Adenomyosis is a benign uterine disorder in which endometrial glands are found in the myometrium of the uterus. Adenomyosis is distinct from endometriosis, which is the presence of endometrial glands outside of the uterus. Adenomyosis is a poorly understood condition.

Two theories prevail regarding the pathogenesis of adenomyosis.^1,2 The first theory suggests that with injury of the endometrium, the basalis endometrium invaginates into the myometrium through an altered or interrupted junctional zone creating adenomyotic lesions. The tissue injury and repair theory may help explain why having a previous uterine procedure (e.g., cesarean delivery, dilation and curettage) increases the risk of subsequent adenomyosis. The second theory suggests that adenomyotic lesions arise from metaplasia of embryonic pluripotent Müllerian remnants. Adenomyosis can be classified as diffuse (involving a large area of endometrium) or focal.¹

Epidemiology

The diagnosis of adenomyosis was previously confirmed in only post-hysterectomy cases, and it was thought to predominate in patients older than 40 years. Improved imaging makes it clear that younger patients also have adenomyosis.¹ In one study of 985 symptomatic patients seen in a gynecology clinic using specific ultrasound diagnostic criteria, adenomyosis had a 20.9% prevalence in the study population (including pre- and postmenopausal, nulligravid, and multiparous patients), with a range of 10% to 35% in histology reports after hysterectomy.³

A population-based study of 650,000 patients estimated the overall incidence of adenomyosis at 1%, or 29 per 10,000 person-years, over a 10-year period based on International Classification of Diseases, 10th ed. (ICD-10) coding.⁴ Of those with adenomyosis, 90.8% had associated clinical symptoms based on chart review.⁴ The incidence of adenomyosis in the study was highest among patients 41 to 45 years of age.⁴ The overall prevalence of adenomyosis in 2015 was 0.8%, with a high of 1.5% among patients 41 to 45 years of age.⁴ The large variations in estimating incidence and prevalence of adenomyosis could be because there are no standard histologic criteria for diagnosis, as well as the recent advent of laparoscopic surgery creating morcellating specimens that alter the arrangement of tissue, leading to a more difficult diagnosis.⁵ Table 1 lists populations in which adenomyosis is commonly diagnosed.¹

CASE

A 42-year-old patient presents with a six-month history of chronic pelvic pain. The patient describes the pain as aching and deep in the pelvis. The patient has regular menses but notes that it has been getting progressively heavier with more dysmenorrhea for the past few years. The patient has a history of infertility, and the uterus feels mildly enlarged and tender on bimanual examination. Pelvic ultrasonography suggests diffuse adenomyosis.

Clinical Presentation

Up to one-third of patients with adenomyosis can be asymptomatic.⁵ Symptoms typically arise between 40 and 50 years of age.⁵ There is no pathognomonic sign or symptom of adenomyosis. Common symptoms include abnormal uterine bleeding (heavy menstrual bleeding and irregular menses) and dysmenorrhea (Table 2). Less common symptoms include dyspareunia and chronic pelvic pain.^6,7

Heavy menstrual bleeding occurs in 40% to 60% of patients with adenomyosis.⁶ Heavy bleeding is likely caused by the increased surface area of the endometrium, subsequent increase in total volume of the endometrium and endometrial glands, or the increased vascularization of the lining of the endometrium and is directly correlated with the extent of myometrial invasion.^5,6 Adenomyosis is part of the American College of Obstetricians and Gynecologists PALM-COEIN acronym for the evaluation of abnormal uterine bleeding in reproductive-aged patients (Table 3).⁸

Dysmenorrhea occurs in 15% to 30% of patients with adenomyosis.⁶ It is postulated that dysmenorrhea is related to the increased number of oxytocin receptors in the endometrium and increased prostaglandin production contributing to uterine contractions causing dysmenorrhea.^5,9 Adenomyosis in a patient with fibroids can cause more severe dysmenorrhea, dyspareunia, or chronic pelvic pain. If a patient with fibroids is having significant dysmenorrhea, dyspareunia, or chronic pelvic pain, an evaluation for adenomyosis may be warranted.