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25 Ultrasound Evaluation of Ectopic Pregnancy
Fig. 25.3 Transvaginal
ultrasound: intrauterine
gestational sac containing a
yolk sac
Fig. 25.4 Transvaginal
ultrasound: thickened edge
of a yolk sac representing
an early developing embryo
(embryonic cardiac activity
may be present)
331
pregnancy dating does not rely on human
chorionic gonadotropin, hCG, levels. Without
such exact pregnancy dating and with no intrauterine pregnancy identifi ed with transvaginal
sonography, the “nondiagnostic ultrasound,”
a serum level of hCG is needed for ultrasound
interpretation [ 6 ]. A word of caution, because of
the variation in vaginal ultrasound technical and
interpretive abilities and lab hCG levels, before
embarking on treatment for a presumed ectopic
pregnancy, especially with methotrexate, give
every pregnancy the “benefi t of the doubt.”
Be certain of the diagnosis or use diagnostic laparoscopy for confi rmation.
Additional information can be gained from
transvaginal ultrasound measurement of the
endometrial echo in early gestation, before the
recognition of a gestational sac. Spandorfer
and Barnhart reported statistically different
endometrial echo thicknesses between patients
with normal intrauterine, failed intrauterine,
and ectopic gestations [ 7 ]. Patients with nor-
mal pregnancies had endometrial echo thicknesses of 13.42 ± 0.68 mm. In contrast, those
with failed intrauterine and ectopic gestations
measured 9.28 ± 0.88 and 5.95 ± 0.35 mm,
respectively ( P < .01). In this report, 97 % of
patients with an echo no greater than 8 mm
332
D.L. Fylstra
had abnormal pregnancies, and 71 % of these
abnormal pregnancies were ectopic in location. Only 41 % of those patients with an echo
thickness greater than 8 mm were abnormal,
and only 14.7 % were ectopic in location. No
patient with an endometrial echo thickness
greater than 13 mm had an ectopic pregnancy,
and no patients with an echo thickness less than
6 mm had a normal pregnancy. These are wellstratifi ed differences, but other authors have
seen much more overlap with endometrial echo
measurements.
Usually, the transvaginal ultrasound identifi cation of an intrauterine pregnancy reliably
excludes an extrauterine implantation, except in
the case of heterotopic pregnancy: the coexistence of an extrauterine implantation with an
intrauterine pregnancy. The natural occurrence of
heterotopic pregnancy is 1 in 4,000 pregnancies,
but the frequency is much greater with pregnancies conceived with assisted reproductive technologies. Should a clinical presentation or
abnormal pelvic ultrasound appearance suggest
an ectopic pregnancy, despite visualization of an
intrauterine gestation, the diagnosis of heterotopic pregnancy should be considered, with the
probable need for diagnostic laparoscopy confi rmation and treatment.
The possibility of ectopic pregnancy is frequently considered before hCG has reached the
discriminatory zone and before ultrasound recognition [ 8 ]. Human chorionic gonadotropin
rises exponentially in early normal pregnancy
and should rise at least by 53 % in 48 h [ 9 ].
This exponential rise is less reliable after
10,000 mIU/ml, and at this level, pregnancy is
better evaluated with ultrasound. Fifteen percent of normal intrauterine pregnancies can
demonstrate an abnormal early rise of hCG, but
for the majority of gestations, when the hCG
rise is abnormal, at a plateau, or falling, an
abnormal pregnancy is confi rmed but not its
location [ 10 ].
Cervical Pregnancy
Less than 1 %, and the rarest, of ectopics are
implanted within the cervical canal below
the level of the internal cervical os [ 11 , 12 ].
The etiology of such implantations is unknown,
but predisposing factors include prior uterine
curettage, induced abortion, Asherman’s syndrome, leiomyomata, presence of an intrauterine
device, in vitro fertilization, and prior in utero
exposure to diethylstilbestrol [ 13 – 16 ] .
Before the now common use of early pregnancy transvaginal ultrasound, cervical pregnancies were frequently diagnosed at the time of
spontaneous abortion or reached the second trimester, both associated with life-threatening
hemorrhage frequently requiring hysterectomy
as treatment. Usually, the fi rst complaint is painless vaginal bleeding and speculum examination
may reveal an open external cervical os with a
fl eshy-type endocervical mass presenting. With
early transvaginal ultrasound, these implantations are easily identifi ed (Fig. 25.5 ) and can,
thus, be treated with conservative fertility- sparing
options.
Rankin suggested that the diagnosis by
ultrasound examination of cervical pregnancy
required 4 criteria: enlargement of the cervix,
uterine enlargement, diffuse amorphous intrauterine echoes, and absence of an intrauterine
pregnancy [ 17 ]. Timor-Tritsch et al. refi ned the
criteria to include the placenta and entire chorionic sac containing the pregnancy must be below
the internal cervical os and the cervical canal
must be dilated and barrel shape [ 18 ].
If necessary to exclude the diagnosis of a
spontaneous abortion in progress, the presence of
embryonic cardiac activity and/or Doppler ultrasound indicating vascular attachment confi rms a
living pregnancy.
Ovarian Pregnancy
One half of one percent to almost 3 % of ectopics
are implanted within the ovary [ 11 , 19 ]. Ovarian
pregnancy like other non-tubal ectopic pregnancies may occur without the usual expected antecedent risk factors for ectopic pregnancy but
does seem to have a strong association with conceptions with an intrauterine contraceptive device
in place [ 20 , 21 ]. The presenting signs and symp-
toms are similar to other ectopic pregnancies:
positive pregnancy test, abdominal pain, and
vaginal bleeding.
25 Ultrasound Evaluation of Ectopic Pregnancy
333
a
b
Fig. 25.5 ( a ) Transvaginal ultrasound, midline sagittal
image: cervical pregnancy, ( closed arrow ) points to the cer-
vical pregnancy within the ( open arrow ) points to cervical
It is diffi cult to preoperatively make the
diagnosis of ovarian pregnancy. An ultrasound
fi nding suggesting ovarian implantation is a
canal. ( b ) Transvaginal ultrasound: 3D rendering of a cer-
vical pregnancy, ( closed arrow ) points to the internal cervi-
cal os
walled cystic mass within or adjacent to an
ovary, but this does not exclude a corpus
luteum and a tubal implantation. Doppler cannot
334
Fig. 25.6 ( a ) Transvaginal
ultrasound of an ovarian
corpus luteum cyst.
( b ) Transvaginal ultrasound:
color Doppler imaging of an
ovarian corpus luteum cyst
D.L. Fylstra
a
b
distinguish between a corpus luteum and an
ovarian pregnancy implantation (Fig. 25.6 ). This
diagnosis is usually a pathological diagnosis:
made by microscopic examination of a surgically removed adnexal mass, via laparotomy or
laparoscopy, based on Speigelberg’s criteria: the
tube must be intact and distinctly separate from
the ovary, the gestational sac must occupy the
normal anatomical location of the ovary, the gestational sac must be connected to the uterus by
the utero-ovarian ligament, and unquestioned
ovarian tissue must be demonstrated in the wall
of the gestational sac [ 22 ].
It is important for the laparoscopic surgeon to
understand that an ovarian pregnancy can look
like a corpus luteum ovarian cyst upon direct
inspection, and cystectomy and pathology only
will reveal the true diagnosis. However, when an
adnexal ectopic is diagnosed with a nonsurgical
algorithm, conservative medical therapy can be
successful without a true diagnosis of location.
Abdominal Pregnancy
Less than 1 % of ectopic pregnancies are
implanted within the abdominal cavity [ 11 , 23 ].
The pathogenesis of abdominal implantation is
controversial. Many are the result of secondary
nidation within the peritoneal cavity after tubal
abortion, tubal rupture or uterine rupture [ 24 ].
True primary abdominal implantation must
25 Ultrasound Evaluation of Ectopic Pregnancy
335
satisfy the criteria of Studdiford. Studdiford,
reporting a primary peritoneal implantation in
1942, established three criteria for such a
primary abdominal pregnancy: normal fallopian
tubes with no evidence of recent or remote
trauma, the absence of any uteroperitoneal
fi stula, and the presence of a pregnancy related
exclusively to the peritoneal surface and early
enough to eliminate the possibility of secondary
implantation following a primary nidation within
the tube [ 25 ].
The most common abdominal implantation
site is the posterior cul-de-sac, followed by the
mesosalpinx, the omentum, the bowel and its
mesentery, and the peritoneum of the pelvic and
abdominal walls, including the anterior cul-desac [ 23 ]. Other reported locations include the ret-
roperitoneal space, the appendix, the liver, and
the spleen [ 26 – 31 ].
With the universal use of early pregnancy
imaging, the diagnosis can be confi rmed at an
early gestational age, but this requires imaging
demonstrating a continuity of the cervix and
uterus without pregnancy contents, like other
ectopic implantations. The presence of an adnexal
mass suggestive of ectopic pregnancy, when no
intrauterine gestation is identifi ed, could be an
ectopic pregnancy of any location, including an
abdominal implantation. Failure to follow basic
ultrasound principles can miss the diagnosis.
Such early diagnosis can spare maternal mortality at the expense of fetal mortality, with a perinatal mortality rate of 40–95 % [ 32 ].
Cesarean Scar Ectopic Pregnancy
Although previously rare, the incidence of pregnancy implantation within the scar of a prior
cesarean is increasing due to the increasing number of cesarean deliveries. The natural history of
such a condition is unknown, but uterine scar
rupture and hemorrhage, even in the fi rst trimester, seems likely if the pregnancy is allowed to
continue, with possible serious maternal morbidity and the possible need for hysterectomy and
loss of subsequent fertility. Early diagnosis of
such implantation is made only with a high level
of suspicion: early ultrasound in a woman with a
prior cesarean delivery (Fig. 25.7 ).
Endometrial and myometrial disruption or
scarring can predispose to abnormal pregnancy
implantation. Trophoblast adherence or invasion
is enhanced when the scant decidualization of the
lower uterine segment is impaired further by previous myometrial disruption. Implantation of a
pregnancy within the uterine scar of a prior cesarean delivery is different from an intrauterine
pregnancy with placenta accreta. Cesarean scar
implantation is a gestation completely surrounded
by myometrium and the fi brous tissue of the scar
and separated from the endometrial cavity or fallopian tube (Fig. 25.7 ). The mechanism that most
probably explains scar implantation, like intramural implantation, is invasion of the myometrium
through a microscopic tract. Like intramural pregnancy, such a tract is believed to develop from the
trauma of previous uterine surgery, such as curettage, cesarean delivery, myomectomy, metroplasty, hysteroscopy, and even manual removal of
the placenta [ 33 – 35 ]. The time interval between
such trauma and a subsequent pregnancy may
impact upon implantation events. Some of the
reported cases were diagnosed and treated within
a few months of a prior cesarean delivery suggesting that incomplete healing of the uterine scar
may contribute to scar implantation [ 36 , 37 ].
Early diagnosis with ultrasound can offer treatment options capable of avoiding uterine rupture
and hemorrhage and, thereby, preserve the uterus.
The differential diagnosis between spontaneous
abortion in progress, cervico- isthmic pregnancy,
and implantation within a cesarean scar can be
diffi cult. Strict ultrasound imaging criteria must
be used to assess the diagnosis of cesarean scar
pregnancy. Ultrasound should reveal an empty
uterine cavity, an empty cervical canal, development of the gestational sac in the anterior part of
the uterine isthmus, and an absence of healthy
myometrium between the bladder and the gestational sac, this last criterion allowing differentiation from cervico-isthmic implantation [ 38 ].
Although cesarean scar pregnancy is an
uncommon occurrence, only with a high index of
suspicion and the use of early endovaginal
sonography can the diagnosis be made early
336
a
D.L. Fylstra
b
Fig. 25.7 ( a ) Transvaginal ultrasound: midline sagittal image with gestation in the anatomical location of a prior
cesarean scar. ( b ) Transvaginal ultrasound: 3D rendering of cesarean scar ectopic
enough to prevent rupture leading to signifi cant
maternal morbidity and loss of future fertility.
Clinical history and endovaginal ultrasound can
aid in differentiating cesarean scar pregnancy
from incomplete abortion and cervico-isthmic
pregnancy. Precise localization of the early
pregnancy by transvaginal ultrasound should be
encouraged in all patients with threatening
gestational pathology. A sagittal ultrasound
view along the long axis of the uterus, through
the gestational sac, can localize precisely a cesarean scar implantation (Fig. 25.7 ).
25 Ultrasound Evaluation of Ectopic Pregnancy
337
Interstitial Ectopic Pregnancy
Two to three percent of ectopics are implanted
within the interstitial portion of the fallopian
tube, that portion of the tube that transitions from
the endometrial cavity to the tubal isthmus
through a wall of myometrium [ 11 ]. The intersti-
tial, or cornual, portion of the fallopian tube is
tortuous, 0.7 mm in diameter, and 1–2 cm in
length [ 39 ]. This is a relatively thick segment of
fallopian tube with a greater capability to expand
a
before rupture than more distal portions of the
fallopian tube [ 40 ]. Since implantation within
this portion of the fallopian is still “within the
tube,” it is associated with the same commonly
recognized risk factors for tubal ectopic pregnancy. No single factor clearly differentiates
women with an interstitial pregnancy from those
with isthmic or ampullary ectopic pregnancies.
Transvaginal ultrasound is the primary
method for diagnosing interstitial implantation
(Fig. 25.8 ). However, many early ultrasounds
Fig. 25.8 ( a ) Transvaginal
ultrasound: transverse view
across uterine fundus
demonstrating an asymmetrically implanted gestation,
concern for interstitial ectopic.
( b ) Transvaginal ultrasound:
3D rendering confi rming
interstitial pregnancy
implantation. ( open arrows )
Point to gestational sac
b
338
Fig. 25.9 Transvaginal ultrasound: angular pregnancy
D.L. Fylstra
show that these pregnancies are surrounded by
myometrium and can be mistaken for normally
implanted pregnancies. Ultrasound fi ndings that
are highly suggestive of interstitial implantation
are the identifi cation of an echogenic line between
the gestational sac and the endometrial cavity,
“the interstitial line sign,” an empty uterine cavity
with a gestational sac eccentrically located outside the endometrial cavity with a thin mantle of
surrounding myometrium less than 5 mm in
thickness [ 41 ]. Collectively, these ultrasound
fi ndings are 88–93 % specifi c but with a sensitivity of only 40 % [ 42 , 43 ]. Coronal images gener-
ated by 3D sonography are helpful in identifying
these features [ 44 ] (Fig. 25.8 ).
Interstitial ectopic pregnancies are frequently
mislabeled as “cornual ectopics.” Cornual pregnancy refers to a pregnancy within the horn of a
bicornuate uterus, communicating or noncommunicating, and the clinical outcome of this
implantation varies greatly and depends upon
the size and expansile capacity of the affected
horn [ 40 ].
Angular pregnancies are implanted in one
of the lateral angles of the uterine cavity,
medial to the uterotubal junction, and must be
distinguished from interstitial implantations.
Angular pregnancies lead to an asymmetric
enlargement of the uterus (Fig. 25.9 ). What dis-
tinguishes an interstitial ectopic pregnancy from
an angular pregnancy is that the laparoscopic
appearance of the bulge of an interstitial pregnancy is lateral to the round ligament, whereas
the bulge of an angular pregnancy is medial to
the round ligament, displacing the round ligament laterally. Over one third of angular pregnancies end in early abortion, but for those that
continue pelvic pain, persistent vaginal bleeding, placental retention during the third stage of
labor, and rarely uterine rupture can be expected
complications.
Ectopic After Hysterectomy
Only 56 cases of ectopic pregnancy after hysterectomy have been reported in the world’s literature and are rarely suspected before surgical
intervention [ 45 ]. Over half of such pregnancies
have been “early presentations,” this occurring
because an unrecognized, preclinical pregnancy existed at the time of hysterectomy:
25 Ultrasound Evaluation of Ectopic Pregnancy
339
a preimplanted fertilized ovum was in transit and
confi ned to the fallopian tube, or sperm was
present within the fallopian when the hysterectomy was performed during a peri-ovulatory
period, allowing postoperative fertilization and
tubal implantation. An immediate pre-hysterectomy pregnancy test would not be expected to be
positive under such circumstances. “Late presentation” ectopics have occurred after all types of
hysterectomy and as remote as 12 years after the
hysterectomy. These post-hysterectomy ectopic
pregnancies occur with retention of one or both
ovaries with the presence of a vaginal-tubal or
vaginal-peritoneal fi stula allowing vaginally
implanted sperm access to ovulated ova.
Because the symptoms of ectopic pregnancy
can be mimicked by common immediate
complications after hysterectomy, such as protracted abdominal pain, pelvic hematoma formation, vaginal cuff infection, and vaginal bleeding,
ectopic pregnancy is rarely expected in most
post-hysterectomy cases until additional imaging
or repeat operation confi rms the diagnosis.
Summary
Ectopic pregnancy occurs in one out of every 50
pregnancies. Early transvaginal ultrasound can
locate most, if not all early pregnancies, and
should be performed on every early pregnancy
with symptoms of gestational pathology or a high
likelihood of ectopic pregnancy based on
gynecologic history. With suspected gestational
pathology, early vaginal sonography should be
performed regardless of hCG level. The late
diagnosis of an ectopic pregnancy increases the
risk for loss of fertility and for maternal morbidity and mortality. Many non-tubal ectopic locations can be diagnosed with early transvaginal
sonography, then with successful medical management. The pregnancy of unknown location,
when diagnosed early and confi rmed to be extrauterine, can, likewise, be managed conservatively and successfully. Medical management
fails more commonly with more advanced, living
ectopic pregnancies, which may occur with nontubal ectopic pregnancies, requiring surgical
intervention [ 46 ]. Therefore, it is extremely
prudent to diagnose gestational pathology early
with transvaginal sonography.
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