Salpingitis isthmica nodosa (SIN) (sometimes also referred to as perisalpingitis isthmica nodosa - PIN) refers to nodular scarring of the fallopian tubes.
The prevailing theories include an inflammatory (salpingitis), a congenital, and more recently an acquired (but not post-inflammatory) etiology.
A characteristic finding is multiple nodular diverticular spaces involving the fallopian tubes (usually involving the proximal 2/3 of the fallopian tubes). A hysterosalpingogram (HSG) of the nodular area with severe SIN shows several pockets (diveritculae) containing the introduced contrast material.
There is an increased risk of tubal ectopic pregnancy.