An odyssey through salpingitis isthmica nodosa.

Salpingitis isthmica nodosa (SIN) is a nodular swelling of the isthmic segment of the fallopian tube. It is of unknown aetiology and is usually an acquired pathologic condition resulting from direct invasion of the muscularis layer by the endosalpinx in the isthmic portion of the fallopian tube between the lumen and the serosa. The clinical significance of SIN rests on its strong association with tubal ectopic pregnancy and subfertility.