1. Tubal ectopic pregnancy
Ultrasound findings:
Adnexal mass separate from the ovary is very specific sign.
The adnexal mass can be differentiated from the ovary by pressing the mass with one hand while performing transvaginal scan with the other hand.
The visualization of an embryo within the extra-uterine gestational sac directly confirms an ectopic pregnancy,
but this finding is rarely observed.
Tubal ring sign, is hyperechoic ring surrounding an extra uterine gestational sac.
Color Doppler ultrasound may show a peripheral vascularity giving the ring of fire sign (differential diagnosis is corpus luteum).
A small amount of intrauterine centrally located fluid called pseudo gestational sac,
estimated to be seen in 10% of patients with ectopic pregnancies.
There may be evidence of a large hemoperitoneum,
especially in cases of rupture ectopic pregnancy (11) (Figure 1).
MRI findings:
On MRI,
it appears as saclike cystic tubal structure with thick wall corresponding to the Tubal ring sign seen on ultrasound.
The wall typically demonstrates high signal intensity on T2-weighted images with areas of hemorrhage showing distinct low T2 signal intensity and intermediate or high signal intensity on T1-weighted images.
Enhancing treelike solid component representing feto-placental tissue may also be seen.
Ascites with hyper intensity on T1-weighted images is consistent with Hemoperitoneum (12).
2. Interstitial ectopic pregnancy
Ultrasound findings:
An eccentrically located gestational sac surrounded by thin layer of myometrium,
measures less than 5 mm in all planes which called myometrial mantle sign.
The eccentric location of the gestational is best seen on sagittal and transverse ultrasound images as characteristic contour bulge in the uterus,
finding termed as the bulging sign.
Interstitial line sign is an echogenic line that extends into the upper regions of the uterine horn and borders the margin of the intramural gestational sac.
It has high sensitivity (80%) and specificity (98%).
3D ultrasound may be helpful for delineating a gestational sac's location (13)(Figure 2,3).
MRI findings:
On MRI,
it appears as heterogeneous masses with predominantly high T2 signal intensity located just lateral to the uterine cornua (13).
3. Cervical ectopic pregnancy
Ultrasound findings:
The hourglass uterus is an ultrasound sign of cervical pregnancy that describes smaller-than-dates uterus with an enlarged cervix and narrowing at the internal Os (14).
A ballooned cervix and closed internal os are also suggestive of cervical ectopic pregnancy.
The sliding sac sign is the movement of gestational sac against the endocervical canal and can be seen in miscarriage in progress but not cervical ectopic pregnancy.
M-mode ultrasound can document cardiac activity,
clearly differentiating a cervical ectopic pregnancy from a miscarriage in progress.
Doppler ultrasound may also show hypervascular trophoblastic ring suggestive of ectopic pregnancy (15) (Figure 4 a,c).
MRI Findings:
On MRI,
it may have the appearance of a lobulated mass with heterogeneous mixed signal intensity and a partial or complete dark rim on T2-weighted images.
Contrast-enhanced imaging would reveal irregular peripheral rim enhancement and densely enhancing solid components.
The heterogeneous signal intensity is likely due to hemorrhage of varying stages,
and the enhancing solid components likely represent remnants of fetoplacental tissues (16) (Figure 4 b,d).
4. Ovarian ectopic pregnancy
Ultrasound findings:
On ultrasound,
a gestational sac with thick echogenic surrounding ring is seen inseparable from the ovary.
Very rarely,
a live fetus can be seen.
Care should be taken to differentiate it from corpus luteal cyst which is much more common than ovarian ectopic.
Wall of corpus luteal cyst is thinner and more hypoechoic than the ectopic gestational sac.
The ring of fire sign can be seen in both ovarian ectopic pregnancies and corpus luteum cysts due to marked peripheral vascularity.
If the patient is stable,
in follow-up ultrasound corpus luteum cyst will demonstrate progressive involution with increasing crenulation of its margins,
whereas intra-ovarian ectopic pregnancy will grow,
with increasingly thick circumferential echogenic margins and development of a yolk sac and fetal pole in the gestational sac (17) (Figure 5 a,b).
MRI findings:
On MRI,
the ovarian ectopic pregnancy appears as gestational saclike structure on or within the ovary,
often containing acute hematoma with distinct low intensity on T2-weighted images (17).
5. Cesarean scar ectopic pregnancy
Ultrasound findings:
Gestation sac is located at cesarean section scar site between the urinary bladder wall and the anterior isthmic portion of the uterus.
There is thinned myometrium between the gestational sac and urinary bladder.
The uterine cavity and the endocervical canal appear empty.
M-mode US can detect fetal cardiac activity in cases of viable pregnancy.
Prominent Vascularity at the scar site is one the signs.
Color Doppler images demonstratehigh-velocity low-impedance vascular flow pattern (18) (Figure 6).
MRI Findings:
On MRI,
the gestational sac is embedded within the site of cesarean scar,
with thin myometrium adjacent to the sac.
Bulging of the sac through the myometrium,
with or without invasion of the urinary bladder may be also seen.
MRI can clearly delineate adjacent organ involvement and therefore helps the surgeon for deciding the operative management if needed (18).
6. Abdominal ectopic pregnancy
Ultrasound findings:
Ultrasound findings seen in abdominal ectopic pregnancies include the absence of myometrial tissue continuing from the uterus around the gestational sac,
abnormal placentation,
oligohydramnios,
and unusual fetal lie.
A misshapen gestational sac and flattened placenta may help distinguish an abdominal ectopic from a late-presenting tubal ectopic pregnancy,
which is more likely to show a rounded gestational sac and crescentic placenta.
Careful sonographic evaluation of the myometrium can also help distinguish a late-presenting abdominal ectopic pregnancy from an intrauterine gestation (19) (Figure 7 a).
MR Findings:
On MRI,
a gestational saclike structure associated with hematoma may be depicted in the pouch of Douglas.
Enhancement of the peritoneum around the saclike structure may also be seen in abdominal pregnancies.
Attempted removal of a placenta that is adherent to abdominal organs can result in fatal hemorrhage.
MRI is useful in the accurate localization of the placenta,
detection of arterial feeders,
and assessment of placental adherence to surrounding organs (20).
RBCs tagged with 99mTc have been used to locate the placenta in an intraabdominal pregnancy after non-visualization using ultrasound and arteriography (21) (Figure 7 b).
7. Heterotopic pregnancy
Ultrasound findings:
Heterotopic pregnancy can be diagnosed by ultrasound when a visible intrauterine gestational sac is associated with a simultaneous extra-uterine adnexal mass that has hyperechoic surrounding margins,
peritrophoblastic flow,
and a possible yolk sac,
fetal parts,
or cardiac activity (22) (Figure 8).
MRI findings:
MRI plays an important role in confirmation of heterotopic pregnancy and to rule out other differential diagnosis which could be mistaken with heterotopic pregnancy (22).
8. Rudimentary horn pregnancy
Ultrasound findings:
Gross features of bicornuate-like uterus are seen with absence of visual continuity between the cervical canal and the lumen of the pregnant horn.
There is presence of thick myometrial tissue surrounding the gestational sac (23) (Figure 9).
MRI findings:
MRI is a noninvasive and useful diagnostic tool for Mullerian anomalies
and can reveal the contour of the uterus,
the unicornuate uterus's connection to the rudimentary horn,
cavitary communication,
and continuity of the rudimentary horn lumen with the cervix.
MRI can be helpful in evaluating for abnormal placentation,
evaluating the vascular supply of the pregnancy and in surgical planning (23) (Figure 9).