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The Normal Uterus
KhaledSakhel, AlfredZ.Abuhamad,
andCallumAndrewPotts
7
Uterus
The uterus is a muscular organ whose purpose is
to provide the implantation site and nutrients to
the developing fetus. It is located in the true pelvis and lies between the urinary bladder anteriorly and the rectosigmoid colon posteriorly. The
space between the uterus and the rectosigmoid is
the posterior cul-de-sac, which is the most dependent area in the peritoneal cavity and where uid
tends to accumulate.
There are three main anatomic components of
the uterus: the upper part or fundus that lies superior to the fallopian tube ostia, the main body or
corpus, and the cervix. The lower segment of the
corpus is sometimes termed the isthmus. The corpus is made up of the muscular myometrium and
the endometrium. The endometrium is hormonally responsive and undergoes changes in
response to ovarian hormones during a menstrual
cycle. These changes prepare for implantation of
the fertilized ovum. The myometrium does not
K. Sakhel (*)
Inova Fairfax Hospital, Department of Obstetrics and
Gynecology, Falls Church, VA, USA
A. Z. Abuhamad
Department of Obstetrics and Gynecology, Eastern
Virginia Medical School, Norfolk, VA, USA
C. A. Potts
Inova Fairfax Hospital, Women’s and Children’s
Hospital, Falls Church, VA, USA
undergo signicant anatomic changes in response
to the menstrual cycle.
This chapter discusses and illustrates the
sonography of a normal uterus, including the
uterine myometrium and endometrium. It also
highlights the changes that occur during a normal
menstrual cycle.
The uterus can be evaluated by transabdominal (transvesical) sonography (TAS) and transvaginal sonography (TVS). Two other techniques
including the transrectal and translabial approach
are seldom used and are usually reserved in
patients where neither TAS nor TVS are
feasible.
The advantage of TAS is the ability to assess
the upper pelvis especially in patients with larger
uteri that are greater than 12 weeks in size.
Disadvantages of the TAS approach include the
requirement of a full bladder and a limited image
resolution especially in patients with large BMI
as well as in patients with lower abdominal scars
from prior surgery.
The TVS approach is clearly superior in imaging quality due to the use of higher frequency
probes and is by far the most commonly used
method for imaging of the pelvis. It is limited,
however, by depth of penetration of the transvaginal ultrasound probe and therefore can only
assess structures in the true pelvis which is adequate in most cases. For TVS the patient is asked
to empty her bladder and lie supine in the lithotomy position with the legs exed. The uterus can
© Springer Nature Switzerland AG 2019
L. A. Stadtmauer, I. Tur-Kaspa (eds.), Ultrasound Imaging in Reproductive Medicine,
https://doi.org/10.1007/978-3-030-16699-1_7
113
114
K. Sakhel et al.
be evaluated using the traditional twodimensional (2D) probe which portrays the image
in the sagittal and transverse planes. It can also be
evaluated using a three-dimensional (3D) probe
which can portray a reconstructed coronal image
of the uterus. Ultrasound is considered the imaging modality of choice for assessing the uterus.
Compared with other modalities including computed tomography (CT) and magnetic resonance
imaging (MRI), ultrasound is less expensive,
faster, better tolerated, and does not expose the
patient to radiation. With the increasing use of 3D
image reconstruction, sonography typically provides at least as much information as MRI [1].
The American Institute for Ultrasound in
Medicine (AIUM) has put forth practice guidelines for the “Performance of Ultrasound of the
Female Pelvis,” “Ultrasound Examinations in
Reproductive Medicine and Infertility,” and
“Focused Reproductive Endocrinology and
Infertility Scan.” These are helpful in establishing
indications and reporting requirements [2–4].
Sonography of the uterus includes examination for size, shape, contour, orientation, and
appearance of the myometrium, endometrium,
and cervix. Unless the fallopian tubes are distended with uid, they are not usually apparent
during routine pelvic sonography. In addition, the
cul-de-sac is routinely evaluated for scar tissue,
uid, and masses [2–4].
The uterus is rst imaged in its long axis on
the midsagittal plane which is obtained by optimizing the long axis of the echogenic endometrium. The midsagittal plane allows the
visualization of a cross section of the myometrium, endometrium, cervix, cul-de-sac, rectum,
and bladder (Fig. 7.1). In this plane, the angle
between the cervix and uterus can be measured.
The midtransverse plane is perpendicular to the
midsagittal plane and can be obtained by rotating
the probe 90° clockwise or counterclockwise. It
allows visualization of a cross section of the uterine structures at different levels from fundus to
outer cervical os (Fig. 7.2). The 3D ultrasound
probe, when available, can acquire a volume of
the uterus, and the software will use the data to
generate and display a coronal image (Fig.7.3).
The coronal plane is that plane that bisects the
uterus parallel to the plane of the ultrasound bed
and the supine body. This has been shown to be
especially helpful in detecting Mullerian anomalies and for IUD localization [1]. The Z-technique
is a simple technique that describes the steps
required for the display of the mid-coronal plane
out of a 3D volume of the uterus [5].
As images obtained during 2D ultrasound
are used to construct the 3D image, initial 2D
image quality is important for diagnostic accuracy [6]. Limitations of 2D imaging, including
obesity, prior surgery, and shadowing or
enhancing artifacts, may be compounded with
3D reconstruction and may mimic pathology.
Hence it is important to review of the original
2D acquisition planes in conjunction with the
3D reconstruction.
Fig. 7.1 Midsagittal plane showing an immediate post-
menstrual cycle thin endometrium (Type A) with an anteverted uterus
Fig. 7.2 Midtransverse plane of the uterus
7 The Normal Uterus
115
Fig. 7.3 The three orthogonal planes, sagittal, transverse, and coronal planes, as well as the rendered image. The coro-
nal image also portrays the hypoechoic junctional zone of the myometrium
Measurements of the uterus include the length,
height, and width. The length and height are measured in the midsagittal plane, whereas the width
is measured in the transverse plane [7, 8]. The
length is measured from outer serosal surface of
the fundus to the external os of the cervix. If volume assessment of the uterus is required, then the
cervical length should be excluded from the
height measurement. Uterine volume may be calculated using the following formula: volume =
length × width × height × 0.52. The length of a
normal nulliparous uterus is 6–8.5 cm, and in
multiparous women it is 8–10.5cm. The height is
measured from anterior to posterior serosal surfaces and perpendicular to the long axis of the
uterus. The height of the normal uterus in nulliparous women is 2–4 cm, and in multiparous
women it is 4–6cm. The width of the corpus is
taken at the widest region of the uterus on a transverse plane. The width of a nulliparous uterus is
3–5cm and 4–6cm in multiparous women.
The orientation of the uterus is described in
the anteroposterior and right-left dimensions in
relation to the supine body. The orientation is
noted once the optimum midsagittal image is
obtained using the echogenic endometrium for
guidance. The direction of the ultrasound probe
can provide the right to left orientation. The orientation in the anteroposterior dimension is
described in terms of version and exion which
require image processing. The uterus is said to be
exed or angled across the isthmus when there is
an angle between the cervix and the corpus of the
uterus (Fig.7.4). The anteroexed and retroexed
uteri can pose a challenge to procedures that
require access to the endometrial cavity. If there
116
Fig. 7.4 Anteroexed uterus with the traced line showing
the sharp angle between the cervix and the endometrial
cavity
Fig. 7.5 Retroverted uterus with minimal angulation
between the cervix and the endometrial cavity
is no angulation between the cervix and the corpus, the uterus is described in terms of version
(Figs.7.1 and 7.5). It is important to describe and
report the orientation of the uterus as part of the
ultrasound examination. This information is
helpful if uterine instrumentation is required.
Myometrium
The uterine myometrium is made of a homogeneous layer of smooth muscle and blood vessels.
The uterine arteries reach the uterus at the level
of the cardinal ligaments and divide into ascending and descending branches that travel within
the layers of the broad ligament along the lateral
wall. Sonographically the normal myometrium
has a medium echogenicity, less than the endo-
K. Sakhel et al.
metrium, with a granular echotexture. The myometrium can be divided into three layers. The
inner or junctional myometrium, which abuts the
endometrium, is thin and hypoechoic compared
to the thicker homogeneous middle layer (see
Fig.7.3) [8, 9]. Thickening of this layer has been
shown to be associated with adenomyosis [10].
The arcuate vessels separate the middle and outer
layer which is also thin and slightly less echogenic than the middle layer. The myometrium
does not appear to change sonographically during the course of the menstrual cycle.
Endometrium
The uterine endometrium is the site of dynamic
changes in response to ovarian hormones during
the menstrual cycle. It can be divided into the
inner functional layer that sloughs during menses
and the outer basal layer which abuts the myometrial junctional layer. The changes that occur during the menstrual cycle can be seen
sonographically, and periodic assessment at different stages of the menstrual cycle may provide
important information about endometrial function and receptivity [8, 9, 11–18].
The immediate postmenstrual endometrium is
a thin echogenic line (Type A) at that intersection
of anterior and posterior uterine walls and normally measures 3–8mm (see Fig.7.1). Assessing
the endometrial thickness in patients presenting
with postmenopausal bleeding is an important
step in the overall evaluation process. It is important to know that a thin endometrium in that setting, typically at less than 5 mm, has been
correlated in multiple studies with absence of
endometrial cancer. When measuring endometrial thickness on ultrasound, it is critical to
ensure that the uterus is in a midsagittal plane, the
whole endometrial stripe is seen from the fundus
to the endocervix, the thickest portion is measured, and the image is clear and magnied.
Under the inuence of increasing estradiol hormone levels secreted by the growing ovarian follicles, endometrial proliferation occurs.
Sonographically this is seen as thickening of the
lining into the so-called trilaminar layer (Type B)
7 The Normal Uterus
Fig. 7.6 Trilaminar endometrium (Type B) pattern
begins to develop under the inuence of increasing estradiol in the early proliferative phase
117
Fig. 7.8 Luteal phase endometrium showing a homoge-
nously thickened hyperechoic stripe (Type D)
ated with poor IVF outcome as compared to at
least 9-mm thickness. There is conicting evidence as to the detrimental effect of increased
endometrial thickness beyond 12mm. Cases of
successful pregnancies in patients with endometrial thickness as low as 4 mm have also been
reported [26].
Fig. 7.7 Late proliferative phase endometrium with an
accentuated trilaminar pattern (Type C)
with an anterior and posterior hypoechoic layer
separated in the midline by a hyperechogenic
central line (Fig.7.6). During the late proliferative period and near the time of ovulation, endometrial lining is 8–12 mm in thickness with an
accentuated trilaminar appearance (Type C,
Fig. 7.7).The postovulatory endometrial lining,
under the inuence of progesterone hormone
secreted by the corpus luteum, is characterized
by loss of the trilaminar appearance and the
development of a uniformly hyperechoic stripe
(Type D, Fig.7.8).
The implantation, pregnancy, and live birth
rates following in vitro fertilization (IVF) are
affected by the midcycle endometrial thickness
[15, 19–25]. Studies have shown that a midcycle
endometrial thickness less than 8mm was associ-
Cervix
The cervix can be divided into the portio vaginalis or ectocervix, the endocervix, and the endocervical canal. It is amenable to imaging using
TAS, TVS, and translabial sonography.
Clinically the presence of endocervical mucus
has been used in the assessment of the presence
of increasing estradiol levels and the lead follicle.
Scoring methods of the cervical mucus including
the Insler and Moghissi that looked at the amount,
consistency, spinnbarkeit, and ferning were introduced [27, 28]. However these often needed to be
performed repeatedly which is not practical and
uncomfortable for the patient. Ultrasound assessment of the cervix, in conjunction with the pelvic
sonography being performed, has been introduced to look at the changes associated with the
menstrual cycle [29].
Sonographically the cervical stroma is usually
of the same consistency as the myometrium. The
endocervical canal is normally spindle shaped
and begins at the bottleneck where the endometrium tapers off. The presence of anechoic pockets within the cervix represents Nabothian cysts
and is a normal nding. The cervical stroma is not
118
Fig. 7.9 Cervix with Nabothian cysts and blood during
menses
K. Sakhel et al.
Fig. 7.11 Cervix in mid-proliferative phase showing a
thicker and hyperechoic endocervix and presence of
Nabothian cysts
Fig. 7.10 Cervix in early proliferative phase after men-
ses showing a thin endocervix
affected by the hormonal changes. The changes
are limited to the endocervix and the appearance
of cervical mucus. The endocervix during menses
is noted to contain complex uid with blood and
mucus (Fig.7.9). After the cessation of menses,
the endocervix is noted to be thin and relatively
hypoechogenic (Fig. 7.10). The endocervix is
noted to increase in echodensity starting on cycle
day 7 or when the leading follicle is 11mm, endometrial thickness of 5.8mm, and estradiol levels
of around 289pmol/l (Fig.7.11). In addition, cervical mucus can be observed within the endocer-
Fig. 7.12 Cervix at day 13 of cycle showing mucus in the
endocervix under the effect of increasing estradiol
vical canal as of cycle day 13 or when the lead
follicle is 16.8mm and endometrial thickness is
7.5mm or when estradiol level exceeds 500pmol/l
(Fig.7.12) [29].
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AA. Transvaginal ultrasonic assessment of endometrial growth in spontaneous and hyperstimulated menstrual cycles. Br J Obstet Gynaecol. 1989;96(8):954–9.
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Congenital Uterine Anomalies
BethW.Rackow
8
Introduction
Congenital anomalies of the female reproductive
tract, or Müllerian anomalies (MA), may involve
the uterus, cervix, fallopian tubes, or vagina. Of
the Müllerian anomalies, uterine anomalies are
the most common; prevalence rates range from
3% to 8% of fertile and infertile women [1–5].
The true incidence of uterine anomalies in the
general population, cited as 0.5% [6], is hard to
determine because reproduction is not always
affected; thus, some individuals are asymptomatic and unidentied, and accurate assessment
and diagnosis has not always occurred [4, 5, 7].
The etiology of MA is poorly understood; the
majority of MA are infrequent and sporadic,
although some familial clustering occurs, and
MA are generally attributed to polygenic and
multifactorial causes [8, 9]. This chapter will
review the embryologic development of the
female reproductive tract, classication of congenital uterine anomalies, gynecologic and
obstetric presentations of congenital uterine
anomalies, imaging techniques, and management
options for uterine anomalies.
B. W. Rackow (*)
Columbia University Medical Center, Department of
Obstetrics and Gynecology, New York, NY, USA
e-mail: bwr2113@cumc.columbia.edu
Embryology oftheFemale
Reproductive Tract
While genetic sex is determined at the time of
fertilization, male or female phenotype is not
dened until after the sixth week of development.
Early in embryologic development, both the
Wolfan (mesonephric) and Müllerian (paramesonephric) ducts are present. The paired Wolfan
ducts connect the embryologic kidney (mesonephros) to the cloaca between 5 and 10weeks of
gestation; development of the functional kidney
(metanephros) is stimulated by an outgrowth of
the Wolfan duct, the ureteric bud. Müllerian
duct development occurs concomitant with the
development of the urinary tract, and kidney and
ureteral anomalies are associated with MA.The
spectrum of renal anomalies includes agenesis,
ectopic location, or abnormal anatomy [10].
Although gonadal development begins at the
same time as Müllerian duct development, at
6weeks of gestation, the two processes are separate and distinct; females with MA usually have
normal ovaries and steroid hormone production.
Normal development of the female tract
involves a complex series of events, and failure of
any part of this process can result in a Müllerian
anomaly. Paired Müllerian ducts arise from coelomic epithelium along the lateral walls of the
urogenital ridge, and these solid ducts are present
by week 6 of development. In the absence of
Müllerian-inhibiting substance released from the
© Springer Nature Switzerland AG 2019
L. A. Stadtmauer, I. Tur-Kaspa (eds.), Ultrasound Imaging in Reproductive Medicine,
https://doi.org/10.1007/978-3-030-16699-1_8
121
122
B. W. Rackow
male gonad, the Müllerian ducts proliferate while
the Wolfan ducts regress. The Müllerian ducts
elongate caudally and cross the Wolfan ducts
medially, and midline fusion of the ducts forms
the primitive uterovaginal structure. By week 10
of development, fusion occurs between the caudal end of the joined Müllerian ducts and the urogenital sinus. Subsequently, the unied Müllerian
ducts undergo internal canalization which results
in two lumens divided by a midline septum.
Resorption of the septum commonly occurs in a
caudal-to-cranial direction. The fused caudal portion of the Müllerian ducts becomes the uterus,
cervix, and upper vagina, and the unfused cranial
portion becomes the fallopian tubes. Uterine
development is completed by week 20 of
development.
The lower vagina has a separate embryologic
origin. At week 10, when the fused Müllerian
ducts connect with the urogenital sinus, the sinovaginal bulbs develop and proliferate toward the
caudal end of the uterovaginal canal, forming a
solid vaginal plate that elongates with time. The
central cells of the vaginal plate degenerate in a
caudal-to-cranial direction, forming a hollow
structure. Vaginal development is also complete
by week 20 of development. The hymenal membrane originates from the sinus tubercle and separates the vaginal lumen from the urogenital
sinus. The central epithelial cells usually degenerate prior to birth, achieving a patent structure
with a thin fold of mucus membrane at the
introitus.
Although the caudal-to-cranial direction of
Müllerian duct fusion and septal resorption is the
traditional theory of female reproductive tract
development, unusual MA have been documented that are exceptions to this order of progression. Examples include a complete septate
uterus with a double cervix and vaginal septum
and a normal uterus and cervix with an isolated
longitudinal vaginal septum [11–14]. Hence,
midline fusion of the Müllerian ducts and septal
resorption may not be a unidirectional process as
theorized but may be bidirectional [15]. Other
constellations of Müllerian anomalies have been
described that further defy the traditional concept
of Müllerian duct development [16].
Classication ofMüllerian
Anomalies
Müllerian anomalies are commonly classied
into three categories: agenesis and hypoplasia,
lateral fusion defects, and vertical fusion defects.
Reproductive tract abnormalities due to in utero
exposure to diethylstilbestrol (DES) comprise a
fourth group of anomalies. Agenesis and hypo-
plasia can occur for a portion of or an entire
Müllerian duct, or for both ducts, affecting one or
multiple Müllerian structures. Lateral fusion
defects are the most common category of
Müllerian defects and originate due to failure of
migration of the ducts, midline fusion of the
ducts, or absorption of the midline septum
between the ducts. A range of anomalies can
occur including symmetric or asymmetric and
nonobstructed or obstructed Müllerian structures.
Vertical fusion defects occur due to disordered
fusion of the Müllerian ducts with the urogenital
sinus or abnormal vaginal canalization and may
present with menstrual ow obstruction.
Although there is no universally accepted
standard classication for Müllerian anomalies,
the American Society of Reproductive Medicine
(ASRM) classication system from 1988 is commonly utilized and provides a standardized
nomenclature to describe anomalies (Fig.8.1) [4,
17]. This classication system focuses on the
major categories of uterine anomalies and
describes them based on their embryologic etiology. Hypoplasia/agenesis (category I) and unicornuate (category II) denote anomalies with
developmental failure of one or both Müllerian
ducts; didelphys (category III) and bicornuate
(category IV) describe anomalies involving a
varying degree of failure of midline fusion; septate (category V) and arcuate (category VI) identify anomalies with some degree of failure of
resorption of the midline septum. DES drugrelated anomalies (category VII) are a separate
category of anomalies and will not be discussed
in this chapter. With this classication system,
associated anomalies of the vagina, cervix, fallopian tubes, and urinary system must be documented separately. Two additional issues with
this classication system are the inability to fully
8 Congenital Uterine Anomalies
Fig. 8.1 Classication of uterine anomalies according to the American Society of Reproductive Medicine [17]. DES,
diethylstilbestrol. (Reprinted from Bermejo etal. [18]. With permission from John Wiley & Sons, Inc.)
123
describe a uterine anomaly when multiple abnormalities are present (i.e., septate uterus with
duplicated cervix) and the lack of specic diagnostic criteria to enable differentiation between
bicornuate, septate, and arcuate uteri [4, 11, 19,
20]. Hence, complex anomalies need to be
described according to the component parts.
Overview oftheUterine Anomalies
Müllerian Agenesis
The most extreme of the Müllerian anomalies is
Müllerian agenesis, otherwise known as MayerRokitansky- Küster-Hauser (MRKH) syndrome,
which occurs due to agenesis or hypoplasia of the
Müllerian ducts and affects approximately 1 in
5000 females [21]. Müllerian agenesis involves
congenital absence of the vagina and variable
uterine development that ranges from agenesis to
hypoplastic and rudimentary structures. One
study demonstrated that in females with MRKH,
87% had Müllerian remnants, 26% of the remnants were cavitated and contained endometrial
tissue, 7% had a Müllerian remnant measuring
>4 cm, and 30% had anomalies of the urinary
tract [22]. Along with urologic anomalies,
Müllerian agenesis is associated with other extragenital anomalies involving skeletal, cardiac, and
auditory systems and digits and palate [23, 24].
Unicornuate Uterus
The unicornuate uterus arises due to agenesis or
hypoplasia of one of the two Müllerian ducts. The
unicornuate uterus is a functional uterus with a
normal-appearing cervix and a single fallopian
tube, and the contralateral side may have a variety
of congurations: agenesis or a rudimentary horn
in 74% [6]. The rudimentary horn can be noncommunicating (70–90%) or communicating with the
unicornuate uterus and may contain functional
endometrium [25]. Women with a rudimentary
uterine horn containing functional endometrium
may present with cyclic or chronic pain, endometriosis, or a horn gestation [25]. Nonfunctional
rudimentary horns are usually asymptomatic.
Lastly, the unicornuate uterus is associated with a
40% incidence of renal anomalies, usually ipsilateral to the anomalous side [25–27].