Abstract
Transvaginal imaging of the pelvic area begins at the perineum. With the probe positioned at the opening of the vagina, in the sagittal plane, the image demonstrates the symphysis pubis anterior towards (left of image) and the rectum posterior (right of image).
Transvaginal imaging of the pelvic area begins at the perineum. With the probe positioned at the opening of the vagina, in the sagittal plane, the image demonstrates the symphysis pubis anterior towards (left of image) and the rectum posterior (right of image).
As the probe is moved further into the vagina the cervix will come into view.
Once the cervix is seen, the probe is moved to observe the posterior wall of the cervix, to assess the position of the uterus in the pelvis. With small moves of the probe follow the line of the cervical canal into the body of the uterus.
Figure 3.1 Begin with the probe in the sagittal plane – 12 o’clock.
Figure 3.2 Transducer is on the peritoneum. The vagina is central, with the symphysis on the left seen as a bright echo with posterior acoustic shadowing and the rectum to the right of the hypoechoic vaginal echo.
Figure 3.3 Hypoechoic bowel wall seen posterior to the vagina, to the right of the image.
Figure 3.4 The transducer is now in contact with the cervix, with the cervical canal seen in the long axis view.
The Cervix
The cervix is located centrally in the pelvis supported by the cardinal ligament (the transverse cervical ligaments located laterally provide the major support to the cervix and uterus). Use the cervix as a reference point to assess the position of the uterus.
Under the effect of oestrogen in the late follicular phase, the endocervical canal contains mucus with a high fluid content.
Figures 3.5 to 3.8 show various positions of the uterine cervix in relation to the ultrasound probe. The posterior wall of the uterus is identified and can be followed to indicate the position of the fundus.
Figure 3.5 Uterine cervix in an anteverted uterus.
Figure 3.6 Mucus can be seen in the cervical canal.
Figure 3.7 Cervix with fluid in the cervical canal.
Anteverted Uterus
When the uterus is anteverted the fundus is seen towards the left side of the image. Move the probe to follow the cervical canal into the endometrial cavity, rotating the probe slightly, as required. Optimise the image by adjusting the depth, focus and gain and time gain compensation. (Figures 3.9 and 3.10)
Figure 3.9 Cervix of an anteverted uterus.
Figure 3.10 When the uterus is in an anteverted position the fundus is towards the left side of the image.
Retroverted Uterus
When the uterus is in a retroverted position, the fundus is located posterior to the cervix. Note the anterior and posterior walls of the cervix in Figure 3.11. While continuing to insert the probe, maintain contact with the cervix and follow the line of the cervical cavity into the body of the uterus. Raise the handle of the TV probe upwards and move the probe to the posterior fornix.
Figure 3.11 The cervix of a retroverted uterus.
As the probe is moved into the posterior fornix the endometrium can be positioned at 90 degrees to the beam. The uterine fundus will be seen on the right side of the monitor. (Figures 3.11 and 3.12)
Figure 3.12 When the uterus is retroverted the fundus will be seen towards the right side of the image.
Figure 3.13 Uterus in the longitudinal plane and the tri-line appearance of the endometrium is difficult to demonstrate.
The Uterus in the Longitudinal Plane
When the uterus is in the mid position or longitudinal plane the endometrium appears more echogenic, due to the many reflections from the blood vessels and glands in the endometrium, being at 90 degrees to the beam. Beam width artifact is also seen at depth.
Scan the uterus completely in the sagittal plane from the right lateral margin through to the left side. Note the smooth outline, the texture of the myometrium, the presence of any pathology and its location and impact or distortion on the endometrium. If there is a Caesarean scar check its integrity.
Measurement of the Endometrium
Measure the endometrium in the mid, longitudinal plane, at the upper third, where it is usually the thickest. Callipers are placed on the outer edge of the basal layers, on the anterior and posterior aspects of the opposing endometrial layers, perpendicular to the cavity.
The thickness of the endometrium increases during the proliferative stage of the normal menstrual cycle. Post menses it is thin (<4 mm) and at ovulation may have increased to 12 mm.
The endometrial cavity is seen as an echogenic line through the uterus. The basal layer develops an echogenic appearance through the proliferative stage of the menstrual cycle, giving the tri-line appearance.
Callipers are placed across the full thickness of the endometrium from basal layer to the opposite basal layer and perpendicular to the uterine cavity.
Figure 3.14 Endometrium is measured with the callipers perpendicular to the uterine cavity.
Figure 3.15 Retroverted uterus with thin endometrium (<2 mm).
Figure 3.16 Anteverted uterus with endometrium 3.5 mm.
Figure 3.17 Endometrium measures 4.5 mm.
Figure 3.18 Endometrium measures 10 mm.
Measurement of the Endometrium in a Retroverted Uterus
When the uterus is in a retroverted position, find the cervix first, ensure sufficient depth (field of view). Note the outline of the uterus coursing posteriorly or deep to the transducer position. Move the probe into the posterior fornix, by withdrawing it slightly, tilt the transducer towards the posterior aspect of the cervix and then gently push it deeper (Figures 3.20a and b).
