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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5786_Библиотеки_им_академика_М_И_Перельмана.pdf
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Scanning techniques in obstetrics and gynaecology
Ilan E Timor-Tritsch Ana Monteagudo
ABSTRACT
In the last 25 years ultrasonography became the ‘right hand’ of modern
obstetricians and gynaecologists. This was possible due to the advances of
ultrasound transducer technology and the ‘explosion’ of computer science. In
order to realize the power of ultrasound diagnostics and the ultrasound-guided
procedures, the astute provider of women's health has to understand how and
when to apply the different scanning techniques.
This chapter enumerates the different ways in which ultrasound is used in
obstetrics and gynaecology. However, it starts with the very basic concepts of
how to set up a simple but efficient ultrasound examining room and the ways
to approach scanning the everyday patient in a simple office setting. The text
leads the reader through the scanning of specific organs as well as some of the
mandatory protocols of obstetric and gynaecological examination. Certain more
prevalent clinical entities are mentioned in greater detail than others.
The interested reader should be clear that ultrasound technology like any other
technology based upon electronics, is developing rapidly and without any doubt,
by the time these pages are read, there will be new and exciting ways to help
us provide better, faster and more accurate diagnoses for our patients. Constant
reading and updating our knowledge in ultrasonography is mandatory.
KEYWORDS
Colour Doppler, gynaecology, obstetrics, transabdominal ultrasound, transvaginal
ultrasound, ultrasound.
INTRODUCTION
The subject of scanning techniques in obstetrics and gynaecology can be presented from various angles. One way is to start with the purely physics aspects of
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scanning. This, however, may deter some clinicians from reading through this part
of the book. The other angle for introducing the ways we scan in the office and
in the dedicated ultrasound laboratories is to describe and discuss the practical
aspects of the daily use of ultrasound in its clinical set-up. We decided to take this
route, thinking that it has more practical value.
An additional decision had to be made: to avoid discussion of older scanning
techniques which were ‘cutting edge’ in their time, but which have no practical
use at the time of this writing.
GENERAL ASPECTS
We will deal with the basic requirements as far as the ultrasound equipment, orientation and aspects of the technicalities involved in conducting the
gynaecological ultrasound examination are concerned. If additional information
is needed, the reader is referred to some of the more detailed resources in the
literature.
6,8,14,16,17,20,28,33,35,40,57
Ultrasound in obstetrics and gynaecology
EMPTY OR FULL BLADDER
It is now known almost to everyone engaging in obstetric and gynaecological
scanning that transabdominal ultrasound is performed most of the time with a
full bladder. The full bladder serves as an acoustic window and pushes the bowel
out of the sound path (Fig. 3.1). However, transvaginal sonography is best performed with an empty bladder, which enables the pelvic organs to reach a closer
proximity to the tip of the high-frequency transvaginal probe. The difference
between the two approaches lies in the different physical properties of the transabdominal and transvaginal probes.
The transabdominal probe produces a more or less panoramic view of the
pelvis, showing the interrelationship of the major anatomical structures within
the pelvis and their possible pathology. The transvaginal probe, however, is able
to furnish a more targeted image of the organ of interest. The transvaginal probe,
10,22,25,27,48,50
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Fig. 3.1 Orientation using transabdominal scanning. (A) Directions in the sagittal plane. (B)
Directions in the transverse plane.
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therefore, will permit an effective imaging usually to not more than 7–10 cm
in depth. Lately more advanced probe technologies as well as signal processing
have enabled deeper penetration with minimal loss of resolution. The bowel
interferes with transvaginal sonography mainly in cases in which the uterus has
been removed and the available space is taken up by the gas/fluid of the bowel.
Depending on the goal of the scan, the sonographer can select the transabdominal or the transvaginal scanning method. It is important to stress the fact that it
is easier and faster to empty the urinary bladder than to fill it up, and this should
always be considered before the patient is sent to empty her bladder.
The protocol of most laboratories is to perform first a general transabdominal
scan of the pelvis, which requires a full bladder to get an overview of the anatomy. However, if a patient presents with an empty bladder, the scan should not be
postponed, and transvaginal sonography can be performed as a first-line imaging
technique. If transabdominal examination of the pelvis is still required, it should
be performed after filling the bladder. Benacerraf et al questioned whether a full
bladder is still necessary for pelvic sonography.
3
After scanning 206 consecutive
patients prospectively, they concluded that transvaginal sonography (TVS) with
an adjunctive transabdominal sonography (TAS) with an empty bladder approach
can replace the full bladder technique for routine pelvic sonography.
Filling the bladder may help in imaging a low-lying placenta, diagnosing placenta
accreta overlying the bladder or outlining the cervix in the median plane, and at the
time of chorionic villus sampling, it may help to ‘straighten’ the uterine body to match
the axis of the cervix and the vagina for better approach by the sampling catheter.
If the patient is suspected of having an ectopic pregnancy, extreme caution
should be exercised to prevent the patient drinking water, because an emergency
surgery can be required if a bleeding ectopic pregnancy is diagnosed. In this case,
if it is really necessary to obtain abdominal views, the bladder should be filled
using an indwelling catheter or by infusing about 1 L of IV fluids.
Scanning techniques in obstetrics and gynaecology
PATIENT INFORMATION
Patient information is important regardless of the gynaecological or obstetric procedure plan. Informing the patient about the transabdominal or transvaginal sonography is essential. Patients usually have a general idea about ultrasound but we should
not take this for granted. There are still countries and communities in which, due to
mostly religious views, transvaginal scanning is not accepted and therefore not used.
The kind of examination she is about to undergo should be explained to the patient
in several short sentences. This information can be conveyed in three ways. The
first, which is probably the best way, is at the time of the bimanual pelvic examination in the office of the gynaecologist or in the emergency room. At this time,
the words ‘transabdominal’ and ‘transvaginal’ should be mentioned and explained.
A second way to inform the patient is by the way of brochures available in several
languages and placed in the waiting area, or given to the patient by the receptionist.
The third and probably the worst way to explain the scanning to the patient is at
the time of the scan itself, while she is seated on the examination table. At this time,
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the patient does not have the opportunity to ask many questions or she is under
stress and does not really remember the right questions to be asked.
The similarity between the familiar vaginal speculum, or the Papanicolau test,
and the vaginal transducer could be used as an effective comparison. The patient
also should be reassured that the dimensions of the probe are small, and it is
helpful to show her the probe. Some laboratories allow the patient to insert the
probe into her own vagina. However, in general, this is not regulated in any way.
Over the years, patient information regarding the use of the transvaginal probe
will probably become redundant. Remember that several years ago, when transabdominal sonography was introduced, emphasis was placed on patient information, and today patients know enough about transabdominal sonography that can
be used almost without any in-depth explanation.
At times transvaginal scanning is contraindicated. Almost similar quality images
can be obtained by using the transrectal approach. The vaginal probe is inserted
in the rectum55 and after its insertion the same protocol as for a vaginal probe can
be followed. The biggest ‘hurdle’ is to properly explain to the patient the harmless nature of such a scan.
Ultrasound in obstetrics and gynaecology
THE EXAMINATION TABLE
It should be explained at the outset that any ultrasound examination can, and
if necessary should, be carried out on any available examination table or even
in the patient's bed. Certain additions, such as elevating the pelvis for a better
transvaginal ultrasound examination, may be necessary. More and more gynaecological and obstetric pelvic scans, however, are performed with the patient on a
gynaecological examination table. This is equipped with a footrest, which allows
the patient to assume the lithotomy position for convenient transvaginal scanning, and a retractable leg support, which can be extracted for a better transabdominal sonographic evaluation of the patient.
It is rather cumbersome and almost impossible to perform transvaginal ultrasound scanning on a flat table, unless an elevation below the pelvis is provided.
Such an elevation will enable the backward tilt of the probe handle. The newer
probes that have the ability to electronically or mechanically steer the scanning
plane may be used even with a flat examination table.
Some gynaecological examination tables are fitted with a swinging arm and a
small platform that can support a small portable ultrasound box, similar to the
swinging arm on the other side of the table supporting the colposcope (Fig. 3.2).
Remember that, for specific reasons, such as a detailed examination of the cervix,
the patient can be scanned, using the transvaginal probe, in a standing position.
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BIMANUAL PELVIC EXAMINATION PRECEDING THE SCAN
Patients undergoing transvaginal or even transabdominal sonography usually have a
pelvic exam that precedes the imaging procedure. If transvaginal ultrasonography is
to be performed in the gynaecologist's office, a bimanual exam should definitely be
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Fig. 3.2 A gynaecological table fitted with a swinging arm on which the small, portable
ultrasound machine is placed. This can be used during examinations performed with the
patient on the table.
performed before the scanning. If the patient is referred to the imaging laboratory,
the gynaecologist should explain the palpatory finding for which the patient is
referred for further imaging studies. The imaging laboratories rely on the information provided by the obstetrician-gynaecologist and are guided by these findings.
These specialized ultrasound laboratories usually do not subject the patient to a
routine pelvic examination. It is, however, a good idea to take the time to examine
the patient before or even after the ultrasound examination to correlate the findings
with the image obtained. Such a pelvic palpatory examination is even more important if a discrepancy between the image obtained and the image expected occurs.
A basic distinction between the transvaginal ultrasound examination in the
gynaecologist's office and that performed in the specialized laboratory must be
made. In the gynaecologist's office, a bimanual examination is performed after
taking the history of the patient. This examination usually guides the clinician
as to the necessity of performing other laboratory tests. Among these laboratory
tests, ultrasound may be considered. If ultrasound equipment is available in the
office, the gynaecologist may proceed to complement and enhance his or her
bimanual palpatory examination with this simple imaging technique. In this case,
the bimanual pelvic examination and the transvaginal ultrasound complement
each other to arrive at the clinical decision. If referral of the patient to a more
sophisticated and usually remotely situated imaging laboratory is selected, the
targeted pelvic ultrasound exam is performed by imaging specialists who must
rely on the pelvic examination previously performed by the referring physician.
Scanning techniques in obstetrics and gynaecology
EQUIPMENT
The practical aspects of using the equipment are discussed below. The first step
in scanning a patient is to prepare the equipment before the patient is examined.
This preparation is even more crucial when a transvaginal scan is planned.
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The patient's demographic data, her last menstrual period and important pertinent observations should be entered. We found it useful to have the last menstrual period appear on the screen of the ultrasound machine next to the patient's
name; thus it will be visible on each of the printed pictures, and it will therefore
be easy to calculate the gestational age of a pregnancy or, in a gynaecological scan,
the day of the patient's cycle.
Recording devices should be switched to a stand-by position that enables their
instantaneous operation. Ultrasound machines now enable recording onto CDs
and even electronic data transmission over networks and the Internet.
It is helpful to have a separate foot-switch which freezes the screen and even a
second one to take hard copies of the desired images. This becomes important when
transvaginal sonography is performed, because the operator needs both hands free,
one to manipulate the transvaginal probe and the second to place on the abdominal wall and facilitate the location and mobilization of the pelvic structures.
All operators should use gloves when scanning. They should at least put a glove
on the hand handling the probe during the examination. This protects the users
from a possible transmittable infection and reassures the patient as to a procedure
Ultrasound in obstetrics and gynaecology
performed under clean circumstances.
Transabdominal probes are usually not covered with a probe cover (unless a sterile procedure is contemplated). However, they should be cleaned between patients.
Probe cleaning is of the utmost importance. Both the transabdominal and transvaginal probe should be wiped, with gel first and then some means of probe cleanser
can be applied. An alcohol spray or sponge or some other disinfectant (usually a
quaternary alcohol compound) may be used to clean the probe. Ordinary bleach
also can be used for this. However, it is important to ask the probe manufacturers about their preferred method of disinfecting the probe. Odwin et al provided
guidelines to the different solutions and their efficacy in cleaning the probes.36
Local disinfection protocols should be followed carefully to minimize the spread of
infection and the liability of the operators.
A clean condom or the digit of a surgical rubber glove should cover the transvaginal probe. These must be clean but need not be sterile. Ultrasound coupling
gel should be placed inside the protective cover to enable smooth passage of the
sound waves from the transducer to the pelvic organs.
A ready-to-use, prelubricated, individually prepackaged, thin plastic transvaginal probe cover is available for use. This cover is particularly useful if the patient
is allergic to latex. Latex allergy is more widespread than believed, therefore it is
a good routine to ask patients about such allergies before using a latex product
at scanning. It is also a good idea to post a sign in the waiting area which asks the
patients to report any previously known latex allergy before the actual scanning.
Coupling gel should be applied to the tip of the probe before its insertion
into the vagina. Coupling gels seem to be important to generate a clear and clinically meaningful ultrasound picture on the screen. K-Y gel (Johnson & Johnson,
Skillman, NJ) or the ultrasound coupling gel, which is basically clean to begin
with, can be used for this purpose. Mineral oil is a good inexpensive coupling
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agent if the more expensive gels are not available. However, infertility patients
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approaching their midcycle should be scanned using normal saline because coupling gels may be detrimental for sperm motility and viability.
ORIENTATION
Orientation using transabdominal probes is simple. On the monitor or any hardcopy picture, it is sufficient to annotate which is the patient's right or left side.
This is much like the conventional orientation used in radiology. On a longitudinal, sagittal transabdominal scan the direction toward the patient's head (cephalad
or superior) is displayed usually on the left side and the direction toward the
patient's feet (caudad or inferior) is displayed on the right side of the monitor
or picture. Anterior (or ventral) points upward and posterior (or dorsal) points
downward on the monitor or the picture (see Fig. 3.1).
In transvaginal sonography, the orientation is entirely different. The images
created are oriented perpendicularly (rotated 90 ° counterclockwise), compared
to those generated by the transabdominal probe. Sonologists from around the
world display sonographic pictures according to different rules.4 Displaying of the
sonographic image requires some explanation, because it becomes important to
understand the onscreen image orientation.
The sonographic picture generated by transvaginal sonography can be displayed
with the apex of the ‘pie’ pointing upward (Fig. 3.3A) or downward (Fig. 3.3B).
Some countries, as well as individuals, believe that displaying images with the apex
pointing down seems more logical. However, at this time, a uniform worldwide display is highly unlikely to occur. Some sonologists think that displaying a transvaginal picture with the apex of the ‘pie’ pointing to the bottom and a transabdominal
picture with the apex pointing to the top would enable a distinction regarding the
scanning routine. For example, in Germany (and in a number of other countries),
one could distinguish between a transvaginal and a transabdominal picture by looking at the picture orientation. It is important and also useful to introduce some
standardization regarding this issue.
In the United States and many other countries, the images are displayed as
follows.
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Scanning techniques in obstetrics and gynaecology
If a •fetus is scanned, the left and right sides will be determined according to
the position of the fetal stomach and the fetal heart.
In the case of a •gynaecological scan, on the longitudinal plane, the bladder
appears on the upper left side of the screen with the external cervical os
pointing toward the right. If the uterus is anteverted, the fundus appears
on the same side as the urinary bladder (Fig. 3.3A). If the fundus in a
retroverted uterus points toward the opposite side of the bladder, the
retroversion can be ascertained (Fig. 3.3C).
In the cross-section of the •pelvis in the transverse (coronal) plane, the
patient's right side will be seen on the left side of the monitor (or picture)
and the left side of the patient on the right side of the monitor (or picture),
as on any radiographic image performed using the coronal plane (Fig. 3.3A).
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Ultrasound in obstetrics and gynaecology
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Fig. 3.3 Orientation in the pelvis using the transvaginal probe. (A) The uterus is displayed
with the apex of the ‘pie’ pointing upward. The general directions within the body are
marked on the pictures. The left image is the picture of the uterus in the sagittal plane,
whereas that on the right side depicts the transverse section. (B) The uterus is displayed with
the apex of the ‘pie’ pointing downward (the European approach). (C) A retroverted uterus
and its relationship with the bladder. The major directions in the pelvis are identical with the
sagittal section of the uterus in Fig 3.3A.
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If the •cervix is scanned usually in the sagittal plane, it is customary that in
an anteverted pregnant uterus the external os is pointing towards the right
side of the picture, while the internal os is on the left side of the image
(Fig. 3.4). Of course, the bladder is kept constantly on the upper left side
of the picture. In the case of a retroverted uterus the bladder is kept on
the upper left side of the picture while the external and internal os are
oriented respectively to the left and right side of the picture.
If the •fetal brain is scanned, a careful assessment of the left and right side is
necessary regardless of TAS or TVS.
– On the coronal planes, the fetal right side should be kept on the left side
of the picture and the fetal left side on the right side of the image. This is
similar to any coronal x-ray picture of the head (Fig. 3.5A).
– On the sagittal planes it is customary to orient the forehead (anterior or
frontal) to the left and the occiput (posterior or occipital) to the right side
of the picture (Fig. 3.5B).
– Using TVS, a series of coronal and sagittal brain sections can be obtained
for better definition of eventual pathology.
30,56
Some authors recommend the use of transverse and anteroposterior planes only
if transvaginal sonography is used.12 A somewhat better approach is to use the
relative position of the target organ within the pelvis, which does not necessarily match the cardinal and classic anatomical planes of the pelvis. This scanning
method is called ‘organ-oriented scanning’ (Fig. 3.6).
38,61
It is practical to refer to the longitudinal axis of the scanned organ, such as the
fallopian tube or the ovary (e.g. ‘the longitudinal image of the tube’, etc.), instead
of using the conventional orientation of the scanning planes with the known
pelvic co-ordinates.
Lately the issue of orientation using three-dimensional (3D) ultrasound has surfaced. Interestingly, the major textbooks on the subject of 3D ultrasound in obstetrics
and gynaecology have not discussed adequately, or at all, orientation in the acquired
volume. It should be stressed that this orientation, mainly in the reconstructed
volumes, is a real but surmountable problem. Some machines have a convenient
Scanning techniques in obstetrics and gynaecology
Fig. 3.4 Sagittal sections of the cervix with a cervical suture. Note that by convention the
external os of the cervix with an anteverted uterus is oriented towards the right of the
picture.
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Fig. 3.5 Orientation in scanning the fetal brain regardless of the scanning route. (A) The
coronal plane. (B) The sagittal plane. Note that the face is on the left side.
labelling protocol which enables the user to label the major directions (right, left,
cranial, caudal, anterior, posterior) at the onset of scanning and incorporate it auto-
Ultrasound in obstetrics and gynaecology
matically in the displayed images (Medison, Kretz and General Electric systems).
These, of course, make orientation in such 3D volumes easier. If, however, such orientation display is not available, the operator should use extreme care to correctly
label the image generated. This may avoid later confusion and medical liability.
The most important message regarding orientation is the fact that it is mandatory to label all images at all times to be able to correctly indicate left and right,
cranial and caudal, sagittal, coronal and axial (horizontal) sections (Fig. 3.7).
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SCANNING ROUTINE
Regardless of the route selected to perform the scan, a methodical and systematic
scanning routine should be followed. The following order was found to be helpful.
Fig. 3.6 The concept of ‘organ-oriented’ scanning in the female pelvis. (A) The tube (chronic
hydrosalpinx) is imaged to display its longest diameter. This is not necessarily in any fixed
plane of the pelvis. It is obtained by trial and error. This is correct also if the ovary is scanned.
(B) Ninety degrees to any plane that detects the longest measurement of the pelvic organ (in
this case an acute salpingitis with the ‘cogwheel sign’) will display the cross-section of that
organ.