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Department of Fetal Medicine and Obstetric & Gynecological Ultrasound, Manipal Hospital, Bangalore, Karnataka, India
Today, with ultrasound, we can actually see pathology, and with a transvaginal ultrasound (TVS), one can not only see the pathology at close range, but also simultaneously touch the various structures that are seen, making it a dynamic and interactive examination (Fig. 2.1). This is a distinct advantage of TVS over CT and MRI. Presently, ultrasound technology has advanced to such an extent that one can see on ultrasound almost as much as a pathologist can see on gross examination of a specimen (both the external surface and cut sections). Not only that, one can in addition see flow patterns within the mass which cannot be ascertained by gross examination of the specimen.
Fig. 2.1
(a) Bimanual per vaginal examination which uses touch sensation to assess pathology of pelvic structures; (b) with TVS, which allows one to see pathology while touching the various structures simultaneously
Ideally a transabdominal scan (TAS) is done first with a full bladder, followed by a transvaginal scan (TVS) after having emptied the bladder. It is important that the technique is standardised, fixed and predetermined.
2.1 Transabdominal Scan
Filling the Bladder
For a good transabdominal scan, the bladder should be sufficiently filled, so as to push the bowels that lie in front of the pelvic organs towards the upper abdomen. Another advantage of a full bladder is that urine, being fluid, enhances the sound waves of the ultrasound beam, resulting in better visualisation. The bladder should not be over-distended because that would cause discomfort to the patient. In addition, a very full bladder increases the distance of the uterus and ovaries from the probe, decreasing resolution and resulting in suboptimal visualisation. A few points to be kept in mind here are:
- 1.
Very often one may be able to see sufficiently well on TAS even with a suboptimally filled bladder. Especially in cases that are to be followed by TVS, there is no need to insist that the bladder should be further filled.
- 2.
In emergency cases (like a case of a ruptured ectopic pregnancy), waiting for the bladder to fill may not be justified.
- 3.
In cases with a previous caesarean, the bladder may be adherent to the uterus at the site of the LSCS scar, and filling the bladder so as to visualise the upper uterus may not be possible. Instead, the more the patient fills her bladder, the more the lower uterine body and cervix get stretched, causing discomfort.
- 4.
With a very large and bulky uterus, a full bladder may not be able to overlie the entire uterus. Very often in these cases, the bulky uterus itself pushes the intestines out of the pelvis into the upper abdomen.
For a transabdominal scan, typically a 3.5–5 MHz transducer is used. The transducer is placed longitudinally on the patient’s abdomen in the midline. It has a groove on one side and it is placed such that this groove lies facing the superior end of the patient. This produces a sagittal section of the uterus, and the area corresponding to the groove is highlighted on the screen by a ‘GE’ mark which is green on the active screen and white on the adjacent frozen image. This corresponds to the upper end of the uterine body. That is, basically, structures that are in the superior part of the patient’s body are seen on the right of the screen, and structures in the inferior part are seen on the left of the screen.
After studying the LS, the probe is rotated in an anticlockwise direction, such that the groove now lies on the right of the patient. The area corresponding to the groove is highlighted by the ‘GE’ mark and is seen on the right side of the screen. Thus, structures on the right side of the patient are seen on the right side of the screen, and those on the left side of the patient are seen on the left side of the screen.
Fig. 2.2
TAS for uterus. (a) Placement of probe for LS scan. Arrow indicative of marker on the probe. (b) Placement of probe for TS scan (after 90° anticlockwise rotation). Arrow indicative of the marker on the probe, now to the right of the patient. (c) Midsagittal section of uterus. Arrow, showing upper end of the uterus, corresponds to the marker on the probe in the image (a). (d) TS of uterus – arrow, showing right side of the uterus, corresponds to the marker on the probe in the image (b). Structures on the right side of the patient are seen on the right side of the screen and, similarly, those on the left side of the patient are observed on the left of the screen
Ovaries and Adnexa
To visualise the ovaries and adnexa, one can move and/or angulate the probe to one side. Regardless of whether one is examining structures on the left or the right, the rotation from LS to TS is always anticlockwise.
Fig. 2.3
TAS for examining the adnexa. (a) The probe can be placed on either side of the midline and the rotation should be anticlockwise from LS to TS. (b, c) Right ovary seen in TS and LS
Advantages of a Transabdominal Scan
TAS provides a panoramic view and thus furnishes a global survey of pelvic anatomy. One is, therefore, less likely to miss any small pathology (like an ectopic pregnancy mass or a pedicle of a torsed ovary), and while doing TVS, one would know exactly where to look in order to study the pathology.
Large masses extending into the upper abdomen are better assessed on TAS and may be missed with TVS alone, as those structures lie too far away from the transvaginal probe (e.g. a subserous or pedunculated fundal fibroid).
The endometrium of mid-positioned uterus is better seen on TAS than TVS. Endometrial polyps can thus be missed on a TVS in a patient with a mid-positioned uterus.
Masses like fibroids in the lower corpus or cervix can cause shadowing resulting in suboptimal visualisation of structures above it, like other fibroids, ovaries, etc. on TVS. In such cases, the structures lying above are best seen on TAS.
In dermoids (particularly large ones) one may not be able to see its superior parts and margins due to shadowing on TVS. Measuring such dermoids is easier on TAS (Fig. 2.4).
Fig. 2.4
Case with a large dermoid. (a) TAS – the entire dermoid seen. (b) TVS – Dermoid was not seen. Due to significant acoustic shadowing by the dermoid, only its lower end which resembles the bowel is seen, making it difficult to visualise the dermoid
TAS in most cases is not time consuming.
Sometimes TAS is the only method to scan a patient who declines a TVS (as is sometimes the case with virgins/unmarried patients). Transrectal scan is another option, provided the patient consents and facilities are available for the same.
Most sonologists measure the uterus and take a cursory look at the rest of the pelvis prior to a TVS. The author, however, prefers to measure the uterus and endometrium and also to study the endometrium qualitatively as in many cases the endometrium of a mid-positioned uterus is not clearly seen on TVS. In addition, large masses extending beyond the pelvis and fibroids high up in the uterine body can be studied in greater detail on TAS. Furthermore, in cases with uterine anomalies, it is preferable to execute the 3D rendering of the uterus on TAS as well, prior to carrying out a TVS. This is recommended because with a full bladder, the uterus is most often stretched, more linear and perpendicular to the probe, which makes 3D rendering of the uterus simpler to obtain and assess.
2.2 Transvaginal Scan
The patient’s bladder should be empty for a TVS.
For a transvaginal scan, typically a 5–9 MHz transducer is used.
The ideal position in such cases is the lithotomy position. This facilitates downward movement of the hand with the probe, so that structures placed anteriorly in the pelvis are clearly seen.
The probe is always covered with a probe cover, with jelly between the two. Air bubbles should be avoided. Jelly is applied to the tip of the probe and then the probe is gently introduced into the vagina.
The transducer has a groove which should face upwards (anterior part of patient’s abdomen) at insertion. This produces a sagittal section of the uterus, and the area corresponding to the groove is highlighted by a ‘GE’ mark on the screen. This corresponds to the anterior part of the uterine body at the UV fold.
The probe is angulated and rotated a little so as to obtain the midsagittal (LS) section of the uterus.
Fig. 2.5
Orientation for TVS. (a) Placement of probe for LS view of uterus. Arrow indicative of marker on the probe seen anteriorly. (b) Midsagittal section of the uterus with footprint (FP) of the probe lying in the lower part of the image. Arrow, showing anterior margin of the uterus (in the UV fold), corresponds to the marker on the probe. (c) Footprint (FP) of the probe lying in the upper part of the image, which is an alternate acceptable method of observing the image on the screen
There are two commonly used methods of observing the image on the screen (Fig. 2.5b, c). The first with the TVS probe footprint below is generally considered ideal because of two reasons:
The image orientation is more natural, with superior structures seen in the upper part of the screen and inferior structures in the lower part. In the alternative method, structures higher up are seen lower down on the screen and vice versa.
There is a clear-cut difference in images that are TAS versus TVS because in the former, the footprint lies above and in the latter the footprint of the probe lies below.
In this book, the images will be seen in the orientation that is considered ideal (that is with the footprint below), as the author has been following that orientation over the years. It is now suggested that students and those learning gynecological ultrasound for the first time should follow the ideal orientation with the footprint at the lower end of the screen. Standardisation of orientation on screen is important. It does not really matter how one is used to observing the image on the screen, provided it is consistently done in the same manner.
The following methodology is one with the footprint of the probe lying in the lower part of the screen, which is considered ideal.
Uterus
To obtain TS of the uterus after LS, on TVS, rotation is done in a clockwise direction. The groove which lay anteriorly now lies on the patient’s left. This produces a transverse section (TS) of the uterus, and the area corresponding to the groove is highlighted by a ‘GE’ mark on the screen. This corresponds to the left side of the uterine body. Structures on the left of the patient are seen on the left of the screen and, similarly, those on the right are seen on the right of the screen.
Fig. 2.6
TVS for uterus. (a) Placement of probe for LS scan. Arrow indicative of marker on the probe. (b) Placement of probe for TS scan (after 90° clockwise rotation). Arrow indicative of the marker on the probe, now to the left of the patient. (c) Midsagittal section of the uterus. Arrow, showing anterior margin of the uterus and UV fold which corresponds to the marker on the probe in (a). (d) TS of uterus. Arrow, showing left side of the uterus which corresponds to the marker on the probe in (b). Structures on the left of the patient are seen on the left of the screen and similarly, those on the right of the patient are observed on the right of the screen
Ovaries and Adnexa
To assess the ovaries and adnexa on either side of the uterus, one can either angulate the probe from the LS section of the uterus to obtain the LS of any adnexa/ovary, or, as is more frequently done, the probe can be angulated from the TS of the uterus to obtain the TS of any adnexa/ovary. On TS, the ovaries are typically seen lying just medial to the external iliac vessels.
Fig. 2.7
Right ovary TS and LS view. Rotation from LS to TS is done in a clockwise direction and vice versa
Rotation from LS to TS is to be done in a clockwise direction. It is imperative to keep in mind that rotation from LS to TS must always be standardised, regardless of which structure or which side is being studied.
A transvaginal probe offers a combination of touch along with simultaneous visualisation of pelvic structures, making TVS dynamic and interactive. TVS should include the following:
Measurement and morphological evaluation of the myometrium, endometrium and ovary (including adnexa) for normal and pathological conditions. The evaluation of the uterus (myometrium and endometrium) is discussed in Chaps. 3 and 4. The ovary and adnexal masses are evaluated as given in Chap. 7.
Assessment of the cervix and vagina has been discussed in Chaps. 5 and 6. These structures are often not given attention during an ultrasound examination because pathologies of these structures are infrequent and visualising them is often challenging. Currently, ultrasound machines provide better resolution, and there is increasing literature available on cervical and vaginal pathologies. This has facilitated diagnosis of vaginal and cervical pathology on ultrasound, and their examination is now considered an integral part of routine pelvic examination.
Assessment of uterine version and flexion – which may serve as a marker to pathology and a guide for possible intrauterine procedures (details provided later in this chapter).
Looking for fixity of ovaries by applying pressure with the probe. By doing this, one can assess whether the ovaries are adherent to the uterus and/or the pelvic walls.
Assessing the fixity of the uterus. In cases where the uterus is adherent posteriorly, a typical ‘ear’- or ‘question mark’-shaped uterus is often noted (details in Chap. 8).
Looking for any tenderness, and if present, that should serve as a guide for a detailed search in that area for any pathology. This ‘pain-guided approach’ is useful in diagnosing conditions like DIE and ectopic pregnancy. In patients presenting with pain, TVS is useful in assessing whether the pathology being observed is the cause for pain. The tender organ will elicit the same pain that the patient complains of.
Assessing whether the bowels are adherent to the posterior wall of the uterus. Normally the large bowel (rectosigmoid), on applying pressure on the cervix and uterus with the probe, is seen to slide smoothly over the posterior cervix and vagina (‘low sliding sign’) and the uterine body and fundus (‘high sliding sign’). The absence of sliding sign indicates that the bowels are adherent to the posterior wall of the uterus and raises a high suspicion of bowel DIE.
Ideally, specific search for DIE nodules (described in Chap. 8) should also be done. This is particularly so in women with pain, endometriomas or any tenderness. The bladder wall and mucosa should also be examined for possible DIE. Since visualisation of bladder DIE requires a partially filled bladder, it is best done towards the end of the TVS evaluation.
Advantages of Transvaginal Scan
Because of the close proximity of the various structures to the probe, a higher frequency probe is used for TVS, which provides a close-up view of pelvic structures with high resolution. Thus:
- 1.
Small lesions not seen on TAS may be observed on TVS (e.g. small endometriotic cysts).
- 2.
There is better characterisation of pathology (e.g. fibroid or adenomyoma).
- 3.
Doppler studies are also better because of proximity of structures to probe.
- 1.
The transvaginal probe offers a superb combination of visualisation of pelvic structures with a simultaneous possibility of touching them. This is analogous to performing an internal physical pelvic examination and simultaneously seeing the structures. This helps us identify which structures are tender or adherent.
Version is the angle between the vagina and the cervix, and flexion is the angle between the cervix and the uterine body. The prefix ‘ante’ is used to denote forward or anterior (i.e. towards the bladder) and the prefix ‘retro’ to denote backward or posterior (i.e. away from the bladder).
In comparison to the vaginal axis (i.e., the direction of the TVS probe), if the cervix is directed towards the bladder, it is termed an ‘anteverted uterus’, and if it is directed away from the bladder, it is termed a ‘retroverted uterus’. Similarly, in comparison with the cervix, if the uterus is directed towards the bladder, it is termed an ‘anteflexed uterus’, and if it is directed away from the bladder, it is termed a ‘retroflexed uterus’. Thus, based on the angle of version and flexion, various uterine positions are possible.
Fig. 2.8
Uterine version and flexion. Yellow/lowest arrows indicate angle of the vaginal axis, red/middle arrows indicate the cervical axis and blue/highest, the axis of the uterine cavity. (a) AVAF uterus. Cervix directed towards the bladder (anteriorly) as compared to the vagina (anteversion). Endometrial axis directed towards the bladder (anteriorly) as compared to the cervix (anteflexed). (b) RVRF uterus. Cervix directed away from the bladder (posteriorly) as compared to the vagina (retroversion). Endometrial axis directed away from the bladder (posteriorly) as compared to the cervix (retroflexed)
Fig. 2.9
Version and flexion. Yellow/lowest arrows indicate angle of the vaginal axis, red/middle arrows indicate the cervical axis and blue/highest, the axis of the uterine cavity. (a) Diagrammatic representation of an AVAF uterus. (b) TAS of an AVRF uterus
2.3 Three-Dimensional Ultrasound (Figs. 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, 2.18, 2.19, 2.20, 2.21, 2.22, 2.23 and 2.24)
The addition of three-dimensional (3D) ultrasound to transvaginal scan has improved the diagnostic utility of ultrasound in gynecological imaging to a great extent. In 3D ultrasound, the entire volume of a tissue block is acquired, from which sections along multiple planes can be displayed and analysed for better assessment. The addition of Doppler to 3D has further enhanced its utility. This means that, in 3D ultrasound, three-dimensional information of the entire volume of the region of interest can be obtained for analysis. This data can even be stored for manipulation at a later time. Four-dimensional ultrasound is useful to assess moving structures (where the fourth dimension is time) like the fetal face and cardia in obstetric ultrasound, but in gynecological ultrasound, since these structures are stationary, 3D is preferred.
In some gynecological conditions 3D ultrasound is essential for proper diagnosis. These include uterine anomalies and pelvic floor studies. In many other conditions, however, it is a value-added modality that increases the clarity and accuracy of the 2D ultrasound findings. The advantages of 3D in gynecological ultrasound are mentioned in the following paragraphs. However, their utility in various gynecological pathologies will be discussed in the relevant chapters.
Rendering (Fig. 2.10)
This is viewing the block along a cut section. Here, masses with different echo densities are well outlined. One of the greatest advantages of 3D ultrasound is the capacity to render an image in various planes, particularly the coronal plane. On 2D, the uterus is generally clearly seen on sagittal and transverse planes both on TAS and TVS. However, 3D is able to provide a coronal section of the uterus, which cannot be visualised on 2D. This is very useful in assessing the shape of the uterine cavity, which is clearly visualised on 3D because of the difference in echo densities between the endometrium and myometrium. 3D can also be used in cases where delineation of masses is difficult on 2D.
Fig. 2.10
Sections of the uterus. (a) Coronal section of the uterus on a 3D rendered image. (b) Sagittal section of the uterus on regular TVS. (c) Transverse section of the uterus on regular TVS
Volume Contrast Imaging (VCI) (Fig. 2.11)
This feature allows the addition of slices of different thickness onto the rendered section, for better contrast differentiation. This provides a better outline of structures and is useful in gynecology to outline a poorly circumscribed fibroid or to assess the endomyometrial junction in cases with adenomyosis or endometrial malignancy (to look for myometrial invasion).
Fig. 2.11
Sagittal section of the uterus showing EMJ. (a, b) Postmenopausal lady with an endometrial polyp, (a) on 2D greyscale, EMJ is seen but not well defined (arrow). (b) 3D image of the same section of the uterus as in (a) with VCI showing a very well-defined EMJ (arrow), as compared to (a). (c, d) Postmenopausal lady with endometrial cancer (c) on 2D greyscale. EMJ not well defined. (d) 3D image of the same section of the uterus as in (a) with VCI showing an irregular EMJ with myometrial invasion (small arrows)
Multiplanar Imaging (Fig. 2.12)
Here, a structure/tissue block can be visualised in all three dimensions simultaneously. There is a dot provided at the intersection of three planes so that one can see the same anatomical landmark in all three planes at the same time. While walking through one plane with the dot, the dot moves to the corresponding spot in the other two planes. This is very helpful when the anatomy is confusing.
Fig. 2.12
Multiplanar imaging. (a) Fibroid seen in all three perpendicular planes of the uterus (LS/TS/coronal). (b) Multiplanar view with all three-dimensional planes visualised simultaneously. Dot (here enlarged and in red) of intersection of the three planes is visualised, which helps in observing the corresponding point in the two other planes
Depth Perception (Fig. 2.13)
3D rendered images, particularly of cystic areas, are able to provide a sense of depth which is useful for a subjective assessment of depth. This helps not only the sonologist but also the patient and referring clinician to understand the pathology better. The addition of cine loop, by which the 3D rendered image can be rotated, and editing the direction of the light source in rendered images further add to this perception.
Fig. 2.13
3D rendered image. (a) HDI view of a papillary cyst (arrow showing papilla). (b) 3D rendered image of a hydrosalpinx showing incomplete septae (short arrows) and compressed mucosal folds (long arrow)
Volume calculation is more accurate with 3D ultrasound using virtual organ computer-aided analysis (VOCAL) software, particularly for masses with irregular outline. This can be done for both solid structures like the endometrium and for cystic spaces. In addition, when there are both solid and cystic components in a mass, the percentage of cystic versus solid can also be calculated. This software can also be used for quick and more accurate assessment of antral follicle count.
Fig. 2.14
3D volume of an adnexal mass with solid and cystic components. (a) VOCAL software used to calculate Volume of the mass. (b) Volume of cystic (‘below threshold’) and the solid components (‘above threshold’) can be assessed separately
Fig. 2.15
Volume assessment of endometrium. VOCAL is especially useful in volume calculation of masses which are not regular in shape, like the endometrium
Fig. 2.16
Antral follicle count with SonoAVC
The vascular pattern of flow indices of the region of interest (ROI) can also be done by a combination of Doppler with 3D (discussed in greater detail later in this chapter, in the section on Dopplers). Flow indices of the ROI can also be obtained.
Fig. 2.17
Fibroid polyp with its vascular morphology using 3D Doppler with glass body display
Fig. 2.18
3D flow assessment in a case of carcinoma endometrium. (a) Volume of endometrium is calculated. (b) VI, FI and VFI of the region of interest (endometrium) are calculated
Working Offline
The advantage of storing 3D volumes is that they can be used to assess the pathology at a later time. This is particularly useful in a busy ultrasound clinic and also when a patient is in pain and one cannot toggle with the probe and knobs for a long time. It has also been used for assessing subjective reproducibility of ultrasound findings in various studies. In difficult cases, these stored volumes may facilitate access to a second opinion from an expert examiner.
Steps in 3D Ultrasound
It is out of the scope of this book to explain in detail the steps involved in 3D ultrasound. This has been briefly discussed as follows:
- 1.
Data acquisition:
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Orientation of 2D image – The 2D image of the region of interest should be well visualised for a proper 3D assessment. The best 2D plane for acquisition of the volume may depend on the structure being assessed, for example, in order to acquire a volume in cases of uterine anomalies, the most commonly used plane is the mid sagittal plane of the uterus.
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Defining the region of interest (ROI) – The region of interest should be completely included within the 3D box, and the angle of acquisition should be such that the entire volume of ROI is included in the 3D sweep.
- (c)
Volume acquisition – Once the ROI and angle of acquisition have been decided, a volume sweep is taken so that the entire volume of ROI is now available for analysis.
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- 2.
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3D/4D Visualisation (Display Mode) (Figs. 2.19, 2.20, 2.21, and 2.22) – Once the volume has been acquired, it is possible to display and study it in various ways:
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Multiplanar display – This basically displays the region of interest in three different orthogonal planes simultaneously. The utility of this has been explained earlier in this section.
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- (a)