Isolated Metastasis to Spleen-Stomach Space From Follicular Thyroid Cancer Combined With a Benign Subcutaneous Nodule on ¹⁸F-FDG PET/CT and ¹³¹I Scintigraphy

A 40-year-old woman with follicular thyroid cancer underwent a systemic PET/CT evaluation before operation and then received total thyroidectomy and radioactive I-131 ablation therapy. Posttreatment imaging of I-131 whole-body scan with SPECT/CT showed that metastasis on the spleen-stomach space coexists with mimicking subcutaneous metastasis, considering their level of I-131 accumulation and morphological changes on PET/CT. However, histopathology confirmed the subcutaneous lesion of fibrous hyperplasia by fine-needle aspiration. This case demonstrates a vital role of SPECT/CT in the diagnosis of metastatic thyroid cancer and mimicking metastasis.