Endometriosis

Endometriosis, commonly seen in women of reproductive age, refers to ectopic estrogen-dependent endometrial-like tissue outside the uterine cavity, characteristically and commonly identified on imaging by the presence of T1 bright T2 dark implants on the ovaries called chocolate cysts.

Description

Endometriosis is a chronic gynaecological disorder characterised by the presence of endometrial-like tissue (glands and stroma) outside the uterine cavity. This ectopic tissue is most commonly found in the pelvis, particularly on the ovaries, cul-de-sac, and uterosacral ligaments, but can be found anywhere in the body. It is a common cause of chronic pelvic pain and subfertility in women.

Pathogenesis

While the exact cause of endometriosis is unknown, the most widely accepted theory is metastatic implantation form retrograde menstruation, which suggests that during menstruation, endometrial cells are transported backwards through the fallopian tubes into the pelvis¹. These cells implant, grow and cause inflammation. Other theories involve coelomic metaplasia and lymphatic or haematogenous spread.

The ectopic endometrial-like tissue, termed endometrioma, exhibits a physiological response to the hormonal fluctuations of the menstrual cycle akin to normal intrauterine endometrium i.e., they undergo cyclical proliferative, secretory, and desquamation phases. Accompanying these changes is the modulation of proinflammatory cytokine and prostaglandin levels, leading to localised inflammation that results in neovascularisation and fibrous tissue proliferation.

The resultant inflammatory milieu and tissue remodelling contribute to the formation of adhesions, which, along with the cyclical bleeding and inflammation, underlie the chronic pelvic pain and subfertility commonly associated with endometriosis. The condition’s pathophysiology encompasses a self-perpetuating cycle of inflammation, tissue damage, and repair, leading to the progressive nature of the disease and its complications.

Subtypes

Endometriosis is often classified according to its location:

Superficial Peritoneal Lesions: These are most common and are found on the peritoneal surface.
Ovarian Endometriomas: Often referred to as chocolate cysts due to their appearance, these are cysts filled with old blood.
Deeply Endometriosis (DE): This is the most severe form. Traditionally considered to extend more than 5 mm under the peritoneal surface but redefined in 2021 as extending to any depth beneath the peritoneal surface.

Epidemiology, Risk Factors & Associations

Reproductive-age women (6-10% of women), mean age of diagnosis 25 – 29 years.

Risk factors include:

Delayed childbearing or nulliparity
Early menarche (typically before 11 to 13 years old), shorter menstrual cycles (less than 27 days), and longer menstrual flow
Family history of endometriosis
Mullerian duct anomalies
Low BMI or height greater than 68 inches
High consumption of transunsaturated fat
Exposure to dieythystilbestrol in-utero

Associations:

Endometrioid carcinoma of the ovary
Clear cell carcinoma of the ovary

Clinical Features

Symptoms do not necessarily correlate with the severity of the disease but may include:

Chronic pelvic pain
Dysmenorrhea and metrorrhagia
Dyspareunia
Infertility
Menstrual irregularities
Painful defecation (in rectovaginal endometriosis)

Complications

Chronic pelvic pain
Infertility or subfertility (30-50% of women with endometriosis)
Adhesion formation leading to bowel and bladder complications
Risk of transformation to ovarian endometrioid carcinoma or clear cell carcinoma is low (<1%)

Pathological Features

Histopathology

Macroscopic: Lesions can appear as clear vesicles, powder burns or dark blue, brown, or red nodules or cysts.
Microscopic: Presence of endometrial glands and stroma outside the uterus.

Serology

CA-125 can be elevated but is non-specific.

Biochemistry

No specific biochemical markers

Radiological Features

General Features

Characteristically demonstrates a range of findings based on the subtype and location, from superficial peritoneal lesions to endometriomas and deep infiltrating endometriosis.
Characteristically, an endometrioma is hyperintense at T1W MR imaging and hypointense at T2W MR imaging. However, not all endometriomas show marked decrease in T2 signal, depending on their age, the amount of haemosiderin, and the protein concentration.
Multiplicity of lesions and endometrial implants elsewhere in the pelvis support the diagnosis of endometriomas over other cystic lesions such as dermoids, cystadenomas, and functional or haemorrhagic cysts
The lack of fat allows one to differentiate endometriomas from dermoids (mature ovarian teratoma)
Lesions are generally hypovascular
Deep endometriosis manifests in the posterior compartment in most cases, including the uterosacral ligaments (most common), rectum and rectosigmoid junction.
Kissing Ovaries Sign – Intrapelvic adhesions between the ovaries.
Transvaginal sonography is the first-line modality for pelvic pain and infertility evaluation.

CT

Non-contrast: May show cystic adnexal masses or nodularity, but is often non-specific.
Contrast-enhanced: Can show enhancement of solid components.

MRI

T1WI: Endometriomas appear hyperintense due to haemorrhagic content.
T1 Fat-Saturation: High signal intensity that persists on fat-suppressed and out-of-phase imaging
T2WI:
- Shading sign – Endometriomas characteristically appear low on T2WI compared to skeletal muscle.
- However, not all endometriomas show marked decrease in T2 signal, depending on their age, the amount of hemosiderin, and the protein concentration.
- DE can appear as low T2 signal nodules.
T1 C+: Endometriomas typically do not enhance post-contrast.
DWI/ADC: Restriction in solid components of endometriosis.

US²

B-mode: Endometriomas appear as cystic adnexal masses with homogenous low-level internal echoes (ground glass appearance). Fluid-fluid levels may be seen. DE can appear as hypoechoic nodules.
Colour: Minimal vascular flow in endometriomas.

NM

PET FDG: Not typically used for endometriosis

Grading and Staging

The American Society of Reproductive Medicine (ASRM) classifies endometriosis into four stages (I-IV) using a point system that evaluates the disease’s severity based on specific criteria. These criteria include:

Location: Where the endometriotic lesions are found within the pelvic region.
Extent: The size or spread of the endometriotic implants.
Depth: How deeply the endometriotic lesions penetrate into the affected tissues.
Presence and Severity of Adhesions: The degree to which fibrous bands of scar tissue have formed, potentially causing organs to adhere together.

Stage I (Minimal): Characterised by isolated implants and possibly small adhesions.
Stage II (Mild): Involves more and slightly deeper implants without significant adhesions.
Stage III (Moderate): Features deeper implants, more extensive adhesions, and may include endometriomas.
Stage IV (Severe): Marked by extensive deep implants, large endometriomas, and severe adhesions.

Diagnosis

Diagnosis is primarily clinical, supported by imaging. However, definitive diagnosis requires histological confirmation, usually through laparoscopy.

Differential Diagnosis

Haemorrhagic functional cysts: Endometriomas tend to have higher T1 and low T2, due to higher protein content and viscosity (T2 shading).
Mature ovarian teratoma
Ovarian cysts: Simple ovarian cysts are anechoic with posterior acoustic enhancement on US, do not show high T1 signal or shading on MRI.
Ovarian neoplasm: Can have complex features including septations, solid components and abnormal vascularity.
Pelvic inflammatory disease: Shows non-specific endometrial fluid with presence gas considered diagnostic. Endometrium thick irregular and hypoechoic endometrium. May have associaed hydrosalpinx or pyosalpinx. Tubovarian abscess may be seen. Fibrosis and adhesions represent end-stage disease.
Adenomyosis: Shows thickening of the junctional zone >12mm on MRI, predominantly affects the uterus.

Management

Management options include hormonal therapy to suppress ectopic endometrial growth, analgesics for pain management, and surgery (laparoscopic excision or ablation of lesions, hysterectomy in severe cases). Fertility treatments may be needed in cases of associated infertility.

References

Updated on 25 July 2024

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