In short
- It is endometrial tissue — the lining of the inside of the uterus — implanted in the scar of the abdominal wall. It responds to the hormones of the cycle as it would inside the uterus.
- 🔑 The clue is the cyclical pattern: a palpable nodule in or near the scar, which hurts with the period and may get bigger on those days.
- It is rare. It is the least frequent form of endometriosis, and the available reviews note that its real incidence is unknown and probably underestimated.
- ⚠️ No risk profile has been identified, so it is not possible to know in advance who it will happen to.
- It is reached through the history and the examination, with imaging in support; confirmation is the study of the tissue.
- The standard treatment is surgical: excising the nodule with a margin.
- 🚨 Telling it apart matters before operating for aesthetic reasons, because removing skin and fat is not the same as excising a lesion that may be infiltrating deep planes.
There is a lump in the caesarean scar that is not an aesthetic sequela, and it is recognised by one thing: it hurts in time with menstruation. Sometimes it also gets bigger on those days. When that pattern is present, the possibility to rule out before any other is endometriosis of the abdominal wall.
It is uncommon — so much so that its real incidence is not known — and that is why this page exists: it is the condition worth identifying before proposing any aesthetic surgery on that area, because its treatment is different and the diagnosis is not made by looking.
This page sets out one of the conditions the caesarean sequelae page mentions as a differential diagnosis.
What it is and why it appears there
The endometrium is the layer lining the inside of the uterus and the one shed each month with the period. Endometriosis is that tissue growing outside the uterus, and the form that appears in the abdominal wall — including the caesarean scar — is one of the least frequent.
The most widely accepted mechanism is direct implantation during the surgery itself: at a caesarean the uterus is opened, and endometrial cells can be left deposited in the planes of the wound. If they take, they go on responding to the hormones of the cycle, bleed each month into a closed space and produce inflammation, fibrosis and a nodule that grows over the years.
🔑 And there is one fact that connects this with the rest of the cluster: a 2026 review of uterine closure notes that when the endometrium is included in the suture, healing is altered and niches, adenomyosis and endometriosis in the area of the scar appear; hence it proposes a technique that deliberately excludes the endometrium from the first layer (Bujold, 2026).
⚠️ This does not mean it is possible to know who it will happen to. The available review of abdominal wall endometriosis is explicit: no constellation of clinical risk factors has been identified that would allow it to be anticipated (Carsote, 2020).
How it is recognised
What is characteristic is the relationship with the cycle, and it is worth being clear about because it is what separates this condition from every other lump in a caesarean scar:
- A palpable nodule in or near the scar, usually firm and well defined, adherent to the planes beneath.
- Pain that appears or intensifies with menstruation, and which usually settles afterwards.
- Increase in size on those days, which the patient herself frequently describes.
- Less often, a change in the colour of the skin above it or, very rarely, bleeding through it.
- Slow progression over months or years, which is different from a lump that appears all at once.
How long it takes to show itself is variable: a long time can pass between the caesarean and the first symptoms, and that is precisely what means it often is not connected with it.
⚠️ Not all the signs need to be present. Cyclical pain is the one that points most strongly; the rest may be missing.
What else produces a lump there
This is the practical use of this page: most lumps in a caesarean scar are not this. The conditions it gets confused with:
| How it behaves | |
|---|---|
| The shelf or “apron” | It is not a nodule: it is a roll of tissue along the whole scar, with the groove depressed in the middle. It does not hurt with the period. It is the caesarean shelf |
| A suture granuloma | A small, superficial nodule, related to a stitch. No cyclical pattern |
| A lipoma | Soft, mobile, painless and unrelated to the cycle |
| A hernia | It becomes more obvious on coughing or straining and usually reduces on lying down. It is covered in shelf, hernia or isthmocele |
| An adhesion | It gives tightness and a stuck scar, not a defined nodule. It is covered in adhesions of the scar |
| An abscess or late infection | An acute course, with redness, heat and sometimes fever |
🚨 And one warning no page should leave out: any nodule that grows rapidly, ulcerates or bleeds needs assessment without delay, regardless of its relationship with the cycle. Scar endometriosis is benign, but the absence of a cyclical pattern does not rule other things out.
How it is investigated
The first step is the clinical history and the examination, and they are often enough to suspect it: a nodule in the scar with cyclical pain in a woman with a previous caesarean is a recognisable picture.
Imaging supports and helps with planning, above all to know how deep the lesion goes and which planes it affects. It is information that changes the surgery, because a subcutaneous nodule is not the same as one infiltrating the aponeurosis.
Confirmation is histological: the study of the excised tissue. The available review says so plainly — the histology report is the main diagnostic tool for confirmation (Carsote, 2020) — and it is why the definitive diagnosis comes after the treatment and not before.
⚠️ What this means in practice: faced with that pattern, what is called for is a specific assessment and not assuming it is “how the scar turned out”. The pathway is gynaecological and surgical, and the specific approach is decided in the consultation.
What treatment it has
Surgery is the first-line treatment: excising the whole nodule, with a margin of healthy tissue, and reconstructing the wall if the defect requires it (Carsote, 2020).
Two things worth knowing beforehand:
- The extent is not fully known until the surgery. That is why the prior assessment matters: if the lesion reaches deep planes, the operation is bigger than the palpable lump suggests.
- Hormone treatment can reduce the symptoms, but it does not remove the lesion. It is considered in particular situations and does not replace excision.
🔑 And here is why this page belongs to this cluster. If a woman with this condition arrives asking for “the caesarean lump” to be corrected, operating on it as though it were a contour problem would be the mistake: tissue that is not the tissue to remove would be excised and what should have been removed would remain. It is the piece that stops someone having surgery for what they do not have.
When both coincide — scar endometriosis and a contour sequela — the order and the approach are decided together; the surgical ladder for the sequelae is in how the surgery is decided.
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Frequently asked questions
I have a lump in my caesarean scar that hurts with my period — what can it be?
That particular pattern — a nodule in the scar, pain coinciding with menstruation and sometimes an increase in size on those days — is what makes one think of scar endometriosis. It is uncommon, but it deserves a specific assessment before proposing anything else on that area.
Is it serious?
It is a benign lesion. What it produces is cyclical pain and slow growth, and its importance lies in identifying it: without a diagnosis the pain becomes chronic and the lesion goes on growing, and with a diagnosis it has a defined treatment.
How is it confirmed?
The suspicion is established by the history and the examination, and imaging helps to know how deep it goes. Definitive confirmation is the study of the tissue once excised, which is the main diagnostic tool according to the available review.
Can it be treated with tablets?
Hormone treatment can relieve the symptoms, but it does not make the lesion go away. The standard treatment is surgical: excising it with a margin.
Is it common after a caesarean?
No. It is the least frequent form of endometriosis and the available reviews note that its real incidence is unknown and probably underestimated. Being rare does not make it irrelevant: it is precisely the condition worth ruling out when there is cyclical pain.
Can it be prevented?
There is no measure that guarantees it, and no risk profile has been identified either. What is discussed in the obstetric literature is the technique for closing the uterus: including the endometrium in the suture is linked with poorer healing and with endometriosis in the area of the scar.
Can I have surgery for the shelf if I have this?
First it has to be clear what is there. If both coincide, the approach is decided as a whole, because removing skin and fat is not the same as excising a lesion that may reach deep planes.
Sources
- Carsote M, Terzea DC, Valea A, Gheorghisan-Galateanu AA. Abdominal wall endometriosis (a narrative review). International Journal of Medical Sciences. 2020;17(4):536-542. PMID 32174784 — Narrative review of abdominal wall endometriosis, including that of the caesarean scar. It notes expressly that the current incidence in obstetric and gynaecological procedures remains unknown and that the disease is probably underestimated, that no constellation of clinical risk factors has been identified, that the histology report is the main diagnostic tool for confirmation and that surgery is the first-line treatment. Verified on 29-08-2026.
- Bujold E, Romero R. Uterine closure after cesarean delivery: surgical technique, biological rationale, and clinical implications. American Journal of Obstetrics and Gynecology. 2026;233(6S):S82-S102. PMID 41485855 — Review of uterine closure technique. It documents that when the endometrium is included in the suture, healing is altered, with the appearance of niches or isthmoceles, adenomyosis and endometriosis in the area of the scar, and proposes a three-layer closure that deliberately excludes the superficial endometrium. Verified on 29-08-2026.
- Loos MJ, Scheltinga MR, Mulders LG, Roumen RM. The Pfannenstiel incision as a source of chronic pain. Obstetrics & Gynecology. 2008;111(4):839-846. PMID 18378742 — Series of 866 women with a Pfannenstiel incision: one in three reported chronic pain at two years and in more than half of those examined for moderate-to-severe pain nerve entrapment was found. It is cited as the main alternative diagnosis for pain in that scar without a cyclical pattern. Verified on 29-08-2026.
- Pelosi MA 2nd, Pelosi MA 3rd, Romero R. The cesarean apron: description, proposed pathophysiology, classification, and prevention through Scarpa fascia closure at cesarean delivery. American Journal of Obstetrics and Gynecology. 2026;233(6S):S118-S128. PMID 41485815 — It supplies the description of the contour bulge after a caesarean, which is the condition a scar nodule is most often confused with and which it has to be separated from before anything is indicated. Verified on 29-08-2026.
Book your consultation
If you have a lump in your caesarean scar and have noticed that it hurts or grows with your period, what is called for is not waiting or proposing an aesthetic correction: it is a specific assessment to find out what is there. If it turns out to be something else, that is known early; and if it is this, it has a defined treatment.
Clinical confirmation by the surgeon
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Last reviewed: 6 September 2026. This content is for information only and does not replace an individual assessment by a healthcare professional.
