An anastomosis (plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between
leaf veins, or
streams. Such a connection may be normal (such as the
foramen ovale in a fetus's heart) or abnormal (such as the
patent foramen ovale in an adult's heart); it may be acquired (such as an
arteriovenous fistula) or innate (such as the arteriovenous shunt of a
metarteriole); and it may be natural (such as the aforementioned examples) or artificial (such as a
surgical anastomosis). The reestablishment of an anastomosis that had become blocked is called a reanastomosis. Anastomoses that are abnormal, whether
congenital or acquired, are often called
The term is used in
Anastomosis: medical or Modern Latin, from Greek ἀναστόμωσις, anastomosis, "outlet, opening", Gr ana- "up, on, upon", stoma "mouth", "to furnish with a mouth".
 Thus the -stom- syllable is cognate with that of
stoma in botany or
stoma in medicine.