Stepwise Approach to the Basic Ultrasound Examination of the Female Pelvis. A Practical Approach

 

Stepwise Approach to the Basic Ultrasound Examination of the
Female Pelvis

INTRODUCTION

Ectopic pregnancy is the leading cause of pregnancy-related deaths during the first trimester (1).

The incidence of ectopic pregnancy has been on the increase over the past several decades (2)

and it continues to contribute significantly to maternal morbidity and mortality, especially in the

developing world (3).

RISK FACTORS

Several risk factors for ectopic pregnancy exist (4) and are listed in Table 13.1. History of tubal

surgery such as prior tubal sterilization or prior tubal surgery for ectopic pregnancy are amongst

the most common risk factors and thus should heighten alertness for the presence of an ectopic

pregnancy in symptomatic patients. Other risk factors include pelvic inflammatory disease,

female infertility and use of an intra-uterine device.

CLINICAL SYMPTOMS

Ectopic pregnancy should be considered when a patient presents with pain and/or vaginal

bleeding in the setting of a positive pregnancy test. The presence of an adnexal mass on physical

examination should also initiate an ectopic pregnancy work-up, when a positive pregnancy test is

present. Clinical symptoms are not specific for ectopic pregnancy and should not be used solely

for diagnosis. The location of the pain may vary (5) and the clinical triad of pain, bleeding and

adnexal mass is present in less than half of patients with ectopic pregnancy (6).

TABLE 13.1 Risk Factors for Ectopic Pregnancy

- History of tubal surgery

- History of prior ectopic pregnancy

- Use of Intrauterine Device

- History of infertility

ANATOMIC LOCATION OF ECTOPIC PREGNANCY

Most ectopic pregnancies are located along the course of the fallopian tube, with the ampullary

and isthmic sections of the tube accounting for the largest proportions of ectopic pregnancies

(Figure 13.1). Other rare tubal locations include the fimbrial end of the tube or the interstitial

(cornual) end of the tube (Figure 13.1). The interstitial or cornual ectopic pregnancy deserves

special mention, as ectopic pregnancies in this location typically present at a more advanced

stage in gestation and are commonly associated with severe hemorrhage and maternal shock at

the time of presentation. Cornual ectopic pregnancies are also more difficult to diagnose by

ultrasound as they mimic a normal intrauterine gestation, especially when they present at an

advanced stage. Figure 13.2 and 13.3 show cornual ectopic pregnancies in the early part of the

first trimester and Figures 13.4 and 13.5 show cornual ectopic pregnancies at more advanced

gestations. Cervical ectopic pregnancies occur in less than 1 % of all ectopic pregnancies and are

typically diagnosed by transvaginal ultrasound (Figure 13.6). Cervical ectopic pregnancies are

best treated with either intramuscular or direct injection, into the gestational sac, of methotrexate

or potassium chloride (into gestational sac) under ultrasound guidance, especially when

preservation of fertility is desired. Conservative management, following injection of

methotrexate or potassium chloride into the gestational sac, is desired, as long as the patient is

not bleeding excessively, as most injected cervical ectopic pregnancies will spontaneously

resolve. In low-resource settings where treatment options are limited, cervical ectopic pregnancy

with heavy vaginal bleeding can be temporarily managed (tamponade) with placement of a

cervical cerclage when technically feasible or by inserting compression (30 cc) Foley ballooncatheter(s) into the cervical canal.

Figure 13.1: Locations of ectopic pregnancies in the pelvis. Most ectopic pregnancies are

located along the course of the fallopian tube, with the ampullary and isthmic sections

accounting for the largest proportions. Abdominal pregnancy is not depicted in this sketch.

Sketch is courtesy of Dr. Igor Palahnuk.

Figure 13.2: Grey scale and color Doppler ultrasound of a cornual ectopic

pregnancy at 6 weeks’ gestation (arrows). Note that the endometrial echo (labeled

as endometrium) is distinctly separate from the cornual ectopic pregnancy

(asterisk). Note the yolk sac within the ectopic pregnancy (labeled).

Figure 13.3: Grey scale ultrasound of a cornual ectopic pregnancy at 7 weeks’

gestation (arrows). Note that the endometrial echo (labeled endometrium) is

distinctly separate from the cornual ectopic pregnancy (asterisk).

Figure 13.4: Transvaginal ultrasound of a transverse plane of the upper uterus

showing a cornual ectopic pregnancy (white arrows) at 9 weeks’ gestation. Note

that the endometrial echo (labeled as endometrium) is distinctly separate from

the cornual ectopic pregnancy (asterisk). The ectopic sac is bulging on the

serosal aspect of the uterus (red arrow heads).

Figure 13.5: Transvaginal ultrasound of an oblique plane of the upper uterus showing a

cornual ectopic pregnancy (arrows) at 13 weeks’ gestation. Note the size of the cornual

pregnancy (labeled) that may be mistaken for an intrauterine gestation. The uterus is

labeled in yellow.

Implantation of a gestational sac in a cesarean section scar is referred to as cesarean scar

implantation and is technically not an ectopic pregnancy as the gestational sac is within the

uterine cavity. Cesarean scar implantation can lead, later in gestation, to severe placental

abnormalities, such as placenta accreta, or rupture of the gestational sac (7, 8). The diagnosis of a

cesarean section scar implantation is performed when a gestational sac is noted by ultrasound to

be located in the lower uterine segment, in or near, a cesarean section scar, in a patient with a

prior cesarean section. Magnification of the ultrasound image may help confirm the diagnosis

(Figure 13.7 and 13.8). Similar to cervical ectopic pregnancy, treatment of cesarean section scar

implantation is best achieved by direct injection of methotrexate or potassium chloride into the

gestational sac, under ultrasound guidance (Figure 13.9 A and B).

Figure 13.6: Transvaginal ultrasound of a sagittal plane of the uterus showing a cervical

ectopic pregnancy (arrows). The uterine fundus and cervix are labeled for image orientation.

Figure 13.7: Transvaginal ultrasound in grey scale of a sagittal plane of the uterus showing a

cesarean scar implantation of a gestational sac (arrows). The cervix is labeled for image

orientation.

Figure 13.8: Transvaginal ultrasound in color Doppler of a sagittal plane of the uterus showing

a cesarean scar implantation of a gestational sac (arrows – same as in figure 13.7). Note the

increased vascularity on color Doppler of the gestational sac. The cervix is labeled for image

orientation.

STEP-WISE ULTRASOUND APPROACH TO THE DIAGNOSIS OF ECTOPIC

PREGNANCY

This section describes the step-wise approach to the work-up of a woman presenting with clinical

symptoms suggestive of the presence of an ectopic pregnancy. Before this stepwise approach is

initiated, it is important to note that taking a detailed history and performing a physical

examination are essential components of the care of the woman and thus should be part of the

initial evaluation. A differential diagnosis should then be formulated as new information and

diagnostic tests are being gathered. Table 13.2 lists a typical differential diagnosis for a woman

presenting with lower abdominal pain and vaginal bleeding.

TABLE 13.2

Differential Diagnosis of a Woman Presenting in the Reproductive Age

Group with Lower Abdominal Pain and Vaginal Bleeding

- Normal pregnancy

- Threatened or impending miscarriage

- Ectopic pregnancy

- Symptomatic ovarian mass (hemorrhagic cyst, dermoid, torsion)

- Pelvic inflammatory disease

- Abnormal uterine bleeding

- Gastrointestinal origin

- Urinary origin

Figure 13.9 A and B: Transvaginal ultrasound of a sagittal plane of the uterus showing in (A)

a cesarean scar implantation (arrows). The figure B shows the same cesarean scar

implantation (arrows) two weeks after direct methotrexate injection. Note the significant

resolution.

Obtaining a pregnancy test should be one of the first diagnostic tests to be performed. A negative

pregnancy test practically rules out a live ectopic pregnancy, assuming that the pregnancy test

that is available has sufficient sensitivity to detect human chorionic gonadotropin (HCG) levels

commensurate with early pregnancy. A positive pregnancy test establishes pregnancy but does

not indicate the location of the gestational sac, or the viability of the pregnancy. Please note that

chronic ectopic pregnancies may coexist with low HCG levels and are typically associated with

chronic pelvic pain. Figures 13.10 and 13.11 show a chronic ectopic pregnancy with an HCG

level of 22 IU / ml. The patient presented with a pelvic mass and chronic right pelvic pain.

Figure 13.10: Transvaginal ultrasound showing a chronic ectopic pregnancy (arrowsconfirmed on pathology) in a woman who presented with chronic pelvic pain. HCG levels

were 22 IU/ml. A separate ovary was noted (labeled). The uterus (labeled) is seen adjacent to

the chronic ectopic.

Figure 13.11: Transvaginal ultrasound with color Doppler in the same woman as in figure

13.10 showing significant vascularity of the chronic ectopic pregnancy (arrows)

Given that this textbook represents a basic approach to the use of ultrasound in obstetrics and

gynecology, we will not expand on the relationship of the serum HCG level with the sonographic

appearance of the gestational sac in the uterus. Suffice it to say that there is a relationship

between rising HCG levels and normal intrauterine pregnancies. In general, normal pregnancies

will show a doubling of the HCG level every 2-3 days (9). This rule however is not exclusive as

1 in 5 ectopic pregnancies will show this rise in HCG levels (9) and thus HCG levels should not

be used alone in excluding an ectopic pregnancy.

The stepwise ultrasound approach hereby described should be initiated if the pregnancy test is

positive.

This stepwise approach is performed by the transvaginal ultrasound:

Step one:

Assess the endometrial cavity for the presence of a gestational sac:

The presence of a gestational sac in the endometrial cavity (Figure 13.12) practically rules out

an ectopic pregnancy. Note that on very rare occasions, a heterotopic pregnancy can occur (a

concurrent intrauterine and an extrauterine pregnancy) (Figure 13.13) – (Clip 13.1). The

incidence of a heterotopic pregnancy in a natural pregnancy is around 1 in 7000 pregnancies.

Heterotopic pregnancies are more common in pregnancies of assisted reproduction (Figure

13.14).

The gestational sac of a normal pregnancy on ultrasound, which appears between the 4th and the

5th menstrual week, corresponds to the chorionic cavity of the embryo (Figure 13.12). The yolk

sac is the first structure to appear on ultrasound within the gestational sac and is typically first

seen at the 5th menstrual week (Figure 13.15), followed by the amnion between the 5th and the

6th week and the embryo by the 6th menstrual week (Figure 13.16). The normal intrauterine

gestational sac has a distinctive ultrasound appearance, with a thick rim of echogenic tissue

(Figure 13.17). This echogenic rim differentiates the gestational sac from blood or fluid

collection within the endometrial cavity. Blood or fluid collection within the endometrial cavity

is commonly called pseudosac (Figure 13-18 A and B). The term pseudosac is used in relation

to the presence of an ectopic pregnancy. For more discussion on the first trimester, please refer to

chapter 4.

If a gestational sac is seen within the endometrial cavity, complete the ultrasound examination by

evaluating the adnexal regions and the cul-de-sac. Go to step 2, if no gestational sac is seen in the

endometrial cavity.

Figure 13.12: Transvaginal ultrasound of a sagittal plane of the uterus showing a gestational

sac (labeled) at about 5 weeks’ gestation. The presence of an intrauterine gestational sac

practically rules out an ectopic pregnancy with some exceptions. See text for details.

Figure 13.13: Transvaginal ultrasound of a heterotopic pregnancy at 6 week’s gestation. Note

the presence of an intrauterine pregnancy (IUP) and a tubal ectopic pregnancy (labeled) in

the adnexa.

Figure 13.14: Transvaginal ultrasound of a heterotopic pregnancy at 7 week’s gestation. Note

the presence of a triplet intrauterine pregnancy (asterisks - Triplet IUPs) and a tubal ectopic

pregnancy (labeled) in the adnexa. This pregnancy was conceived by assisted reproduction.

Figure 13.15: Transvaginal ultrasound of a sagittal plane of the uterus showing a gestational

sac at 5 weeks’ gestation with a yolk sac (labeled). Note that the yolk sac is the first structure

to appear within the gestational sac and is typically first seen at the 5th menstrual week.

Figure 13.16: Transvaginal ultrasound of a gestational sac at 6 weeks’ gestation showing an

embryo (measured). The yolk sac (not labeled) is seen next to the embryo. CRL = crown rump

length, GA = gestational age and EDD = estimated date of delivery.

Figure 13.17: Transvaginal ultrasound of a sagittal plane of the uterus with a normal

gestational sac (labeled) at 5 weeks’ gestation. Note the echogenic rim surrounding the

gestational sac (dashed circle).

Step Two:

Assess the cul-de-sac for the presence of fluid:

The presence of fluid in the cul-de-sac is an important part of this evaluation as it may suggest

the presence of blood from a ruptured ectopic pregnancy or a ruptured ovarian cyst. The cul-desac can be assessed for fluid or blood on ultrasound by imaging the space posterior to the cervix

and the lower uterine segment in a sagittal plane of the uterus and cervix using the transvaginal

approach (Figure 13.19). Low-velocity color Doppler, if available, can be used to confirm the

absence of vascular flow within the blood clots. It is important to note that the mere presence of

fluid in the cul-de-sac in a patient with a suspected ectopic pregnancy should be concerning for

the possibility of intra-abdominal bleeding and this information should be considered in the

overall management of the patient. If fluid is noted in the cul-de-sac region in significant

quantity, assessing the regions in the upper gutters of the abdomen is important as the presence

of fluid in those locations will confirm that a significant amount of free fluid is present in the

abdomen and pelvis and will raise the suspicion for significant intra-peritoneal bleeding. It is

also important to note that the presence of fluid in the cul-de-sac in small amount is a normal

finding and is part of the normal physiologic changes of the menstrual cycle.

Figure 13.18 A and B: Transvaginal ultrasound of sagittal planes of two uteri (A) and (B) with

endometrial fluid (arrows) in the setting of suspected ectopic pregnancies. The term pseudosac is used

when endometrial fluid is noted in association with an ectopic pregnancy.

Step 3:

Assess the Adnexal Region for the Ectopic Gestational Sac:

The third step in the ultrasound examination of the pelvis includes a thorough evaluation of both

adnexal regions in transverse and sagittal scanning planes. This evaluation should include

assessment of the ovaries and the surrounding anatomic regions, looking for fluid, blood and for

the ectopic gestational sac. The ectopic gestational sac, when present in the adnexal region, is

commonly in the fallopian tube. It is typically round in shape and has an echogenic ring and an

anechoic center (Figure 13.20 A and B). Commonly, the patient’s symptoms correlate with the

location of the ectopic pregnancy in the pelvis but with noted exceptions. It is also important not

to confuse an ectopic gestational sac with a corpus luteum (Figure 13.21), which is commonly

located on the ovary of the same side as the ectopic. Table 13.3 shows differentiating

characteristics of the corpus luteum from the ectopic gestational sac. Figures 13.22 and 13.23

show tubal ectopic pregnancies on ultrasound. Color Doppler is not helpful in the differential

diagnosis given the overlap with corpus luteum flow and the varying degrees of blood flow

patterns in ectopic pregnancies. Figure 13.24 A-C shows varying degrees of blood flow on color

Doppler in three different ectopic pregnancies.

Figure 13.19: Transvaginal ultrasound of a sagittal plane of the uterus in a patient with a

ruptured ectopic pregnancy. Note the presence of free fluid in the cul-de-sac and surrounding

the uterus (asterisks). A blood clot (labeled) is also noted in the cul-de-sac. In this image, the

endometrial thickness is also measured (yellow calipers).

Figure 13.20 A and B: Tubal ectopic pregnancies in A and B (arrows) imaged on transvaginal

ultrasound. Note the echogenic ring and the anechoic center (doughnut-like appearance) in both

ectopic pregnancies. Color Doppler in B shows moderate ectopic sac vascularity. The ovary is seen

(labeled) in A.

Figure 13.21: Transvaginal ultrasound in grey scale and color Doppler of a corpus luteum (arrows)

within the ovary (labeled). See Table 13.3 for differentiating features from an ectopic pregnancy.

TABLE 13.3 Differentiating Features of a Corpus Luteum From an Ectopic Pregnancy

- Corpus luteum is located within the ovary

- Corpus luteum is surrounded by normal ovarian tissue

- Corpus luteum moves with the ovary with manipulation

- Corpus luteum typically does not have a thick echogenic ring

- Color Doppler and pulsed Doppler cannot differentiate between the two entities

Figure 13.22: Transvaginal ultrasound showing a tubal ectopic pregnancy (arrows). Note the

separation of the ectopic sac from the ovary (labeled). The ectopic sac has echogenic borders and an

anechoic center (doughnut-like appearance).

Figure 13.23: Transvaginal ultrasound showing a tubal ectopic pregnancy (arrows). Note the

echogenic thick borders and an anechoic center (doughnut-like appearance). The ovary is

labeled and is typically lateral to the ectopic gestation.

Figure 13.24 A, B, and C: Tubal ectopic pregnancies in A, B and C (arrows) imaged on transvaginal

ultrasound with color Doppler at similar velocity scale and filter set-up. Note the varying degrees of

vascularity between ectopic pregnancies with minimal to absent in A, moderate in B and excessive in C.

Color Doppler is not a helpful differentiating feature of ectopic pregnancy.

The presence of an ectopic gestational sac in the adnexa that is distinctly separate from the ovary

in a woman presenting with symptoms suggestive of an ectopic pregnancy, especially in the

absence of an intra-uterine gestational sac, establishes the diagnosis of an ectopic pregnancy. The

additional presence of fluid in the cul-de-sac confirms the diagnosis. When ultrasound findings

are not diagnostic of ectopic pregnancy, it is important to consider all findings and make a

judgment based upon available information. Given that significant change in the normal

gestation occurs in the first trimester in a short time-frame, a follow-up ultrasound within a short

period of time such as in 3 to 4 days when the woman’s medical condition is stable and

compliance is adequate, may help clarify the diagnosis. If the woman’s condition is unstable,

intervention is warranted irrespective of the ultrasound findings.

A rare presentation of an ectopic pregnancy is the abdominal pregnancy. Abdominal pregnancy

can be associated with significant morbidity, especially if the pregnancy is allowed to grow.

Placental insertion on the bowels or pelvic vasculature can result in significant bleeding if

removal is attempted. If an advanced abdominal pregnancy is encountered, it is prudent to

remove the fetus but keep the placenta in situ to avoid massive bleeding. Figures 13.25 and

13.26 show an abdominal pregnancy at 14 weeks gestation in the right adnexa. The patient

presented with lower abdominal pain. This abdominal ectopic pregnancy was treated with direct

injection of potassium chloride and methotrexate into the gestational sac under transvaginal

ultrasound guidance. No further intervention was needed and the woman’s symptoms improved

immediately following this procedure.

Figure 13.25 A and B: Transvaginal ultrasound of an abdominal ectopic pregnancy at 14

weeks gestation in the right pelvis. Figure 13.25-A shows a sagittal view of the uterus with

pelvic free fluid (asterisks). Figure 13.25-B shows the abdominal pregnancy (arrows) in the

right pelvis.

Figure 13.26: Transvaginal ultrasound of an abdominal ectopic pregnancy at 14 weeks

gestation in the right pelvis (same as in figure 13.25) following direct injection of potassium

chloride and methotrexate. The uterus (labeled) is seen separate from the ectopic pregnancy.

The macerated fetal head is labeled.

CLIP 13.1

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