Continuing Education Activity

Pelvic ultrasound is the imaging modality of choice to evaluate the uterus, cervix, ovaries, and adnexa. In the postmenopausal patient, it is performed for a variety of reasons, but most often for the evaluation of postmenopausal bleeding or an adnexal mass. This activity reviews pelvic ultrasound in the postmenopausal patient and highlights the interprofessional team's role in performing and evaluating these imaging studies.

Objectives:

• Describe the normal findings seen on ultrasound in those who are postmenopausal.

• Outline the workup of a patient with postmenopausal bleeding and the role of ultrasound in that evaluation.

• Review the ideal technique to measure endometrial thickness while performing pelvic ultrasound.

• Review how ultrasound can be used to characterize adnexal masses in those who are postmenopausal.

Introduction

Ultrasound is the first imaging modality of choice for the female pelvis. It allows for real-time, fast, and portable imaging of the uterus, cervix, ovaries, and adnexa without the use of ionizing radiation. Here, we aim to summarize the use of pelvic ultrasonography in the postmenopausal population specifically.

Anatomy and Physiology

Changes After Menopause

In general, the same principles apply when imaging the postmenopausal pelvis in terms of anatomy.[1] It is important to be aware of ultrasound changes after menopause due to normal hormonal changes.

Uterus

Excluding pathologies such as fibroids or adenomyosis, the postmenopausal uterus tends to be smaller in overall size (as measured by uterine length, uterine height, and uterine width) compared to the reproductive-age uterus. The uterus can continue to decrease in size throughout menopause.[2] Additionally, there is a reduction in the corpus-cervix ratio in postmenopausal women such that it returns to a configuration more similar to that seen in the pediatric or prepubescent uterus.[3] The normal postmenopausal endometrium should be thin and appear atrophic (see Image. Thin Endometrial Stripe in Postmenopausal Individual, Ultrasound). 

Ovaries

Postmenopausal ovaries will also appear smaller and more homogenous, with occasional small hypoechoic follicles on ultrasound compared to those found in reproductive-age women (see Image. Ovary With Small Follicles in Postmenopausal Individual). Because of this, it can be common not to visualize the ovaries on ultrasound in a postmenopausal woman, and this should not lead to concern. Similarly to the uterus, the ovaries can continue to decrease in volume through menopause.[2]

Indications

Some of the common indications for a pelvic ultrasound in postmenopausal women include postmenopausal bleeding, pelvic pain, history of ovarian cysts, abdominal bloating, increasing abdominal girth, or pelvic pressure.

Postmenopausal Bleeding

Postmenopausal bleeding is a common indication for ultrasound evaluation of the postmenopausal pelvis. Even though the most common cause of postmenopausal bleeding is atrophy of the vagina and/or endometrium due to decreased estrogen, it is the presenting symptom for nearly 90% of women with endometrial cancer.[4] Thus, it is important to quickly and accurately diagnose or exclude neoplasia in patients presenting with postmenopausal bleeding.

Transvaginal ultrasound measuring endometrial thickness is a reasonable first non-invasive step in evaluating a patient with postmenopausal bleeding. Through multicenter trials and retrospective meta-analyses, an endometrial thickness of 4 mm has been well established as the threshold above which endometrial sampling should be considered. With an endometrial thickness of 4 mm or less, the negative predictive value for endometrial cancer is greater than 99%.[5] Smith-Bindman et al conducted a meta-analysis of 35 studies, including 5892 women, to endorse this cut-off value. At varying endometrial thicknesses from 3 mm to 10 mm, the mean weighted pooled estimates for sensitivity and specificity were calculated. They were able to find that using a 5 mm cutoff to define abnormally thick endometrium was 96% sensitive for detecting endometrial cancer and 92% sensitive for detecting any endometrial disease (including polyps and hyperplasia). Other studies, such as Timmermans et al, found that a 3 mm cutoff was ideal, having a sensitivity of 97.9% for detecting endometrial cancer.[6] However, these studies and others found that endometrial thickness is not very specific for detecting endometrial cancer: at 5 mm, Smith-Bindman et al. calculated 61% specificity, and at 3 mm, Timmermans calculated only a 35.4% specificity.[6] Thus, it is clear that transvaginal ultrasound is not ideal for predicting disease, so women with postmenopausal bleeding and thickened endometrium on imaging should undergo sampling.[7]

However, endometrial cancer can present with thin endometrium in rare cases, so recurrent or persistent postmenopausal bleeding should prompt pathologic evaluation. Additionally, these cutoffs do not consider personal risk factors for endometrial cancer, such as obesity, diabetes, family history, or genetic conditions that may raise one’s suspicion of endometrial cancer despite a thin endometrial lining.[5] The gold standard for diagnosis or exclusion of endometrial cancer would be endometrial sampling via dilation and curettage. In-office endometrial biopsy is also an option but is not as accurate as it is often performed blindly. However, both procedures are invasive, and patients do not always well tolerate in-office endometrial biopsy. Ultrasonography of the pelvis, specifically transvaginal sonography, can be an important screening tool to determine which patients require sampling, either blind or targeted. Transvaginal ultrasound to evaluate the endometrium can have its limitations. For example, if a patient has a history of uterine fibroids, adenomyosis, obesity, or prior surgeries, it can be difficult to assess the endometrial lining fully. In those cases, endometrial sampling, office hysteroscopy, or saline-infusion sonogram should be performed as the next step in evaluation. 

Incidental Thickened Endometrium

At times, postmenopausal women will undergo pelvic ultrasound for indications other than postmenopausal bleeding and are found to have an endometrial thickness greater than 4 mm. In these asymptomatic women, the guidelines are not as clear when sampling should be performed. Smith-Bindman et al concluded that an endometrial thickness greater than 11 mm places an asymptomatic postmenopausal woman at approximately 6.7% risk of cancer, similar to an approximate 7.3% risk of cancer in a woman with postmenopausal bleeding and an endometrium measuring 5 mm.[8][9][8]

Retrospective studies in asymptomatic women who underwent transvaginal ultrasound and endometrial sampling also support a cutoff of 11 mm. Still, they have found poorer sensitivity for detecting endometrial cancer than compared to symptomatic women.[10] Thus, while an 11 mm cutoff for asymptomatic women may be a helpful starting point, physicians should still exercise clinical judgment when deciding how to manage an incidentally found thickened endometrium in a postmenopausal patient. The American College of Obstetricians and Gynecologists, ACOG, recommends that the decision to evaluate asymptomatic postmenopausal women with thickened endometrial stripe needs to be an individualized, case-by-case decision based on risk factors and patient characteristics rather than the endometrial thickness cut off used for postmenopausal bleeding patients (see Image. Thickened Endometrial Stripe in Postmenopausal Individual, Ultrasound). 

Adnexal Masses

Adnexal masses are another frequent indication for a pelvic ultrasound in postmenopausal females. While most often found incidentally, adnexal masses may be felt on the exam or cause symptoms such as pain, pressure, increasing abdominal girth, or fatigue. Most adnexal masses are benign, but with increasing age, there is an increasing concern for ovarian carcinoma: it is estimated that women older than 65 are 6 times more likely to receive a diagnosis of ovarian cancer than women younger than 65.[11] Unfortunately, the presenting symptoms of ovarian carcinoma are vague and usually diagnosed at an advanced stage. Thus, there is great interest in distinguishing benign from malignant adnexal masses. However, due to the relatively low prevalence of ovarian cancer, high prevalence of benign cysts, and poor specificity of ultrasound, routine yearly ultrasonography on all postmenopausal women as a screening tool for ovarian cancer is not indicated.

The postmenopausal ovary is not necessarily totally quiescent. Simple cysts up to 1 cm in diameter may be seen in up to one-fifth of postmenopausal women and do not need to be followed. Also, simple cysts up to 3 cm in diameter can be seen and often spontaneously regress.[3] Current guidelines suggest that simple cysts between 1 cm and 7 cm in diameter should be followed at least yearly by ultrasound in a postmenopausal patient.[12] Larger or more complex cysts may require evaluation through additional imaging or surgery. 

Granberg et al first showed that an ovarian mass’s gross appearance could be related to its malignancy risk. By evaluating over 1000 tumors, they were able to find that unilocular cysts are associated with a 0.3% chance of malignancy, complex multiloculated cysts are associated with a 36% chance of malignancy, and predominantly solid cysts are associated with a 39% chance of malignancy.[13] Particularly with high image quality in the transvaginal setting, pelvic ultrasound can thus be used to characterize the morphology of adnexal masses and potentially stratify the risk of malignancy.

However, descriptions of adnexal masses on ultrasound can often be subjective. There have been several scoring systems proposed to standardize the sonographic evaluation of adnexal masses. These systems often include overall morphology, ovarian volume, wall thickness, and the presence of internal nodules or papillary excrescences or septations. A review by Myers et al found that the most frequently used scoring systems had a pooled sensitivity and specificity for detecting malignancy of 82-91% and 68-77%, respectively.[14] The International Ovarian Tumor Analysis (IOTA) group first aimed to standardize sonographic descriptions of adnexal masses. In doing so, they developed two related scoring systems that have been validated. The first, the IOTA Simple Rules, involves two sets of ultrasound characteristics for benign and malignant masses (see Table. International Ovarian Tumor Analysis Simple Rules).[15]

Table. International Ovarian Tumor Analysis Simple Rules

If one or more malignant features are present with no benign features, then the mass is considered malignant. If one or more benign features are present with no malignant features, then the mass can be considered benign. If either of those conditions is not met, then the result is inconclusive.[16] In a meta-analysis, these simple rules were 93% sensitive and 81% specific for detecting malignancy.[17] More recently, the IOTA group has developed the ADNEX (Assessment of Different Neoplasias in the Adnexa) model to more specifically predict whether an adnexal mass is benign, borderline, early-stage-malignant, late-stage malignant, or metastatic. This model uses similar ultrasound criteria as the Simple Rules and clinical criteria to calculate risk (see Table. Assessment of Different Neoplasias in the Adnexa Model Criteria).[15]

Table. Assessment of Different Neoplasias in the Adnexa Model Criteria

The ADNEX model was found to have either comparable or superior sensitivity and specificity to both the Simple Rules and other existing scoring systems in external validation studies. At malignancy, risk cutoffs of 1%, 10%, and 30%, sensitivities approach 100%, 97%, and 86%, respectively. Similarly, at malignancy risk cutoffs of 1%, 10%, and 30%, near 12%, 75%, and 89%, respectively.[18][19][18] Thus, the IOTA Simple Rules and ADNEX model are promising methods for standardizing the sonographic evaluation of adnexal masses in postmenopausal patients. However, these algorithms are not yet widely implemented within the United States, partly because they were validated in Europe. Proponents of the IOTA algorithms are hopeful that their use may become more widespread in the United States and improve patients' triage and treatment with adnexal masses. Nonstandard descriptions of adnexal masses notwithstanding, there can be other challenges with evaluating the postmenopausal adnexa by ultrasound. As mentioned before, postmenopausal ovaries are atrophic and may be difficult to visualize. Additionally, other structures within the pelvis, such as the bowel, fallopian tubes, and peritoneal cysts, may mimic the ovaries on imaging.

Contraindications

There are few contraindications to transvaginal ultrasound. Virginal patients or patients with significant vaginal atrophy may not be able to tolerate a transvaginal ultrasound.

Equipment

An ultrasound machine along with transabdominal and/or transvaginal ultrasound probes are needed.

Personnel

A sonographer or physician may perform an ultrasound. Often it is a physician, either specializing in obstetrics and gynecology or radiology, who interprets the images.

Preparation

To better visualize the reproductive organs, a full bladder is preferred for a transabdominal scan compared to an empty bladder for a transvaginal scan.

Technique or Treatment

While evaluating the female pelvis, it is customary to perform both transabdominal and transvaginal imaging.

Transabdominal

Transabdominal imaging of the postmenopausal pelvis is usually of limited utility due to the normal atrophic changes of the reproductive organs. However, it may be helpful in patients that have an especially enlarged uterus or large pelvic masses due to a broader field of view compared to transvaginal imaging. It is also helpful in patients who are unable or unwilling to tolerate a transvaginal ultrasound. Transabdominal imaging is typically performed with a full bladder using 2.5 to 5 MHz transducers. 

Transvaginal

A transvaginal approach is the technique of choice when performing an ultrasound on a postmenopausal patient due to its high-resolution images. A transvaginal scan is performed after emptying the bladder using a higher frequency transducer (5-8 MHz). The endometrial thickness is calculated as the maximum anterior to the endometrium's posterior dimension when viewed in the sagittal or long-axis view of the uterus (see Image. Endometrial Stripe, Sagittal View of the Uterus on Ultrasound). Occasionally, a small amount of anechoic fluid is noted in the endometrial canal in postmenopausal women. In such cases, the endometrial thickness is measured by measuring the anterior and posterior dimensions of the endometrium separately and adding them together. These transabdominal and transvaginal imaging modalities are also useful in evaluating adnexal masses by identifying the origin, physical characteristics like size, contents like solid or cystic, septations, laterality, presence of papillary excrescences, presence or absence of free fluid in the pelvis. Apart from identifying the gynecological causes for adnexal masses, ultrasound can also be used to identify other non-gynecological causes for adnexal masses like appendicitis, appendicular abscess, or pelvic kidney or peritoneal inclusion cysts. 

Saline Infusion Sonography

Saline-infusion sonography, or SIS, can be a helpful adjunct to transvaginal ultrasound in evaluating the lesions in the endometrial cavity or in patients with difficulty visualizing the endometrial lining. In SIS, a small catheter is inserted through the cervix into the endometrial canal. Saline is then infused through the catheter while a transvaginal ultrasound is performed. The saline distends the endometrial cavity, allowing for intracavitary lesions such as endometrial polyps or submucosal fibroids to be seen more easily. In the case of postmenopausal bleeding, SIS can help determine if the endometrium is only focally thickened (in the case of a polyp) or more globally thickened (in the case of hyperplasia or malignancy).

Doppler

Doppler ultrasound, with which blood flow through vessels can be evaluated, is another technique that may be applied when imaging a postmenopausal patient. Doppler can be helpful in the differentiation of a benign from a malignant adnexal mass.[20]

Clinical Significance

As noted above, pelvic ultrasound in the postmenopausal patient is key in evaluating postmenopausal bleeding and adnexal masses. Thus, these imaging studies can be key in the early detection of endometrial or ovarian cysts and lead to improved outcomes in patients.

Enhancing Healthcare Team Outcomes

Pelvic ultrasound in the postmenopausal female is the imaging study of choice to evaluate the uterus, endometrium, cervix, and adnexa. It is important to recognize when a pelvic ultrasound should be performed on a those who are postmenopausal. Knowing the indications for a pelvic ultrasound and how to interpret the imaging findings can improve patient outcomes. For the sonographer performing the ultrasound, it is important to have the proper technique to evaluate possible pathologies fully.

If a standard transvaginal ultrasound is inconclusive or suboptimal, knowing how to perform saline-infused sonohysterography may add diagnostic information. The ordering or interpreting physician needs to know when an ultrasound is indicated for a postmenopausal patient to decrease the need for potentially unnecessary further testing. Additionally, it is important to know how to interpret the ultrasound findings in a postmenopausal patient. In particular, knowing the appropriate endometrial thickness in a postmenopausal patient with bleeding and concerning ultrasound features of an adnexal mass can help determine the need for further workup and guide management in these patients. With open communication and collaboration between the healthcare team members (including clinicians, mid-level practitioners, specialists, and nurses), a properly performed and interpreted pelvic ultrasound in the postmenopausal woman can have important diagnostic consequences and lead to improved outcomes in patients.