C-Section Scar Endometriosis and the Tummy Tuck: The Painful Lump That Flares With Your Period, the Belly Button Nodule, and Why It Has to Come Out Before the Skin Does

The patient is 38. Two cesareans, the last one five years ago. They have come in for a tummy tuck, not to ask about C-section scar endometriosis, a phrase they have never heard. They mention, almost as an afterthought, that there is a lump at the left end of the scar. It is the size of a grape. Most of the month it barely registers. For a few days around each period it swells, turns tender, and sometimes looks faintly blue through the skin. Their obstetrician said it was probably scar tissue. A friend said it was probably a stitch.

It may be neither. A firm nodule in a cesarean scar that hurts on a monthly rhythm is the textbook picture of C-section scar endometriosis, also called abdominal wall endometriosis or scar endometrioma. It is uncommon. It is also one of the few lumps in the lower abdomen where the order of operations really matters, because the obvious plan (take the skin, and the lump goes with it) is often wrong.

This piece is about what that lump is, how it is confirmed, what treatment actually removes it, and how it fits around a tummy tuck or any other cosmetic work on the abdomen.

What is C-section scar endometriosis?

The short answer: it is tissue similar to the lining of the uterus growing in the abdominal wall, usually in or under a cesarean scar, most likely because endometrial cells were carried into the wound during the operation and took root there.

Endometriosis is usually discussed as a disease of the pelvis: the ovaries, the ligaments behind the uterus, the lining of the pelvic cavity. The abdominal wall form is different. In the version that follows a cesarean, the leading explanation is mechanical. When the uterus is opened, cells from its lining can be transferred on instruments, gloves, sponges, or simply along the path of the incision. Most die. A few implant in the fat, the fascia (the tough sheet over the abdominal muscles), or the rectus muscle itself, and then respond to the same monthly hormonal signals as the lining of the uterus. They swell, bleed a little into themselves, and scar.

The numbers are small and inconsistent. Published estimates for how often it follows a cesarean range from about 0.03 percent to roughly 1 percent, and a 2024 case report and literature review in Frontiers in Surgery by Triantafyllidou and colleagues quotes the 0.03 to 1 percent range. A widely cited review of 445 published cases by Horton and colleagues found that 57 percent arose in a cesarean scar, 11 percent in a hysterectomy scar, and most of the rest in other surgical scars, including laparoscopy port sites. Any operation that opens the uterus or handles endometrial tissue can, in principle, seed the wall.

A few features of the condition explain why it is so often misread:

• The delay is long. Horton's review put the average interval from surgery to symptoms at about 3.6 years. Other series report a median of seven years, with a range from a month to more than a decade. Few patients connect a lump today with a delivery from years ago.
• It does not need pelvic endometriosis. Many patients with the scar form have never been diagnosed with endometriosis anywhere else.
• It lives at the edges. The Frontiers review notes lesions after cesarean sit in the scar and are reported more often on the left side of the incision. A lump at one end of the scar is easy to dismiss as a "dog ear" of fat.

If the abdomen also carries other history, such as laparoscopy for pelvic endometriosis or a hysterectomy, it is worth reading our piece on old abdominal surgery scars and the tummy tuck, because each of those scars changes the plan in its own way.

How do you know the lump in your C-section scar is endometriosis?

The short answer: suspicion comes from the story (a firm scar nodule that hurts or swells with the menstrual cycle), support comes from ultrasound or MRI, and certainty comes only from the pathologist looking at the removed tissue.

In Horton's 445 cases, 96 percent of patients had a palpable mass, 87 percent had pain, and 57 percent described the pain as cyclic. That last number matters. Cyclic pain is the classic clue, but four in ten patients in that series did not report it. A painful scar lump without a monthly pattern does not rule the diagnosis out.

The list of things a lump in a lower abdominal scar might be is long, and most of it is benign:

• Suture granuloma, a reaction around a buried stitch, which can surface as a small tender bump or a draining spot.
• A lipoma or cyst, which our piece on cyst and lipoma removal covers.
• An incisional hernia, where a gap in the fascia lets fat or bowel push through. This one usually gets bigger when you cough or strain and may flatten when you lie down.
• Fat necrosis, a hematoma, or a seroma, if there has been recent surgery.
• A keloid or hypertrophic scar, which is raised and firm but sits in the skin itself rather than beneath it.
• Rarely, a tumor, including a desmoid tumor of the abdominal wall, which also has a reported association with pregnancy.

Imaging narrows the field. On ultrasound, the Frontiers review describes a typical lesion as a hypoechoic (darker than surrounding tissue) nodule with irregular, spiculated margins that often reaches down toward the fascia, sometimes with a bright rim and small cystic pockets. MRI shows how deep the lesion goes and whether it has invaded the rectus muscle, and lesions are often bright on both T1 and T2 sequences because of old blood. For surgical planning, the depth is as important as the diagnosis, and MRI or a careful ultrasound by someone who looks at abdominal walls regularly is the usual way to map it.

Needle biopsy is possible and is sometimes used to exclude something worse, but it is often inconclusive for endometriosis. The Frontiers review notes that even in surgical specimens, the classic combination of endometrial glands, stroma, and blood-stained macrophages is present in only about a third of cases, and special stains may be needed. That is why the real answer usually arrives in the pathology report after surgery. Ask for it, and read it.

"A lump that keeps time with your period is telling you what it is made of. Treat it as a diagnosis to confirm, not a contour to smooth."

One more variant deserves its own paragraph. Umbilical endometriosis is a firm, often dark or bluish nodule in the belly button that may bleed or ache cyclically. Some cases are secondary, arising at a laparoscopic port placed through the navel. Others are primary, appearing with no prior surgery at all, a presentation known as Villar's nodule. Case series describe excision with a margin down to the fascia and reconstruction of the navel, and some authors suggest checking the pelvis for coexisting disease. For anyone planning abdominal surgery, a nodule in the navel is a reason to stop and investigate before the belly button is reshaped or relocated, not after.

Why can't a tummy tuck just remove it with the skin?

The short answer: a tummy tuck removes skin and fat above the fascia, while scar endometriosis frequently sits on, in, or under the fascia, so the skin excision can leave the lesion behind, cut through it, or cover it with a flap that makes the next operation harder.

The logic that leads patients and occasionally surgeons astray is understandable. A standard abdominoplasty incision runs low, across the same zone as a cesarean scar, and the block of skin and fat removed between the incision and the navel usually takes the old C-section scar with it. If the lump is "in the scar," surely it goes in the bin with everything else.

Sometimes it does. A small, superficial nodule sitting in the subcutaneous fat right under the scar may be removed whole. But the published series describe many lesions that reach the anterior rectus sheath or extend into the muscle. An abdominoplasty lifts the flap at the level just above the fascia. A lesion that sits deeper stays in the patient, now under a tight flap, and announces itself again a few months later. A lesion that sits right at the plane of dissection may be cut across, which is the opposite of what the treatment for this condition requires.

There are three further problems with discovering it mid-operation:

• The margin is wrong. Endometriosis in the abdominal wall is treated by removing the whole nodule with a rim of normal tissue around it. A lesion cut across during flap elevation is, by definition, a positive margin, and positive margins are the main thing tied to recurrence.
• The fascia plan changes. Many tummy tucks include plication of the rectus muscles, stitching the fascia together down the midline. If a piece of fascia has to be removed with the lesion, the surgeon is suddenly repairing a defect, possibly with mesh, in the same field where tension is being placed. That can be done well. It is not something to improvise.
• The recurrence becomes harder to reach. A deposit left behind is now under a thinned, repositioned flap with a long scar and a new blood supply pattern. Reoperating there is more complicated than the first excision would have been.

It is also why liposuction aimed at a "stubborn bump" near the scar is a poor idea when the bump has not been explained. A cannula does not distinguish an endometrioma from fat, and our piece on liposuction revision for lumps and irregularities is mostly about what happens when a contour problem was misread the first time.

A related question comes up with patients who notice a tender nodule months or years after a tummy tuck. An abdominoplasty does not open the uterus, so it is not the usual seeding route. In a patient who also had cesareans, a nodule near the scar that behaves cyclically is more likely an old deposit that was never removed than a new one created by the cosmetic operation. Either way, the work-up is the same.

What actually treats scar endometriosis: hormones, excision, or mesh?

The short answer: hormonal treatment can quiet symptoms for a while but does not remove the lesion, and the standard definitive treatment is a wide local excision with clear margins, with a fascial repair and sometimes mesh when the lesion takes part of the abdominal wall with it.

Hormones first, because many patients are offered them first. Combined oral contraceptives, progestins, and drugs that suppress ovarian hormones can reduce the monthly swelling and pain. The Frontiers review is blunt that this is temporary, describing relief that tends to fade and recurrence after the medication stops. Its own case patient took a daily progestin for eight years before the lesion was finally excised. Hormonal suppression can be a reasonable bridge, for example while someone is still planning a pregnancy. It is not a cure, and it should not be the reason a growing lump is left uninvestigated for years. If you are on hormonal treatment and planning surgery, the clot question becomes relevant too, which our piece on birth control before cosmetic surgery covers.

Surgery is the definitive treatment, and the details are specific:

• Wide local excision. The lesion is removed as a single block with a margin of normal tissue, often described as at least 1 centimeter, including any involved fascia or muscle.
• Clear margins. The pathologist confirms that the edges of the specimen are clear of endometriosis. Recurrence rates across published series range from about 4.3 to 17.2 percent, and the Frontiers review ties recurrence to positive margins.
• Repair of the defect. Small fascial defects can be closed directly. Larger ones need reinforcement. The Frontiers review describes mesh as generally needed for defects larger than about 3 centimeters, and other series link the need for mesh to lesion size and to invasion of the rectus muscle.
• Follow-up. Some groups recommend a follow-up ultrasound around a year after excision. Recurrence is usually diagnosed the same way the original lesion was: a lump and a pattern of pain coming back.

Outcomes, when the excision is complete, are generally good. Many reports describe most patients losing their symptoms after surgery. A recurrence is treated with re-excision.

One last subject, handled with the proportion it deserves. Cancer arising in abdominal wall endometriosis is extremely rare. The published literature amounts to a few dozen cases; a 2021 systematic review pooled 46 patients. That review found cesarean scars to be the most common site, clear cell carcinoma the most common type, and the prognosis poor. Nobody should be frightened by a number that small, but it is one more reason the lump goes to pathology rather than into a liposuction canister, and one more reason a lesion that grows quickly, stops behaving cyclically, or recurs repeatedly deserves a fresh look.

How should scar endometriosis and a tummy tuck be sequenced?

The short answer: identify it before surgery, excise it properly as the priority, and then either combine the cosmetic work into a single planned operation with the right team or stage the tummy tuck later, but never treat the lesion as an incidental find.

There is no society guideline written for this exact combination, and the literature on combining scar endometriosis excision with abdominoplasty is limited to case reports and small series. What follows is the reasoning a careful team tends to apply.

Step one is recognition. The intake form should ask about every abdominal operation, and the surgeon should examine the scar with the patient both lying down and tensing the abdomen. Any firm nodule in or under the scar, any navel nodule, and any history of cyclic scar pain should trigger imaging before a surgical date is set. This takes a week or two. It is cheap insurance.

Step two is deciding who does what. Excision of abdominal wall endometriosis is done by general surgeons, gynecologists, and plastic surgeons, depending on the hospital and the depth of the lesion. What matters is that the person removing it is planning a margin and a fascial repair, and that a gynecologist has been asked whether there is reason to suspect pelvic disease too. A plastic surgeon who is board certified and comfortable with abdominal wall reconstruction can often do both parts. If not, a two-surgeon plan is ordinary.

Step three is choosing between combined and staged. Both are defensible.

• Combined. A small, superficial lesion with a clear imaging picture may be excised through the abdominoplasty incision at the start of the case, with a proper margin taken before the flap is raised. The advantage is one anesthetic and one recovery. The surgeon must still be ready for a deeper lesion than expected.
• Staged. A larger lesion, one that invades the muscle, one likely to need mesh, or one whose diagnosis is uncertain is often better removed first, with the tummy tuck several months later once pathology is back and the repair has healed. The cosmetic result is planned around a known abdominal wall rather than an improvised one.

A few practical points sit around either choice. A patient who still wants more children should think hard about the timing of any abdominoplasty, as our pieces on mommy makeover timing and pregnancy after a tummy tuck explain, and should mention any mesh repair to their obstetrician. A patient with heavy periods from uterine fibroids or endometriosis elsewhere may also be anemic, which should be fixed before any elective surgery. And a patient who is simply looking for a smaller scar should know that the "C-section shelf" is a different problem with different answers, covered in our pieces on panniculectomy versus tummy tuck and the mons pubis lift.

Afterward, the aim is a quiet scar and no monthly signal. Ordinary scar care applies. What does not apply is patience with a new cyclic lump. If the old pattern returns, the answer is imaging and a call to the surgeon who did the excision, not another year of telling yourself it is a stitch. Pain in the abdominal wall that persists for months after surgery for other reasons is a separate subject, covered in our piece on chronic pain after cosmetic surgery.

Prevention, for completeness, belongs mostly to the obstetrician. Reviews list measures such as irrigating the wound, changing gloves and instruments that touched the uterus before closing the abdominal wall, and avoiding wiping the uterine cavity with a sponge that then touches the wound. The Frontiers authors note that none of these has been tested in prospective trials. They are sensible. They are not proof.

The honest summary

C-section scar endometriosis is a small problem with an outsized ability to derail a tummy tuck. It is uncommon, with published estimates from about 0.03 to 1 percent after cesarean, and it often appears years after the delivery, which is why patients and doctors tend to blame a stitch, a lump of fat, or ordinary scar tissue.

The pattern to remember is simple: a firm nodule in or under a cesarean scar, or in the navel, that swells or hurts around your period. Not every patient has the cyclic pain, so a painful scar lump deserves imaging either way. Ultrasound or MRI shows how deep it goes. Pathology confirms what it is.

Hormones can calm it, temporarily. Removing it, as a single block with a clear margin and a proper repair of whatever fascia comes with it, is what treats it. Recurrence happens, mostly when the margins were not clear. Cancer arising in these lesions is very rare, but it exists, which is one more reason the tissue belongs in front of a pathologist.

None of this rules out a tummy tuck. It changes the order. Find the lump before the operation, decide who will remove it and how, and then either fold the cosmetic work into a single deliberate plan or do it later on a healed, known abdominal wall. A surgeon who asks about the lump at the end of your scar, and wants a picture of it before discussing your waistline, is doing the job properly.