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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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Fig. 3.7 Three-dimensional image of the uterus. The upper left image is in the sagittal
plane, the upper right in the axial plane, the lower left in the coronal plane. The lower
right image is the rendering of the uterine cavity in the coronal plane which is almost never
achieved using two-dimensional transvaginal scanning.
OBSTETRIC SCANNING
Different countries use different protocols for the structures to be included in
obstetric scans. These requirements should be kept in mind when performing
ultrasound examinations of the fetus.
It is customary to divide the scanning routine in obstetrics as follows: firsttrimester scan, basic exam and comprehensive fetal exam. When performing the
first-trimester scan (usually between 11 and 14 postmenstrual weeks), a transabdominal or transvaginal probe may be used.
mation should be obtained.
1,9,13,29,34,42-44,51,60
The following infor-
Scanning techniques in obstetrics and gynaecology
Presence or absence of an intrauterine gestational sac
•
Identification of embryo or fetus
•
Yolk sac
•
Fetal number
•
Presence or absence of fetal cardiac activity
•
Crown–rump length (CRL)
•
Evaluation of uterus and adnexal structures
•
Evaluation and measurement of the nuchal translucency.
•
If any obvious anomaly is seen, which may be the case if high-resolution equipment is used, this should trigger a more intensive scan and obviously a follow-up
scan.
The basic fetal exam should provide the following information.
Fetal number
•
Fetal presentation
•
Documentation of fetal life
•
Placental location
•
Assessment of amniotic fluid volume
•
Assessment of gestational age
•
Survey of fetal anatomy for gross malformations
•
Evaluation of the ovaries and possible maternal pelvic masses.
•
43
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This is primarily a biometric examination. Nonetheless, a brief survey of fetal anatomy and maternal pelvic organs should be performed. Some major structural malformations of the fetus may be identified during basic examinations, and some basic
examinations may suggest the need for a more comprehensive survey.
In certain circumstances, a ‘limited’ ultrasound examination may be appropriate and desirable. Such circumstances commonly relate to the specific nature of
the information required or the urgent nature of the clinical situation. A limited
examination may be useful to collect information such as the following.
Assessment of amniotic fluid volume – amniotic fluid index (AFI)
•
Fetal biophysical profile (BPP) testing
•
Ultrasonography-guided amniocentesis, chorionic villus sampling (CVS)
•
Nuchal translucency measurement
•
Perumbilical blood sampling (PUBS)
•
External cephalic version
•
Confirmation of fetal life or death
•
Localization of placenta in antepartum haemorrhage
Ultrasound in obstetrics and gynaecology
•
Confirmation of fetal presentation.
•
A comprehensive ultrasound examination may be indicated for a patient who
is suspected of carrying a physiologically or anatomically defective fetus by history, clinical evaluation or prior ultrasound examination. A limited examination,
as defined above, may be performed by ultrasonographers or specially trained
personnel. The basic examination, however, should be performed or reviewed by
an appropriately trained operator. An operator with experience and expertise in
such scanning should perform the comprehensive examination.
In some situations, it may not be possible to perform a full fetal survey. These
include:
9,34,44
13,29,34,60
44
oligohydramnios
•
hyperflexed position of the fetus
•
engagement of the head
•
compression of some fetal parts
•
maternal obesity.
•
Biophysical profile
Biophysical profile testing consists of a non-stress test with the addition of four
observations made by real-time ultrasound, each receiving a score of two. The five
components are as follows.
Reactive non-stress test.
•
Fetal breathing movements (one or more episodes of rhythmic fetal
•
breathing movements of 30 seconds or more within 30 minutes).
Fetal movement (three or more discrete body or limb movements within
•
30 minutes).
Fetal tone (one or more episodes of extension of a fetal extremity with
•
return to flexion).
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Quantitation of amniotic fluid volume. There is no universal agreement
•
as to the optimal method of assessing amniotic fluid volume. Some
investigators consider the detection of a single pocket of amniotic fluid
exceeding 2 cm in two perpendicular planes to be adequate. A semiquantitative, four-quadrant assessment of amniotic fluid depth (AFI) is
widely used, and cross-sectional nomograms have been developed.
32,39
Ideal
cut-off levels for intervention using the AFI have yet to be established.
With this method, a score of 2 (normal) or 0 (abnormal) is assigned to each of the five
observations. A score of 8–10 is normal; a score of 6 is considered equivocal (a fetus
should be retested in 12–24 hours) and a score of 5 or less is abnormal. In the presence
of oligohydramnios, further evaluation may be warranted.
26,39
See also Chapter 7.
GYNAECOLOGICAL SCANNING
If transabdominal sonography is performed, the sonographer may select other
target areas for the scanning, such as looking for free fluid in the abdominal cavity, in Morrison's pouch, along the right axial line or below the liver, or scanning
the patient's kidneys. It should be stressed that adequate training should preclude
scanning non-gynaecological structures.
It is important to use the largest possible magnification, which enables orientation as well as recognition of organs and their pathologies. Magnification usually
does not alter the resolution of high-frequency probes. The following routine has
proven to be effective.
2
Scanning techniques in obstetrics and gynaecology
The uterus
When evaluating a suspected uterine mass, the practitioner should identify the
appropriate anatomical structures. The initial step is to identify the bladder anteriorly and the rectosigmoid posteriorly. The position of the uterus depends on the
distension of the bladder and rectosigmoid, masses that may be present extrinsic
to the uterus, and intrinsic uterine masses. The normal uterus appears sonographically as a uniform structure.
By resting a hand on the abdomen and using the intermittent pressure of a transvaginal probe, the practitioner can determine the mobility of the uterus, the ovaries
or any pelvic structure. This sliding movement of the organs can be related to each
other or the stationary pelvic floor (‘sliding organs sign’).57 The origin of structures
(e.g. ovary versus a pedunculated fibroid) or adhesions can be diagnosed using this
manoeuvre. Testing for pain is also possible, with the vaginal probe identifying the
touched structure in question on the screen. Lately 3D ultrasound became the most
informative and powerful technique to image the uterus. Its main strength is that
along with the sagittal and transverse planes, the coronal plane can be displayed.
The cervix
Scanning the uterine cervix is an integral part of the gynaecological as well as
the obstetric ultrasound examination. A wide variety of pathologies ranging from
benign or prevalent Nabothian (inclusion) cysts to cervical fibroids or the rare
45
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cervical pregnancy can be identified. The importance of transvaginal ultrasound
scanning of the cervix has increased in recent years as it has been found to be
predictive of preterm deliveries. Usually the closed cervical canal length is measured. If funnelling is seen the funnel length and width can be measured. Cervical
sutures can and should also be evaluated periodically.
The myometrium
The sonographic appearance of the myometrium and the arcuate vessels within
the myometrium should be noted. Leiomyomata tend to be discrete, multiple,
spherical masses of varying size. They can be found almost entirely within the
endometrial cavity (submucosal) (Fig. 3.8A–C), within the myometrium (intramural) or on the surface of the uterus (subserosal).
Ultrasonographically, a leiomyoma often appears hypoechogenic. However, its
appearance may vary depending on its location and whether it has undergone
internal changes, such as hyaline degeneration, fatty degeneration, calcification
or haemorrhagic necrosis. These changes will alter the sonographic appearance of
the leiomyoma; for example, the presence of calcium will result in an increase in
Ultrasound in obstetrics and gynaecology
echogenicity, whereas degeneration will produce a cyst-like structure.
Submucosal leiomyomata may give the appearance of a bulge in the endometrial
lining. A more detailed investigation of this sign is warranted. This can be accomplished by instilling normal saline via a thin catheter placed in the uterine cavity.
The saline will serve as a contrast medium and will outline the mass (Fig. 3.8D,E).
Serial ultrasonography can be used to determine whether the leiomyomata are
growing or shrinking. This can be especially useful in patients entering menopause.
When the uterus of a reproductive-age woman with leiomyomata is evaluated,
46
Fig. 3.8 Examples of submucous fibroids enhanced by saline infusion sonohysterography.
(A,B) Almost entirely intracavitary submucous myoma. (C) It is possible to study the Doppler
signal of the feeding vessel to the fibroid. (D,E) Partially submucous myoma bulging into the
cavity with approximately 30–40% of its volume.
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the practitioner should be alert to the possibility of a small (4–6 weeks of gestation size) chorionic sac. These small gestations may be difficult to detect and may
be found in odd locations.
Adenomyosis is diagnosed by noting the presence of endometrial tissue in the
stroma of the myometrium. Although this condition may be suspected by the
presence of small sonolucent areas and linear shadowing within the myometrium,
it cannot be confirmed only on that basis. Usually the anterior or posterior wall
containing the adenomyosis is thicker than the other wall. The diagnosis rests on
clinical parameters and histological confirmation.
The endometrium
Sonographically, the interface of the two endometrial surfaces appears as a thin,
echogenic line that can be evaluated throughout the menstrual cycle. The endometrium varies in thickness and appearance depending on the stage of the menstrual cycle or the use of exogenous hormones. Measurement of the endometrial
thickness should be done on the long axis, with a combined anterior–posterior
wall measurement. If fluid is found in the uterine cavity, the measurement should
exclude that fluid interface (Fig. 3.9).
In postmenopausal women with bleeding, studies indicate that when there is a
thin distinct endometrial echo less than 4–5 mm maximum anteroposterior thickness read from a long axis view, this finding is consistently associated with lack
of significant tissue on sampling. Thus, such patients may be able to avoid invasive sampling and its risks, expense and discomfort. Presence of an endometrial
echo greater than 5 mm is not compatible with atrophy and thus, depending on
hormonal status, may indicate the need for sampling. Saline infusion sonohysterography can be used to distinguish symmetrically thickened endometrium in
Scanning techniques in obstetrics and gynaecology
Fig. 3.9 The technique of measuring endometrial thickness in the presence of intracavitary
fluid.
47
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which the process is global from endometrial changes that may be focal. In the
former, blind sampling is appropriate, whereas the latter requires hysteroscopically directed evaluation. It is to be hoped that current research in 3D techniques,
particularly in volume rendering, may prove to be an added source of information
distinguishing benign from malignant pathology. Finally 3D techniques are proven
to be useful in diagnosing the different degrees of uterine malformations by displaying the contour of the fundus and the cavity at the same time (Fig. 3.10).
It is also important to examine carefully the entire length of the myometrial–
endometrial interface. If the endometrium is irregular or if there is an enlarged
area of echogenicity, endometrial pathology should be suspected. An endometrial
biopsy or dilation and curettage should be performed to determine the histological status of the endometrium. The myometrial–endometrial interface should be
evaluated by continuously shifting the transducer through its long axis and corresponding coronal planes.
Increasing attention is being given to the presence of heterogeneous central
uterine changes in women who receive tamoxifen for breast cancer. In some such
cases, changes originally interpreted as endometrial are actually in the proximal
Ultrasound in obstetrics and gynaecology
myometrium. Sonohysterography may be used to determine the location (endometrial vs proximal myometrial) of such heterogeneous echoes.
During the follicular phase, the endometrium is thin, with a ‘pencil-line’ echo
of the cavity and hypoechoic functional endometrium on both sides of the cavity
line (three-line sign). This phase is followed by gradual thickening, which reaches
its peak immediately prior to ovulation. Following ovulation, coincidental with
the rise in progesterone, the echogenicity of the endometrium on both sides of
the cavity line increases and equals that of the cavity line, which gradually disappears within the hyperechoic endometrium. This hyperechoic endometrium is
then ‘broken down’ at the time of the menstrual flow. The endometrium can be
31
48
Fig. 3.10 Three-dimensional rendering of the uterus in the coronal plane. Note the clear
contours of the fundus (arrows) and the septated uterus.
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measured throughout the first part of the cycle. The endometrium can serve as a
natural contrast material in the uterus, leading to better definition of the endometrial–myometrial interface and detection of polyps or submucous leiomyomata,
or both.
Patients with irregular uterine bleeding may have an endometrial polyp, submucosal myoma or adenomatous hyperplasia. Polyps can occur in patients of
any age but tend to be more common in perimenopausal women. Polyps are
usually seen as a prominent endometrial echo complex; rarely, discrete masses
occupying the endometrial cavity are found. Sonohysterographic fluid enhancement through a thin intrauterine catheter may improve diagnostic capability.18
The branching appearance of the feeding blood vessel can be detected by turning
on the colour Doppler feature.
Although neither transvaginal nor transabdominal ultrasound evaluation can
confirm the presence or absence of cancer of the endometrium, ultrasonography
can provide information to aid in diagnosis. In early stages, endometrial carcinoma can appear as a change in the thickness of the endometrial lining and in
the endometrial echogenicity. Advanced endometrial or cervical carcinoma may
appear as hydrometra, pyometra or haematometra. These conditions will appear
sonographically as fluid collection within the uterine cavity. The endometrial–
myometrial interface should be defined and monitored to detect pathology at
that level.
Other conditions that may be detected by ultrasound examination of the endometrium are Asherman syndrome and retained products of conception following
spontaneous abortion, therapeutic abortion or delivery. A diagnosis of Asherman
syndrome can be strengthened by the presence of an irregular echogenic picture
and, occasionally, by the finding of calcification. On ultrasonography, calcification is intensely echogenic and causes acoustic shadowing. The diagnosis can be
firmly established by hysteroscopy. Retained products usually can be detected if
an irregularly shaped, dilated endometrial cavity containing echogenic material
is noted. Asherman syndrome can best be distinguished from retained products
of conception by evaluating the patient's history. Uterine anomalies including
septae, bicornuate uteri and didelphys may be identified especially when using
3D ultrasonography using ‘thick-slice’ or inversion rendering. Sonohysterography
may be useful to measure a fundal septum prior to hysteroscopic resection when
habitual abortion is present.
Scanning techniques in obstetrics and gynaecology
ADNEXAL MASSES
Ultrasonographic examination of the adnexa encompasses evaluation of the ovaries, fallopian tubes and parametrial areas. It is important that the examiner be
familiar with other anatomical structures in this area, such as the external and
internal iliac artery and vein, ureter and bowel.
The ovaries usually lie in the ovarian fossa found along the lateral pelvic wall.
The ovary can be located by identifying a pulsating linear echo; superior to this is
the external iliac artery and posterior and inferior to this the ureter.
49
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The normal ovary of teenagers and young adults measures approximately
2 × 2 × 3 cm. The size of the ovary should be measured according to the largest
diameter in the three planes. Some investigators have recommended determining ovarian volume, using the formula (length × width × height)/2. The ovarian volume in teenagers and young adults can reach 14 cm3. In postmenopausal
women, the average ovarian volume is 2.5 cm3 or less.
The following aspects of an adnexal mass should be evaluated.
•Mobility – the mass should be moved by the vaginal probe or by the hand
of the operator that is resting on the abdomen (‘sliding organs’ sign).
•Pain – its location should be established by watching the on-screen picture
when touching different organs with the tip of the transvaginal probe.
•Wall structure – features of an ovarian mass, such as thickness and outer
and inner surface irregularities and papillae, should be described and
measured.
Septations – the thickness of the septations should be reported.
•
Ultrasound in obstetrics and gynaecology
•Echogenicity of the mass – the mass can be completely sonolucent and may
have low-level echogenic contents, may be with or without an echogenic
core, may have mixed echogenicity containing all of these components or
may be completely echogenic.
The presence of the following conditions may make it more difficult to detect
ovarian or adnexal masses with ultrasonography.
Fluid-filled loop of bowel
•
Faeces in loop of bowel
•
Closed-loop bowel obstruction
•
Artifact of multipath reflection of sound waves (stratified echo pattern
•
resulting from echoes bouncing back and forth) from fluid-filled structure
(e.g. bladder)
Mesenteric cysts
•
Peritoneal inclusion cysts (postoperative or after infections)
•
Nabothian cysts
•
Hydrosalpinges (acute and chronic)
•
Large fibroids.
•
57
50
The clinical findings of acute salpingitis may be strengthened by ultrasonographic
findings of tubo-ovarian complexes of a fluid-containing structure with thickened
walls sensitive to the touch of the probe, adnexa adherent to loop of bowels, or
collection of fluid in the cul-de-sac. Chronic salpingitis can be diagnosed on the
basis of a painless (to the touch of the probe), thin-walled, pear-shaped, fluidfilled adnexal structure. Abscesses can be detected by ultrasonography, which can
also be used to characterize the abscess as unilocular or multilocular and determine the thickness of the abscess wall and anatomical location. This information
should be integrated into clinical findings (e.g. pain, fever) and is helpful in determining whether the abscess may be drained percutaneously or transvaginally or
whether surgical intervention is required.
54
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PERITONEAL FLUID
Small amounts of fluid in the lower pelvis can be visualized with ultrasonography. The fluid should be examined for the presence or absence of floating debris,
which will appear as low-level echoes. The tip of the probe can be used to rock
the fluid slightly, thus aiding in the observation of floating particles. If the nature
of the fluid must be determined, culdocentesis can be accomplished with the aid
of transvaginal sonography, which offers the best guidance for needle placement
through the needle guide mated to the shaft of the probe.
Attempts to assess the quantity of pelvic fluid have been reported in the literature. The smallest amount of fluid that can be detected is about 20–30 mL if a
5 MHz transvaginal probe is used. Although experienced sonographers can estimate
the approximate amount, this should be done with extreme caution. Figure 3.11
demonstrates how the approximate amount of free or loculated pelvic fluid collection can be estimated using perpendicular scanning planes.
If a larger amount of abdominal or pelvic fluid is suspected, the space between
the liver and the right kidney (the Morrison pouch) should be examined. This can
be achieved by placing an abdominal transducer parallel to the sagittal plane and
overlying the right upper abdomen.
One should distinguish between free fluid in the pelvis and loculated fluid. The
loculated fluid is found usually as a consequence of pelvic surgery or an inflammatory process. It is characterized by flimsy or denser adhesions creating the
pseudoseptations in the fluid. The wall of the pseudocyst is the pelvic wall itself.
Scanning techniques in obstetrics and gynaecology
URINARY BLADDER
Ultrasonography can be used to examine the bladder for the presence of extrinsic or intrinsic pathological masses. The urethra and the bladder can be viewed
on the sagittal and on an extremely anteriorly directed coronal plane. A transverse scan through the superior portion of the bladder reveals the bladder to be
rounded. If the bladder is scanned inferiorly, it will appear square, whereas a longitudinal scan will make it appear triangular. The thickness of the bladder and the
Fig. 3.11 The technique of estimating the almost free (or loculated) pelvic fluid. The
formula of the ovoid is used (a × b × c) 0.523 = mL.
51
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Fig. 3.12 Using transvaginal colour Doppler, the ureteral jets of the left (A) and right (B)
ureter can be studied.
presence of polyps or bladder stones will be outlined by the sonolucent urine.
A scan performed at the base of the bladder, just proximal to the urethrovesical
Ultrasound in obstetrics and gynaecology
junction, will permit visualization of the urethral orifices. Ultrasonography may
be used to estimate the volume of postvoid residual and, in incontinent women,
the mobility of the urethrovesical junction. Observing the urinary jets arising
from the two ostia by using grey-scale or colour Doppler, it is possible to determine ureteral patency (Fig. 3.12).
52,53
52
OTHER FINDINGS
Other pathologic processes that can affect organs in the lower pelvis can also be
detected. The most prevalent bowel diseases that can be observed are diverticulosis and various degrees of dilation of the small bowel. Dilation of the bowel
that can be mistaken for cystic structures can often be differentiated by the presence of peristalsis. Ectopic or low-lying horseshoe kidneys can also be detected
by sonography. Transabdominal sonography can be used to identify appendicitis;
however, considerable experience is required to do so.
COLOUR DOPPLER STUDIES
An increasing number of laboratories are now offering colour flow-directed
measurements such as pulsatility and resistance indices as well as flow veloci-
2,13,26,29,32,39,57,60
ties.
the USA. The pulsatility index is calculated by the following formula:
The resistance index is calculated by the following formula:
Some colour flow studies are still considered investigational in
Systolic Velocity − Diastolic Velocity
Mean Velocity
Systolic Velocity − Diastolic Velocity
Systolic Velocity