Clinical analysis of a patient with a benign lesion of the pharynx misdiagnosed as functional thyroid cancer metastasis.

Papillary thyroid carcinoma (PTC) usually has a lower malignancy rate and better prognosis than other types of thyroid cancer. It tends to spread through the lymphatic system, and the percentage of lymph node metastasis to the neck is 50-70% in patients at the time of diagnosis. Iodine-131 (131I) whole-body scanning is very valuable in the diagnosis and positioning of functional metastatic lesions. However, a variety of comprehensive test results are frequently required to make an appropriate judgment. The present case report describes the case of a patient with PTC where a benign lesion of the pharynx was misdiagnosed as functional metastasis. Some remnant thyroid tissue and an abnormal accumulation of 131I in the oropharynx and at the right side of the neck were observed by 131I whole-body scanning one week after the first therapeutic dose. Following the second therapeutic dose, quasi-circular trapping of 131I by the pharynx persisted. Magnetic resonance imaging enhanced scanning of the oropharynx showed markedly uneven enhancement inside the lesion, and it was considered as a metastatic lesion. However, the serological test results of the patient revealed that there was no increase in the thyroglobulin level and did not support the diagnosis of progressive disease. Therefore, a biopsy on the lesion was conducted under local anesthesia. The histopathological examination exhibited salivary gland tissue and chronic inflammation. Thus, it was necessary to analyze the imaging results, as well as serologic testing outcomes and pathological findings comprehensively, in order to make the correct diagnosis.