The purpose of this study is to evaluate benign and/or malignant thyroid tumors with 201TI thyroid scan. We studied 76 cases of histologically verified thyroid tumors, all seen as cold nodules on the 123I thyroid scan. 201TI thyroid scan was performed 5–15 minutes (early scan) and 3–5 hours (delayed scan) after intrayenous administration of 1.5–2.0 mCi of 201TI. In 35 (94.6%) of 37 malignant tumors (anaplastic carcinoma, six; papillary carcinoma, 23; follicullar carcinoma, five; epidermoid carcinoma, one; malignant lymphoma, 1), 201TI accumulated in the cold nodule of the 123I thyroid scan on both early and delayed scans. On the other hand, the delayed 201TI scan was negative in 35 out of 39 (89.7%) benign tumors. Employing early and delayed 201TI scans, we were able to differentiate most malignant thyroid tumors from those which were benign. False‐negative and ‐positive cases are discussed.

We present an unusual case of a cervical thymoma arising from an undescended thymus, which showed a remarkable accumulation of Thallium-201 Chloride on scintigraphy.

When the bone scintigram reveals high diffuse skeletal activity, it may be misinterpreted as normal. Some authors have reported such scintigrams in articles entitled "Significance of absent or faint kidney sign on bone scan" and "False negative bone scintigram". Three cases with bone metastasis showing high diffuse skeletal activity are presented in this paper. The recognition of abnormally high diffuse skeletal activity on bone scintigrams is discussed. The exposure time of all three cases was short when compared with normal cases, when the bone image was taken with a preset count. Therefore, exposure time is very important for objective differentiation between the cases showing high diffuse skeletal activity and normal cases.

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