Endometriosis is a disorder of females in the reproductive age group, and it is defined as the presence of endometrial glands or stroma outside the uterine cavity. The most common sites of pelvic endometriosis involve the ovary, uterosacral ligaments, ovarian fossa, the pouch of Douglas, and the bladder. Endometriosis is characterized as endopelvic or extrapelvic/extragenital, depending on the sites involved.
Cutaneous endometriosis can be placed into the subtype of extrapelvic endometriosis. Cutaneous endometriosis is uncommon and occurs when nonneoplastic endometrial tissue is found on the skin. Patients usually complain of cyclic pain during menstruation, a palpable mass, swelling, or even bleeding over the affected sites on the skin. Scar endometriosis is the term used for endometriosis that occurs in the surgical scars, and this can be cutaneous or subcutaneous depending on the location of the lesions.
Cutaneous endometriosis can be divided into primary cutaneous endometriosis and secondary cutaneous endometriosis. The etiology of primary cutaneous endometriosis is unclear and is known to occur spontaneously. The cause of secondary cutaneous endometriosis is assumed to occur due to seeding after procedures relating to abdominal or pelvic surgery resulting in implantation of endometrial tissue into the skin.
The incidence of endometriosis in women of childbearing age is around 5% to 15%. The prevalence of cutaneous endometriosis is 0.5% to 1%. The prevalence of primary cutaneous endometriosis is less than 30% in all cases of cutaneous endometriosis. Umbilical endometriosis represents 30% to 40% of the cases of cutaneous endometriosis. Endometriosis in an episiotomy scar occurs in 0.00007% of births; however, this incidence is thought to be underestimated.
The theories that provide a basis on the pathophysiology of primary cutaneous endometriosis may be explained by the theory of cellular metaplasia, vascular, and lymphatic migration. Meyer, in 1903, proposed the theory of tissue differentiation of the mesothelial cells of the peritoneum into endometrial glands and stroma as a cause of endometriosis. Halban in 1924 proposed the theory of dispersion of cells of the endometrium from the lymphatic vessels, and similarly, Sampson in 1925 supported this theory of dispersion of cells through the hematogenous route.
The pathophysiology of secondary cutaneous endometriosis is described on the basis of implantation of the endometrial cells on the cutaneous sites during surgical procedures and those cells behaving as being similar to uterine endometrial cells that undergo proliferation and shedding during the menstrual cycle.
Histopathological examination demonstrates the combination of endometrial glands and stroma in a biopsy specimen obtained from the lesions.
Females within the reproductive age group are usually affected. However, adolescents are also known to be affected. The patient may have a history of prior surgical procedures such as cesarean section, laparoscopy, tubal ligation, hysterectomy, hysterotomy, or episiotomy that might have predisposed the implantation of the endometrial tissue into the scar. The patient usually presents with cyclic pain during menstruation, swelling that may increase at the time of menstruation, a palpable mass, or bleeding from the affected areas in the skin.
The classic presentation of cutaneous endometriosis is a firm papule or nodule which averages a size of 2 cm in diameter. Umbilical endometriosis is to be suspected if a patient arrives with a nodule at the umbilicus with symptoms such as pain, itching, bleeding, or discharge. There may be local signs of inflammation, such as erythema in the affected areas.
Any similar signs and symptoms, particularly at the scar sites and extremities, should arise suspicion in favor of cutaneous endometriosis. The average time interval between the history of surgical procedures and the onset of symptoms in cases of endometriosis in the gynecological scar is 4.2 years.
Evaluation of cutaneous endometriosis begins with clinical suspicion, which aids in diagnosis. However, the confirmation of the diagnosis can be done by biopsy of the lesion, followed by histopathological examination. History of any surgical procedures done prior is particularly helpful in classifying the disease into primary or secondary lesions.
The use of fine-needle aspiration (FNA) in the diagnosis of scar endometriosis is controversial as this may cause seeding of the endometriotic tissue in new areas, further aggravating the condition. Therefore surgical excision, when done with a safety margin that is at least 1 cm away from the solid lesion, will serve as both a diagnostic and therapeutic option in cases of scar endometriosis.
Imaging studies such as computed tomography (CT) scan and magnetic resonance imaging (MRI) should be done and are helpful if there is suspicion of cutaneous metastases of a tumor as in a gastrointestinal malignancy presenting as Sister Mary Joseph’s nodule, which is a differential diagnosis of umbilical endometrioma.
Some patients may undergo a secondary evaluation with biopsy whereby patients were treated with intralesional corticosteroids with no response initially thinking that the cutaneous lesion was a keloid.
Patients diagnosed with cutaneous endometriosis may need a gynecological workup to evaluate for pelvic endometriosis as studies in patients with endometriosis in gynecological scars have found that 14% of the total patients have associated pelvic endometriosis.
The treatment approach for cutaneous endometriosis can be hormonal or surgical management. Pain management is another aspect, and nonsteroidal anti-inflammatory drugs (NSAIDs) can be used. Hormonal treatment includes the use of gonadotropin-releasing hormonal agonists, danazol, and oral contraceptives. The main mechanism of the hormonal agent is to decrease the cyclical proliferation of the endometrial tissue.
Hormonal treatment is usually meant for reducing the size of the lesions and also provides symptomatic relief for patients before undergoing surgery. Before starting hormonal treatment, patients have to be counseled regarding the side effects such as amenorrhea with the use of danazol and leuprolide. In addition, the symptoms of the disease may return once the hormonal treatment is stopped. Danazol use is associated with side effects such as acne, weight gain, hirsutism, and deepening of the voice. Hormonal treatment serves as an alternative treatment for those who do not opt for surgical treatment and also for those with coexistent pelvic endometriosis. However, surgical excision of the lesion with a wide margin is the treatment of the choice.
The recurrence rate is very rare with complete surgical excision. Recurrence is seen if there is an incomplete excision. Regarding the perioperative management of the lesions, the recommendation varies on either performing the surgery at the end of the menstrual cycle, whereby the lesions are smaller in size or initiating preoperative hormonal agents to reduce the size. Postoperative use of hormonal agents can also be done, and the goal is to prevent a recurrence. The combination of hormonal treatment followed by surgical excision is a better approach for many cases.
A strong suspicion is needed for diagnosis of cutaneous endometriosis since this condition might be mistaken for diseases such as keloid, dermatofibroma, dermatofibrosarcoma protuberans, cutaneous metastasis of cancer (e.g., Sister Mary Joseph nodule), or melanoma. The main feature to keep in mind while suspecting cutaneous endometriosis is that the symptoms it produces are of cyclical nature that may range from cyclical pain only to cyclical increase and decrease in the size of the mass relating to the start and end of the menstruation cycle.
The prognosis of cutaneous endometriosis is considered favorable. If the patient has undergone surgical excision of the lesion, the recurrence rate is low. In a study conducted by Lopez-Soto et al. (2018), out of 33 women who underwent treatment for cutaneous endometriosis, only three had a recurrence (9%).
Although endometriosis is considered to be a benign condition, malignant transformation has been reported. However, the exact figure of malignant transformation of endometriosis is unknown. Furthermore, the causes of malignant transformation of endometriosis are not clear, but genetic, immunologic, and hormonal factors have been implicated. One of the complications to be mentioned relating to cesarean scar endometriosis is the ability of the lesion to undergo malignant transformation (typically with an endometrioid or clear cell carcinoma histology), which have a more aggressive behavior. Recurrences after the treatment can also be one of the complications.
There are no preventive measures in the case of cutaneous endometriosis. Careful clinical and histological evaluation is warranted for any cutaneous lesion, particularly for any lesion occurring at a previous cesarean scar. As patients may mistake such lesions for a tumor, this can be addressed with an appropriate diagnosis and educating the patient on the treatability of the lesion.
Cutaneous endometriosis is best managed by an interprofessional team approach. The team may include a primary care clinician, a dermatologist, a gynecologist, a pathologist, and a pharmacist. The presentation of cutaneous endometriosis can be confusing. The patient may first present to a clinician who may be unaware of the cyclical nature of the disease presentation. Once the proper diagnosis is made, treatment can be started. Even after treatment, patients need regular follow up to look for recurrences.
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