Diagnostic ultrasound ( PDFDrive )

CHAPTER 15 The Uterus 531
are usually the same and the uterus is most frequently anteverted
and antelexed. 19 Anteverted, retrolexed position has been
associated with prior cesarean section. 19 Occasionally the sagittal
axis of the uterus is the same as the sagittal axis of the vagina.
Such a position usually limits TVS evaluation of the uterus.
Variable terms have been used to describe this latter position of
the uterus, including “axial,” “vertical,” “midposition,” or “partly
retroverted.” 19-21 One can try to change the uterine position by
moving the transducer into the anterior or posterior vaginal
fornix and applying gentle pressure with the transducer and/or
the nonscanning hand on the lower abdominal wall.
Uterine size varies depending on patient age and gravidity. 13,22-24
In nulliparous adult women, a normal uterus has a pear-shaped
appearance, with the diameter and length of the body about
double that of the cervix. 25 In general, it measures less than about
8 cm in length, 5 cm in width, and 4 cm in anteroposterior (AP)
diameter. Parity (pregnancy) can increase the normal size by 1
to 2 cm in each dimension. 23,22,26 Ater menopause the uterus
atrophies, with the most rapid decrease in size occurring in the
irst 10 years ater cessation of menstruation. 23 In patients older
than 65 years, the uterus ranges from 3.5 to 6.5 cm in length
and 1.2 to 1.8 cm in AP diameter. 26
In premenopausal patients the endometrium varies in appearance
and thickness during the menstrual cycle 27-32 (Fig. 15.3).
he endometrium is composed of a supericial functional layer
and a deep basal layer. he functional layer thickens throughout
the menstrual cycle and is shed with menses. he basal layer
remains intact during the cycle and contains the spiral arteries,
which become tortuous and elongated to supply the functional
layer as it thickens. he proliferative phase of the cycle before
ovulation is under the inluence of estrogen, whereas progesterone
is mainly responsible for maintenance of the endometrium in
the secretory phase following ovulation.
When obtaining an endometrial thickness measurement,
one should make the measurement in the sagittal plane of the
uterus, perpendicular to the long axis of the endometrium, at
the endometrium’s thickest point, including both the anterior
and posterior layers. 33 If luid is present in the endometrial cavity,
it should be excluded from the measurement. If one cannot see
the entire endometrium, which may occur in up to 10% of patients,
a thickness measurement should not be reported and instead
one should report that it cannot be reliably measured. 33 Such
limited assessment of the endometrium may occur for various
reasons including ibroids, marked obesity, and uterine position. 34
SHG may be helpful in these patients.
During the menstrual phase the endometrium is usually a
thin hyperechoic line but may be irregular or contain a small
amount of luid from blood. During the proliferative phase the
endometrium thickens slightly, and later in the proliferative phase
develops a multilayered appearance, also known as trilaminar
or triple layer. his appearance is due to the thin echogenic line
centrally that represents the opposed endometrial mucosal
surfaces, the functional layer of the endometrium that becomes
relatively hypoechoic, and a thin echogenic outer line. he thin
echogenic outer line may be the basal layer of the endometrium
or the interface between the endometrium and the myometrium.
One potential pitfall in measuring the endometrium is to mistake
the hypoechoic inner myometrium as part of the endometrium.
One can usually make the distinction because the multilayered
appearance of the proliferative phase has a distinct outer echogenic
line, whereas the hypoechoic inner myometrium has no such
deining outer echogenic line. Ater ovulation, in the secretory
phase the functional layer of the endometrium becomes hyperechoic,
usually starting on the outer edge and progressing inward.
It generally becomes uniformly hyperechoic by the mid to late
secretory phase. 29-32 he endometrium tends to have more distal
acoustic enhancement in the secretory phase, which can potentially
be mistaken for the endometrium itself when the endometrium
is poorly seen. he secretory endometrium may measure
up to 16 to 20 mm (though there is no accepted upper limit of
normal), and the appearance may be heterogeneous. One may
occasionally see endometrial folds that can simulate polyps during
the secretory phase. 33,34 One should be cautious before diagnosing
polyps or an abnormally thick endometrium during this phase
of the menstrual cycle and consider follow-up ultrasound in the
proliferative phase.
In postmenopausal women the endometrium is normally
homogeneously hyperechoic in appearance. In postmenopausal
women without vaginal bleeding, the upper limit of acceptable
thickness is 8 to 11 mm. 35-40 It should be noted that these limits
are greater than expected for an atrophic endometrium and that
polyps or hyperplasia could be present. However, because cancer
tends to bleed early, this higher threshold in postmenopausal
women who are not bleeding is acceptable in order to limit the
number of endometrial biopsies for benign disease. When there
is abnormal vaginal bleeding, the upper limit of normal thickness
is based on the trade-of between sensitivity and speciicity, and
thresholds of 3 to 5 mm have been suggested. hese are described
in more detail in the section on endometrial bleeding.
he myometrium is normally homogeneous in echogenicity.
he normal myometrium consists of three layers, although they
are not distinctly separated from one another. he intermediate
layer is the thickest and has a uniformly homogeneous texture
of low to moderate echogenicity. he inner layer of myometrium
is thin, compact, and relatively hypovascular. 41,42 his inner layer,
which is hypoechoic and surrounds the relatively echogenic
endometrium, has also been referred to as the subendometrial
halo. It should be noted that this is not necessarily the same as
the junctional zone on magnetic resonance imaging (MRI). 43
he thin outer layer is slightly less echogenic than the intermediate
layer and is separated from it by the arcuate vessels.
he arcuate arteries lie between the outer and intermediate
layers of the myometrium and branch into the radial arteries,
which run in the intermediate layer to the level of the inner
layer. he radial arteries then branch into the spiral arteries,
which enter the endometrium and supply the functional layer.
he uterine veins are larger than the accompanying arcuate
arteries and are frequently identiied as small, focal anechoic
or hypoechoic areas on both TAS and TVS. 44 hese veins can
occasionally be prominent and simulate cystic areas (Fig. 15.4).
Although Doppler imaging may be helpful in conirming the
vascular nature of these spaces, the low may be too slow to be
detected by color Doppler imaging. Power Doppler imaging may
be helpful in this instance; however, observation of these spaces