Exophytic pancreatic lymphoepithelial cyst incidentally detected in a differentiated thyroid cancer patient on whole-body I-131 scan: a case report

Background Radioiodine (I-131) whole-body scintigraphy (WBS) is a useful modality for identifying functionally preserved thyroid tissue and metastases from differentiated thyroid cancer (DTC); however, the specificity of I-131 uptake is limited, and its accumulation in the pancreas has not been well described. Case presentation A 70-year-old male patient with DTC who had previously undergone total thyroidectomy (pT3N1bM0 Stage IV) received radioiodine treatment at our facility. After treatment, an I-131 WBS revealed abnormal I-131 uptake in the head of the pancreas. Computed tomography identified a round hypodense mass (10 × 20 mm) adjacent to the pancreas head that was impervious to fluorodeoxyglucose ( 18 F-FDG) during subsequent 18 F-FDG-positron emission tomography. A diagnosis of pancreatic metastasis from the DTC could not be excluded; therefore, local resection was performed for diagnostic certainty and treatment. Histopathology confirmed the mass to be an exophytic lymphoepithelial cyst (LEC) of the pancreas. The patient also had a transient pancreatic leak which spontaneously resolved after surgery, and he was discharged from the hospital on postoperative day 8. Conclusion To the best of our knowledge, this is the first reported case of an exophytic pancreatic LEC producing a false-positive result during I-131 WBS. Knowledge of all potential I-131 false-positive findings may help improve the management of patients with DTC and circumvent misdiagnoses.