Cesarean scar endometriosis: Clinical presentation and imaging features with a focus on MRIEducational Exhibit at the European Congress of Radiology, Vienna, 2012Authors: A. S. Dumitrescu, T. Herold; DOI: 10.1594/ecr2012/C-0505Learning objectivesEndometriosis is a common and important clinical problem of women, predominantlythose in the reproductive age group. Endometriosis of the abdominal wall is less frequentand is mostly associated with cesarean section scars. It can pose diagnostic difficultiesand should be in the differential diagnosis of abdominal wall lumps in females.The purpose of this exhibit is:1. to review the clinical presentation and imaging findings of abdominal wallendometriosis with intramuscular as well as subcutaneous lesions following caesariansection;2. to discuss diagnostic strategies with a focus on MRI imaging;3. to briefly review this conditions incidence, pathology and treatment.
BackgroundEndometriosis was first described by Rokitansky in 1860 and is defined as the presenceof endometrial glandular tissue outside of the uterus.Clinical presentationThe most common symptoms are dysmenorrhea, dyspareunia, pelvic pain, and infertility,although only a minority of patients present with all the symptoms and many patients areAsymptomatic.LocalizationFrequent localizations in the pelvis include the ovaries, uterine ligaments, serosalsurfaces, cul-de-sac, fallopian tubes, rectosigmoid, and urinary bladder (Fig. 1). Extrapelvic endometriosis are bladder, kidney, bowel, omentum, lymph nodes,lungs, pleura, extremities, umbilicus, hernial sacs, and the abdominal wall. PathologyThe foci of endometrial tissue are generally small (Fig. 2 on page 4). Typicalhistopathologic features are endometrial glands, endometrial stroma and hemosiderin-laden macrophages (Fig. 3).Ectopic endometrial glandulartissue is influenced by ovarianhormones and undergoes cyclicbleeding. Over time, the repeatedhemorrhaging can produceextensive fibrosis surrounding theendometrial tissue, which canresult in adhesions to neighboringstructures, e.g. adnexal structures,peritoneum, bowel, depending onthe localization. 
EpidemiologyThe prevalence of endometriosis is difficult to determine accurately; however, it has been estimated to affect 5–10% of both symptomatic and asymptomatic women, the frequency being higher in women with infertility and pelvic pain.  Localization in the abdominal wall (Fig. 4) is comparatively rare and most frequently follows obstetrical and gynecological surgeries. The actual incidence of abdominal wall endometriosis is unknown but one series reported that only 6% of these were unrelated to scars.  In another series the prevalence of surgically proven endometriosis in scars was 1.6%. TherapyTreatment of endometriomas is most often surgical. Wideexcision of abdominal wall lesions may sometimes requiremesh placement. Medical treatment involves use of progestogens, oralcontraceptive pills, danazol, and gonadotrophin agonists. It provides only partial relief in symptoms with nochange in the lesion size and involves numerous sideeffects such as amenorrhea, weight gain, hirsutism, andacne.Surgically treated patients need to be followed up becauseof the chances of recurrence, which require re-excision. Incases of continual recurrence the possibility of malignancyneeds to be ruled out.
Imaging considerationsEndometriosis, in patients with scars, is more common in the abdominal skin and subcutaneous tissue compared to muscle and fascia. Endometriosis involving only the rectus muscle and sheath is very rare. In this unusual localization, clinical as well as initial imaging findings are likely to be misinterpreted by physicians and radiologists (e.g., as abscesses or malignant tumors). Along with the comparative rarity of the disease this leads to frequent overlooking of the correct diagnosis. [8,9,10]Usually, the initial imaging examination for suspected endometriosis is pelvic ultrasound. Magnetic resonance imaging (MRI) provides superior anatomic detail and better defines abnormalities found using ultrasonography. The multiplanar capability, high sensitivity for detection of blood products, and ability to identify sites of disease hidden by dense adhesions have made MRI the noninvasive imaging technique of choice for more accurate disease detection and staging. [13,14] It has been shown that MRI has high accuracy in assessing the extension of the disease and assisting surgical treatment planning. Most endometriomas have a relatively homogeneous high signal intensity on native T1-weighted images. On T2-weighted scans, endometriomas often exhibit a phenomenon known as T2-shading, i.e. T2 shortening often associated with a dependent layering on T2-weighted scans reflecting the chronic accumulation of blood degradation products resulting from repeated hemorrhaging over months and years. [16,17] Fat suppression narrows the dynamic signal range, thereby accentuating differences in tissue signal. Thus, lesion conspicuity is improved. Furthermore, differentiation between hemorrhagic and fat components is also facilitated. This has been shown to improve the sensitivity of MR imaging in the detection of small lesions and to increase its specificity, since fat-containing lesions such as dermoids are eliminated from the differential diagnosis. [18, 19, 20] Contrast-enhanced sequences are useful for detection of very small endometrial implants associated with inflammatory reaction, as well as assessing for malignant change. 
Sample caseA 33 years old female Caucasian patient was referred to our department for imaging of a painful, subcutaneous nodular lesion in the left lower quadrant of the anterior abdominal wall situated at the site of the cesarean section she had undergone 2 years before. Clinical examination at admission revealed a palpable, hard nodule, sensitive to pressure. The patient reported having noticed this some 18 months before, the nodule becoming progressively painful over time. Initial imaging involved ultrasound examination at admission as well as contrast-enhanced CT of the abdomen and pelvis in our department. The CT scans revealed two adjacent solid nodular lesions, each some 2 cm in size, one in the left rectus abdominis muscle (Fig. 5) and another in the corresponding subcutaneous fat (Fig. 6), along with signs of a localized inflammatory reaction in the surrounding fat tissue (Fig. 7).
The lesions solid density and the absence of discernible gas inclusions virtually ruled out an abscess of the abdominal wall. Rather, the findings were interpreted as pointing primarily towards a chronic inflammatory, i.e. granulomatous lesion of as yet unclear aetiology, with a soft tissue tumor as a possible differential diagnosis, possibly associated with a secondary hematoma of the abdominal wall. Subsequently the patient was referred to MRI for further, more differentiated imaging. Here, renewed questioning of the patient revealed that pain and swelling associated with the lesion showed a certain periodicity and peaked at the time of menstruation.
The examination confirmed the presence of two neighboring foci in the left rectus abdominis muscle as well assubcutaneous, with limited inflammation of the surrounding fat tissue. On the T1-weighted scans the lesionsshowed slight hyperintensity, both native and fat saturated.
The T2-weighted scans showed low lesion signal, a phenomenon known as T2 shading :
Furthermore, in all performed scans but especially in the inversion recovery scans (TIRM) the lesion showed smallsignal-free dots characteristic of small hemosiderin inclusions.
After contrast injection the lesions showed marked enhancement:
The MRI appearance of the lesions ruled out an abscessand confirmed the similarity of the intramuscular andsubcutaneous foci. It further suggested subacute andchronic micro-hemorrhaging within the lesions, possiblyconsistent with hypervascularized tumors such asmelanoma or soft tissue sarcoma but also with ectopicendometrial tissue islands, i.e. endometriosis.At this stage correlation with anamnestic data (especiallythe fluctuation of symptoms with the menstrual cycle)proved crucial, ultimately tipping the balance of evidence infavor of endometriosis. This diagnosis was confirmed bysubsequent biopsy and surgical therapy was succesfullyperformed.
ConclusionEndometriosis is a common and important clinical problem of women, predominantly those in thereproductive age group. The condition is associated with islands of ectopic endometrial tissue.Localization in the abdominal wall as presented above is rare and mostly associated with acesarean section. Such lesions can mimic tumors of the soft tissue or hematomas of other origin.It is important to keep this rare differential diagnosis in mind and to inquire about any associationof the clinical symptoms with the menstrual cycle, since the presence of cyclic pain in a cesareanassociated incisional mass is almost pathognomonic for the condition.The noninvasive imaging method of choice is contrast-enhanced MRI. Biopsy is necessary toconfirm the diagnosis. Upon confirmation the lesions must be surgically removed, lest they leadto significant reduction in quality of life and fertility. Here, MRI imaging is also important in surgicaltreatment planning, especially in finding additional lesions that need to be treated.
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