DSJUOG Ultrasound Imaging10.5005/jp-journals-10009-1500 of Early Extraembryonic Structures REVIEW ARTICLE Ultrasound Imaging of Early Extraembryonic Structures 1Sándor Nagy, 2Zoltán Papp ABSTRACT to arrive at an accurate diagnosis and appropriate dis- Transvaginal sonography is the most useful diagnostic method position, thus providing efficient care that benefits both to visualize the early pregnancy, to determine whether it is intra- patients and doctors. The specific sonographic appear- uterine or extrauterine (ectopic), viable or not. Detailed examina- ance of normal pregnancy depends upon the gestational tion of extraembryonic structures allows us to differentiate the age. As the gestational age increases, the ability to assess types of early pregnancy failures and highlights the backgrounds the location and normal development of the pregnancy of vaginal bleeding, as the most frequent symptom of the first trimester of gestation. The reliable ultrasonographic sign of an becomes better. intrauterine pregnancy is visualization of double decidual ring, Spontaneous abortion is one of the most common which represents the trophoblast’s layer. The abnormality in the complications of pregnancy; every 12 to 15 out of 100 sonographic appearance of a gestational sac, a yolk sac, and conceptus are miscarried in the first half of gestation. a chorionic plate can predict subsequent embryonic damage and death. Vaginal bleeding is one of the most serious symptoms of the spontaneous abortion, which the pregnant are afraid Keywords: Blighted ovum, Chorionic plate, Extraembryonic structures, Gestational sac, Missed abortion, Subchorionic of, especially when extrachorial bleeding is detected by hemorrhage, Yolk sac. ultrasound. Transvaginal sonography is the optimal way to image How to cite this article: Nagy S, Papp Z. Ultrasound Imaging of Early Extraembryonic Structures. Donald School J Ultrasound a patient with developing gestation. Indications for this Obstet Gynecol 2017;11(1):11-19. examination include not only the need to identify the Source of support: Nil location and number of gestational sacs (GSs), date the age of a pregnancy, and determine whether the embryo Conflict of interest: None has a normal appearance, but also to vizualize the extra- embryonic structures, which help to predict early preg- INTRODUCTION nancy failures. The first visible structures in pregnancy are The use of ultrasonography in the very early stages of extraembryonic parts of the gestation. In order to predict pregnancy enables to confirm the status of intrauterine the outcome of pregnancy, we need to fully appreciate living embryo or diagnose extrauterine pregnancy for the development and pathological conditions of early which medical treatment with low morbidity is feasible extraembryonic structures. with early detection. First trimester ultrasonography before 12-weeks of gestation is a valuable tool for pre- GESTATIONAL SAC dicting pregnancy outcomes, particularly with respect The GS corresponds to the chorionic cavity. Its size has to detecting complicated or unviable pregnancies with been used to evaluate normal progress of the early preg- the exception of aneuploidy.1 Transvaginal sonography nancy. After 7 days of conception, the blastocyst reaches of first trimester pregnancy is a core bedside ultrasound the uterine cavity. It embeds into the secretory phase application, an essential component of the evaluation endometrium, and begins to implant. The trophoblast of pregnant women, and helps to vizualize the early cells penetrate into the decidualized endometrium, embryonic and extraembryonic structures. Along with erode the maternal capillaries, and make contact with the other clinical data, ultrasound findings allow obstetricians maternal circulation. The trophoblast and the decidual cells form the GS. It is the first visible structure in early pregnancy. It can be detected by transvaginal ultrasono- 1 2 Associate Professor, Honorary Professor graphy after the 4th menstrual week. 1Department of Obstetrics and Gynecology, Aladár Petz County The GS is a large cavity of fluid surrounding the Teaching Hospital, Győr, Hungary embryo. During early embryogenesis, it consists of the 2Maternity Private Hospital for Obstetrics and Gynecology extraembryonic coelom, also called the chorionic cavity. Semmelweis University, Budapest, Hungary By approximately 9 weeks of gestational age, the amniotic Corresponding Author: Zoltán Papp, Honorary Professor sac has expanded to occupy the majority of its volume, Maternity Private Hospital for Obstetrics and Gynecology eventually filling the entire space. The GS is usually con- Semmelweis University, Budapest, Hungary, e-mail: papp. [email protected] tained with the uterus. It is the only available structure Donald School Journal of Ultrasound in Obstetrics and Gynecology, January-March 2017;11(1):11-19 11 Sándor Nagy, Zoltán Papp that can be used to determine if an intrauterine pregnancy The size of the GS also correlates with the health (IUP) exists until the embryo is identified. The GS is an of the developing fetus. If a GS is small for gestational anechoic fluid-filled collection surrounded by a thickened age, it carries a poor prognosis and a serial sonographic decidua within the uterus that represents an early IUP. examination should be performed to assess the rate of The appearance of a GS is the earliest sign of an IUP. Using growth. A GS with a growth rate of <1 mm/day usually vaginal transducers with frequencies of at least 5 MHz, has a poor prognosis. A small GS may be due to oligo- the earliest evidence of a GS is seen at 4 to 5 weeks and hydramnios, which is a predictor of poor outcome, even appears as a small 2 to 3 mm cystic structure embedded in the presence of normal embryonic cardiac activity. As in thickened endometrium; this appearance has been a rule of thumb, if the difference between the mean sac described as the intradecidual sign. Small sacs are usually diameter (MSD) and crown-rump length are <5 mm, there round, but with growth they frequently become elliptic. is an 80% risk of pregnancy loss. Using transvaginal sono- The GS is a ring-shaped structure with a double- graphy, a GS with an MSD of 8 mm without a yolk sac, layered wall, embedded eccentrically into the endome- and a GS with an MSD > 16 mm without an embryo are trium. It is important to differentiate it from the pseu- important predictors of a nonviable gestation. A blighted dogestational sac of ectopic pregnancy (Table 1). The ovum or anembryonic pregnancy is an early failure of the pseudogestational sac is in fact a fluid-filled cavity between embryo to develop within the GS. A pseudogestational the layers of the enlarged endometrium. It has a thin simple sac is seen with an ectopic pregnancy and corresponds wall, and is usually in central position. Peritrophoblastic to intrauterine fluid collection rimmed by the endome- activity is never visible in the underlying layers (Figs 1A trium. It is centrally located in the uterine cavity (a true and B). Approximately 20% of ectopic pregnancies have an sac is eccentric), has sharp angulations, and has an absent intrauterine pseudogestational sac and it is important to double decidual sign without a yolk sac. The normal GS be aware of the rare possibility of concurrent intrauterine has a regular contour, whereas an abnormal sac has an and extrauterine pregnancy. More recent studies have irregular contour. Other findings that suggest an abnor- found a somewhat lower incidence of approximately mal sac include a decidual reaction <2 mm, low position, 10%. It is likely that many of the early descriptions of absent double decidual sac, decreased echogenecity of pseudogestational sacs were due to hypoechoic areas in choriodecidual reaction, and a small sac.3 the decidua appearing anechoic, since we have rarely seen pseudogestational sacs in recent years.2 BLIGHTED OVUM A blighted ovum (also known as anembryonic gestation) Table 1: The difference between gestational and the is a pregnancy in which the very early pregnancy appears pseudogestational sac normal on an ultrasound scan, but as the pregnancy Gestational sac Pseudogestational sac progresses a visible embryo never develops or develops Localization Lateral Central and is reabsorbed. The presentation of women with an Shape Spheroid Ovoid Contour Thick, double- Thin, mono-layered “empty sac” is common, with up to 10% of patients with layered wall wall uncertain viability in pregnancy. Early normal pregnan- Peritrophoblastic Exists Nonexistent cies always show a GS, but no detectable embryo during circulation a brief, but finite stage of early development. Once a GS A B Figs 1A and B: Pseudogestational sac (A) Dilated tuba (B) ectopic pregnancy 12 DSJUOG Ultrasound Imaging of Early Extraembryonic Structures has been documented subsequent loss of viability remain layers: (i) An inner layer, the cytotrophoblast, and (ii) an around 11%, there is no difference between GS diameter outer zone, the syncytiotrophoblast. The syncytiotropho- when compared with pregnancy outcome. If an embryo blasts penetrate into the stroma and erode the endothelial has developed up to 5 mm length, loss of viability occurs lining of maternal capillaries. These congested and dilated in 7.2% of cases. Persistence of yolk sac has been found capillaries are known as sinusoids. The sincytial lacunae inside the GS after embryonic demise. If the volume of then become continuous with the sinusoids, and mater- the sac is less than 2.5 mL and is not increasing in size