The uterine isthmus, the narrowest portion of the uterus, plays an essential role in female reproductive health and can be the site of several gynecological pathologies. Due to its strategic location, lesions in this region have unique characteristics and can lead to a wide variety of symptoms and diagnostic challenges. Diagnosis is usually made through imaging tests, such as ultrasound (US) or magnetic resonance imaging (MRI), with appropriate treatment depending on the precise identification of the type of lesion and evaluation of factors such as size, location, and risk of malignancy. This pictorial essay provides a comprehensive, image-rich review of multiple uterine isthmic lesions—including isthmoceles (cesarean scar defects) and their complications, fibroids in the isthmus, cesarean scar ectopic pregnancies (CSEP), isthmic endometriosis, adenomyosis/adenomyomas, post-curettage vascular malformations, niche-related intrauterine device (IUD) malposition, trophoblastic tissue implants, and endometrial polyps—highlighting their MRI appearances, epidemiological and clinical correlations, and management options.
