Diagnostic clue of nodular fasciitis mimicking metastasis in papillary thyroid cancer, mismatching findings on¹⁸F-FDG PET/CT and¹²³I whole body scan: A case report

This study reports a case of nodular fasciitis incidentally detected in a patient with papillary thyroid cancer. A 47-year-old woman underwent a total thyroidectomy and radioactive iodine therapy for papillary thyroid cancer. On a follow-up fluorodeoxyglucose (¹⁸F-FDG) PET/computed tomography (CT) scan after 12 months, a focal ¹⁸F-FDG-avid lesion was incidentally detected in the paraspinal muscle. It was well-enhanced on CT and magnetic resonance imaging, indicating metastasis. However, the lesion was not iodine avid on the ¹²³I whole body scan, which favored benign etiology over metastasis from thyroid cancer. For pathological confirmation, surgical excision was performed and the paraspinal lesion was finally confirmed as nodular fasciitis. Therefore, it was suggested that nodular fasciitis may be included in the differential diagnosis of a ¹⁸F-FDG avid/iodine non-avid soft tissue lesion in patients with thyroid cancer. In such circum-stances, ¹²³I whole body scans may serve a role in non-invasive work-up, and prevent unnecessary surgical procedures.