The Alien Antenna Sign: Physiological ⁶⁸Ga-FAPI Uptake in the Round Ligament.

Abstract

68 Ga-FAPI PET/CT has emerged as a promising molecular imaging modality targeting cancer-associated fibroblasts, rather than tumor cells. We report a novel physiological uptake pattern on 68 Ga-FAPI PET/CT in a 56-year-old woman with newly diagnosed invasive lobular carcinoma of the right breast undergoing staging. 68 Ga-FAPI PET/CT demonstrated intense tracer uptake in the primary right breast tumor and a right level I axillary lymph node, consistent with FAPI expression in the primary malignancy and suspicious nodal involvement. In addition, bilateral linear, rope-like tracer uptake extending from the uterus through the inguinal canals along the round ligaments was observed, creating an "Alien Antenna" appearance. Recognition of this physiological uptake pattern is essential to avoid misinterpretation as peritoneal or metastatic disease.