Ultrasound features of tubal ectopic pregnancy

During the last two decades, there have been tremendous advances in the recognition and management of ectopic pregnancies (EPs); nevertheless, EP remains a major cause of maternal morbidity and mortality. In westernised countries like the United Kingdom, the rate of EP is 11/ 1000 pregnancies with maternal mortality of 0.2/1000 (NICE guidelines 2012). While in the United States of America 9% of maternal mortality is attributed to EP. In Australia, there were three maternal deaths between 2006 and 2010 (in comparison with two between 2000 and 2005) all of which were preventable. The rates of EP are even higher in developing countries. Importantly, we must also not underestimate the psychological trauma associated with EP and the impact on future fertility. Early recognition and prompt referral are key factors to prevent catastrophic events such as tubal rupture and collapse. Early diagnosis allows the clinician to decide for more conservative approaches in EP management avoiding surgery and its associated risks of anaesthesia, blood loss and inadvertent injury to vascular and other pelvic structures at the time of laparoscopy. Ultrasound is the imaging method of choice to diagnose EP. In the 1970s, the diagnosis of EP was based upon non-visualisation of a gestational sac inside the uterus, utilising transabdominal scan at different cut-off values of serum human chorionic gonadotrophin (hCG). ln the 1980s and 1990s, transvaginal ultrasound scan (TVS) was introduced and became widely used, resulting in earlier recognition of the EP mass at lower levels of quantitative hCG. The diagnosis of EP in modern practice is based upon the positive visualisation of an extrauterine mass on TVS rather than the absence of an intrauterine gestational sac. At the first presentation, TVS has a sensitivity of 73.9–74.7% in detecting EP, and the overall sensitivity of TVS in detecting EP in subsequent visits is 87–99% with specificity of 94–99%. There are four distinct TVS morphologic criteria used to classify women with a tubal EP: (i) an inhomogeneous mass or ‘blob’ sign adjacent to the ovary and moving separately from the ovary; or (ii) a mass with a hyper-echoic ring around the gestational sac or ‘bagel’ sign; or (iii) a gestational sac with an embryonic pole with cardiac activity; or (iv) a gestational sac with an embryonic pole without cardiac activity. According to a consensus statement in 2011, only the presence of a gestational sac with embryo (with or without cardiac activity) is considered to be a definite diagnosis of EP. According to the same consensus, the other two morphological ultrasound types ‘blob’ and ‘bagel’ signs are classified as probable EPs. The prevalence of these different morphological types in TVS has changed over the years. The most common morphological types are the ‘blob’ and ‘bagel’ signs accounting for almost 80% of all tubal EPs, whilst the presence of an embryo with or without cardiac activity accounts for 10–13%. The association between these different EP morphological types and management success has been examined in several studies. The presence of fetal cardiac activity on TVS is considered an indication for surgical management. A gestational sac with yolk sac on TVS appears to be highly associated with failure of non-surgical management. Various studies have also looked at predictors of tubal rupture from ultrasound findings, but none have been shown to be a true predictor. There are varying reports as to whether or not the size of the EP mass on TVS is a significant predictor of success for expectant management. Although ultrasound plays a major role in the diagnosis and management of EP, its role is subject to the competency level and experience of the operator. The more experienced the operator, the higher the rate of EP detection at the initial TVS and the lower the rate of women classified with a pregnancy of unknown location (PUL). PUL is defined as the absence of an intraor extrauterine gestational sac on TVS and these women should be followed up to determine the final outcome. Implementation of consultant-led early pregnancy assessment units, accessibility to high-resolution TVS under strict supervision provision and focused teaching programmes to recognise the risk factors for EP have led to recognisable improvements in the quality and reporting of early pregnancy TVSs. The future for EP management is to explore whether early detection of EP with the adaptation of conservative management strategies will reduce the future rate of EP morbidity and mortality.