Early Detection and Screening in Endometriosis

Endometriosis affects 1 in 10 women of reproductive age and is often diagnosed after years of symptom onset. Although population-wide screening is not recommended in asymptomatic women, targeted imaging-based assessment in symptomatic high-risk groups offers a feasible pathway for early detection. This article summarizes the evidence supporting imaging-led diagnostic strategies for early disease detection. The concept of augmented pelvic ultrasound and the role of MRI for disease detection are described. MRI for presurgical disease mapping and the added value of structured reporting are explained. The pillars of a successful screening program in screening eligible diseases and how these strategies can be extrapolated for endometriosis diagnosis in an enriched population are proposed.

Key points

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Absence of a robust noninvasive biomarker for screening of endometriosis in a high-risk population is a major hurdle for early disease detection.
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Gynecologic societies endorse use of transvaginal ultrasound (TVUS) as the first-line imaging tool for diagnosis of pelvic endometriosis replacing diagnostic laparoscopy except in special circumstances.
•
Expert interpreted MR imaging complements TVUS in detection and presurgical mapping of pelvic and extrapelvic disease.
•
Presence of an endometrioma—the most recognizable imaging feature of endometriosis—can be used to trigger additional evaluation for deep endometriosis, which is the less recognized but more debilitating disease phenotype.
•
Use of standardized imaging techniques, structured reporting templates, and a multidisciplinary approach to management are key to optimize patient outcomes.

Abbreviations

AEI	advanced endometriosis imaging
AI	artificial intelligence
APU	augmented pelvic ultrasound
CI	confidence interval
DE	deep endometriosis
ESHRE	European Society of Human Reproduction and Embryology
IDEA	International Deep Endometriosis Analysis
PCP	primary care physician
POD	pouch of Douglas
QI	quality improvement
SRU	Society of Radiologists in Ultrasound
TVUS	transvaginal ultrasound

Video content accompanies this article at http://www.radiologic.theclinics.com .

Introduction

Endometriosis is a chronic systemic disease caused by the presence of endometrium-like tissue outside the uterus, responsive to cyclic estrogen. This results in local bleeding, inflammation, and fibrosis, leading to a broad spectrum of clinical manifestations and complications that directly impact the quality of life of young women. ^, It is a relatively common disease affecting approximately 10% of reproductive age women worldwide with a prevalence of 28.1% (95% confidence interval [CI], 26.9%–29.4%) in women presenting with chronic pelvic pain, and in 24.8% (95% CI, 23.9%–25.8%), of women with infertility. Despite the prevalent nature of the disease, there is a documented delay of 5 to 12 years from the time of first symptom onset to a definitive diagnosis. This contributes to significant health care costs, consistent across multiple international studies, with productivity loss representing 75% to 84% of total costs in some populations. ^,^, The vast variability of presenting symptoms, symptom dismissal by patients and health care providers or lack of sufficient awareness of the disease by providers are some explanations for the existing challenge in making an early diagnosis. This is compounded by a lack of availability of a validated noninvasive test for early detection. Population-based screening for endometriosis is not supported or recommended by major gynecologic societies. The United States Preventive Services Task Force explicitly states that there is insufficient evidence to recommend routine screening pelvic examinations for the early detection of benign gynecologic conditions, including endometriosis, in asymptomatic women. It highlights the uncertain benefit of early detection in asymptomatic individuals, and potential harms from false positives and unnecessary interventions. However, there is merit in early detection of disease in symptomatic patients, who can benefit from early intervention to avoid or delay development of adhesions, deep infiltrating lesions, and infertility. ^,^, This approach has elevated the importance of imaging-led disease diagnosis in high-risk patients, made possible due to a key update in 2022 by the European Society of Human Reproduction and Embryology (ESHRE). ESHRE endorsed the use of transvaginal ultrasound (TVUS) and MR imaging as first-line, noninvasive tests in place of diagnostic laparoscopy. They recommended that the diagnosis be made based on clinical symptoms, physical examination, and imaging findings, reserving laparoscopy when imaging was inconclusive or when surgical management was indicated. In this article, “screening” refers specifically to targeted or risk-stratified early detection among symptomatic or high-risk women, rather than population-based screening of asymptomatic individuals, which current guidelines do not recommend.

Disease phenotypes and imaging in early disease detection

Disease Phenotypes

There are 4 phenotypic subtypes of endometriosis. ^,^, These include superficial/peritoneal endometriosis which is better detected at laparoscopy with a sensitivity of 90% to 97%, and a specificity of 40% to 77%. ^, The second is ovarian/adnexal endometriomas that are identified by TVUS with a sensitivity of up to 93%, specificity of up to 96% and on MR imaging with a sensitivity of 95% and specificity of up to 91%. The next subtype is deep endometriosis (DE), the most debilitating form of the disease, identified by TVUS with a sensitivity of 79% to 89.8% and a specificity of 75.9% to 94% when compared with surgical visualization or histology and on MR imaging with a sensitivity of 83% to 94% and specificity of 77% to 95%. The last subtype is extrapelvic endometriosis, imaging visualization of which is site specific, with MR imaging scoring over TVUS but without published pooled estimates of sensitivity or specificity.

Role of Imaging in Early Detection

Imaging, especially TVUS, has been used to diagnose endometriosis for more than a decade, ever since the International Deep Endometriosis Analysis (IDEA) consensus was published in 2016. This protocol was designed to improve detection and preoperative mapping of DE using ultrasound. It was performed in specialist centers requiring dedicated training and expert interpretation, which, although an excellent protocol, is not universally adapted. Building on the IDEA approach, a more recent and simplified TVUS protocol has been published by the Society of Radiologists in Ultrasound (SRU) called the augmented pelvic ultrasound (APU) technique. The APU technique can be performed in 5 minutes or less and can be added to routine pelvic ultrasound workflows. This requires some additional training and can be used in a preselected high-risk population with the goal of early disease detection.

Defining the at-risk population that may benefit from imaging

The SRU consensus panel recommends performing APU in symptomatic premenopausal and early postmenopausal women within 5 years of menopause. These high-risk symptoms include chronic pelvic pain or period-related pain (dysmenorrhea) that affect daily activities; deep dyspareunia; cyclical gastrointestinal symptoms (especially painful bowel movements) or cyclical urinary symptoms (hematuria, dysuria); infertility/subfertility with any of the above symptoms; adolescents with severe or refractory dysmenorrhea or school absence despite initial therapy. ^,^,

Symptomatic adolescents or patients with superficial disease may be imaging negative and would qualify for a diagnostic laparoscopy at the discretion of the treating physician. DE may be incidentally seen on imaging in asymptomatic patients, in whom the disease should be reported; however, current guidelines do not recommend any treatment in these patients.

The Augmented Pelvic Ultrasound Technique

The APU includes 2 maneuvers focusing on the site that is most affected by DE that is, the posterior pelvic compartment located between the posterior surface of the uterus and the anterior rectosigmoid colon. These include (1) posterior-compartment directed sagittal and transverse cine images and (2) the uterine sliding sign. The former targets the torus uterinus and retrocervical space (including the uterosacral ligaments)], parametrial, midrectal, and pararectal regions—sites that are most affected by DE. The uterine sliding sign is a dynamic TVUS maneuver to look for adhesions in the pouch of Douglas (POD). A retrospective case-control study noted an addition of an average of 5.4 minutes to routine TVUS when the examination was catered to detect endometriosis by trained sonologists. This further emphasizes the feasibility of using TVUS in a high-risk population without significantly disrupting the existing workflow. The APU technique is outlined in Table 1 .

Table 1

Transvaginal ultrasound protocol for suspected endometriosis

Study Components	Scan Plane(s)
Initial Transabdominal Component
1. Uterus midline (with measurement)	Sag
2. Fundus (with measurement)	Trans
3. Right and left ovary/adnexa	Sag
4. Cine: Uterus, ovaries/adnexa	Sag & Trans
Transvaginal Component (TV)
5. Uterus (midline, lateral R/L, with measurement)	Sag
6. Endometrium (with measurement)	Sag
7. Cul-de-sac	Sag
8. Fundus, uterine body (with measurement), lower segment, cervix	Cor
9. Ovaries (right and left) with measurements (length, AP, width)	Sag & Cor
10. Cine: Uterus (x2), ovaries, adnexa	Sag & Cor
11. Cine: Sliding sign focusing on the posterior compartment	Sag

Abbreviations: AP, anteroposterior; Cor, coronal; Sag, sagittal; Trans, transverse.

No special preparation is required for APU. The timing of the scan does not have to match the patient’s menstrual cycle. Although the urinary bladder is typically empty (or minimally filled) for TVUS, a modestly filled bladder can help evaluate the anterior compartment (bladder base/dome) when needed. No bowel preparation is mandated, unlike the practice at specialist centers when bowel preparation is advocated for detailed presurgical planning. ^, Table 2 outlines the normal pelvic anatomy as seen on TVUS.

Table 2

Normal pelvic anatomy on transvaginal ultrasound

Anatomic Region	Structures Evaluated	Normal Sonographic Appearance
Anterior compartment	Urinary bladder	Anechoic lumen with smooth, thin wall; inner and outer hyperechoic lines separated by hypoechoic muscular layer.
	Bladder base and trigone	Smooth interface with anterior vaginal wall or cervix; no focal thickening or tethering.
	Urethra	Short, tubular structure anterior to the vagina; central echogenic mucosal stripe.
	Vesicouterine pouch (anterior cul-de-sac)	Potential space between bladder and uterus; free gliding motion on gentle probe pressure.
Middle compartment	Uterus (body, fundus, isthmus)	Smooth external contour; anteversion and retroversion are normal variants.
	Myometrium	Homogeneous, medium-level echotexture; may show subtle striae; no focal posterior serosal irregularities or nodules.
	Endometrium	Central echogenic stripe; thickness and echogenicity vary with menstrual cycle or therapy.
	Junctional zone	Smooth and regular; irregular thickening suggests adenomyosis.
	Cervix	Homogeneous echogenic stroma; nabothian cysts (anechoic or hypoechoic) may be seen as benign variants.
	Ovaries	Elliptical, containing multiple anechoic follicles of varying size with normal homogeneous stroma.
	Adnexa/fallopian tubes	Fallopian tubes usually not visualized unless fluid-filled; absence of tubular, noncompressible structures indicates normal appearance.
Posterior compartment	Pouch of Douglas (rectouterine pouch)	Potential space between posterior uterus/cervix and anterior rectum.
	Torus uterinus (posterior isthmus)	Subtle ridge posterior to cervix; appears thin and smooth without hypoechoic nodules.
	Uterosacral ligaments	Slender, linear echogenic bands extending posterolaterally from cervix; usually nontender.
	Rectovaginal septum	Smooth interface between posterior vaginal wall and anterior rectum; no hypoechoic plaques or distortion.
	Posterior vaginal fornix	Smooth mucosal contour; preserved separation from rectum.
	Rectum and rectosigmoid colon	Typical gut signature with alternating echogenic and hypoechoic mural layers; compressible, with thin regular wall and smooth anterior serosal line.
Lateral pelvic sidewall and ureteric corridor	Pelvic peritoneum	Smooth peritoneal surface without nodules or thickening.
	Distal ureters	Visualized near bladder trigone; intermittent color Doppler ureteric jets and peristalsis.
	Parametrial and pararectal regions	No focal thickening, nodularity, or tethering to adjacent structures.

Abbreviation: TVUS, transvaginal ultrasound.

Abnormal findings on transvaginal ultrasound at augmented pelvic ultrasound

SRU classifies endometriosis observations into categories in decreasing order of specificity/association with DE.

Category A or direct observations result from the presence of ectopic endometrial glands and/or stroma outside the uterus. These include ovarian endometriomas ( Fig. 1 ) and DE observations in locations—such as posterior uterine serosa ( Fig. 2 ), retrocervical space ( Fig. 3 ) and uterosacral ligaments, rectovaginal space ( Fig. 4 ), rectosigmoid colon ( Fig. 5 ), posterior bladder or uterovesical space ( Fig. 6 ).

Three panels with a left ovarian endometrioma show an avascular, homogeneously hypoechoic cyst with low-level internal echoes on transvaginal ultrasound and T 1, T 2 dark of the cyst contents. — Fig. 1

A transvaginal ultrasound image shows a hypoechoic soft-tissue plaque along the posterior uterine serosa, outlined by a dotted oval, consistent with deep endometriosis. — Fig. 2

Two panels show retrocervical deep endometriosis with a hypoechoic plaque bridging the posterior cervix to the anterior rectal wall on transvaginal ultrasound and a T 2-dark plaque with tethering. — Fig. 3

A sagittal transvaginal ultrasound shows a bilobed hypoechoic soft-tissue lesion in the rectovaginal septum between the rectum and vagina, consistent with deep endometriosis. — Fig. 4

Five panels show rectosigmoid deep endometriosis with an omega-shaped hypoechoic lesion invading the anterior rectal wall on transvaginal ultrasound and a T 2-dark plaque with mushroom cap sign. — Fig. 5

Five panels show bladder deep endometriosis with a hypoechoic nodule along the posterior bladder wall on transvaginal ultrasound and a T 2-dark lesion with T 1 foci at the bladder dome on M R I. — Fig. 6

Category B or indirect observations are associated findings or sequelae of endometriosis present at imaging without direct visualization of DE implants, such as fixed uterine retroversion ( Fig. 7 ), abnormal ovarian location ( Fig. 8 ) or mobility, and tethering of bowel loops to the posterior uterus ( Fig. 9 ), but without visualization of DE.

Two panels show fixed uterine retroflexion with posterior uterine tilt around the uterocervical long axis on sagittal transvaginal ultrasound and sagittal T 2-weighted M R I. — Fig. 7

Two panels show a posteriorly located left ovary on transvaginal ultrasound and a retropositioned left ovary on axial T 2-weighted M R I, with the uterus marked by a star. — Fig. 8

Two panels show bowel tethering with beak-like anterior rectal wall angulation toward the posterior uterine serosa on transvaginal ultrasound and T 2-weighted M R I. — Fig. 9

Category C or endometriosis-associated observations are associated with endometriosis but are not always a direct result of DE or are rarely seen in isolation, including adenomyosis, hydrosalpinx, and hematosalpinx ( Fig. 10 ).

Five panels show adenomyosis with heterogeneous posterior myometrium and Venetian blind appearance on ultrasound, and bilateral hydro- and hematosalpinges on ultrasound and M R I. — Fig. 10

Table 3 lists the SRU proposed observations of endometriosis on TVUS.

Table 3

Sonographic findings of deep endometriosis by site

Anatomic Site	Typical Sonographic Appearance	Characteristic Signs/Secondary Findings
Posterior uterine serosa/torus uterinus	Ill-defined hypoechoic plaques or nodules along posterior uterine wall, may extend into myometrium	Posterior uterine tethering; adjacent cystic foci or echogenic dots
Uterosacral ligaments (USLs)	Linear or nodular hypoechoic thickening near cervix extending posterolaterally	Often associated with retrocervical or torus lesions; focal tenderness on probe pressure
Retrocervical space/torus region	Smooth or irregular hypoechoic lesions posterior to cervix, midline	“Kissing ovaries” or rectal tethering commonly coexist
Rectovaginal septum	Hypoechoic nodule or plaque below posterior cervical lip	Loss of fat plane between posterior vagina and anterior rectum
Rectosigmoid colon	C-shaped or omega-shaped hypoechoic thickening of anterior rectal wall with tapering ends	Multifocal bowel involvement is associated with involvement of torus uterinus and USLs, adhesions to posterior uterus
Bladder/vesicouterine space	Isoechoic to hypoechoic nodular thickening at bladder base or dome; sometimes intraluminal protrusion	May be invisible on cystoscopy if not full-thickness; smooth or irregular margins
Ovarian/adnexal (OMA)	Homogeneous low-level internal echoes within cystic lesion; typically avascular	“Ground-glass” appearance; no solid component unless suspicious for malignancy
Indirect signs	Fixed uterine retroversion, kissing ovaries, bowel tethering	Adhesions, abnormal ovarian position or mobility ; kissing ovaries, when present with or without OMA, significantly raises the probability of advanced stage endometriosis.
Adenomyosis	Heterogeneous myometrium with myometrial cysts, hyperechoic islands, or echogenic buds	Globular uterine contour, asymmetric wall thickening, fan-shaped shadowing, or irregular junctional zone
Hydrosalpinx	Tubular anechoic or cystic structure separate from ovary	Incomplete septations, “waist sign,” endosalpingeal folds, or chain-of-cysts appearance
Hematosalpinx	Tubular cystic structure with low-level internal echoes	May accompany OMA or DE; absence of infection/ectopic pregnancy favors endometriosis