Endosalpingiosis is a benign condition in which tissue that looks and behaves like the lining of the fallopian tubes grows in places where it doesn’t belong. It is most often discovered by accident during pelvic surgery or when a tissue sample is examined under a microscope for another reason. The condition is far more common than previously thought, and while it rarely causes symptoms on its own, it has drawn attention for its occasional association with certain gynecologic cancers.
How Endosalpingiosis Differs From Endometriosis
The name sounds similar to endometriosis, and the two conditions do share a basic concept: tissue growing where it shouldn’t. But what’s growing is different. In endometriosis, the misplaced tissue resembles the lining of the uterus. In endosalpingiosis, the misplaced tissue resembles the lining of the fallopian tubes. Under a microscope, pathologists look for three specific cell types that define fallopian tube lining: ciliated columnar cells (cells with tiny hair-like projections that move fluid along), non-ciliated mucus-secreting cells, and narrow “peg” cells wedged between them. When all three show up in tissue outside the fallopian tubes, the diagnosis is endosalpingiosis.
Another key distinction is what’s missing. Endometriosis includes endometrial stroma, the supportive tissue that surrounds uterine glands, and it typically triggers inflammation. Endosalpingiosis has neither. There’s no stromal tissue and usually no inflammatory response, which is one reason it so often flies under the radar.
That said, the two conditions frequently coexist. In women aged 31 to 50, about 32% who have one also have the other. This overlap can complicate diagnosis and sometimes leads to both being identified at the same time during surgery.
Where It’s Found in the Body
Endosalpingiosis most commonly appears in the pelvis. A single-center study of 77 patients found that roughly 90% of lesions were located in the pelvic cavity, with the most frequent sites being the ligaments behind the uterus (about 25% of cases), the peritoneum lining the space behind the uterus (21%), the bladder peritoneum (20%), and the ovaries (16%).
A larger systematic review of over 1,100 cases found a slightly different pattern, likely because it included more incidental findings from surgeries that removed lymph nodes. In that data, the ovaries were the most common location (23%), followed by the fallopian tubes (20%) and lymph nodes (19%). Rare cases have been reported in unusual locations, including the vagina and inguinal (groin) lymph nodes.
How Common It Is
For years, the reported prevalence of endosalpingiosis was low, around 1.5% to 3.5% of women undergoing gynecologic surgery. But those numbers appear to have been a significant undercount. When researchers at one academic center switched to a more thorough method of examining surgical tissue (a protocol that sections and examines fallopian tube specimens more completely), the detection rate jumped from about 2.5% to 22%. In women over 50, the prevalence was even higher, reaching 66% when tissue was examined carefully.
This suggests endosalpingiosis is not rare at all. It simply goes unnoticed when pathologists aren’t specifically looking for it.
Symptoms and How It’s Found
Most people with endosalpingiosis have no idea they have it. In a retrospective study of 16 confirmed cases, 38% of women had no complaints whatsoever, and their endosalpingiosis was discovered incidentally during surgery for something else. Among those who did have symptoms, the most common were pelvic pain (38%) and painful or heavy periods (38%). A small number had persistent ovarian cysts or infertility, though these may have been caused by coexisting conditions rather than the endosalpingiosis itself.
The researchers concluded that endosalpingiosis is more likely an incidental finding associated with other pelvic conditions than a direct cause of chronic pelvic pain. Still, because it often overlaps with endometriosis, sorting out which condition is responsible for symptoms can be difficult.
How It’s Diagnosed
There is no blood test or imaging study that reliably identifies endosalpingiosis. Ultrasound and MRI typically show nothing specific, though mass-forming cases can occasionally appear as multilocular cysts. The only way to confirm the diagnosis is by examining tissue under a microscope after a biopsy or surgical removal. Pathologists confirm it by identifying those three characteristic fallopian tube cell types and ruling out endometriosis by checking for the absence of endometrial stroma.
In practice, this means most diagnoses happen after a laparoscopy or other pelvic surgery performed for a different reason, such as investigating pelvic pain, removing cysts, or evaluating infertility.
What Causes It
The exact cause is unknown, but two main theories exist. The first, called coelomic metaplasia, proposes that the cells lining the peritoneum (the membrane inside the abdomen) transform into fallopian tube-type cells. This is plausible because both the peritoneum and the fallopian tube lining originate from the same embryonic tissue, the coelomic epithelium. If those peritoneal cells retain the ability to “switch” into their developmental cousins, it could explain why fallopian tube tissue appears in scattered locations across the pelvis.
The second theory is transplantation: that actual fallopian tube cells physically migrate or are displaced to new sites, possibly during surgery, through the normal movement of fluid in the pelvis, or through lymphatic channels. The finding that nearly one in five cases in the systematic review involved lymph nodes lends some support to the idea that these cells can travel through lymphatic pathways.
Connection to Cancer
Endosalpingiosis is classified as benign, and for most people it stays that way. However, the relationship between endosalpingiosis and certain gynecologic cancers has become a growing area of concern. A 20-year retrospective analysis of nearly 1,000 patients found that endosalpingiosis was present alongside a malignancy in 40% of specimens across all subgroups examined.
The cancer most closely linked to endosalpingiosis is low-grade serous carcinoma, a slow-growing subtype of epithelial ovarian cancer driven by specific genetic mutations. There are documented cases of this cancer arising directly from endosalpingiosis tissue, including in unusual locations like inguinal lymph nodes far from the ovaries or fallopian tubes. A handful of cases have also shown endosalpingiosis occurring alongside ovarian tumors in patterns that initially mimicked metastatic cancer on imaging.
These findings don’t mean endosalpingiosis will turn into cancer in most people. But they do suggest it is not entirely without clinical significance, particularly in postmenopausal women where the prevalence appears to be highest. Pathologists are increasingly paying attention to it when evaluating gynecologic tissue samples.
Treatment and Management
When endosalpingiosis is found incidentally and causes no symptoms, it typically requires no treatment. Most women are simply informed of the finding and monitored as part of routine gynecologic care.
When endosalpingiosis is found alongside endometriosis or is thought to contribute to symptoms like pelvic pain, surgical excision of the affected tissue is the primary approach. The role of hormonal therapy after surgery remains debated. Short courses of hormonal treatment (three to six months) have shown limited benefit for preventing recurrence. Some evidence suggests that longer-term hormonal therapy after surgery may help, particularly when endosalpingiosis coexists with deep endometriosis, but the data supporting this is not yet strong enough for it to be standard practice. The decision is typically made on a case-by-case basis depending on the extent of disease and whether endometriosis is also present.