False-positive 131I whole-body scan and shrinkage of a pulmonary aspergilloma under 131I therapy in a patient with thyroid cancer

Radioiodine sinus uptake related to mucosal thickening or aspergilloma: a case series of an unrecognized event well evidenced by SPECT/CT

Background

False-positive radioiodine (RAI) uptake related to chronic sinusitis and mucocele has only rarely been reported in patients with differentiated thyroid cancer (DTC) even with the recent use of single photon emission tomography with computed tomography (SPECT/CT) acquisition. No other etiology of sinus RAI uptake has been mentioned to date.

Objectives

We report five cases of DTC patients with sinus RAI uptake on post-RAI scintigraphy. SPECT/CT clearly localized RAI uptake either in the sphenoid, the maxillary or the frontal sinus and highly suspected mucosal thickening in four patients and sinus aspergilloma in one patient.

Conclusion

These data confirm the possibility of false-positive sinus RAI uptake, provide a new cause of such benign uptake, i.e. sinus aspergilloma, and demonstrate the clinical relevance of head and neck SPECT/CT acquisition in the diagnosis of such uptake. Nuclear medicine physicians should be aware of this pitfall when interpreting post-RAI scintigraphy.

Microbial Transformation of Iodine: From Radioisotopes to Iodine Deficiency

Iodine is a biophilic element that is important for human health, both as an essential component of several thyroid hormones and, on the other hand, as a potential carcinogen in the form of radioiodine generated by anthropogenic nuclear activity. Iodine exists in multiple oxidation states (-1, 0, +1, +3, +5, and +7), primarily as molecular iodine (I₂), iodide (I^-), iodate [Formula: see text] , or organic iodine (org-I). The mobility of iodine in the environment is dependent on its speciation and a series of redox, complexation, sorption, precipitation, and microbial reactions. Over the last 15years, there have been significant advances in iodine biogeochemistry, largely spurred by renewed interest in the fate of radioiodine in the environment. We review the biogeochemistry of iodine, with particular emphasis on the microbial processes responsible for volatilization, accumulation, oxidation, and reduction of iodine, as well as the exciting technological potential of these fascinating microorganisms and enzymes.

Pulmonary aspergilloma mimicking metastasis from papillary thyroid cancer

BACKGROUND

Whole-body scans (WBSs) based on diagnostic or therapeutic doses of I-131 can visualize metastatic lesions in thyroid cancer patients who have undergone total thyroidectomy. However, a variety of unusual lesions may cause false-positive results, and therefore, careful evaluation of abnormal scans is imperative to avoid unnecessary surgical removal or high-dose radioiodine treatment. Here, we report a patient with pulmonary aspergilloma mimicking metastasis of thyroid cancer on WBS.

SUMMARY

A 53-year-old woman with papillary thyroid cancer stage III (T1N1aM0) who had undergone total thyroidectomy and 150 mCi of radioiodine treatment for remnant ablation was found to have focal intense radioiodine accumulation in the left lung field by WBS, suggestive of pulmonary metastasis, at 5 days after I-131 administration. Whole-body F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) and Tc-99m methoxyisobutyl isonitrile scans showed no remarkable tracer accumulation at the pulmonary nodule. An enhanced chest CT scan demonstrated a nonenhancing pulmonary nodule with an air-crescent sign suggestive of pulmonary fungus ball. A subsequent blood test for precipitating antibodies to Aspergillus antigens produced a result of 29.9 U/mL (reference range: 0-8 U/mL). The patient was clinically diagnosed as having pulmonary aspergilloma based on serologic test and radiologic imaging results.

CONCLUSION

Extreme caution should be exercised when interpreting abnormal radioiodine WBS findings when the serum thyroglobulin is normal and imaging characteristics indicate a benign condition. Pulmonary aspergilloma is a cause of a false-positive lesion when radioiodine WBSs are performed.