To better understand the anatomy of interstitial pregnancy. The interstitial part of the fallopian tube is the proximal portion located into the muscular wall portion of the uterus. Pregnancies implanting in this site are considered interstitial or cornual. The interstitial part of the tube has a significant capacity to expand before rupture because of its thickness; rupture can result in massive hemorrhage from the vascular anastomoses between the ovaries and uterine arteries.