Salpingitis Isthmica Nodosa (SIN) — Definition, Diagnosis, Fertility Impact & Treatment

Salpingitis isthmica nodosa (SIN) is a non-infectious condition characterised by nodular thickening of the proximal (isthmic) portion of the fallopian tube. It is caused by tiny pockets of tubal lining (diverticula) that grow into the tubal muscle wall, creating a nodular appearance. Despite its name, SIN is not caused by active infection — "salpingitis" refers to historical inflammation, not a current infection. SIN causes bilateral proximal tubal obstruction and is a significant risk factor for ectopic pregnancy.

On an HSG (hysterosalpingogram), SIN typically shows as bilateral proximal (cornual) tubal obstruction — contrast dye injected through the cervix is blocked at both tube entrances and cannot flow through. If some contrast does enter the proximal tube, it may show an irregular "beaded" or "diverticular" filling pattern from the diverticula. SIN is commonly misdiagnosed as tubal spasm (a common false-positive proximal block on HSG) or as pelvic TB. The key differentiator: SIN does not respond to antispasmodics; spasm does.

Tubal surgery (salpingostomy, tuboplasty) does not work well for SIN — unlike simple tubal blockage that can be opened surgically, SIN involves structural changes throughout the tubal wall (diverticula). Even if the tube is surgically opened, the diverticula remain and the ectopic pregnancy risk persists. IVF is the treatment of choice for SIN — it bypasses the tubes entirely. Bilateral salpingectomy before IVF is recommended to eliminate the risk of ectopic pregnancy from embryos becoming trapped in the diverticula of the tube.

Yes — SIN significantly increases the risk of ectopic pregnancy. The diverticula (pockets) within the tubal wall create spaces where a fertilising embryo can become trapped as it travels through the tube. Instead of completing the journey to the uterus, the embryo implants within the tube — an ectopic pregnancy. For this reason, any woman with SIN who becomes pregnant (through IVF or spontaneously) should have an early ultrasound at 5–6 weeks to confirm intrauterine location. Bilateral salpingectomy before IVF eliminates this ectopic risk.

SIN is definitively diagnosed histologically — when the removed fallopian tube is examined under a microscope, epithelial crypts (glandular pockets) embedded within the tubal muscle wall are the hallmark. Clinically (without surgery), SIN is suspected from: HSG showing bilateral proximal obstruction with irregular diverticular filling; laparoscopy confirming bilateral proximal block with possible visible nodular thickening of the isthmic segment; failure to respond to antispasmodic agents during selective salpingography. Most women with SIN are not diagnosed until after laparoscopic salpingectomy with histopathological analysis.