibi uptake and retention. ((C) 2001 Lippincott Williams & Wilkins).