Isthmus

ISTHMUS (from Greek isthmos - neck), an anatomical term for designating those narrow places or isthmuses in solid and hollow organs which are to some extent boundaries between different parts of these organs. Thus, one speaks of the I. of the aorta at the place where the ductus arteriosus Botalli empties into it, of the I. faucium (the narrow space between the root of the tongue and the pharyngeal cavity, bounded by the lower edge of the soft palate, the pillars of the fauces, and the tonsils), of the I. of the body of the uterus (the narrowed part of the uterine cavity near the transition into the cervical canal), of the I. of the stomach at the place of transition of the body of the stomach into the pyloric region near the so-called vestibulum pyloricum. The areas of the I. are sometimes sites of predisposition for the development of certain pathological processes; thus, corresponding to the I. of the stomach, ulcers and cancers often arise; corresponding to the I. of the aorta, phenomena of stenosis are sometimes observed.