Adenomyosis

Etiology

While the histology is well-described, the etiology of adenomyosis is not known definitively. Researchers have postulated several theories. The most commonly accepted theory is that adenomyosis results from a disrupted boundary between the deepest layer of the endometrium (endometrium basalis) and the underlying myometrium. This process leads to a cycle of inappropriate endometrial proliferation into the myometrium with subsequent small vessel angiogenesis as well as adjacent myometrial smooth muscle hypertrophy and hyperplasia. Data demonstrating a higher prevalence of adenomyosis following dilation and curettage and cesarean section support this theory.[2][3]

A second theory proposes an embryologic mechanism whereby pluripotent Mullerian stem cells undergo inappropriate differentiation leading to ectopic endometrial tissue. This theory has support from evidence demonstrating altered expression of specific genetic markers, in addition to case reports of endometrial tissue found in women with Rokitansky-Kuster-Hauser syndrome (Mullerian agenesis).[4][5][6][7]

Other less well-accepted theories propose altered lymphatic drainage pathways and displaced bone marrow stem cells to explain the presence of ectopic endometrial tissue.[8]

Epidemiology

Accurate demographics and disease prevalence are unclear due to previous underreporting and under-diagnosis. Estimates range from 5% to 70% with more recent data suggesting a prevalence of 20% to 35%.[8][9] Classically, adenomyosis is described as a disease of pre-menopausal, multiparous women in their thirties to forties; however, this reflects the inherent bias towards women undergoing a hysterectomy. Improvements in the diagnostic ability of ultrasound and MRI criteria have led to more insight about affected populations. 

A rare form of the disease, termed juvenile cystic adenomyosis, is characterized by more extensive hemorrhage within myometrial cysts and is typically seen in women younger than 30. Symptoms are typically refractory to medical therapy and require surgery, either myomectomy or hysterectomy.[10][11]

Risk factors for adenomyosis include conditions leading to increased estrogen exposure (increased parity, early menarche, short menstrual cycles, elevated body mass index, oral contraceptive pill use, tamoxifen use) and prior uterine surgery (dilation and curettage, cesarean section, myomectomy, etc.).[8]

Pathophysiology

Inappropriate endometrial tissue proliferation within the myometrium leads to symptoms through a variety of mechanisms. Normal endometrial tissue is responsible for prostaglandin production which drives the contractions of menstruation. Ectopic foci of adenomyosis lead to increased levels of prostaglandins which result in dysmenorrhea which characterizes the disease. Estrogen also drives endometrial proliferation, which medical therapies aim to reduce.

Heavy menstrual bleeding is thought to be caused by a combination of factors which include increased endometrial surface area, increased vascularization, abnormal uterine contractions, and increased cell signaling molecules such as prostaglandins, eicosanoids, and estrogen.[8][12][13][14]

Histopathology

Histologic diagnosis of adenomyosis is the presence of endometrial stroma and glandular tissue within the smooth muscle of the myometrium. Different definitions of the required depth of invasion exist, some using an absolute measurement between 2.5 to 8 mm while others use a percentage. Additionally, several histologic grading classifications attempt to characterize the burden of disease.[9] Overall, the histologic diagnosis is not entirely standardized and significantly affected by the quality of tissue sampling.

History and Physical

The clinical diagnosis of adenomyosis is difficult as a variety of common gynecologic conditions share the signs and symptoms. The most common symptoms include heavy menstrual bleeding or painful menses. Clinical diagnostic accuracy is neither sensitive nor specific.[9] Other less common symptoms include chronic pelvic pain and dyspareunia.[8] It is also crucial to note that up to 33% of women with adenomyosis may be asymptomatic.[8] While infertility is often considered a potential presenting symptom, the data is inconclusive with some sources reporting an association of 11% to 12% with adenomyosis.[8]

The physical exam classically demonstrates a “boggy” enlarged uterus due to the combined effects of increased vascularization from ectopic endometrial tissue and smooth muscle proliferation. As compared to the enlarged leiomyomatous uterus, a tender uterus is more common.[15]

Evaluation

Laboratory Evaluation

Laboratory testing is useful to rule out other disease entities included in the differential diagnosis, in addition to identifying certain complicating features such as anemia due to heavy menstruation. While some biomarkers do exist, none are specific for adenomyosis.[9]

Radiologic Evaluation

Imaging is the primary means of making the diagnosis. Previously the preferred modality was MRI; however, recent data has shown the transvaginal ultrasound to match the sensitivity and specificity of MRI (89% sensitivity, 86% specificity).[16] The availability of ultrasound and the increased costs of MRI have led to ultrasound becoming the preferred modality for the initial evaluation, reserving MRI for equivocal cases.[17]

Ultrasound

Transvaginal ultrasound is the preferred diagnostic imaging modality for adenomyosis. The characteristic findings reflect the histopathologic changes of the disease process and can be broken down into three categories:

• Endometrial infiltration: Echogenic striations and nodules, myometrial cysts, and “lollipop” diverticula (cystic striations)
• Smooth muscle proliferation: Focal or diffuse myometrial thickening with indistinct borders more commonly involving the posterior fundus and heterogenous echotexture manifesting as “venetian blind” appearance of thin linear shadows
• Vascularity: Color Doppler demonstrating an increased number of tortuous vessels throughout the involved myometrium as opposed to leiomyomas which displace vessels

A number of mimics can have similar findings on the ultrasound exam, including tamoxifen use, prior endometrial ablation, endometriosis, uterine contractions, vascular malformations, leiomyomas, and cancer. Certain techniques such as low-frequency, coronal reconstructions, 3-D ultrasound, cine-clips, color Doppler, and saline infusion sonohysterography (SIS) can be used to differentiate between these entities.

MRI

Characteristic findings on MRI parallel the same features seen on ultrasound:[18][19]

• On T2-weighted imaging, uterine enlargement characterized by ill-defined, low-signal-intensity regions within the junctional zone is reflective of smooth muscle hyperplasia (junctional zone thicker than 12 mm is generally accepted as diagnostic)
• T2 hyperintense myometrial cysts reflecting regions of ectopic endometrial tissue (can also have increased intrinsic T1 signal or increased susceptibility in hemorrhagic foci)
• Contrast enhancement is generally not reliable for assessment of vascularity as compared to color Doppler ultrasound

Similar to ultrasound, a variety of mimics ranging from co-existing gynecologic pathologies to physiologic variants exist. Susceptibility weighted imaging, diffusion-weighted imaging, MR spectroscopy, cine MR imaging, and increased 3T field strength are all problem-solving strategies.[18]

It is important to obtain the MRI in the late proliferative or secretory phase (days 7 to 28) due to the decreased signal of normal myometrium during the early proliferative phase (days 1 to 6).[18]

Treatment / Management

The first consideration in treatment selection is the desire for fertility, which will guide treatment considerations. Hysterectomy is the definitive cure. The remaining options target the primary symptoms of heavy, painful menstrual bleeding while preserving the uterus.

Medical Therapies

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the primary medical therapies. These medications target the cyclooxygenase enzyme which produces the prostaglandins responsible for painful cramping during menstruation.[8][20](A1)

Various hormonal therapies are available which include oral contraceptive pills (OCPs), levonorgestrel intrauterine device (IUD), danazol, and aromatase inhibitors. These therapies aim to reduce the estrogenic effects which lead to endometrial proliferation. Data to support a particular therapy lack well-powered randomly controlled trials (RCTs); however, levonorgestrel IUDs are generally considered to be the primary therapy due to decreased side effect profile and overall success rates.[8][21][22](B3)

Minimally Invasive/Surgical Therapies

Several interventional radiologic procedures exist which may be options for the patient who fails medical therapy but desires future fertility. MRI-guided and ultrasound-guided high-intensity ultrasound thermal ablation can be done to target focal disease.[23][24][25] Uterine artery embolization reduces blood flow to the uterus as a whole, thereby inducing necrosis leading to an overall reduction in uterine size.[26][27][28] These therapies show promise but require additional data on direct treatment comparisons and long-term outcomes.[9] While these therapies aim to preserve fertility, infertility is an understood risk.(B2)

Endometrial ablation may be considered in patients who do not desire future fertility but prefer a less invasive alternative to hysterectomy. Limitations include the inability to target deeper adenomyotic foci due to its superficial approach.

Myomectomy and partial hysterectomy are more invasive options that aim to preserve fertility. These options allow for targeting of deeper foci; however, subsequent scarring may lead to disease recurrence as the endometrial-myometrial interface is disrupted, a risk factor for adenomyosis. Additional considerations include the potential for future pregnancy complications due to altered uterine anatomy with an increased risk of uterine rupture, premature rupture of membranes, premature labor, and spontaneous abortion.[8][9]

Hysterectomy remains the definitive cure for adenomyosis.

Differential Diagnosis

The differential diagnosis of adenomyosis is broad. The signs and symptoms of adenomyosis are similar to other disease entities characterized by abnormal uterine bleeding, dysmenorrhea, or infertility. The Federal International Board of Gynecology (FIGO) classification scheme utilizes the PALM-COEIN mnemonic as a clinical tool for more consistent reporting practices.[9][29] The mnemonic divides the diagnosis of abnormal uterine bleeding into structural and non-structural categories with each letter representing the following entities:

• Polyps
• Adenomyosis
• Leiomyoma
• Malignancy/hyperplasia
• Coagulopathy
• Ovulatory dysfunction
• Endometrial
• Iatrogenic
• Not yet classified

Adenomyosis often co-exists with other entities within the differential diagnosis, most commonly leiomyoma (50%), endometriosis (11%), and endometrial polyps (7%).[8][30]

Prognosis

Adenomyosis is a difficult diagnosis to manage as multiple clinical factors must be considered, including fertility, confidence in diagnosis, side effects of medical management, and risk of invasive procedures. Recent data showing an increased prevalence of adenomyosis in younger populations and asymptomatic patients reflects a spectrum of disease which is incompletely understood. Symptoms seem to correlate with the number of adenomyosis foci and the depth of invasion.[31] The consensus to treatment is a stepwise approach with medical therapy to include anti-inflammatory and hormonal agents with progression to minimally invasive procedures such as endometrial ablation/myomectomy or uterine artery embolization. The definitive cure remains hysterectomy.

Complications

The correlation between adenomyosis and infertility is not clearly defined. While some authors cite an association of 11% to 12%, contradictory data also exists.[8] Due to a multitude of confounders and variable diagnostic criteria for adenomyosis, no clear association has been established.[9]

With more validated diagnostic imaging criteria of ultrasound in recent years, future research will be able to characterize associations between adenomyosis and infertility more confidently.