A transvaginal ultrasound offers an invaluable avenue for imaging the female pelvic anatomy. It augments transabdominal ultrasound for a more complete evaluation of the ovaries, adnexa, uterus, cervix, and surrounding pelvic regions. Typically, an ultrasound technician will conduct the scanning and take images of the normal structures, with more dedicated images or cine clips obtained of aberrant anatomy, pathologic processes, or pregnancy. The images are read by a radiologist, guiding the treatment by an interprofessional team.
Review the purpose of the transvaginal ultrasound.
Explain how to perform the endovaginal ultrasound.
Outline the utilities and limitations of the transvaginal ultrasound.
Describe the basics of interpreting an endovaginal ultrasound by an interprofessional team.
Transvaginal ultrasound imaging is unique in its ability to closely visualize the female reproductive organs that would otherwise be difficult to see on transabdominal ultrasound. Additionally, unlike computer tomography (CT), this is a more up-close imaging modality without the utilization of ionizing radiation. There are many indications for this, both diagnostic and interventional. An ultrasound technician first conducts a transabdominal scan for a thorough exam and follows it with a transvaginal ultrasonographic exam. Images are uploaded to a picture archiving and communication system or PACS system for the radiologist to interpret.
Adnexal/ovarian masses and cysts, endometrial pathologies, fibroids, and pregnancy (ectopic and intrauterine), as well as evaluation of developmental anomalies, are a non-exhaustive list of indications that are commonly evaluated with this imaging modality.
Anatomy and Physiology
The ability to properly evaluate the female pelvis sonographically requires proficiency in anatomy. An ultrasonographer will always position the probe so that a marker that propagates on every image consistently indicates cephalad on sagittal imaging and the right side on transverse imaging. Beginning externally, the introitus gives way to the vaginal canal, which ends at the cervix. The cervix has two portions: the ectocervix, which protrudes out into the vagina, and the supravaginal portion, which connects with the uterus.
The endocervical canal connects the vagina and uterine cavity. Circumferentially to the cervix, the fornices are invaginations of the distal vaginal mucosa. A transvaginal ultrasound probe may be placed anteriorly, posteriorly, or on either side of the cervix by placement within the fornix. The posterior fornix creates the inferior border of the Pouch of Douglas, while the anterior fornix borders the vesicouterine pouch inferiorly.
The external os of the cervix gives rise to the endocervical canal and terminates at the internal cervical os. This marks the entrance to the uterus. The fallopian tubes are located on either side of the uterus and are composed of three regions. The portion of the fallopian tube closest to the uterus is called the isthmus, followed by the ampullary segment and then the infundibulum. On the ends of the infundibulum, there are finger-like projections called fimbriae that move like cilia and are responsible for drawing an ovulated ovum into the fallopian tubes. The junction between the uterus and the fallopian tube is termed the cornu.
The ovary is suspended to the pelvic sidewall by the infundibulopelvic ligament (suspensory ligament of the ovary), containing the ovarian vessels. The utero-ovarian ligament extends from the uterus to the ovaries and carries a blood supply from the uterine artery.
Indications for ultrasonographic evaluation of the female pelvis include, but are not limited to the following:
Evaluation of pregnancy
Evaluation of cause
Evaluation of treatment
Abnormal uterine bleeding
Presence of pelvic mass
Presence of infection
Evaluation of anomalous anatomy
Aid in performing an interventional procedure
Other non-gynecologic entities may be evaluated as well as listed below:
Contraindications to the transvaginal ultrasound are the following:
Rupture of membranes in a pregnant patient, as they are at an increased risk of chorioamnionitis
Recent vaginal surgery
Lack of patient's consent
Contraindications in pregnant women are premature rupture of membranes and bleeding from placenta previa.
Ultrasound machine with a transvaginal ultrasound probe
Table: The table may be specialized for patient placement in the lithotomy position with stirrups. If this specialized table is unavailable, the patient may lie on a flat table and have a rolled towel or pillow under her pelvis to allow for probe maneuverability.
An ultrasound technician conducts a transabdominal ultrasound and then follows with a transvaginal sonographic exam. Images are uploaded to a PACS system which is made available to the radiologist for review and interpretation. The image quality and thoroughness of evaluation are largely dependent on the technician's proficiency and perspective to identify pathology and relay the images in a way that sufficiently allows the radiologist to interpret the ultrasound. A chaperone may be offered to the patient as this decreases misinterpretation or miscommunication during the exam.
The patient is asked to undress from the waist down and cover themselves with a gown. Lying supine, transabdominal ultrasound is first performed. A full bladder is recommended as this displaces the adjacent bowel loops that would otherwise distort the image and create an acoustic window, illuminating the organs behind it. Once completed, the patient is asked to empty their bladder. A disinfected transvaginal ultrasound probe is prepared by placing lubricant gel within the tip of the probe cover and then inserting the probe into it. Careful attention should be made to eliminate any bubbles which may interfere with imaging quality as an artifact.
The transvaginal transducer is inserted, with special attention being made to the orientation of the image. A marker on the screen may be used to indicate cephalad from caudad on sagittal imaging or right from left on transverse imaging, though various protocols are institution-specific.
The probe is placed in the distal vagina or against the external cervical os. Changing the depth of the ultrasound probe will create a different focal point and thus bring different areas within view. Sagittal imaging is obtained with side-to-side movements of the probe, from one adnexa to the other. Turning the probe to 90° will give us a transverse/semi-coronal orientation. The transverse on endovaginal imaging is more of a coronal plane, while the true transverse image is done transabdominally. Subsequent imaging is performed by moving the probe anterior to posterior. A general survey is first performed as an initial evaluation by sweeping the probe from the midline to the lateral margins at the bilateral adnexa. The probe is then rotated 90° and swept in the anterior-posterior direction. The cervix, internal os, endocervical canal, and occasionally the external os is imaged in both sagittal (long-axis) and transverse (short-axis) orientations.
The cervix is normally 2.5 to 3 cm and may be measured if there is an indication for it, such as recurrent second-trimester miscarriages in the setting of an incompetent cervix. Benign nabothian cysts may be seen here, which are small and anechoic. Concerning the uterus, size, orientation, contour irregularity, and myometrial pattern should be addressed. The length of the uterus is measured on sagittal orientation, from the fundus to the external cervical os if able to image. Transverse/semi-coronal images should also be obtained with anteroposterior and transverse diameters measured. Volume may be calculated from these values. An anteverted uterus, which is the most frequently seen presentation, rests its fundus forward on the bladder, best appreciated on sagittal imaging, with the fundus oriented towards the top of the image. A retroverted uterus displays a fundus that orients posteriorly towards the rectum. To see a retroverted uterus may not have any clinical significance, though it may be associated with deep infiltrating endometriosis in the posterior cul-de-sac or abdominal adhesions, particularly if it is fixed in this position. The myometrial pattern should be homogeneous, and the uterine contour should be smooth. Heterogeneous parenchyma is non-specific though it may be attributable to adenomyosis or fibroids. Not all fibroids need to be measured, but the ones that are measured should be measured in at least 2 dimensions. The location within the layers of the uterus (subserosal, mucosal, submucosal) and which area of the uterus (left wall, fundus, lower segment, etc.) should be reported.
The endometrium, also referred to as the endometrial stripe, is delineated by its normal echogenic nature, surrounded by the hypoechoic uterine myometrium. The thickest portion on true sagittal imaging should be measured. If the endometrial cavity has contents such as fluid or an intrauterine device, then it should be documented. The sum of the thickness of the two parallel endometrial lines is recorded as the endometrial thickness in these cases. Normal thickness varies for a premenopausal woman, which may be 3-5 mm during the proliferative phase of the cycle, with an upper limit of 6-12mm during the secretory phase. A maximum thickness of 5 mm is normal in a postmenopausal woman, even in women on hormonal replacement therapy or tamoxifen. Endometrial irregularity, thickening, or cysts may be seen in the setting of adenomyosis. Endometrial thickness may also provide clinically useful information. Saline-infused sonohysterography is a technique to augment visualization of the endometrial lining and cavity and evaluate fallopian tube patency.
Ultrasonography is the best way to identify the location of early pregnancy in the setting of an elevated beta-hCG; however, a very early intrauterine pregnancy may be missed. Furthermore, an ectopic pregnancy cannot be excluded. Hence a follow-up transvaginal ultrasound and b-hCG are advised . An ectopic pregnancy may occur almost anywhere along with the female reproductive system; however, the majority (95%) implant within the fallopian tubes.
The bilateral ovaries should be measured in three dimensions with the calculation of the volumes. Any masses or prominent cysts should be measured as well. Physiologic follicles in a reproductive-aged woman may be seen. Masses, dilated tubular structures, and other abnormalities should be evaluated in the adnexal regions. However, the fallopian tubes are not typically visualized if there is no pathology present.
Dynamic imaging may be performed by a sonographer via placing a hand over the lower abdomen, palpating, and observing the mobility of the internal organs in real time. “Slide sign” is when the organs move relatively freely against one another. When they are more fixed during palpation, this is indicative of adhesions. Additionally, regional sensitivity to probe maneuvers and anterior abdominal palpation may be pertinent to identify pathology. Another form of dynamic imaging may be performed by taking a cine-loop (video clip). When an area of interest is identified, a cine-clip will allow the interpreting radiologist to characterize pathology more accurately than static images alone. Some protocols have cine-clip imaging as a part of their requirements. The use of color Doppler has many utilities. It can assess the vascularity of an identified lesion, assess for hyperemic states such as infection, or assess for lack of flow, such as in the case of ovarian torsion. When a color Doppler is utilized, this must be mentioned in the reporting technique and findings.
Once the examination is complete, the probe cover is removed, and running water and soap are used to remove any gel. After drying the probe, the utilization of a high-level disinfectant is recommended.
Typically, there are no major complications with this procedure. The patient may experience some discomfort but should not feel any pain.
Ultrasound is a tool that is widely available, relatively inexpensive, and timely, which makes it invaluable in evaluating emergency situations. One of these medical emergencies is ovarian torsion, in which there is twisting about the vascular pedicle of the infundibulopelvic ligament and utero-ovarian ligament. Venous wave-forms are expected to initially become absent because vein walls are thinner and more compressible than their arterial counterparts.
Because of variability in blood flow appearance secondary to setting adjustment, the contralateral normal ovary should be compared. The ovary will appear enlarged, and edematous and pelvic free fluid may be seen. A hallmark characteristic is the whirlpool sign, which is torsion at the infundibulopelvic ligament is evaluated in cross-section.
Seeing some or all of these findings on ultrasound will strongly suggest ovarian torsion. However, there are a few caveats. Due to the dual blood supply from both the ovarian artery running through the infundibulopelvic ligament and the uterine artery from the abdominal aorta, a patient without symptoms may demonstrate an apparent lack of blood flow to the ovary.
Furthermore, the ovary may alternate between being torsed and reconfigured to its original position, which means that some of the aforementioned signs may not be present at the time of the ultrasound. Direct visualization is the mainstay for diagnosis. An appropriate diagnosis of ovarian torsion is made about 84% of the time. The shortcomings of this modality should be known because ultrasound alone may not be sufficient to make a diagnosis.
Enhancing Healthcare Team Outcomes
The proximity of the transvaginal ultrasound probe to the regions of interest allows for better image quality than its transabdominal counterpart. It operates with a higher frequency transducer (5 to 7.5 MHz), resulting in less artifact. A higher frequency can only penetrate so much through tissue, making it ideal in the transvaginal route. Additionally, there is marked difficulty in obtaining proper transabdominal sonographic images in an obese patient because of the amount of soft tissue the sound waves need to traverse; the transvaginal probe will bypass the pannus.
The transabdominal counterpart operates at a lower frequency (around 3.5 MHz), allowing for deeper signal penetration (as is required) at the expense of poorer resolution. The transabdominal ultrasound also allows more flexibility to image a larger field of view, such as in the setting of the high-positioned adnexa because the probe may be moved anywhere across the abdomen.
Each modality has its strength and shortcomings. Hence, the combination of the two methods provides more accurate evaluation and earlier detection of pathology. [Level 2]
(Click Image to Enlarge)
The semicircular region in the superior portion of the image indicates that this is a transvaginal ultrasound. This is a sagittal image (long axis) of the uterus with the cephalad portion on the left as indicated by the LOGIC label. This is a retroflexed uterus that may be a normal variant or occurs as a result of endometriosis in the posterior cul-de-sac or from surrounding adhesions. The endometrium as indicated by the calipers is of normal thickness and echogenic pattern.
Contribution by Suraya Nahlawi, DO
(Click Image to Enlarge)
This is a sagittal image of the left ovary. Physiologic follicles are noted.
Contributed by Suraya Nahlawi, DO
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