Umbilical endometriosis is a condition where tissue similar to the uterine lining grows in or around the belly button. It accounts for 0.5 to 1% of all cases where endometriosis appears outside the reproductive organs, making it uncommon but well-documented. The hallmark sign is a small, often darkened nodule at the navel that becomes painful and sometimes bleeds in sync with your menstrual cycle.
Primary vs. Secondary Umbilical Endometriosis
There are two distinct forms. Primary (or spontaneous) umbilical endometriosis appears without any history of abdominal surgery or prior pelvic endometriosis. It develops on its own, and exactly why it targets the navel remains debated. Secondary umbilical endometriosis, the more common type, is linked to surgical scars. It can follow cesarean sections, laparoscopic procedures, or other abdominal surgeries when endometrial cells are inadvertently displaced to the skin surface during the operation.
The distinction matters because primary umbilical endometriosis is genuinely rare and may require a different diagnostic thought process. If you’ve never had abdominal surgery and notice a new nodule at your belly button, it’s less likely to be on a clinician’s radar initially.
How Endometrial Tissue Reaches the Navel
For the secondary form, the explanation is straightforward: surgical instruments can carry endometrial cells from the uterus to the incision site, where they implant and grow. The primary form is harder to explain, and several theories compete.
One theory suggests that endometrial cells travel from the pelvis to the umbilicus through blood vessels or lymphatic channels, essentially migrating through the body’s internal transport systems. When pelvic endometriosis and umbilical endometriosis coexist in the same patient, this explanation is generally favored. A second theory proposes that remnants of the urachus, a structure that connects the bladder to the navel during fetal development, can transform into endometrial-like tissue through a process called metaplasia. This theory is more commonly invoked when umbilical endometriosis appears in complete isolation, with no pelvic involvement at all.
What It Looks and Feels Like
The classic presentation is a small, firm nodule at or near the belly button, typically ranging from 0.5 to 4 cm in size. The nodule is often darkly pigmented and dome-shaped. What sets it apart from other lumps is its cyclical behavior: the pain, swelling, and any bleeding tend to follow your menstrual cycle, worsening during your period and easing afterward.
The pain is commonly described as sharp and intermittent, getting progressively worse over the course of menstruation. In some cases, the nodule produces a bloody discharge from the navel itself. One documented case described pain that was cyclical, occurring monthly, lasting about two weeks, and worsening as menstruation progressed. Not everyone experiences all of these symptoms, though. Some women notice only a painless lump, which can delay diagnosis.
How It’s Diagnosed
A physical exam revealing a nodule with cyclical symptoms is a strong starting point, but imaging helps confirm the diagnosis and rule out other possibilities. On ultrasound, umbilical endometriosis appears as a well-defined dark (hypoechoic) mass in the skin at or near the navel, sometimes with small blood vessel spots visible on Doppler imaging. In some cases, the endometriosis is found herniating through a gap in the connective tissue of the abdominal wall.
MRI provides a more detailed picture and is the preferred tool for mapping exactly which tissues are involved, particularly when deep endometriosis is suspected in other locations. The definitive confirmation, however, comes from examining the tissue under a microscope after removal. A pathologist looks for endometrial glands and supporting tissue (stroma) within the specimen.
Conditions That Can Mimic It
Several other conditions can produce a lump at the belly button, and some are more serious than endometriosis. The differential diagnosis includes:
- Sister Mary Joseph’s nodule: a metastatic deposit from an internal cancer, most often originating in the gastrointestinal tract or ovaries. This is painless and not cyclical, but it requires urgent evaluation.
- Umbilical hernia: a bulge caused by abdominal contents pushing through a weak spot. Unlike endometriosis, hernias are typically reducible (you can push them back in) and produce a cough impulse.
- Keloid: thickened scar tissue, often linked to a history of skin trauma or navel piercing.
- Omphalith: a hardened mass of dead skin and oil that accumulates inside the navel, associated with poor hygiene rather than cyclical symptoms.
- Primary umbilical tumor: a rare growth originating in the navel tissue itself.
The cyclical pattern of symptoms is the single most useful clue separating umbilical endometriosis from these other conditions. If pain and swelling track your menstrual cycle, endometriosis moves to the top of the list.
Treatment Options
Surgical excision is widely considered the gold standard for umbilical endometriosis. The procedure involves removing the entire nodule with a margin of healthy tissue around it (wide local excision) to reduce the chance of leaving any endometrial cells behind. In a 30-year study at a single center, 84% of patients were treated surgically, and the results showed a high rate of patient satisfaction along with a low risk of the nodule coming back when it was fully removed in one piece.
Hormonal therapy, including birth control pills, progestins, or medications that suppress estrogen, can shrink endometriosis and relieve pain. For deep endometriosis in general, hormonal treatment relieves pain in more than 90% of women at one year. It’s a reasonable option if you prefer to avoid surgery or as a bridge before a planned procedure. The trade-off is that about 30% of women find hormonal therapy either ineffective or hard to tolerate due to side effects like irregular bleeding, weight gain, reduced sex drive, or headaches. Hormonal treatment also does not cure the nodule. It manages symptoms for as long as you take it.
Surgery has one additional advantage worth noting: it allows pathological examination of the removed tissue. This matters because umbilical endometriosis carries an estimated 3% risk of malignant transformation over time. Removing the nodule and examining it rules out that possibility entirely.
What to Expect After Surgery
Recovery from wide local excision of an umbilical nodule is typically straightforward, as the procedure involves a relatively small area of skin and underlying tissue. The main cosmetic concern is the appearance of the navel afterward. Depending on the size and location of the nodule, the belly button’s shape may change slightly. Some surgical approaches aim to preserve the natural contour as much as possible, while larger or deeper lesions may require more tissue removal.
Recurrence rates after complete removal are low, though no large-scale studies have established a precise long-term number. Some clinicians recommend post-operative hormonal therapy to further reduce the risk of symptoms returning, particularly in women who also have pelvic endometriosis, though this practice is not yet supported by strong comparative data.