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The uterus is a thick-walled, pear shaped,
muscular organ lying posterior to the bladder
and anterior to the rectum. A central
echogenic line represents the endometrial
cavity. Small cysts in the cervical region are a
common normal variant and are known as
Nabothian cysts. The uterus is composed of
four parts: the fundus, the corpus (body), the
isthmus, and the cervix.
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Normal uterine measurements in nulliparous
menstruating women are 6 to 9 cm in length
and up to 4 cm in anterior posterior diameter
and width. The uterus of parous women will
have slightly larger dimensions. Before
puberty the uterus is about 3 cm long and
more or less tubular in shape. After
menopause the uterus shrinks in size but
retains the shape it adopted with the onset of
puberty.
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The menstruating uterus widens toward the
fundus and the cornua, the bilateral
somewhat triangular regions where the
fallopian tubes insert. It is tubular in the part
near the vagina known as the cervix.
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Usually the uterus is tilted anteriorly
(Anteversion); but may be normally tilted
posteriorly (retroversion). An acute angulation
in the midportion is known as anteflexion or
Retroflexion. Although usually in a midline
position, the uterus may lie obliquely to the
left or the right.
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Uterine positional variations
◦ Anteversion: Refers to the cervix, which is anchored
at the angle of the bladder and less freely movable
than the corpus (body) and Fundus (top), forming a
90-degree angle with the vagina
◦ Retroversion: refers to the cervix oriented more
linearly in relation to the vagina.
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The lining of the endometrial cavity is partially
shed each month at menstruation, with
consequent changes in cavity appearance during
the course of the cycle. During the pre-ovulatory
(Proliferative) phase, the endometrial cavity echo
is only about 3mm thick and surrounded by an
echopenic halo. Shortly before ovulation, two
additional linear echoes outline the echopenic are
(the “three line sign”). The echopenic area
becomes more echogenic so that in the
postovulatory (secretory or luteal) phase, the
cavity echo becomes brighter and thicker. At this
point, the width of the canal is between 9mm and
1.3 cm thick.
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The lumen of the normal fallopian tubes
cannot be seen. The fallopian tubes lie within
the broad ligament. They can often be traced
from the uterine fundus to the ovaries on
endovaginal view. This is especially easy if
there is cul-de-sac fluid.
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The ovaries are usually found at the level of
the uterine fundus where the uterus becomes
triangular (the cornu). Often the broad
ligament can be traced laterally to the ovary.
The ovaries often lie adjacent to the
Iliopsosas muscle, within which lies an
echogenic focus that is due to the femoral
nerve sheath. The iliac vessels usually lie
laterally to the ovary.
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In the menstruating woman, ovaries normally
measure approximately 2 x 2.5 x 3cm. There
is variation, so 5 x 2 x 1.5 cm or 4 x 3 x 1.5
cm, for example, are measurements that may
be within normal limits. The ovaries are about
1 cubic centimeter in young girls, gradually
increasing in size as puberty approaches. In
menopausal women, the size of the ovary
gradually decreases.
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Normally, one follicle grows to a size of between 1.4
and 2.5cm, alternating sides each menstrual cycle.
Hormonal stimulation with drugs such as Pergonal or
Clomid increases the number of dominant follicles,
which may number as many as six or more in each
ovary. Follicles are not seen in menopausal women,
but are often seen in young girls before puberty. A
dominant follicle normally bursts and disappears at
mid-cycle. It is replaced by a corpus luteum.
Typically, a corpus luteum has a thick, slightly
echogenic vascular rim (the rim of fire on color
Doppler) and an echopenic center. The central
echopenic area may be large if there is much
bleeding at the time of ovulation. The corpus luteum
will usually disappear within a week or so.
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The ovarian arteries should be demonstrated
using color Doppler.
Uterine artery should be demonstrated using
color Doppler.
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Small amounts of fluid may normally collect
behind the uterus in the poster cul-de-sac;
also know as the pouch of Douglas. The fluid
may result form normal ovulation.
The anterior cul-de-sac is anterior and
superior to the uterine fundus.
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Bands of muscle tissue play an important role in
maintaining the position of the uterus and
ovaries. The broad ligament extends from the
lateral uterine walls to the pelvic sidewalls. The
obturator internus muscles lay alongside the
bony wall, lateral to the ovaries. The Iliopsoas
muscles are lateral and anterior to the iliac crest;
the femoral nerve sheath is seen as an echogenic
area within the muscle. The levator ani,
piriformis, and coccygeus muscles make up the
pelvic floor and are located posterior to the
uterus, vagina, and rectum.
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Distention of the urinary bladder is essential for a
high-quality transabdominal pelvic sonogram.
The full bladder displaces bowel and repositions
the uterus in a more longitudinal fashion that
allows the US beam to transect the uterus
perpendicularly. The urinary bladder provides an
acoustic window for better visualization of the
pelvic structures. Over-distention or underdistention of the bladder can distort or obscure
the view. A sufficiently full bladder will extend
just over the uterine fundus. If the bladder is too
full, encourage the patient to void into a paper
cup so she does not empty her bladder
completely.
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The sonographic examination should begin in
a longitudinal fashion by attempting to align
the uterus with the vagina. The uterus can be
recognized by the central line of the
endometrial cavity and by its alignment with
the vagina. The vagina is visualized as an
echogenic line with relatively sonolucent
walls. The uterus is normally located in the
midline, but it may be deviated to either side
in an oblique axis. Make sure that the bladder
is full enough to show the fundus when the
uterus is examined. An Anteflexed or
retroverted uterus may become more normal
in position and shape if the bladder is filled.
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Scanning at right angles to the axis of the
uterus should demonstrate the ovaries. The
ovaries are usually close to the triangular
cornual regions near the uterine fundus.
Caudal angulations are helpful for visualizing
the pelvic musculature and retroverted uteri.
Cranial or caudal angulations may be
necessary to see the ovaries.
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A water enema can be helpful in the positive
identification of bowel. Only a small amount
of fluid need be run into the rectum through
a small enema tube during observation with
real-time. A flickering motion is visible when
the water is running through the bowel. Do
not mistake aortic pulsation or respiratory
motion for peristalsis. This technique is rarely
used now that endovaginal Sonography is
available.
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Transverse
Lower uterine segment
Mid uterine segment
Upper uterine segment
Left adnexae to show left ovary and ligaments
Right adnexae to show right ovary and ligaments
Longitudinal
Mid line to show endometrial strip concurrent with
the vaginal stripe
Fundus must be delineated via a full urinary bladder
RT adnexae to show ovary and ligaments
Left adnexae to show ovary and ligaments
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Rectus abominis
Psoas Major
Iliacus
Levantor ani and coccygeus
Obturator Internus
Piriformis
HomeworkSubmit ultrasound images and diagrams of the
above pelvic musculature ESPECIALLY the Psoas
Major and Levantor ani muscle groups.
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HOMEWORK
Create a story board outlining the technique
of examining the uterus with a Transabdominal approach.