MR features of ectopic pregnancy.

Ectopic pregnancy (EP), in which a fertilized ovum implants outside the uterine cavity, is the leading cause of pregnancy-related death in the first trimester. EP is usually suspected by a positive pregnancy test and an empty uterus on transvaginal sonography (TVS). Although TVS is the initial modality of choice, it may occasionally fail to demonstrate the implantation site. When TVS findings are indeterminate, magnetic resonance imaging (MRI) may provide better delineation of the focus of EP owing to its excellent tissue contrast. The key MRI features of EP include gestational sac (GS)-like structures that typically appear as a cystic sac-like structure, frequently associated with surrounding acute hematoma of distinct low intensity on T2-weighted images. In tubal pregnancy, an enhanced tubal wall on postcontrast images may be another diagnostic finding. Ruptured EP is inevitably associated with acute hematoma outside these structures. In intrauterine EP, recognition of the relationship between GS-like structure and the myometrium can aid in differentiating from normal pregnancy. Diagnostic pitfalls include heterotopic pregnancy, decidual changes in endometrial cyst and theca lutein cysts mimicking GS-like structures. Knowledge of a spectrum of clinical and MRI features of EP is essential for establishing an accurate diagnosis and determining appropriate management.