Pelvic Ultrasonography 

Updated: Apr 12, 2022
Author: Shoreh Kooshesh, MD; Chief Editor: Mahan Mathur, MD 

Overview

Practice Essentials

Pelvic ultrasonography is one of the best imaging modalities used to evaluate nonspecific pelvic pain, pregnancy complications, anatomy of pelvic organs, and various ovarian pathologies.[1, 2, 3, 4, 5]  Ultrasound is the key modality for evaluation of contents of the female pelvis. It allows ready (and portable) imaging of the uterus, ovaries, and other structures at a reasonable cost and without ionizing radiation. Lack of irradiation is important because the ovary in young patients and in those of reproductive age is particularly sensitive to radiation.[6]

Pelvic ultrasonography is performed via a transabdominal (TA) or transvaginal (TV) approach. A urine-filled bladder helps lift the small bowel superiorly out of the pelvis, creating an optimal acoustic window and preventing bowel air from refracting or degrading the ultrasound beam. Ultrasound traverses the pelvis unimpeded through bladder fluid, insonating pelvic contents and returning to the transducer to be processed by the machine.[6]

In transabdominal ultrasonography, a low-frequency transducer and a full bladder are used to displace bowel gas and provide an acoustic window to improve image resolution while allowing a large viewing field of the pelvis. The transvaginal approach, also known as endovaginal scanning, is a painless procedure that resembles a pelvic exam. A thin, covered wand or probe is placed into the vagina, and the examiner directs the probe toward the uterus and ovaries. This type of ultrasound produces a better image than is attained by a scan through the abdominal wall because the probe can be positioned closer to the ovaries. This is the best test for diagnosing an ovarian cyst.

Endovaginal scanning, using a high-frequency transducer, is the preferred technique for evaluation of ovarian pathologies; a full bladder is not necessary.[2]  Endovaginal scanning is preferred over computed tomography because of improved visualization of pelvic organs, the absence of radiation exposure with ultrasonography, decreased length of hospital stay, and reduced cost for the patient.[3]

According to practice parameters of the American Institute of Ultrasound in Medicine (AIUM), indications for pelvic ultrasonography of the female pelvis include, but are not limited to, the following[7] :

  • Evaluation of pelvic pain; pelvic masses; endocrine abnormalities, including polycystic ovaries; dysmenorrhea (painful menses); amenorrhea; abnormal uterine bleeding; postmenopausal bleeding; delayed menses; signs or symptoms of pelvic infection; congenital uterine, gonadal, and lower genital tract anomalies; excessive bleeding, pain, or signs of infection after pelvic surgery, delivery, or abortion; and incontinence of pelvic organ prolapse.
  • Follow-up of a previously detected abnormality.
  • Evaluation, monitoring, and/or treatment of patients with infertility.
  • Evaluation when clinical examination of the pelvis is limited.
  • Further characterization of a pelvic abnormality noted on another imaging study.
  • Localization of an intrauterine device (IUD).
  • Screening for malignancy in high-risk patients.
  • Guidance for interventional or surgical procedures.
  • Preoperative and postoperative evaluation of pelvic structures.

​Use of ultrasound for the male pelvis is limited. The presence of free abdominal fluid can be assessed. Undescended testes in the groin and hernias can be seen with the use of high-frequency linear array transducers. Transabdominal ultrasound can allow visualization of the dilated urethra in posterior urethral valves. and,occasionally a valve itself can be seen in real time. Inferiorly angled midline views are most helpful. Transperineal ultrasonography can be utilized for diagnosis of posterior urethral valves.[6]

(The video below depicts a demonstration of transvaginal ultrasonography.)

Demonstration of a transvaginal ultrasonographic pelvic evaluation. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.

 

Background

 

 

 

 

 

Workup

Approach Considerations

Evaluation of pelvic pain

Ultrasonography can be used to evaluate pelvic pain, which is a common presentation in the emergency department (ED). It evaluates emergent entities such as ovarian cysts and rupture, tubo-ovarian abscesses, uterine fibroids, ectopic pregnancy, uterine rupture, and even ovarian torsion. Although point-of-care ultrasound applications continue to expand, there are findings that are not within the scope of emergency ultrasound. It is important for emergency physicians to be aware of incidental findings that can be identified on comprehensive ultrasound performed by other imaging departments to fully understand the limitations of bedside ultrasound.[8]  Endovaginal scanning uses a high-frequency transducer and enables optimal imaging of organs close to the probe, including endometrium, myometrium, cul-de-sac, and ovaries, which can be seen in detail with better resolution.[4, 9, 10, 11]

In a female patient who is obese, pelvic ultrasonography can enhance evaluation of the pelvis, as the physical exam alone will be difficult and will have limitations. The endovaginal transducer is preferred for obese patients because it has the ability to visualize pelvic organs far better than any other modality. Its limitations in overweight and obese girls are real and must be considered. If utilization of an endovaginal transducer is not feasible in young virginal girls, pelvic magnetic resonance imaging could be a useful alternative, allowing greater delineation of structural components of the ovary and better appreciation of both its volume and its structural alterations.[12]

The differential diagnosis of pelvic pain should be divided between patients who are pregnant and those who are not pregnant. All pregnant patients with no sonographic evidence of an intrauterine pregnancy and no periovarian/ovarian abnormalities should be monitored with serial beta-human chorionic gonadotropin (HCG) levels every 48 hours and repeat ultrasound with urgent obstetric/gynecologic consultation. 

The most urgent cause of pelvic pain with a positive pregnancy test is ectopic pregnancy. The worldwide incidence is 1 in 200. Serum beta-HCG levels are not reliable in determining what can be visualized in evaluation of a pregnant pelvis, and use of a beta-HCG discriminatory zone in the differentiation of normal and ectopic pregnancy is unreliable. Endovaginal ultrasonography can detect intrauterine pregnancy earlier than transabdominal ultrasonography.[13, 14, 15]

Ovarian torsion is often a difficult diagnosis of intermittent pelvic pain that must be considered in nonpregnant patients.[5, 16]  The ovaries appear almond shaped, typically lateral to the uterus and anterior to the internal iliac vasculature. Ovarian morphology, including the presence and number of contained follicles/cysts, varies with age, endocrine function, and time in the menstrual cycle. Knowledge of normal volumes for individuals of various ages is important when a patient is evaluated for ovarian torsion. Torsed ovaries can enlarge to 3 to 4 times normal ovarian volume.[6]  An enlarged ovary is the first sign of torsion; identification of a complex ovarian mass greater than 5 cm increases the probability of torsion.[17]

Ovarian torsion is a rather frequent occurrence worldwide among women of reproductive age. Etiologies are diverse, with ovarian lesions and corpus luteal cysts being the 2 most common. Pelvic or intravaginal ultrasound remains the first-line imaging modality for diagnosis and evaluation of suspected ovarian torsion.[18]  Endovaginal scanning, which is the only modality used to assess degree of color flow to and from the ovary, can facilitate the diagnosis of ovarian torsion.[19]  

Pelvic masses, including uterine fibroids, ovarian cysts, and cancer, can cause pelvic pain. More rare etiologies of pelvic masses include, but are not limited to, pseudomyxoma peritonei, desmoid tumors, and mesothelial tumors.[20]  To diagnose the specific etiology of the pelvic mass, further imaging and biopsy are needed. Outpatient evaluation and repeat pelvic ultrasonography are performed in cases of ovarian cysts and fibroids.

Authors of a British study suggested that transvaginal duplex ultrasonography could be the gold standard in assessing pelvic vein reflux. Comparison of transvaginal duplex ultrasonography with outcomes from selective treatment of veins identified as having pathologic reflux with coil embolization revealed no false-negative diagnoses and only 1 false-positive finding.[21]

A retrospective review of patients aged 13-21 years who underwent pelvic ultrasound in the emergency department (ED) found that use of ED bedside ultrasound by trained emergency medicine and pediatric emergency medicine physicians led to a significant reduction in length of stay in the ED, regardless of whether a radiology ultrasound technologist was available.[22]

Endometriosis is a painful disorder in which tissue similar to tissue lining the inside of the uterus grows outside the uterus. This common and often debilitating gynecologic disorder affects 5-10% of women. Endometriosis most commonly involves the ovaries, the fallopian tubes, and tissue lining the pelvis. Researchers have reported how routine ultrasound examination can easily be extended beyond the uterus and ovaries into posterior and anterior pelvic compartments to detect endometriosis, allowing earlier diagnosis and better surgical outcomes for all women with this disorder.[23]

Evaluation of a pelvic mass

Pelvic ultrasonography can be used to determine the etiology of a pelvic mass.[20, 24, 25, 26]

Compared with endovaginal ultrasonography, transabdominal ultrasonography uses a lower frequency and can penetrate farther, with a large field of view. Thus, fibroids, ovaries, or cysts located high in the pelvis may be out of the focal range of an endovaginal probe. Masses palpated on physical examination can be further evaluated with ultrasound.[6]  In addition, pelvic kidneys can be visualized.

Uterine fibroids can be diagnosed by pelvic ultrasonography. They may be submucosal, intramural, or subserous. Sometimes they arise from supportive structures of pelvic organs such as broad ligaments. Transabdominal and endovaginal scanning can be done to assess for fibroids. Pelvic masses may also arise from other pelvic organs, including the urinary system, adjacent soft tissues, or the gastrointestinal system, or they can even occur as metastases. 

Ovarian cysts can be quite large, can cause torsion, and can rupture. They can be nonhemorrhagic or hemorrhagic, simple or complex. Pelvic ultrasonography can provide the information needed to diagnose and delineate the above complications.

Nabothian follicles or cysts are caused by dilation of the endocervical glands; they are located in the uterine cervix and are identified as cystic lesions.[20]

Evaluation of vaginal bleeding in early pregnancy

Ectopic pregnancy is the emergent process that must be considered in all pregnant patients who present with vaginal bleeding.[27]  In addition to visualizing an ectopic pregnancy, pelvic ultrasonography can be used to identify a pseudosac. A pseudosac is an empty sac illustrated by an intrauterine fluid collection that forms in response to hormonal influences of an ectopic pregnancy in the endometrium. When no defintive intrauterine pregnancy is identified, evaluation of ovarian and periovarian regions is of utmost importance. The presence of any abnormalities increases the suspicion of ectopic pregnancy; absence of ovarian or periovarian abnormalities requires daily follow-up ultrasound and monitoring of beta-HCG levels. 

Subchorionic hemorrhage (implantation bleeding) is a common cause of spotting. Depending on the size and location of the hemorrhage, pelvic ultrasonography can be used to diagnose this cause of vaginal bleeding in pregnant patients.

Intrauterine pregnancy can be illustrated by visualization of a double-decidual sac sign on ultrasonography. Pelvic ultrasonography can show a double layer of echogenic deciduas separated by a hypoechoic endometrial cavity.[13]  It can also show a gestational sac with a measured fetal pole and yolk sac, or a gestational sac with a beating fetal heart illustrating a live intrauterine pregnancy.

Although there are no absolute contraindications to the use of ultrasound, transvaginal ultrasonography may be relatively contraindicated in late pregnancy or in high-risk patients.[6]

Evaluation of postpartum vaginal bleeding

Postpartum hemorrhage (PPH) is the leading cause of maternal morbidity.[28]  Postpartum hemorrhage can be defined as primary or secondary. Primary PPH occurs within 24 hours after delivery. Causes include uterine atony, lower genital tract lacerations, and retained products of conception (this usually presents as late-postpartum hemorrhage).[28]

Retained products of conception can be evaluated via pelvic ultrasonography.[29, 30, 31]  Transabdominal ultrasound shows a thickened, heterogeneous stripe or an irregular heterogeneous endometrial cavity.[32]  Postpartum patients may also present with fever, and if retained products of conception are present, an obstetric/gynecologic consultation is warranted for urgent evacuation.

A new technique involves performing endovaginal ultrasound scanning of the anal sphincter complex during the immediate postpartum period. Immediate postpartum endovaginal ultrasonography offers promise for improving management of perineal trauma after vaginal delivery.[33]

Evaluation of pelvic infection

Pelvic inflammatory disease (PID) is one of the most common causes of acute pelvic pain in sexually active women. Pelvic inflammatory disease should be suspected in all patients with pelvic pain, cervical motion tenderness, fever, and leukocytosis. Infection can ascend from cervicitis to involve the uterus and the fallopian tubes. If treatment is delayed, PID can ultimately result in tubo-ovarian abscess, which is difficult to diagnose with physical examination alone.

A normal fallopian tube may not be visualized on endovaginal ultrasonography; however, a fluid- or pus-filled tube can be identified. Resulting tubal damage and scarring increase the risk for long-term complications, including infertility and chronic pelvic pain.[13]

Endovaginal ultrasound scan. Endometritis with air Endovaginal ultrasound scan. Endometritis with air in the endometrial cavity and bilateral tubo-ovarian abscesses are shown.

Localization of an intrauterine device or a foreign body

Ultrasonography can aid in localization or detection of an intrauterine device or a foreign body.

An intrauterine device produces a characteristic acoustic artifact (shadow), which is helpful to the sonographer.[34]

Evaluation of trauma

Ultrasonography is used as a screening tool for all trauma patients who present with blunt or penetrating chest trauma or blunt or penetrating abdominal trauma.

Views of the sagittal and transverse pelvis via the transabdominal transducer are used to detect free fluid or clotted blood, which can be present in the pouch of Douglas (cul-de-sac).

Views of the pelvis obtained before a Foley catheter is inserted are helpful because of the acoustic aid of a full bladder when the transabdominal transducer is used.

In cases of significant high-grade-mechanism trauma to the pelvis, the abdomen must always be considered. Focused assessment with sonography for trauma (FAST) is a valuable tool for assessing the unstable trauma patient with blunt abdominal injury, although the diagnostic utility of FAST is not as well defined in cases of primary pelvic trauma.[35]

A new technique involves performing endovaginal ultrasound scanning of the anal sphincter complex during the immediate postpartum period. Immediate postpartum endovaginal ultrasound offers promise for improving management of perineal trauma after vaginal delivery.[33]

Imaging Studies

Much information of clinical significance is discovered when the pelvis is imaged on ultrasound. This includes information about the uterus—its shape, size, and characteristics—and about the endometrial cavity and its contents. Identification and evaluation of ovarian size and morphology help the clinician to determine if there are any abnormalities in the ovary for an individual of a given age. Ultrasonography can identify masses in structures other than the uterus and ovaries, such as adnexal cysts. Ovarian neoplasms can be assessed for size and morphology and growth over time. These may include ovarian teratomas with their usual cystic and solid (Rokitansky nodule) contents, including bone or calcium. Rectal contents can be evaluated, especially in neonates or young children. Thick bowel walls of chronic inflammation or tumor may be noted at times. Urethral cysts may be seen, particularly in adult females. Rarely, an abnormality of the bony pelvis may be noted.[6]

A urine-filled bladder is optimal for viewing pelvic contents through the transabdominal technique. No particular preparation is required for transvaginal imaging.[6]

Transabdominal imaging uses a low frequency and is performed to view large fibroids and ovaries that are high in the pelvis; to determine the shape and size of the bladder, uterus, vagina, and cervix; and to illustrate intrauterine or ectopic pregnancy.

Pelvic ultrasound is the ideal imaging technique for pregnant women, as it does not entail use of contrast or x-rays. This technique can be performed at the bedside and is cost-effective.[6]

A full bladder provides a sonographic window for evaluation of the uterus and the adnexa. A full bladder has a teardrop-shaped appearance on the longitudinal view and is rectangular on the transverse view.

(See the images below.)

Transabdominal longitudinal view of the female pel Transabdominal longitudinal view of the female pelvis.
Transabdominal transverse view of the female pelvi Transabdominal transverse view of the female pelvis: The bladder is rectangular. The ovaries are seen bilaterally in the adnexa.

The uterus (longitudinal orientation) is oval, is more echogenic than the bladder, and is located posterior to the bladder, appearing to wrap under it and ending in the cervix and the vaginal canal. The endometrial stripe is an echogenic (bright) line in the central uterus.

The vagina is a hypoechoic tubular structure posterior to the bladder and caudal to the uterus. A vaginal stripe can be identified.

The cervix is seen between the uterus and the vaginal canal.

The cul-de-sac is important, especially for evaluation of patients at risk for ectopic pregnancy. It is also evaluated during trauma assessment. A small amount of fluid can be seen in the middle of the menstrual cycle. Otherwise, the cul-de-sac is considered a potential space.

Adenomyosis occurs when tissue that normally lines the uterus grows into the muscular wall of the uterus. Gynecologists rely on diagnostic imaging to guide treatment. Accuracy of both pelvic ultrasonography and magnetic resonance imaging (MRI) for specific evaluation of adenomyosis is high. However, without direct communication to evaluate for adenomyosis, pelvic ultrasound and MRI may underestimate or misreport adenomyosis. Providers should be aware of these discrepancies when relying on radiology reports to guide treatment and potential interventions for diagnosing and managing adenomyosis.[36]

Patients with gonadal dysgenesis (GD) with a Y chromosome have increased risk for a gonadal neoplasm. Both ultrasound and MRI are relatively poor at identifying and characterizing intra-abdominal gonads in patients with GD. Most patients with a neoplasm have normal imaging findings. In one study, gonads that were definitively visualized on ultrasound were more likely to contain neoplasms that could not be visualized, perhaps because of tumor growth. This retrospective review concluded that when discussing gonadectomy with patients with GD, one should not be reassured by "normal" imaging findings. Data show that neither ultrasound nor MRI should be relied on for surveillance in patients with GD who decide against gonadectomy. Normal ultrasound or MRI findings do not rule out neoplasm in patients with intra-abdominal gonads.[37]

Polycystic ovary syndrome (PCOS) is a common reproductive endocrinopathy in women of childbearing age, affecting 5%-15% of women in this age group. Suggestive cardinal features comprise hyperandrogenism, ovulatory dysfunction, and/or a polycystic appearance of the ovary. The gold standard radiologic tool is pelvic ultrasound. Its limitations in overweight and obese girls are real and must be considered. If utilization of an endovaginal transducer is not feasible in young virginal girls, pelvic MRI could be a useful alternative, allowing greater delineation of structural components of the ovary and better appreciation of both its volume and its structural alterations.[12]

Two-dimensional transperineal ultrasonography and 3-dimensional endovaginal ultrasound are useful in imaging suburethral masses. Ultrasound shows good to excellent agreement with MRI in identifying and measuring suburethral masses; therefore, these 2 modalities can be used interchangeably, depending on availability of equipment and expertise.[38]

Ovaries may not be clearly identified on transabdominal images. Ovaries have a characteristic follicular appearance and may appear in various positions.[4] Endovaginal scanning uses a high-frequency transducer and provides high-quality images of endometrium, myometrium, cul-de-sac, and ovaries.

The uterus usually is easily identified posterior to the bladder. In the longitudinal/sagittal view, the fundus is located on the left side of the imaging screen, with the cervix on the right. The entire uterus may not be seen at the same time or on a particular endovaginal view. The uterus is pear-shaped on the longitudinal view and is round on the transverse view.

The endometrial stripe is located within the central uterus; its thickness varies with the patient's menstrual cycle. The stripe is thin and is less echogenic after menses but becomes thick and echogenic from ovulation to the secretory phase.

Endovaginal longitudinal view of the uterus: The e Endovaginal longitudinal view of the uterus: The endometrial stripe (st) is thickened. The arcuate vessels (arc) can be seen within the uterus and should not be confused with free fluid in the cul-de-sac.

The ovaries usually are located posterior and lateral to the uterus and anterior to the internal iliac artery and vein. They usually are medial to the external iliac vessels. The iliac vessels provide an anatomic landmark for localization of the ovaries.

Endovaginal view of the ovary: Note its location a Endovaginal view of the ovary: Note its location adjacent to an iliac vessel.

The typical follicular appearance of the ovaries aids in their identification; however, the follicles can be confused with vessels. Using the nonscanning hand, the ultrasonographer can place gentle pressure over the lower abdomen; this may help in moving the ovary into the ultrasound image.[4]

Some ultrasound machines have endovaginal transducers that are capable of color flow imaging. This feature usually is seen on more expensive machines. This capability is helpful in localizing vessels within the pelvis and in determining blood flow to the ovaries, as is required to diagnose or exclude ovarian torsion.[19, 39]

Video depicts 2 findings: first, it shows an enlarged hypovascular left ovary; second, it shows flow in the healthy right ovary. A small amount of intraperitoneal fluid surrounds the left ovary.

Use of color flow imaging in ectopic pregnancy has been documented.

Transvaginal 3D imaging is as reliable as 2D imaging in evaluating the uterus.[40]

The videos below depict abnormal transvaginal ultrasonographic findings. If abnormalities are noted on pelvic ultrasonography, an obstetrician/gynecologist or a radiologist can be consulted for further evaluation. Color flow Doppler imaging may be helpful in some cases (eg, ovarian torsion).

Cine loop depicting transvaginal ultrasonography with free fluid in the uterus and right ovary. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.
Cine loop of transvaginal ultrasonography showing free fluid in the uterus. Video courtesy of Meghan Kelly Herbst, MD. Also courtesy of Yale School of Medicine, Emergency Medicine.