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Imaging
Vol 17 No 1 Autumn 2015 15
adnexal mass that moves separately to the ovary will usuallybe
seen. It may range in appearance from an inhomogeneousmass through
to a distinct gestational sac with or without a fetalpole, yolk sac
or fetal heart. The latter finding will usually bein the presence
of an empty uterus and hCG level well above
the discriminatory threshold. The corpus luteum can be seen asa
‘ring of fire’ on colour Doppler and will be on the ipsilateralside
in 70–85 per cent of tubal pregnancies.3 About 60 percent of
tubal pregnancies will appear as an inhomogeneousmass, 20 per cent
will appear as a hyperechoic ring(sometimes called a ‘bagel sign’)
and only 13–15 per cent willhave an obvious gestation sac and fetal
pole, with or withoutfetal cardiac activity.4,8
• Interstitial pregnancy – one to five per cent of
ectopicpregnancies lie in the interstitial part of the Fallopian
tube(the part of the Fallopian tube that traverses the
myometrium).The gestation sac will lie outside the cavity in the
interstitialarea surrounded by a thin continuous rim of myometrium.
An‘interstitial line’ is often seen consisting of a thin echogenic
linethat extends from the central uterine cavity to the periphery
ofthe interstitial sac and presumably represents the
endometrialcanal of the interstitial part of the Fallopian
tube.12
• Cervical pregnancy – these occur in less than one per centof
ectopic pregnancies. The uterine cavity will appear emptyand cervix
may appear barrel shaped with the gestation sacor trophoblastic
mass lying below the level of the internalcervical os. There may be
a negative ‘sliding organ sign’ – in amiscarriage a gestation sac
lying within the cervical canal willslide against the endocervical
canal when transducer probepressure is applied to the cervix, but
an implanted cervicalpregnancy will remain fixed.
• Caesarean section scar pregnancy – in women with a
previous
caesarean section these may make up to six per cent of
allectopic pregnancies. Appearances can be similar to a
cervicalpregnancy, but gestation sac or trophoblastic mass is
locatedanteriorly at the level of the internal os covering the
visible orlikely site of the caesarean section scar.
• Ovarian pregnancy – this is a much rarer form of
ectopicpregnancy, but will appear as a cystic structure or
gestation sacwithin or on the ovary. The gestation sac cannot be
separatedfrom the ovary on gentle palpation.
• Abdominal pregnancy – most of these pregnancies will be
theresult of tubal abortion with re-implantation in the
abdominalcavity, usually on the broad ligament. Rarely, a
primaryimplantation in the abdominal cavity will occur. It is
oftendifficult to distinguish from a tubal pregnancy on
ultrasound.
• Heterotopic pregnancy – risk factors include in vitro
fertilisationand super-ovulation-based fertility treatments. In
women withno history of fertility treatment, the risk is less than
one in10 000 pregnancies. They may occur in between one andthree
per cent of women undergoing fertility treatment andshould be
looked for in such women presenting with earlypregnancy bleeding or
pain.
A final word Always take a careful history,
pinpointing if possible the exact datesof the last menstrual
period, the dates of a positive pregnancy test,and dates of early
pregnancy bleeding and pain. Early pregnancytransvaginal ultrasound
requires a high level of operator skilland experience. Ultrasound
is a dynamic investigation and, as a
gynaecologist, relying on the written interpretation of
ultrasoundimages alone will expose you to a greater risk of delayed
ormisdiagnosis. Where possible, review the images with
yourradiologist or, if your work setting permits, be present when
the scan
is performed so ultrasound images can be correlated with
patienthistory, symptoms, hCG levels and examination findings.
References1 Lewis G (ed). Saving Mother Lives: Reviewing
Maternal Deaths
to make Motherhood Safer – 2006-2008. The Eighth Report
onConfidential Enquiries into Maternal Deaths in the United
Kingdom.BJOG. 2011;118(suppl 1) 1-205.
2 Kirk E, Papageorghiou AT, Condous G et al. The
diagnosticeffectiveness of an initial transvaginal scan in
detecting ectopicpregnancy. Human
Reproduction. 2007;22:2824-2828.
3 Condous G, Okaro E, Khalid A et al. The accuracy of
transvaginalsonography for the diagnosis of ectopic pregnancy prior
to surgery.Human Reproduction. 2005;20:1404-1409.
4 Atri M, Valenti DA, Bret PM et al. Effect of transvaginal
sonography onthe use of invasive procedures for evaluating patients
with a clinicaldiagnosis of ectopic pregnancy. Journal of Clinical
Ultrasound. 2003;31:1-8.
5 Shalev E, Yarom I, Bustam M et al. Transvaginal sonography as
theultimate diagnostic tool for the management of ectopic
pregnancy:experience with 840 cases. Fertility and
Sterility. 1998;69:62-65
6 Barnhart K, van Mello NM, Bourne T et al. Pregnancy of
unknownlocation: a consensus statement of nomenclature, definitions
andoutcome. Fertility and Sterility. 2011;95:857-866.
7 Kirk E, Condous G, Bourne T. Pregnancy of unknown
location.Best Practice and Research in Clinical Obstetrics and
Gynaecology. 2009;23:493-499.
8 Kirk E, Daemen A, Papageorghiou AT, et al, Why are some
ectopicpregnancies characterized as pregnancies of unknown location
atthe initial transvaginal ultrasound examination? Acta Obstet
GynecolScand. 2008;87:1150-1154.
9 Mol BW, Hajenius PJ, Engelsbel S et al. Serum human
chorionicgonadotrophin measurement in the diagnosis of ectopic
pregnancywhen transvaginal ultrasonography is inconclusive.
Fertility and Sterility.1998;70:972-981.
10 Visconti K, Zite N. hCG in ectopic pregnancy. Clinical
Obstetrics and
Gynecology. 2012;55:410-417.11 Braffman BH, Coleman BG,
Ramchandani P, et al. Emergency
department screening for ectopic pregnancy: a prospective US
study.Radiology. 1994;190:797-802.
12 Akerman TE, Levi CS, Dashefsky SM, et al. Interstitial line:
sonographicfinding in interstitial corneal ectopic pregnancy.
Radiology. 1993;189:83-87.
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