Can a Normal TV Ultrasound Miss an Endometrial Polyp?

Yes, it is entirely possible to have an endometrial polyp (a usually benign growth of the uterine lining) even if your standard transvaginal ultrasound (TVUS) was interpreted as completely normal. While a TVUS is an excellent first step for evaluating the uterus, it does not reliably exclude a polyp. Studies pooling data from multiple groups show that standard transvaginal ultrasounds miss a significant number of polyps—with approximate missed rates ranging from 38% to 45%, depending on the study population and equipment used ^[1][2].

If you are still experiencing symptoms like abnormal bleeding, a “normal” ultrasound result lowers the chance of certain conditions, but it is not the final word.

Why Do Polyps Hide on a Standard Ultrasound?

The inside of the uterus (the uterine cavity) is not a hollow space; it is a “potential space.” Normally, the front and back walls of the uterus rest against each other. During a standard TVUS, there is no fluid to separate these walls, which limits how well the cavity can be distended. Because of this, soft tissue lesions can easily blend in with the surrounding endometrium (the uterine lining).

Research has identified specific characteristics that make a polyp much easier to miss on a standard ultrasound ^[3]:

• Size: Small polyps, particularly those under 15 millimeters (1.5 cm), are harder to spot.
• Shape: Polyps that are sessile (flat against the uterine wall) are more difficult to distinguish than those that are pedunculated (hanging from a stalk).
• Vascularity: Polyps often have a tiny blood vessel feeding them, but if this vessel is not visible on the ultrasound, the polyp is harder to identify.
• Image Quality: Acoustic artifacts (shadows on the ultrasound image) or a heterogeneous (uneven-looking) uterine lining can obscure small lesions.

Next Steps for Persistent Symptoms

If you continue to have abnormal bleeding, spotting, or pelvic symptoms despite a normal TVUS, your clinician will likely consider other common causes of bleeding. A missed polyp is just one possibility; other causes include fibroids, adenomyosis, hormonal imbalances, medication effects, or even pre-cancerous changes.

Depending on your age, whether you have gone through menopause, and your specific bleeding pattern, further testing may be recommended to get a clearer picture of the uterine cavity:

Saline Infusion Sonohysterography (SIS)

Also called a saline ultrasound, this test adds fluid contrast to a standard ultrasound. A small amount of sterile saline is gently placed into the uterus through the cervix to separate the uterine walls. This creates a dark background on the monitor that makes polyps and other focal lesions stand out. In studies, using fluid contrast improved the detection rate of polyps to approximately 87% to 92% ^[1][2]. Keep in mind that while SIS is excellent for finding polyps, it cannot determine if a polyp is benign or cancerous; that requires a tissue sample sent to pathology.

Endometrial Biopsy

An office endometrial biopsy is often an appropriate initial test to check for abnormal cells in the uterine lining. However, because it is a “blind” procedure (done without a camera looking inside), the sampling instrument can sometimes completely miss a small, focal lesion like a polyp ^[4]. If your bleeding continues after a negative or insufficient biopsy, further evaluation is still needed ^[4].

Hysteroscopy

A hysteroscopy involves inserting a very thin, lighted camera through the vagina and cervix to inspect the uterine cavity directly. This is the most direct way to evaluate a suspected focal abnormality. If a polyp is found, the doctor can perform a visually directed biopsy or remove the polyp entirely so the tissue can be analyzed by a pathologist ^[5][6]. Hysteroscopy can cause cramping, and your clinician will discuss options for pain management, sedation, or anesthesia depending on whether it is done in the office or operating room.

A Special Note on Postmenopausal Bleeding

Any bleeding after menopause should be evaluated promptly. A standard TVUS is often the first test used to measure the thickness of the endometrial lining. An endometrial thickness of 4 millimeters or less on a high-quality scan is highly reassuring, as it has a negative predictive value of over 99% for endometrial cancer ^[7].

However, this threshold does not rule out polyps or all cancers ^[7]. A thin lining does not mean your symptoms should be ignored. If your postmenopausal bleeding continues or returns after a reassuring ultrasound, further assessment—which may include an endometrial biopsy, a saline ultrasound, or a hysteroscopy—is still warranted to find the cause ^[8].

When to Seek Urgent Care

While investigating the cause of your symptoms, it is important to know when to seek immediate medical attention. Go to urgent care or an emergency room if you experience:

• Bleeding that rapidly soaks through a pad or tampon every hour for two or more hours
• Fainting or severe dizziness
• Shortness of breath
• Severe or rapidly worsening pelvic pain
• Fever
• Any bleeding if there is a possibility you might be pregnant