**5. Pathologic lesions might show false positive radioiodine uptake**

A variety of pathologic lesions producing a false positive radioiodine whole body scan have been reported and contrary to the physiologic uptakes that usually do not create diagnostic confusion, they might be tricky enough to cause some patients to undergo unnecessary fruitless invasive surgical or high dose radioiodine treatment.(Mitchell, Pratt et al. 2000) The not uncommon pathologic lesions showing radioiodine uptake are cystic, inflammatory, non-thyroidal neoplastic diseases. Cystic lesions in various organs can accumulate radioiodine and the mechanism of the uptake is passive diffusion of the tracer into the cysts. Radioiodine accumulation in ovarian, breast and pleuropericardial cysts has been reported.

Physiologic and False Positive Pathologic Uptakes on Radioiodine Whole Body Scan 17

Fig. 21. Pathologic uptake of radioiodine in a pulmonary fungus ball. There was also noted tracer uptake in the thyroid bed area (by the remnant tissue of the gland) and the liver (by

anterior posterior CT

Fig. 22. Pathologic uptake of radioiodine in a skin wound. There was tracer uptake in the left lower leg where the skin wound was located. There was tracer uptake in the salivary gland (by the NIS expression of the glands), thyroid bed (by the remnant tissue of the gland) and the liver (by metabolism of the radioiodinated thyroglobulin and thyroid hormones).

External contamination by physiological or pathological body secretions or excretions can cause positive radioiodine uptake and this mimics metastatic involvement of differentiated thyroid cancer.(Bakheet, Hammami et al. 2000) Sweat, breast milk, urine, vomitus and nasal, tracheobronchial, lacrimal, salivary secretions and faeces contain radioiodine and their contamination on the hair, skin or clothes can be misinterpreted as metastasis of thyroid cancer.(Shapiro, Rufini et al. 2000) Any focus of radioiodine uptake that cannot be explained by physiological or pathological causation must also be suspected as arising from contamination by secretions. Fortunately, the contaminations are usually easily recognized by their pattern and acquiring images after removing the contamination with decontaminating procedures and with taking the stained clothes off. However, unusual patterns of contamination might occur and suspecting uptake lesions as contamination would be difficult.

**6. Contaminations by physiological secretions** 

metabolism of the radioiodinated thyroglobulin and thyroid hormones).

anterior

(Shapiro, Rufini et al. 2000) Effusion of the pleural, pericardial and peritoneal cavities can also have radioiodine uptake by the same mechanism.(Shapiro, Rufini et al. 2000)

A variety of inflammatory and infectious disease can have radioiodine accumulation by increased blood flow that delivers increased levels of radioiodine to the site, and enhanced permeability of the capillary that increases diffusion of the tracer to the extracellular water space.(Shapiro, Rufini et al. 2000) Radioiodine accumulation in bronchiectasis, pulmonary aspergilloma, skin wound, arthritis, paranasal sinusitis, skin infection, myocardial infarction and dacryocystitis has been reported.(Shapiro, Rufini et al. 2000; Ahn, Lee et al. 2011)

Even though only a minority of such lesions accumulate the tracer, a variety of nonthyroidal neoplasms are also known to take up radioiodine. The suggested mechanisms are i) a tumour expression of the NIS, which actively accumulates the tracer and ii) increased vascularity and enhanced capillary permeability that might be secondary to the inflammatory response associated with the neoplasm.(Mitchell, Pratt et al. 2000; Shapiro, Rufini et al. 2000) Radioiodine accumulation in breast cancer, gastric adenocarcinoma, bronchial adenocarcinoma, bronchial squamous carcinoma, salivary adenocarcinoma, teratoma, ovarian adenocarcinoma and meningioma has been reported.(Shapiro, Rufini et al. 2000)

Fortunately, false positive uptake on a radioiodine whole body scan can be interpreted with using the serum thyroglobulin value, which is very sensitive marker for residual or recurrent thyroid cancer. Therefore, the false positive uptake usually does not cause a diagnostic dilemma for experienced practitioners. The clinical features and other imaging studies can also help to distinguish the false positive pathologic lesions from true positive metastatic thyroid cancer lesions.(Mitchell, Pratt et al. 2000; Ahn, Lee et al. 2011)

Fig. 20. Pathologic uptake of radioiodine in the bronchectatic lesions of both lungs. There was also noted intense tracer uptake in the thyroid bed area (by the remnant tissue of the gland).

(Shapiro, Rufini et al. 2000) Effusion of the pleural, pericardial and peritoneal cavities can

A variety of inflammatory and infectious disease can have radioiodine accumulation by increased blood flow that delivers increased levels of radioiodine to the site, and enhanced permeability of the capillary that increases diffusion of the tracer to the extracellular water space.(Shapiro, Rufini et al. 2000) Radioiodine accumulation in bronchiectasis, pulmonary aspergilloma, skin wound, arthritis, paranasal sinusitis, skin infection, myocardial infarction

Fortunately, false positive uptake on a radioiodine whole body scan can be interpreted with using the serum thyroglobulin value, which is very sensitive marker for residual or recurrent thyroid cancer. Therefore, the false positive uptake usually does not cause a diagnostic dilemma for experienced practitioners. The clinical features and other imaging studies can also help to distinguish the false positive pathologic lesions from true positive

metastatic thyroid cancer lesions.(Mitchell, Pratt et al. 2000; Ahn, Lee et al. 2011)

Fig. 20. Pathologic uptake of radioiodine in the bronchectatic lesions of both lungs. There was also noted intense tracer uptake in the thyroid bed area (by the remnant tissue of the

CT

anterior

right lateral left lateral

also have radioiodine uptake by the same mechanism.(Shapiro, Rufini et al. 2000)

and dacryocystitis has been reported.(Shapiro, Rufini et al. 2000; Ahn, Lee et al. 2011) Even though only a minority of such lesions accumulate the tracer, a variety of nonthyroidal neoplasms are also known to take up radioiodine. The suggested mechanisms are i) a tumour expression of the NIS, which actively accumulates the tracer and ii) increased vascularity and enhanced capillary permeability that might be secondary to the inflammatory response associated with the neoplasm.(Mitchell, Pratt et al. 2000; Shapiro, Rufini et al. 2000) Radioiodine accumulation in breast cancer, gastric adenocarcinoma, bronchial adenocarcinoma, bronchial squamous carcinoma, salivary adenocarcinoma, teratoma, ovarian adenocarcinoma and meningioma has been reported.(Shapiro, Rufini et

al. 2000)

gland).

Fig. 21. Pathologic uptake of radioiodine in a pulmonary fungus ball. There was also noted tracer uptake in the thyroid bed area (by the remnant tissue of the gland) and the liver (by metabolism of the radioiodinated thyroglobulin and thyroid hormones).

Fig. 22. Pathologic uptake of radioiodine in a skin wound. There was tracer uptake in the left lower leg where the skin wound was located. There was tracer uptake in the salivary gland (by the NIS expression of the glands), thyroid bed (by the remnant tissue of the gland) and the liver (by metabolism of the radioiodinated thyroglobulin and thyroid hormones).
