Pulmonary Recurrence of Colorectal Mucinous Adenocarcinoma and Sarcoidosis on 18F-FDG PET/CT.

A 67-year-old woman, previously diagnosed with pulmonary sarcoidosis and sigmoid colon mucinous adenocarcinoma with pulmonary metastasis, showed an enlarged pulmonary nodule in routine follow-up. Because of the absence of treatment for either condition over the past 3 years, the nodule raised concerns of cancer recurrence or sarcoidosis progression. Its distinctive 18F-FDG PET/CT appearance, compared with other pulmonary lesions, suggested a mucinous histology. The diagnosis was confirmed by pathological examination. This emphasizes the importance of knowledge of the 18F-FDG PET/CT phenotype of neoplastic histological variants to address challenging diagnostic scenarios.