3d Render of the Isthmus of the Uterus

Description

Anteriorly, the uterine corpus narrows into the uterine isthmus, a short segment of myometrium and endometrium positioned immediately superior to the cervix and inferior to the uterine body. Externally, the contour change sits between the broader fundus and body above and the more cylindrical cervix below, with the uterine horns and proximal uterine tubes expected superolaterally near the fundus. Laterally, the uterine margins lead toward the broad ligament attachments, while the inferior uterine segment blends into the supravaginal cervix at the level of the internal os region. A boundary you can teach from. Clinically, the isthmus corresponds to the nonpregnant internal os area and becomes the lower uterine segment in pregnancy, the tissue plane most relevant to a low transverse cesarean incision and its relationship to the bladder reflection and vesicouterine pouch. Hypertrophic scarring and thinning at this site underlie cesarean scar niche (isthmocele), a recognized cause of postmenstrual spotting and secondary infertility, and the isthmus is also the target region assessed when describing cervical competence and internal os dilation on ultrasound. Orientation matters here, because small differences in where you place the cervicoisthmic junction change how learners interpret normal anatomy versus pathology. Use this rendering to anchor lectures in gynecologic anatomy, obstetrics modules on lower uterine segment formation, and publisher figures that need a clean external landmark for the cervix versus uterine body without crowding the page with internal mucosal detail. It also suits patient education materials that explain where a cesarean scar sits relative to the womb and cervix. Anatomical accuracy verified by SciePro's Medical Advisory Board.