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"Medical Journeys" is a set of clinical resources reviewed by doctors, meant for physicians and other healthcare professionals as well as the patients they serve. Each episode of this 12-part journey through a disease state contains both a physician guide and a downloadable/printable patient resource. "Medical Journeys" chart a path each step of the way for physicians and patients and provide continual resources and support, as the caregiver team navigates the course of a disease.

Endometrioma is the most common form of endometriosis that is present on or in the ovary. Endometriomas not only can cause painful symptoms, but also pose the greatest threat to ovarian reserve and fertility. These lesions occur in 17-44% of those with endometriosis and account for 35% of all benign .

Generally responding poorly to standard medical treatment, these cavities are filled with old, dark brown menstrual blood -- hence are sometimes called chocolate cysts. Whether adhering to the surface or penetrating into the ovary, these fluid-filled sacs can damage healthy ovarian tissue, foster a toxic environment for fertility, and lead to damaging invasive surgeries that may trigger premature loss of ovarian function.

Pathogenesis of Endometriomas

There are several theories about how endometriomas develop. "Most of them involve some sort of invagination," said Ja Hyun Shin, MD, MS, of Weil Cornell Medicine in New York City. "Endometriosis deposits adhere to the surface of the ovary, there's buildup of toxic fluid, and the tissue is able to invade the ovary."

Put more technically, endometriomas may form by inversion and subsequent progressive invagination off the ovarian cortex with endometriotic implants filling the cyst with hemolyzed blood. Another explanation is metaplasia of invaginated ovarian which creates active endometrial tissue within the ovary.

Ovulation may be a particularly for the ovary -- a point when endometriotic tissue can more easily gain access to the follicles.

Endometriomas can affect one ovary or both simultaneously: approximately 28% of endometrioma patients have .

Risk Factors, Recurrence

The risk factors for developing these stubborn cysts are generally the same as for endometriosis itself – i.e., early menarche, shorter intervals between periods, later menopause, and more exposure of the menstrual cycle. The patient's family history is also important -- if a mother or a sister had endometriomas, for example, a daughter or another sister may develop them as well.

Recurrence of endometriomas is common, but the frequency is unclear. "We do not have exact data on endometriomas per se for recurrence," said Joseph Nassif, MD, of Baylor College of Medicine in Houston, "but according to an English study, 48% of patients with endometriosis or endometriomas will need surgery and one-fifth of these will need another surgery."

An analysis by reported cumulative recurrence rates at 12, 24, 36, and 60 months of 3.7%, 6.7%, 11.1%, and 16.7%, respectively, after conservative surgery and hormonal treatment in woman ages 40 to 49. Recurrence correlated with multilocular cysts, previous surgical history of ovarian endometrioma, and salpingectomy, but not use or duration of postoperative medication. In multivariate analysis, large cysts (>5.5 cm) was the only risk factor for recurrence in this age group.

Treatment of Endometriomas

Suspected endometriomas can sometimes be found by palpation during a pelvic exam, Nassif noted. "If you're not sure, you go to intrapelvic ultrasound or magnetic resonance imaging, with or without contrast." Definitive diagnosis requires microscopic examination of the lesion. Shin stressed that early diagnosis is essential.

If no malignancy is found and the patient is not experiencing symptoms or showing progression of endometriomas, active surveillance may be enough, Nassif said. "If she's not symptomatic, we can wait and see." He recommends regular follow-up every 3 to 6 months for 3 years to monitor for progression and then yearly after that.

However, since endometriomas do not respond well to medical therapies such as progesterone, combination oral contraceptives, or agents targeting gonadotropin-releasing hormone (GnRH) such as GnRH agonists and antagonists, symptomatic lesions or those threatening fertility may need to be removed surgically. Surgical treatment can be in the form of ovarian cystectomy or oophorectomy depending on the patient's overall clinical picture, reproductive desires, and treatment goals.

According to , while surgical treatment may improve spontaneous pregnancy rates by restoring pelvic anatomy, it remains unclear whether operating on the ovary itself is beneficial as it may not reverse the inflammatory and biomolecular changes that adversely influence fertilization and implantation.

"There's a big decision to be made," said Shin. "Should you do surgery, and when should you do it?" That requires a careful conversation about how to proceed with both a surgeon and a reproductive medicine specialist. Competing risks need to be balanced: "While endometriomas can interfere with egg retrieval, extracting them from surrounding ovarian tissue can also damage the ovary," she cautioned.

"Since medical treatment is not always very effective, surgery is the standard, especially if a woman is going to undergo ART [assisted reproductive technology]," Shin added. Medical therapy after excision, however, is offered to lower the risk of recurrence. Again, these therapeutic agents include combined estrogen/progestins such as oral contraceptives, progestin-only medications, and GnRH agonists or antagonists, which help to suppress possible residual lesions owing to their estrogen-reducing effects.

Assessing Surgical Candidates

In planning individualized treatment for each patient, multiple factors come into play, said Nassif. These include the age of the patient, the presence and severity of her symptoms, the laterality and size of the endometriomas, concern for malignancy, her ovarian reserve, the potential for recurrence, and her intention to have a family.

In the case of a woman hoping to become pregnant, does she want to conceive spontaneously out of personal preference or for religious or financial reasons, or is she able and willing to undergo ART?

With larger cysts impeding access to the eggs during ART, surgery may be the best route. Despite a lack of compelling evidence, the European Society of Human Reproduction and Embryology cautiously suggests that surgery may be to enhance fertility.

As to the type of invasive intervention, Shin stressed that candidate lesions should be surgically excised when possible, rather than drained or ablated. In rare situations, these non-excisional techniques are considered if the ovarian reserve is a significant concern after discussion with the reproductive endocrinologist, understanding the lack of pathologic diagnosis and that recurrence is more common without excision.

Ablative procedures such as electrocautery, microwave, radiofrequency, or cryoablation may leave behind residual tissue that can lead to recurrence. As with any treatment, patients should be aware of the risks and benefits of each technique and be actively involved in the shared decision-making process with their provider.

Conserving Fertility

For women who want to have a family either immediately or further into the future, the option of oocyte cryopreservation is important to discuss before surgery. "I make it a point to discuss saving eggs with my patients of reproductive age," said Shin. "This approach gives them a sense of security."

The tissue to be preserved should be taken before rather than during the surgery to remove the endometrioma, Nassif cautioned. "More and more patients today are asking for this procedure."

At the end of the day, early diagnosis and careful follow-up of these patients are key, said Shin. "Endometrioma can be a complex disease. And if patients do need surgery, they should be referred to specialized surgeons with expertise in minimally invasive gynecologic surgery to remove the lesions without damage to the remaining ovarian tissue."

Although endometriomas pose significant challenges, approaches from surveillance to surgery can help affected women, said Nassif. And if standard gynecologic treatment isn't enough, "there's an increasing number of specialty centers all over the world. Patients can be referred to these for very good care."

Read previous installments of this series:

Part 1: Endometriosis: Understanding the Pathogenesis and Pathophysiology

Part 2: Diagnosing Endometriosis

Part 3: Managing Endometriosis: Research and Recommendations

Part 4: Case Study: Endometriosis or Hernia?

Part 5: Endometriosis: Fertility and Pregnancy