Endometrial tissue localized outside the uterine cavity is defined as endometriosis. It commonly has been demonstrated in the ovaries, peritoneal surfaces, vagina, scar tissues, cervix, fallopian tubes, rectum, urinary tract, pouch of Douglas and possibly any organ in the abdomen15. The estimated prevalence reported in literature ranges from 8-15%5 , 9. Extra-pelvic localization of endometriomas are relatively rare. Especially abdominal wall placements are very infrequent. Usually such cases are associated with surgical scars5. The proposed mechanisms that have been put include retrograde menstruation, venous or lymphatic dissemination or metastasis, and mechanical transplantation into scars at the time of surgery8.
Herein, is presented a case of endometrioma localized in the rectus abdominis muscle.
A 31 year old female with a history of two cesarean sections, the last one of them three years prior, presented with a painful mass in the left lateral side of the Pfannenstiel incision which had been steadily growing. The same patient went a month ago to our institution's urology clinic with pain in the inguinal region. After a detailed history and physical examination an ultrasonography was performed that revealed a 20X12 mm hypo-echoic nodular mass, neighboring the rectus abdominis muscle, with minimal vascularization. The differential diagnosis included endometriosis and a possible desmoid tumor. The patient was referred to our clinic for further evaluation. The pain started on the left lower quadrant and radiated towards the inguinal region, and was associated with menstruation. In physical examination a 2 cm wide mass was palpated in the previously described localization. Magnetic resonance imaging was performed which revealed a 20x11 mm mass which is slightly hyper-intense in the T1 sequence, and contrast enhanced after IV gadolinium injection in the T2 sequence, with increased signal intensity and nodular appearance in diffusion weighted sequences. These were found to be consistent with an endometrial implant (Figures 1A and 1B). Examination of the uterine cavity showed effusion which was at most 15 mm in width when measured. A little free fluid, indicating peritoneal irritation was present in between the intestinal loops. No pathological lymph nodes were present in the lower abdomen.
Ectopic endometrial tissue localized in the rectus abdominis tissue is a very rare occurrence. Previously there have been only 20 reported cases in literature5. The first one of these cases was presented by Amato et al.2, in 1984. Giannella et al.7 has reviewed the previously reported cases extensively; their clinico-pathological characteristics, summarized, were: endometriosis with rectus abdominis placement usually is seen in premenopausal women, aged 27-42y, and history of previous surgery (77%), similarly to this patient. The average size of the endometriomas were 4X4 cm in diameter. This case had a much smaller dimension. The imaging studies' measurements were 2 cm at the greatest width. While CT scan has most commonly been used, in this case imaging diagnosis preferred to use ultrasound followed by an MRI7. Fine needle aspiration has also been tried in these cases; however, failed to prove effective in establishing diagnosis3.
Cesarean section is very frequently associated with abdominal wall endometriosis. The incidence, as reported in previous literature, can be as high as 1%. One of the proposed theories for how this occurs, takes into consideration the possibility that during the operation, endometrial cells may escape through the incision in the uterus and implant themselves within the abdominal incision site3.
This patient presented with cyclic symptoms that were associated with menstruation. The differential diagnosis of cyclic pain in general include lymphadenopathy, mesenteric lymphadenitis, lipoma, abscesses, hernias, hematomas, soft tissue sarcomas, desmoid tumors (which was considered in differential diagnosis) and even metastatic cancer. Previously some studies have looked into the utility of biochemical markers for tracking endometriosis. These markers include CA-125, C-reactive protein, anti-mullerian hormone, follistatin6 , 11 , 12 , 13.
Previously conducted sonographic studies have determined that abdominal wall endometriomas (which were first demonstrated via ultrasound in 197914) are commonly hypo-echoic, well defined, solid masses; this is consistent with sonographic findings of this case1. Medical treatment for these conditions, which have been previously utilized in literature, include danazol and progesterone; however, this treatment is frequently inefficacious, and therefore must be reserved for cases in which surgical treatment is not preferred10.
To summarize, in masses which present with cyclic pain and growth, localized to the abdominal surface, endometriomas must be considered in the differential diagnosis. Surgical removal, as evidenced previously reported cases, is successful, especially when limited and localized within in the rectus abdominis muscle. Sonography followed by resonance, provides the most definitive imaging. Molecular markers are currently not established enough to be considered as a standard of diagnosis. Further large-scale studies or reviews are necessary to determine which approach is the best, with consideration of the patient's request.
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