Can You See Endometriosis on an Ultrasound?

Ultrasound can detect certain forms of endometriosis with impressive accuracy, but it misses others almost entirely. The answer depends on which type of endometriosis you’re talking about and who is holding the probe. Ovarian endometriomas show up well on a standard scan. Deep infiltrating endometriosis can be found by an experienced sonographer using the right technique. But the shallow, scattered implants that make up superficial peritoneal endometriosis remain largely invisible to ultrasound, and that form happens to be among the most common, especially in younger patients. A normal ultrasound, in other words, does not mean you don’t have endometriosis.

Ovarian Endometriomas Are the Easiest to Spot

Endometriomas, sometimes called “chocolate cysts” because of their dark, old-blood contents, are the form of endometriosis that ultrasound handles best. On a transvaginal scan, they have a distinctive look: a cyst filled with uniform, low-level echoes that sonographers describe as “ground glass.” A large study of endometrioma features found that about half were single-chambered cysts with that ground glass pattern, and the combination of ground glass echogenicity, fewer than five compartments, and no solid growths with blood flow was the best predictor in premenopausal patients.¹ If your ultrasound report describes a cyst matching that profile, the diagnosis is fairly straightforward.

One challenge is telling an endometrioma apart from a hemorrhagic ovarian cyst, which can look similar on a single scan because both contain blood products. Certain texture features on grayscale imaging, including homogeneous low-level echoes and a clearly visible cyst wall, are more strongly associated with endometriomas than with hemorrhagic cysts.² A hemorrhagic cyst also tends to change or resolve over a few menstrual cycles, so a follow-up scan a couple of months later often settles the question.

Deep Infiltrating Endometriosis and Where It Hides

Deep infiltrating endometriosis, often called DIE, is tissue that grows more than five millimeters beneath the peritoneal surface, burrowing into structures like the bowel wall, the tissue behind the cervix, the ligaments supporting the uterus, the bladder, and the ureters. Ultrasound can find these lesions, but accuracy varies sharply by location.

The rectosigmoid colon is one of the most reliably detected sites. A systematic review pooling data from multiple studies found that transvaginal ultrasound picked up rectosigmoid endometriosis with about 91% sensitivity and 97% specificity.³ A separate study reported similar numbers, with transvaginal ultrasound detecting intestinal endometriosis at around 93% sensitivity.⁴ Bowel nodules are relatively large and create recognizable thickening of the intestinal wall, which helps explain why ultrasound does well here.

Other locations are trickier. For the uterosacral ligaments, one meta-analysis found pooled sensitivity around 53%, meaning nearly half of lesions were missed, though specificity was high at 93%.⁵ A more recent meta-analysis found somewhat better sensitivity for uterosacral ligaments, around 67%, suggesting that technique improvements have helped over time.⁶ The rectovaginal septum, a thin partition between the vagina and rectum, remains one of the harder spots, with sensitivity hovering around 49–59% across reviews.⁷

Superficial Endometriosis Is Where Ultrasound Struggles Most

Superficial peritoneal endometriosis consists of small, flat implants scattered across the lining of the pelvis. These lesions are thin, don’t create large masses, and blend in with surrounding tissue on imaging. It is the type most likely to be present when an ultrasound looks completely normal.

Research attempting to detect superficial endometriosis on the uterosacral ligaments found that while specificity was very high (96%), sensitivity was just 10%, meaning the scan identified only a tiny fraction of confirmed cases.⁸ A newer study looking at the peritoneum of the pouch of Douglas did somewhat better, achieving about 52% sensitivity with 94% specificity for superficial disease.⁹ Progress is being made, but for now, superficial disease remains the form most likely to go undetected on a scan.

This matters because superficial endometriosis can still cause severe pain. Its invisibility on imaging is a major contributor to the well-documented diagnostic delay that many patients experience, sometimes stretching years from the onset of symptoms to a confirmed diagnosis.¹⁰

The Sliding Sign and Dynamic Techniques

A standard ultrasound captures still images or short clips. But some of the most useful information for endometriosis comes from moving structures against each other in real time during the scan. The most established dynamic technique is the “sliding sign,” in which the sonographer uses the ultrasound probe to gently push the uterus against the bowel and watch whether the two surfaces glide freely past each other.

When the pouch of Douglas (the space between the uterus and rectum) has been scarred shut by endometriosis, those surfaces stick together and refuse to slide. The original study describing this technique found it had 83% sensitivity and 97% specificity for predicting this type of scarring, called pouch of Douglas obliteration.¹¹ A later meta-analysis confirmed strong performance, with pooled sensitivity of 88% and specificity of 94%, and showed that a positive finding raised the probability of obliteration from 37% to 90%.¹²

The sliding sign can’t diagnose endometriosis implants directly, but it reveals the adhesions and scarring that severe disease causes. For surgeons, this is critical information: knowing whether the bowel is stuck to the uterus changes the entire operative plan.

Why the Person Performing the Scan Matters So Much

Perhaps the single most important variable in whether endometriosis shows up on your ultrasound is who is doing it. A routine pelvic ultrasound, the kind ordered for general gynecologic complaints, typically focuses on the uterus and ovaries. It will catch an endometrioma if one exists, but it rarely includes the systematic assessment of surrounding structures needed to find deep endometriosis.

A retrospective comparison between routine transvaginal ultrasound and expert-guided scans in the same patients found a stark difference: routine scans picked up endometriosis in 25% of confirmed cases, while expert scans detected it in 78%.¹³ The routine scans identified disease almost exclusively by finding endometriomas, while the expert scans found additional disease locations in 97% of detected cases. A separate study comparing expert and first-level operators found sensitivity of 77% versus 45%, respectively.¹⁴

So if you’ve had a normal pelvic ultrasound but still have symptoms, it’s worth asking whether the scan was performed by someone trained in endometriosis mapping. Not all ultrasound exams are the same exam.

Standardized Protocols Have Improved Detection

Historically, one reason ultrasound results varied so much between centers was that everyone described findings differently and looked at different structures. The International Deep Endometriosis Analysis (IDEA) consensus, published in 2016, aimed to fix this by establishing standard terms, definitions, and a systematic step-by-step approach for evaluating the pelvis.¹⁵ The IDEA protocol tells the sonographer exactly which structures to check, what to call them, and how to measure lesions.

A prospective international pilot study testing the IDEA approach found that it provided strong diagnostic accuracy for deep endometriosis, with sensitivity exceeding that reported in earlier meta-analyses.¹⁶ The shift toward these standardized scan protocols represents one of the biggest practical improvements in endometriosis imaging over the past decade, and the ESHRE 2022 guideline update reflects this by positioning imaging as a frontline diagnostic tool rather than just a supplement to surgery.¹⁷

When MRI Adds Something Ultrasound Doesn’t

You might wonder whether you should skip ultrasound and go straight to an MRI. In practice, clinical guidelines recommend transvaginal ultrasound as the first-line imaging tool for suspected endometriosis, with MRI reserved for specific situations.¹⁸ This isn’t because ultrasound is always better. It’s because ultrasound is cheaper, more widely available, and in experienced hands performs as well or better than MRI for several locations.

One head-to-head comparison found that transvaginal ultrasound actually outperformed MRI for rectosigmoid and retrocervical deep endometriosis, achieving sensitivity of 98% and 95% respectively at those sites, compared with 83% and 76% for MRI.¹⁹ MRI has the edge for certain locations, however. Endometriosis in the uterosacral ligaments, intestinal wall layers, and the bladder region may be better characterized on MRI.²⁰ MRI also has a role when a previous ultrasound was normal but symptoms remain, particularly in younger patients who may not have had a transvaginal scan.²¹

Bowel Preparation Can Make a Difference

For scans focused on suspected bowel endometriosis, some centers ask patients to do a bowel preparation beforehand, typically a mild laxative or rectal enema. The idea is simple: an empty, less gassy bowel is easier to see through. A prospective study found that bowel preparation before transvaginal ultrasound improved detection of small and superficial bowel nodules, as well as nodules on the front wall of the sigmoid colon.²² Other research confirmed that ultrasound with bowel prep provides detail about which layers of the intestinal wall are affected and how far a lesion sits from the anal border, information that directly shapes surgical decisions.²³

Not every scan requires bowel prep. It’s most useful when there’s already a suspicion of bowel involvement based on symptoms like painful bowel movements, rectal bleeding around menstruation, or a prior scan that suggested disease near the rectum.

A Normal Ultrasound Does Not Rule Out Endometriosis

This is the single most important takeaway for anyone reading this while trying to get a diagnosis. European and international guidelines explicitly state that a negative ultrasound does not exclude endometriosis, particularly superficial peritoneal disease.²⁴ The same is true for adolescents, in whom superficial disease is especially common and abdominal (rather than transvaginal) ultrasound is often the first imaging performed. Transabdominal ultrasound can identify ovarian cysts but is not useful for non-ovarian endometriosis.²⁵

If you have classic symptoms, including cyclical pelvic pain, painful periods, pain during sex, or difficulty getting pregnant, and your ultrasound comes back clean, that does not mean the symptoms are unexplained or “just bad periods.” It means the type of endometriosis you may have is the kind ultrasound isn’t good at finding. The appropriate next step, depending on your situation, could be an MRI, a referral to an endometriosis specialist, empirical treatment, or in some cases a diagnostic laparoscopy. The ESHRE guideline now recommends laparoscopy only when imaging is negative and empirical treatment has failed or isn’t appropriate.²⁶

How Ultrasound Shapes Surgical Planning

Beyond diagnosis, a detailed endometriosis ultrasound serves a practical surgical purpose. When a patient is heading toward surgery, the surgeon needs to know exactly where disease is, how deep it goes, and which organs are affected. A thorough preoperative ultrasound map can guide the choice of surgical approach, help decide whether a bowel surgeon or urologist needs to be in the room, and reduce the risk of unexpected findings mid-operation.²⁷

Urinary tract involvement is a good example. Endometriosis can silently compress or invade the ureters, potentially causing kidney damage if missed. Transvaginal ultrasound has proven reliable for detecting ureteral involvement, including identifying the level and degree of obstruction.²⁸ A meta-analysis found that ultrasound detected ureteral endometriosis with about 97% sensitivity and 100% specificity, numbers that actually exceeded MRI’s performance at that location.²⁹ For bladder endometriosis, both ultrasound and MRI performed well, with ultrasound sensitivity around 72% and specificity at 99%.³⁰

Pain During the Scan Can Itself Be Informative

Transvaginal ultrasound for endometriosis is not always a comfortable experience, and some patients dread it. But the tenderness provoked during the scan can actually contribute to the clinical picture. A study examining patients with uterosacral ligament endometriosis found a strong correlation between ultrasound findings and pain scale scores during the exam. Patients with confirmed endometriosis had substantially higher pain scores during the scan than those without, and patients with identifiable uterosacral nodules scored even higher.³¹ The scan is not just about what the images show; where it hurts and how much it hurts when the probe presses against specific structures gives the examiner real-time diagnostic information.

Newer Techniques on the Horizon

Ultrasound technology for endometriosis continues to evolve. One area of active research is elastography, a technique that measures tissue stiffness. Endometriosis lesions tend to be stiffer than surrounding tissue because of their fibrotic content. A systematic review found that elastography showed high sensitivity and specificity for deep pelvic endometriosis, with lesion stiffness correlating well with the degree of fibrosis found on pathology. It also helped distinguish endometriomas from hemorrhagic cysts and malignant tumors based on stiffness differences.³² Artificial intelligence is another frontier, with researchers developing algorithms that may eventually help less experienced operators identify endometriosis features more reliably.³³

An economic analysis from Australia estimated that integrating expert-level deep endometriosis ultrasound into the standard workup could save the healthcare system roughly AU$924,000 per 1,000 patients annually, mainly by reducing unnecessary diagnostic surgeries and streamlining care pathways.³⁴ The push to make specialized endometriosis scanning more widely accessible is as much about economics as it is about clinical accuracy. For patients, the practical implication is that the quality of your scan depends heavily on where you get it and who does it, and that gap is slowly closing as training protocols and standardized methods spread.