Abdominal scar endometrioma mimicking incisional hernia

Elisabeth Garwood, BS

PACCTR Visiting Fellow

Department of Surgery

University of California San Francisco

San Francisco, CA

Pennsylvania State University

College of Medicine

Hershey, PA

Anjali Kumar, MD, MPH

Chief Resident

General Surgery

University of California

San Francisco?East Bay

San Francisco, CA

Gregory Moes, MD

Attending

Department of Pathology

Kaiser Permanente Oakland

Medical Center

Oakland, CA

Jonathan Svahn, MD

Attending

Department of Surgery

Kaiser Permanente Oakland

Medical Center

Oakland, CA

Abdominal scar endometrioma presents as a painful, slowly growing mass in or near a surgical scar. It poses a diagnostic challenge to physicians and frequently results in a referral to a general surgeon for incisional hernia repair. Because abdominal scar endometriomas are not well-recognized among general surgeons, these lesions are rarely diagnosed preoperatively. Increased awareness of the characteristics of abdominal scar endometrioma will allow general surgeons to include this condition in their differential diagnosis of painful abdominal masses, thereby enhancing preoperative diagnosis.

Endometrioma is defined as a well-circumscribed mass of endometriosis or ectopic endometrial tissue.^1,2 In the medical literature, the terminology used to describe endometrioma varies and the presence of endometrioma in association with an abdominal surgical scar is referred to as surgical scar, incisional, subcutaneous, or abdominal wall endometrioma.

Surgical scar endometriomas, especially those associated with Cesarean and hysterectomy incisions, are well described in the gynecologic literature but are not as well-recognized among general surgeons. Surgical scar endometrioma typically presents as a slow-growing, painful abdominal mass in or around the site of a past surgery. There is, however, considerable variation, because some masses grow quite rapidly and others inflict no pain. The nonspecific nature of endometrioma presents a diagnostic challenge, and it is often considered an incisional hernia, suture granuloma, abscess, lipoma, or one of several other conditions, until surgical excision and histological studies confirm the diagnosis.^3-5 Accurately diagnosing endometrioma is important to provide alleviation for the pain and anxiety associated with this disease, obtain appropriate surgical treatment, and avoid further postoperative diagnostic studies. We report a case of surgical scar endometrioma associated with a Pfannenstiel incision made during a Cesarean section. The endometrioma initially was thought to be an incisional hernia.

Case report

A 26-year-old woman was referred for a general surgery consultation by her primary care physician for a suspected incisional hernia. The patient had delivered a child via Cesarean section 2 years earlier and recently had developed a painful mass along the lateral aspect of her Pfannenstiel incision. She noted that the pain over this site worsened during menstruation.

The patient had a medical history of oral herpes, hypertension during pregnancy, and asymptomatic intermittent heart palpitations. Her only medication was a daily oral contraceptive. Her surgical history included the Cesarean section 2 years earlier and an elective abortion 9 years earlier. She had no history of endometriosis.

On physical examination, a fixed, hard abdominal mass was located on her left side, superior to the Pfannenstiel scar. Although a palpable fascial defect was present, the mass, which measured approximately 3 x 4 cm, was not reducible. Because the mass did not appear to be a true incisional hernia, the patient underwent ultrasonography, which revealed a round, hypoechoic, extrafascial, extramuscular mass in the left subcutaneous area (Figure 1). This finding led to a diagnosis of abdominal scar endometrioma.

After the case was discussed with the patient and her family and informed consent was obtained, she underwent excision of the abdominal mass. Surgical incision removed a 3 x 3-cm mass from the subcutaneous tissue, just above the fascia of the anterior abdominal wall (Figure 2). The remaining defect did not reveal full-thickness abdominal wall involvement; however, there was some attenuation of the fascia superficially. The wound was irrigated thoroughly with warm, normal saline before closure.

Gross examination of the abdominal mass showed a semi-firm cut surface with cystic structures measuring up to 0.4 cm in diameter and filled with a dark brown material (Figure 3). Diagnosis of endometrioma was confirmed by histologic examination of the excised mass, which showed three characteristics of endometriosis: benign endometrial glands, endometrial stroma, and brown pigment-laden macrophages (Figure 4).

Discussion

Endometrioma is a mass of endometriosis, a benign disorder characterized by the presence and proliferation of endometrial glands or stroma in abnormal locations outside the uterus. Within the uterus, endometrial glands function to prepare the uterine lining for fetal implantation. Outside the uterus, ectopic endometrial tissue continues to proliferate, secrete mucous, and cyclically hemorrhage. This continued proliferation of ectopic cells contributes to endometrioma formation while the hemorrhage and secretions, and those undergoing abdominal surgery.⁷ Extrapelvic endometriosis, while less common, may affect every organ system except the heart and spleen.

The relationship between intrapelvic endometriosis and extrapelvic endometrioma is not clear. Only 26% of patients presenting with extrapelvic endometrioma also have intrapelvic endometriosis.⁸ Among women with a confirmed diagnosis of intrapelvic endometriosis, only 1.6% were found to have extrapelvic endometrioma presenting as either incisional or umbilical endometrioma.⁵ The abdominal wall is the most common location for extrapelvic manifestations of endometriosis, with the endometrioma usually, but not always, developing in proximity to a surgical scar.⁹ Abdominal wall endometrioma is generally confined to the cutaneous or subcutaneous tissues, although the rectus abdominus muscle occasionally is involved.

Surgical scar endometrioma is relatively uncommon and is usually associated with Cesarean sections or hysterectomy. Its incidence after Cesarean section is difficult to determine, but estimates range from 0.03% to 0.47%.⁵ Mid-trimester abortion via hysterotomy, a procedure that is performed far less often than Cesarean sections or hysterectomies, is associated with the highest occurrence rates (2%) of surgical scar endometrioma.² Although surgical scar endometrioma may occur in association with a variety of other incisions, it usually is attributed to gynecologic or obstetric procedures and develops from 1 to 20 years postoperatively.² No particular type of Cesarean incision has been identified as carrying higher or lower risk for endometrioma development; however, in cases where the incision type was specified, the Pfannenstiel incision was associated with endometriomas more often than the midline incision.¹⁰ The left lateral predisposition of intrapelvic ovarian endometrioma is known,¹¹ but extrapelvic endometrioma has not been identified as having a preferential position. Rarely will endometrioma develop in the absence of a surgical scar, and in these cases, it adheres to or infiltrates the muscles of the abdominal wall. The pathogenesis of scarless endometrioma, commonly thought to result from retrograde menstruation or metaplasia, differs from surgical scar endometrioma, which generally results from mechanical transplantation during a surgical procedure.^3,9

Most features of our case, such as the patient's medical and surgical history, her symptoms, and the physical examination findings, illustrate a very typical presentation of surgical scar endometrioma. To our knowledge, she did not have concomitant intrapelvic endometriosis, which we would expect to be absent in most patients presenting with extrapelvic endometrioma. She also had none of the typical risk factors for intrapelvic endometriosis, which includes a family history of endometriosis, menarche at an early age, short menstrual cycles (< 27 days), long duration of menstrual flow (> 7 days), nulliparity, delayed childbearing, and defects in the uterus or fallopian tubes. Although intrapelvic endometriosis is more common in our patient?s age group (25?30 years), extrapelvic endometriosis usually manifests in women who are between the ages of 35 and 40 years.

The etiology of surgical scar endometrioma is straightforward and involves mechanical transplantation of endometrium or placental cells into the wound during a surgical procedure.⁴ To prevent surgical scar endometrioma, thorough saline irrigation of the surgical site before wound closure is recommended.¹² The pathogenesis of intrapelvic or extrapelvic endometriosis in the absence of surgery is unknown. Four theories have been postulated to explain the origin of this disorder: (1) metaplastic, (2) Mulleriosis, (3) vascular/lymphatic dissemination, and (4) regurgitation. The metaplastic theory posits that metaplasia of the peritoneal membrane gives rise to cells that assume the anatomic appearance and biologic response of endometrial tissue. The Mulleriosis theory attributes the presence of endometrium in pouches of the peritoneum to anatomic deformities of the broad ligament and posterior peritoneum or to unsuccessful formation of Mullerian ducts during embryogenesis. According to the vascular/lymphatic dissemination theory, endometrial cells are transported through lymphatic or venous channels to distant sites, where they establish themselves and proliferate. The regurgitation theory suggests that layers of the endometrium sloughed off into the endometrial cavity during a nonconceptive menstrual cycle exit the cavity by menstruation through the cervical canal and retrograde menstruation through the fallopian tubes. In both surgical scar endometrioma and endometriosis, misplaced endometrial cells continue to multiply and secrete under the influence of estrogens, eventually becoming symptomatic.

Various medical treatments are available to manage intrapelvic endometriosis, all of which depend primarily on creating a hypoestrogenic environment that deprives the endometriosis of nourishing hormonal stimulation. Low-dose estrogen oral contraceptives are often used to alleviate pain from endometriosis and limit the extent of cell growth. Medical treatment for extrapelvic endometrioma, however, has generally been found to be ineffective.^2,13 This was true for our patient, who was taking oral contraceptive pills but still experienced tumor growth and symptoms. Since medical treatment is ineffective, surgical excision remains the treatment of choice. Surgery is curative for extrapelvic endometrioma in the vast majority of cases.

Preoperative diagnosis of endometrioma is possible, based primarily on clinical presentation, obtaining a thorough history, and physical examination. Computed tomography scanning, magnetic resonance imaging, or ultrasonography have some utility in ruling out hernia and other conditions (ie, neoplasm, lipoma, abscess, suture granuloma, hemangioma, calcifications, sebaceous cysts) and in determining the exact location of the mass. Because no imaging features can facilitate a definitive diagnosis of endometrioma, extensive imaging studies are unnecessary.

Fine needle aspiration has been used to confirm the diagnosis of endometrioma before surgical excision.¹⁴ There is concern that this procedure has the potential to seed the needle tract with cells and cause recurrence, especially in patients with concomitant intrapelvic endometriosis,⁶ although this has not been reported. Most commonly, the diagnosis is made on postoperative histological examination, in which the presence of at least two of the following confirms the diagnosis of endometrioma: endometrial glands, stroma, or hemosiderin pigment (Figure 4).

Conclusion

Endometrioma should be included in the differential diagnosis for any abdominal mass in women of childbearing age, especially if it is in close proximity to a surgical scar. Greater awareness of endometrioma by general surgeons can increase preoperative diagnosis, guide surgical treatment, and potentially eliminate the need for postoperative diagnostic studies.

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