Assessment of the fetal thymus by two- and three-dimensional ultrasound during normal human gestation and in fetuses with congenital heart defects

Prenatal cardiac findings and 22q11.2 deletion syndrome: Fetal detection and evaluation

Clinical features of 22q11.2 microdeletion syndrome (22q11.2DS) are highly variable between affected individuals and frequently include a subset of conotruncal and aortic arch anomalies. Many are diagnosed with 22q11.2DS when they present as a fetus, newborn or infant with characteristic cardiac findings and subsequently undergo genetic testing. The presence of an aortic arch anomaly with characteristic intracardiac anomalies increases the likelihood that the patient has 22q11.2 DS, but those with an aortic arch anomaly and normal intracardiac anatomy are also at risk. It is particularly important to identify the fetus at risk for 22q11.2DS in order to prepare the expectant parents and plan postnatal care for optimal outcomes. Fetal anatomy scans now readily identify aortic arch anomalies (aberrant right subclavian artery, right sided aortic arch or double aortic arch) in the three-vessel tracheal view. Given the association of 22q11.2DS with aortic arch anomalies with and without intracardiac defects, this review highlights the importance of recognizing the fetus at risk for 22q11.2 deletion syndrome with an aortic arch anomaly and details current methods for genetic testing. To assist in the prenatal diagnosis of 22q11.2DS, this review summarizes the seminal features of 22q11.2DS, its prenatal presentation and current methods for genetic testing.

Decreased fetal thymus size in pregnancies after assisted reproductive technologies

OBJECTIVE

To compare the size of the fetal thymus, using both fetal thymic-thoracic ratio and fetal thymus transverse diameter values in Assisted reproductive technologies (ART) or naturally conceived pregnancies.

METHODS

In this retrospective study, fetal thymic-thoracic ratio and fetal thymus transverse diameter were evaluated in 204 pregnant women. Patients were examined in two groups. The study included 58 Intracytoplasmic sperm injection (ICSI) patients (study group) and 146 healthy pregnant women (control group).

RESULTS

Fetal thymic-thoracic ratio in ART pregnancies were found to be statistically significantly lower than that of the control group (p = .001). Also, the fetal thymus transverse diameter value was found to be statistically significantly lower in ART pregnancies compared to that of the control group (p = .001).

CONCLUSIONS

The size of the fetal thymus, manifested with a decrease in both fetal thymic-thoracic ratio and thymus transverse diameter values, decreased in ART pregnancies.

Assessment of fetal thymus size in pregnant women with rheumatic diseases: A case-control study

PURPOSE

To investigate the fetal thymic-thoracic ratio (TT-ratio) in pregnancies diagnosed with rheumatoid arthritis (RA) and ankylosing spondylitis (AS).

METHODS

Thirty-two pregnant women with rheumatic disease and 96 low-risk pregnant women between 20 and 37 weeks were included in the study. Three control patients were randomly selected for each study patient. TT-ratio was calculated by measuring the anterior-posterior diameter of the thymus and the intrathoracic mediastinal diameter. Data were compared between the study group, including RA and AS, and the control group.

RESULTS

Thirty-two pregnant women with arthritis, 19 diagnosed with RA and 13 with AS, were evaluated. The mean value of the study group TT-ratio was 0.33; control group, 0.36; a statistically significant difference was found (p < 0.001). Perinatal outcomes were not different when compared with control patients. There was a negative correlation between disease duration, maternal C-reactive protein, erythrocyte sedimentation rate, and TT-ratio.

CONCLUSION

This is the first study to prospectively evaluate the fetal TT-ratio in patients with RA and AS. Systemic inflammation appears to affect fetal thymus size. Appropriate management of maternal rheumatic diseases is essential for developing the thymus, a vital immune system component.

Prenatal Sonographic Three-dimensional Virtual Organ Computer-assisted Analysis Thymic Volume Calculation May Predict Intrauterine Growth Restriction

Background

Intrauterine growth restriction (IUGR) refers to fetuses that are small for their gestational age. There is no effective test to predict this disease. The aim of our study is whether fetal three-dimensional (3D) ultrasonography (USG)-assisted thymus volume (TV) measurement predicts IUGR cases.

Methods

Fetal 3D USG thymus measurement between 15 and 24 weeks of gestation was performed in a total of 100 women of reproductive age. Fetal TV was measured using the virtual organ computer-assisted analysis system program. All cases were followed up in terms of pregnancy complications until delivery.

Results

IUGR was developed in six cases in total. In cases with IUGR, mean fetal TV was found to be statistically significantly lower than in healthy cases without it. When the fetal TV was taken as 0.1645, the sensitivity was calculated as 89.5% and the specificity as 50% for predicting IUGR. The use of low fetal volume parameters is a significant and good indicator for predicting IUGR according to the binary logistic regression analysis result.

Conclusion

According to the results of this study, 3D fetal TV measurement may be used in routine second-trimester sonographic anomaly screening to predict the development of fetal IUGR. In this way, fetal mortality and morbidity caused by IUGR may be reduced.

Prenatal Screening and Diagnostic Considerations for 22q11.2 Microdeletions

Diagnosis of a chromosome 22q11.2 microdeletion and its associated deletion syndrome (22q11.2DS) is optimally made early. We reviewed the available literature to provide contemporary guidance and recommendations related to the prenatal period. Indications for prenatal diagnostic testing include a parent or child with the 22q11.2 microdeletion or suggestive prenatal screening results. Definitive diagnosis by genetic testing of chorionic villi or amniocytes using a chromosomal microarray will detect clinically relevant microdeletions. Screening options include noninvasive prenatal screening (NIPS) and imaging. The potential benefits and limitations of each screening method should be clearly conveyed. NIPS, a genetic option available from 10 weeks gestational age, has a 70-83% detection rate and a 40-50% PPV for most associated 22q11.2 microdeletions. Prenatal imaging, usually by ultrasound, can detect several physical features associated with 22q11.2DS. Findings vary, related to detection methods, gestational age, and relative specificity. Conotruncal cardiac anomalies are more strongly associated than skeletal, urinary tract, or other congenital anomalies such as thymic hypoplasia or cavum septi pellucidi dilatation. Among others, intrauterine growth restriction and polyhydramnios are additional associated, prenatally detectable signs. Preconception genetic counselling should be offered to males and females with 22q11.2DS, as there is a 50% risk of transmission in each pregnancy. A previous history of a de novo 22q11.2 microdeletion conveys a low risk of recurrence. Prenatal genetic counselling includes an offer of screening or diagnostic testing and discussion of results. The goal is to facilitate optimal perinatal care.

Finding the best method for screening for gestational diabetes mellitus: fetal thymic-thoracic ratio or fetal thymus transverse diameter

OBJECTIVE

The aim of this study was to compare the efficiency of fetal thymic-thoracic ratio and fetal thymus transverse diameter measurements in gestational diabetes mellitus.

METHODS

Fetal thymic-thoracic ratio and fetal thymus transverse diameter were assessed in 360 pregnant women. Patients were examined in two groups: 180 gestational diabetes mellitus (study group) and 180 healthy pregnant women (control group).

RESULTS

There were no statistically significant differences between the cases with gestational diabetes mellitus and the control group in terms of fetal thymus transverse diameter; however, the fetal thymic-thoracic ratio was found to be significantly lower in cases with gestational diabetes mellitus compared to that in the control group (p<0.001).

CONCLUSION

The fetal thymic-thoracic ratio is superior to the fetal thymus transverse diameter in evaluating the fetal thymus size.

Antenatal diagnosis of chorioamnionitis: A review of the potential role of fetal and placental imaging

Chorioamnionitis is present in up to 70% of spontaneous preterm births. It is defined as an acute inflammation of the chorion, with or without involvement of the amnion, and is evidence of a maternal immunological response to infection. A fetal inflammatory response can coexist and is diagnosed on placental histopathology postnatally. Fetal inflammatory response syndrome (FIRS) is associated with poorer fetal and neonatal outcomes. The only antenatal diagnostic test is amniocentesis which carries risks of miscarriage or preterm birth. Imaging of the fetal immune system, in particular the thymus and the spleen, and the placenta may give valuable information antenatally regarding the diagnosis of fetal inflammatory response. While ultrasound is largely limited to structural information, MRI can complement this with functional information that may provide insight into the metabolic activities of the fetal immune system and placenta. This review discusses fetal and placental imaging in pregnancies complicated by chorioamnionitis and their potential future use in achieving non-invasive antenatal diagnosis. This article is protected by copyright. All rights reserved.

Ultrasonographic evaluation of the fetal thymic-thoracic ratio and its association with conotruncal heart defects

OBJECTIVE

To evaluate the thymic-thoracic ratio (TT ratio) on fetal ultrasound and its association with conotruncal heart defects.

METHODS

A case control study was carried out to retrospectively assess the TT ratio on fetal echocardiograms performed between 19 and 39 weeks of gestation, showing congenital heart defects, from January to December 2018. The control group was comprised of fetuses with no echocardiogram evidence of congenital cardiac malformations. Cases of multiple pregnancies and patients where the TT ratio could not be established have been excluded.

RESULTS

A total of 338 pregnancies have been analysed. Fifty-two pregnancies were diagnosed with fetal heart defects (15%), 17 of which showed conotruncal heart defects (32.7%). The TT ratio in normal fetuses (286 pregnancies) increased with gestational age, and had an average of 0.43 ± 0.06. Compared to the control group (normal fetuses), fetuses with conotruncal heart defects had significantly lower mean TT ratio (0.33 ± 0.07). Those that were diagnosed with nonconotruncal heart defects did not show any statistically significant difference in the TT ratios compared with the control group (0.40 ± 0.09 vs. 0.43 ± 0.06, respectively).

CONCLUSION

The TT ratio was significantly lower in fetuses with conotruncal heart defects compared with both the control group (normal fetuses) and the fetuses with nonconotruncal heart defects.

Impact of antenatal corticosteroid exposure on thymus size in premature infants

BACKGROUND

This study examined the effect of corticosteroids on the thymic index (TI) and the thymus/weight index (TWI) in infants exposed to antenatal corticosteroids (ACS).

METHODS

This prospective study was conducted between August 2014 and October 2018. A thymus ultrasound was performed to assess thymus size on the second day of life. Thymus size was assessed as TI and TWI.

RESULTS

In total, 167 neonates (≤34 weeks gestation)  constituted the study population, including 94 ACS-exposed infants and 73 untreated infants. The treatment group exhibited significantly lower birth weight and significantly shorter birth length than the ACS (-) group. Therefore, TI was smaller in the treatment group than in the untreated group (6.96 ± 4.05 cm³ vs. 5.64 ± 3.39 cm³). The TWI was 3.69 ± 1.8 cm³/kg in the ACS (-) group versus 3.32 ± 1.56 cm³/kg in the ACS (+) group. The median anteroposterior diameter of the right lobe was 1.33 cm (range, 0.45-2.40) in the ACS (-) group compared to 1.15 cm (range, 0.47-2.40) in the ACS (+) group. The median anteroposterior diameter of the left lobe was 1.40 cm (range, 0.43-2.20) in the ACS (-) group and 1.19 cm (range, 0.32-2.36) in the ACS (+) group. The median largest sagittal area was 2.64 cm² (range, 0.5-5.46) in the ACS (-) group versus 2.20 cm² (range, 0.55-5.90) in the ACS (+) group.

CONCLUSION

We found that TWI was not significantly changed by ACS exposure in premature infants.

Assessment of the fetal thymus gland: Comparing MRI-acquired thymus volumes with 2D ultrasound measurements

OBJECTIVES

The fetal thymus gland has been shown to involute in response to intrauterine infection, and therefore could be used as a non-invasive marker of fetal compartment infection. The objective of this study was to evaluate how accurately 2D ultrasound-derived measurements of the fetal thymus reflect the 3D volume of the gland derived from motion corrected MRI images.

STUDY DESIGN

A retrospective study was performed using paired ultrasound and MRI datasets from the iFIND project (http://www.ifindproject.com). To obtain 3D volumetry of the thymus gland, T2-weighted single shot turbo spin echo (ssTSE) sequences of the fetal thorax were acquired. Thymus volumes were manually segmented from deformable slice-to-volume reconstructed images. To obtain 2D ultrasound measurements, previously stored fetal cine loops were used and measurements obtained at the 3-vessel-view (3VV) and 3-vessel-trachea view (3VT): anterior-posterior diameter (APD), intrathoracic diameter (ITD), transverse diameter (TD), perimeter and 3-vessel-edge (3VE). Inter-observer and intra-observer reliability (ICC) was calculated for both MRI and ultrasound measurements. Pearson correlation coefficients (PCC) were used to compare 2D-parameters with acceptable ICC to TV.

RESULTS

38 participants were identified. Adequate visualisation was possible on 37 MRI scans and 31 ultrasound scans. Of the 30 datasets where both MRI and ultrasound data were available, MRI had good interobserver reliability (ICC 0.964) and all ultrasound 3VV 2D-parameters and 3VT 3VE had acceptable ICC (>0.75). Four 2D parameters were reflective of the 3D thymus volume: 3VV TD r = 0.540 (P = 0.002); 3VV perimeter r = 0.446 (P = 0.013); 3VV APD r = 0.435 (P = 0.110) and 3VT TD r = 0.544 (P = 0.002).

CONCLUSIONS

MRI appeared superior to ultrasound for visualization of the thymus gland and reproducibility of measurements. Three 2D US parameters, 3VV TD, perimeter and 3VT APD, correlated well with TV. Therefore, these represent a more accurate reflection of the true size of the gland than other 2D measurements, where MRI is not available.

Antenatal thymus volumes in fetuses that delivered <32 weeks' gestation: An MRI pilot study

INTRODUCTION

Infection and inflammation have been implicated in the etiology and subsequent morbidity associated with preterm birth. At present, there are no tests to assess for fetal compartment infection. The thymus, a gland integral in the fetal immune system, has been shown to involute in animal models of antenatal infection, but its response in human fetuses has not been studied. This study aims: (a) to generate magnetic resonance imaging (MRI) -derived fetal thymus volumes standardized for fetal weight; (b) to compare standardized thymus volumes from fetuses that delivered before 32 weeks of gestation with fetuses that subsequently deliver at term; (c) to assess thymus size as a predictor of preterm birth; and (d) to correlate the presence of chorioamnionitis and funisitis at delivery with thymic volumes in utero in fetuses that subsequently deliver preterm.

MATERIAL AND METHODS

Women at high-risk of preterm birth at 20-32 weeks of gestation were recruited. A control group was obtained from existing data sets acquired as part of three research studies. A fetal MRI was performed on a 1.5T or 3T MRI scanner: T2 weighted images were obtained of the entire uterine content and specifically the fetal thorax. A slice-to-volume registration method was used for reconstruction of three-dimensional images of the thorax. Thymus segmentations were performed manually. Body volumes were calculated by manual segmentation and thymus:body volume ratios were generated. Comparison of groups was performed using multiple regression analysis. Normal ranges were created for thymus volume and thymus:body volume ratios using the control data. Receiver operating curves (ROC) curves were generated for thymus:body volume ratio and gestation-adjusted thymus volume centiles as predictors of preterm birth. Placental histology was analyzed where available from pregnancies that delivered very preterm and the presence of chorioamnionitis/funisitis was noted.

RESULTS

Normative ranges were created for thymus volume, and thymus volume was standardized for fetal size from fetuses that subsequently delivered at term, but were imaged at 20-32 weeks of gestation. Image data sets from 16 women that delivered <32 weeks of gestation (ten with ruptured membranes and six with intact membranes) and 80 control women that delivered >37 weeks were included. Mean gestation at MRI of the study group was 28⁺⁴  weeks (SD 3.2) and for the control group was 25⁺⁵  weeks (SD 2.4). Both absolute fetal thymus volumes and thymus:body volume ratios were smaller in fetuses that delivered preterm (P < .001). Of the 16 fetuses that delivered preterm, 13 had placental histology, 11 had chorioamnionitis, and 9 had funisitis. The strongest predictors of prematurity were the thymus volume Z-score and thymus:body volume ratio Z-score (ROC areas 0.915 and 0.870, respectively).

CONCLUSIONS

We have produced MRI-derived normal ranges for fetal thymus and thymus:body volume ratios between 20 and 32 weeks of gestation. Fetuses that deliver very preterm had reduced thymus volumes when standardized for fetal size. A reduced thymus volume was also a predictor of spontaneous preterm delivery. Thymus volume may be a suitable marker of the fetal inflammatory response, although further work is needed to assess this, increasing the sample size to correlate the extent of chorioamnionitis with thymus size.

Ultrasound Monitoring of Thymus Involution in Septic Mice

Thymus involution is characterized by a progressive regression of thymus size and contributes to immunosuppression in sepsis. High-frequency ultrasonography is a non-invasive monitoring system in multiple organs, including the thymus, in mice. However, thymus involution has not been studied using ultrasonography in septic mice. This study reports ultrasound approaches to monitoring septic thymus involution in mice. Sepsis was induced by cecum ligation and puncture (CLP). Mice were euthanized at three time points: baseline and days 3 and 10 after CLP. Thymus areas and volumes were measured using 2-D and 3-D ultrasound approaches. Thymus weights were measured ex vivo. Compared with values at baseline, both thymus area and volume decreased significantly at days 3 and 10. In addition, thymus areas and volumes correlated positively with thymus weights. In conclusion, ultrasonography provides reliable thymus measurements and is an optimal technique for monitoring thymus involution in septic mice.

Fetal thymus in the middle and late trimesters: Morphometry and development using post-mortem 3.0T MRI

The present study aimed to investigate the anatomical microstructure, features and signals of the fetal thymus by 3.0T FS-T2 weighted turbo spin echo sequences, which could provide imaging evidence for the evaluation of early-stage development of fetal thymus. In addition, the T2-weighted three-dimensional (3D) sequences and the 3D processing may contribute to the establishment of reference ranges for the fetal thymus. A total of 64 specimens obtained from the fetuses of 16-39 weeks of gestational age (GA) were scanned by 3.0T MRI. Morphological changes and quantitative measurements of the fetal thymus were assessed, including the anteroposterior diameter, width, height, surface area and volume. The shape of fetal thymus varied and the majority were X-shaped, with a narrow top and wide bottom. Morphology measurements demonstrated gradual growth with increasing GA. There were high linear correlations between width, height, surface area and volume and GA. No significant differences were observed between the sexes. Post-mortem 3.0T MRI clearly demonstrated changes in external contours and internal structure with GA. The images and data obtained reflect normal development of the fetal thymus and enrich the imaging data of fetal morphometry.

Antenatal corticosteroid administration is associated with decreased growth of the fetal thymus: a prospective cohort study

OBJECTIVE

To examine the effect of antenatal corticosteroid administration (ACS) on fetal thymus growth in women who received ACS compared with gestational-age-matched controls.

STUDY DESIGN

Fetal thymus size and growth were measured in women at risk for preterm delivery who received ACS and compared with a matched cohort of women who were at low risk for preterm delivery and did not receive ACS. Fetal thymus perimeter and diameter were measured by 2-D ultrasound at baseline and every 2 weeks until delivery.

RESULTS

After adjusting for confounders, ACS exposure was associated with a significant reduction in thymus perimeter size (-0.70; 95% CI: -1.33, -0.07; P = 0.03). For every additional week of exposure, thymus growth trajectory was significantly decreased in ACS-exposed fetuses (P = 0.04).

CONCLUSION

The association between ACS and reduced fetal thymus growth should be further examined to establish the impact of ACS on childhood thymus development and immune programming.

Foetal thymus size in pregnancies after assisted reproductive technologies

PURPOSE

The aim of our study was to compare thymus sizes in foetuses conceived using assisted reproductive technologies (ART) to those conceived naturally (control group).

METHODS

Sonographic foetal thymus size was assessed retrospectively in 162 pregnancies conceived using ART and in 774 pregnancies conceived naturally. The anteroposterior thymic and the intrathoracic mediastinal diameter were measured to calculate the thymic-thoracic ratio (TT-ratio). The ART cases were subdivided into two groups: (1) intracytoplasmic sperm injection (ICSI; n = 109) and (2) in vitro fertilisation (IVF; n = 53).

RESULTS

The TT-ratio was smaller in pregnancies conceived using ART (p < 0.001). In both ART subgroups (ICSI and IVF), the TT-ratio was lower compared to the control group (p < 0.001). However, no difference between the two subgroups could be detected (p = 0.203).

CONCLUSIONS

Our data show reduced thymus size in foetuses conceived using ART compared to controls. These findings indicate that the use of ART may lead to certain deviations in organogenesis.

Correlation Between the Thymic-Thoracic Ratio and Cardiac Axis in Healthy Fetuses

OBJECTIVES

The aim of this study was to assess the correlation between the thymic-thoracic ratio and cardiac axis in healthy fetuses.

METHODS

The fetal thymic-thoracic ratio and cardiac axis were measured in 220 healthy fetuses. The normal ranges of the fetal thymic-thoracic ratio and cardiac axis for each gestational week were established. The Pearson correlation coefficient was calculated to analyze the relationship between the thymic-thoracic ratio and cardiac axis.

RESULTS

The mean fetal thymic-thoracic ratio increased slightly throughout the pregnancy, from 0.33 at 17 weeks' gestation to 0.37 at 37 weeks. No statistically significant correlation was found between the thymic-thoracic ratio and cardiac axis in healthy fetuses.

CONCLUSIONS

In healthy fetuses, the thymus occupies an increasingly larger portion of the upper mediastinum when the pregnancy advances. The cardiac axis is not affected by the thymic-thoracic ratio in healthy fetuses.

Sonographic measurement of fetal thymus size in uncomplicated singleton pregnancies

PURPOSE

To establish sonographic reference ranges of the normal fetal thymus size between 17 and 38 weeks of gestational age (GA).

METHODS

The study was conducted between April 1 and December 31, 2013. Low-risk singleton pregnancies without obstetrical and medical complications at the GAs between 17 and 38 weeks were recruited for thymus measurement. The fetal thymus was identified on transabdominal sonography at the three-vessel view. Maximal transverse diameter, perimeter, and thymus/thoracic ratio were measured. The best-fit models in predicting thymic dimensions as a function of GA and biparietal diameter (BPD) were determined using regression analysis, and percentile charts for predicting thymic dimensions were constructed.

RESULTS

A total of 296 singleton pregnancies were recruited in this study. Maximal transverse diameter, perimeter, and thymus/thoracic ratio increased throughout pregnancy. The regression equation for maximal transverse diameter of the thymus as a function of GA was as follows: Predicted mean thymus diameter (mm) = -25.904 + 2.476 × GA - 0.019 × GA² (r = 0.915; p < 0.001) with predicted standard deviations of thymus diameter (mm) = 1.428 + 0.044 × GA (r = 0.017; p < 0.001).

CONCLUSIONS

Sonographic reference ranges of the normal fetal thymic dimensions between 17 and 38 weeks of GA have been established. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:150-159, 2017.

Ultrasonographic approach to diagnosis of fetal inflammatory response syndrome: a tool for at-risk fetuses?

Preterm parturition is a syndrome that may result from many underlying mechanisms. Infection and inflammation are the prominent ones. Intrauterine infection and inflammation have an effect akin to sepsis, and that is similar to systemic inflammatory response in adults. Indeed, there is evidence to support the association of a fetal inflammatory response syndrome (FIRS) to systemic infection and inflammation. The utilization of invasive procedures for the prenatal diagnosis of FIRS is associated with a risk for complications resulting from the invasive method. The progress in the imaging quality of obstetrical ultrasound and the development of novel methods for functional anatomical assessment of the fetal organs may help to identify, noninvasively, fetuses at risk for FIRS in patients presenting with preterm labor. We review the studies describing advanced sonographic modalities and the imaging findings in the heart, thymus, kidney, adrenal glands, and spleen of these fetuses.

The use of imaging technology in the assessment of the fetal inflammatory response syndrome-imaging of the fetal thymus

The fetal inflammatory response syndrome (FIRS) describes a state of extensive fetal multi organ involvement during chorioamnionitis, and is associated with grave implications on perinatal outcome. The syndrome has been linked to the preterm parturition syndrome and is associated with inflammation/infection processes in most of the fetal organs. The fetal thymus, a major organ in the developing immune system involutes during severe neonatal disease and has been shown to be smaller in fetuses with FIRS. Various methods for imaging of the fetal thymus and measurement are described. Currently the only method to diagnose FIRS prenatally is through amniocentesis. We suggest that women who are admitted with preterm labor with intact membranes and those with PPROM should have a detailed sonographic examination of the fetal thymus as a surrogate marker of fetal involvement in intrauterine infection/inflammation processes.

Sonographic Evaluation of the Fetal Thymus Using the Thy-Box Technique Between 13 and 16 Weeks' Gestation

OBJECTIVES

The purposes of this study were to assess the feasibility of fetal thymus measurement between 13 and 16 weeks' gestation, to evaluate the potential difference using color Doppler sonography with the thy-box technique, and to construct normal percentile ranges.

METHODS

This retrospective study included 287 healthy singleton pregnancies. The fetal thymus was shown in an axial plane of the upper mediastinum. Color Doppler imaging was applied to outline the thy-box: ie, the area between the brachiocephalic artery posteriorly and internal mammary arteries laterally. Measurements of the lateral and anteroposterior diameters of the thymus with and without color Doppler imaging were compared.

RESULTS

The thymus was shown in 95% of the cases (273 of 287) between 13 and 16 weeks' gestation. The mean lateral thymus diameter ± SD with color Doppler imaging (5.30 ± 0.7 mm) was significantly longer in comparison to the measurement without color Doppler imaging (5.06 ± 0.8 mm; P < .001), whereas the anteroposterior diameter was significantly shorter (3.19 ± 0.9 versus 3.26 ± 0.8 mm; P = .044). Normal percentiles of thymus measurements for gestational age were constructed.

CONCLUSIONS

The fetal thymus can be clearly and accurately shown as early as 13 weeks' gestation by using the thy-box. Measurements with color Doppler imaging were significantly different from those without and hence are preferable, as color Doppler imaging can delineate the thymus borders more accurately.

Fetal thymus: visualization rate and volume by integrating 2D- and 3D-ultrasound during 2nd trimester echocardiography

OBJECTIVE

To assess the visualization rate and transverse diameter of fetal thymus by two-dimensional ultrasound (2DUS) as well as the fetal thymus volume by three-dimensional ultrasound (3DUS) during the 2nd trimester echocardiography.

METHODS

A prospective cross-sectional study involving 100 normal fetuses between 18w0d and 23w6d was performed. The identification of fetal thymus and peri-thymic vessels was realized at level of three vessels and trachea (3VT). The transverse diameter was obtained placing a line cursor perpendicular to the line connecting the sternum and the spine. The fetal thymus volume was obtained by virtual organ computer-aided analysis (VOCAL) with 30° of rotation. We used the percentage of visualization rate of 2D structures and means and 95% confidence intervals (CI) for fetal thymus transverse diameter and volume.

RESULTS

The visualization rate of fetal thymus by 2DUS was of 100% in all gestational ages using the 3VT view. Addition of color Doppler ultrasound facilitates identification of the thy-box and enhanced the calculation of both fetal thymus transverse diameter and volume. The mean fetal thymus transverse diameter by 2DUS ranged from 11 mm at 18 weeks to 19 mm at 23 weeks of gestation. The mean fetal thymus volume by 3DUS ranged from 1.25 cm(3) at 18 weeks to 2.61 cm(3) at 23 weeks of gestation.

CONCLUSION

We demonstrated a high visualization rate of fetal thymus and peri-thymic vessels by 2DUS during the 2nd trimester echocardiography. The measurements of transverse diameter by 2DUS and the volume by 3DUS also showed a high success rate.

The thy-box for sonographic assessment of the fetal thymus: nomogram and review of the literature

OBJECTIVES

To assess the feasibility and reproducibility of fetal thy-box visualization and to set normative data for the fetal thymus using this technique.

METHODS

We performed a cross-sectional observational study in pregnant women in their second trimester of pregnancy who attended the fetal medicine unit of the Hospital Gregorio Marañón from March 2011 to March 2013. Using thy-box sonography, which sets boundaries within the thymus, we assessed the feasibility of the thy-box and analyzed the factors related to its visualization. Measurements of the thy-box anteroposterior and transverse diameters were performed in healthy fetuses. Interobserver agreement was studied for both items. We set normative data for the thy-box diameters in singleton and twin pregnancies.

RESULTS

A total of 337 patients from 15 to 37 weeks were recruited after exclusion criteria. Thy-box feasibility was 74.2% (250 of 337). Nonfeasible cases were related to the fetal anterior spine and advanced gestational age. Assessment of the thy-box anteroposterior and transverse diameters was achievable in 250 fetuses. Interobserver agreement was good for feasibility and measurements (κ = 0.80). Linear growth of the thy-box in both diameters was observed in relation to gestational age during the second half of pregnancy. Thy-box diameters did not show significant differences according to the type of gestation, fetal sex, or chorionicity.

CONCLUSIONS

Thy-box diameters are achievable and reproducible by sonography in normal singleton and twin pregnancies during the second trimester; however, although feasible, the thy-box transverse diameter measurement is not reliable beyond 28 weeks. Further studies are needed to evaluate thy-box diameters in pathologic cases, especially conotruncal anomalies.

Variety of prenatally diagnosed congenital heart disease in 22q11.2 deletion syndrome

Objective

To analyze the spectrum of prenatally diagnosed congenital heart disease in a Korean population with 22q11.2 deletion syndrome, and to provide guidelines for screening 22q11.2 deletion prenatally.

Methods

This retrospective study evaluated 1,137 consecutive fetuses that had prenatal genetic testing for 22q11.2 deletion because of suspected congenital heart disease between September 2002 and December 2012, at Asan Medical Center, Seoul, Korea.

Results

Main cardiovascular diseases in the 53 fetuses with confirmed 22q11.2 deletions were tetralogy of Fallot (n = 24, 45%), interrupted aortic arch (n = 10, 19%), ventricular septal defect (n = 5, 9%), double outlet right ventricle (n = 4, 8%), and coarctation of the aorta (n = 4, 8%). Other cardiac defects were rarely associated with 22q11.2 deletion. One fetus had persistent truncus arteriosus, one had aortic stenosis, and one had hypoplastic right heart syndrome. Two fetuses had normal intracardiac anatomy with an isolated right aortic arch, and one had an isolated bilateral superior vena cava.

Conclusion

A variety of congenital heart diseases were seen during the prenatal period. Conotruncal cardiac defects except transposition of great arteries were strongly associated with 22q11.2 deletion. When such anomalies are diagnosed by fetal echocardiography, genetic testing for 22q11.2 deletion should be offered. Even if less frequent deletion-related cardiac defects are detected, other related anomalies, such as thymic hypoplasia or aplasia, should be evaluated to rule out a 22q11.2 deletion.

Reliability of fetal thymus measurement in prediction of 22q11.2 deletion: a retrospective study using four-dimensional spatiotemporal image correlation volumes

OBJECTIVES

To evaluate the thymic-thoracic ratio (TT-ratio) method in assessment of the fetal thymus in normal fetuses and in those with cardiac abnormalities, in the presence or absence of 22q11.2 deletion.

METHOD

Database records were reviewed for cases of conotruncal and arch abnormalities found on fetal echocardiography between January 2007 and September 2011. The 22q11.2 deletion status was retrieved and cases in which this was not known were excluded from the analysis, as were fetuses with aneuploidy or other genetic disorders. An additional 55 normal fetuses were analyzed as a control group. The TT-ratio was measured retrospectively using stored spatiotemporal image correlation (STIC) volume datasets.

RESULTS

Sixty-nine fetuses with relevant cardiac diagnoses were identified and, of these, 18 (26%) had 22q11.2 deletion. The mean gestational age at diagnosis was 22 weeks. Significant pairwise differences, but also overlap, were observed between all three groups (i.e. fetuses with heart defects with and without the 22q11.2 deletion and controls). The mean TT-ratio was 0.44 in our normal control group and was significantly smaller in fetuses with 22q11.2 deletion, corresponding to previously published data. However, the mean TT-ratio in the group with conotruncal anomalies but without the 22q11.2 deletion was also smaller than that in controls, in contrast to previously published data. The TT-ratio was above the normal mean, regardless of fetal karyotype, in all cases of interrupted aortic arch.

CONCLUSION

The TT-ratio method is a feasible and potentially useful tool during detailed fetal heart assessment. However, the absolute measurement is not reliable for prediction of 22q11.2 deletion and the obtained results should therefore be interpreted with caution. Fetal karyotyping should be recommended in cases with conotruncal heart abnormalities, irrespective of the TT-ratio.

Thymic-thoracic ratio in fetuses with trisomy 21, 18 or 13

OBJECTIVES

To assess thymic size expressed as the thymic-thoracic ratio (TT-ratio) in fetuses with trisomy 21, 18 or 13.

METHODS

The TT-ratio, the quotient of the anteroposterior thymic and the intrathoracic mediastinal diameter, was measured in 65 trisomic fetuses between 15 and 36 weeks' gestation, including 30 cases with trisomy 21, 19 with trisomy 18 and 16 with trisomy 13. In addition these 65 fetuses were divided into two groups, according to whether they showed growth that was appropriate-for-gestational age (AGA) (n = 39) or intrauterine growth restriction (IUGR) (n = 26). Measurements were compared with reference ranges from 302 normal fetuses.

RESULTS

The TT-ratio was low in 27.7% (n = 18) of the 65 fetuses with aneuploidy. In comparison to normal fetuses (mean TT-ratio, 0.44), those with trisomy 18 or 21 had a significantly smaller TT-ratio (mean, 0.38 (P < 0.001) and 0.40 (P < 0.05), respectively), while those with trisomy 13 did not (mean, 0.43). These values were not as low as those observed previously in fetuses with del.22q11, suggesting a mechanism involving accelerated thymic involution rather than primary thymic hypoplasia. Furthermore, the TT-ratio was significantly lower than normal in both AGA (P < 0.05) and IUGR (P < 0.001) fetuses.

CONCLUSION

Fetuses with trisomy 18 or 21, but not trisomy 13, have a small thymus, suggesting accelerated thymic involution in utero. IUGR may contribute to the reduced thymic size in trisomy 18 fetuses. Trisomy 21 fetuses seem to have additional factors leading to a small thymus which could be a possible confirmation of the reduced immune response observed in fetuses and neonates with Down syndrome.

Thymic volume in healthy, small for gestational age and growth restricted fetuses

OBJECTIVE

The aim of this study was to verify the hypothesis that a difference in thymic size exists between small for gestational age (SGA) fetuses, likely constitutional, and intrauterine growth restricted (IUGR) fetuses because of placental causes.

METHODS

We studied 27 SGA and 36 control fetuses. SGA was defined as fetal abdominal circumference (AC) and birthweight <10th percentile for gestational age. We defined as constitutional SGA those with normal uterine and umbilical artery Doppler flow velocity waveforms (FVW), and as IUGR those with abnormal uterine FVW. IUGR were further divided based on normal or abnormal umbilical FVW. Fetal thymic volume (TV) was acquired by three-dimensional ultrasound and reconstructed with virtual organ computer-aided analysis. To correct for the influence of fetal size on thymic dimension, TV/AC ratio was calculated.

RESULTS

Controls presented a higher TV/AC compared with each group of SGA (p < 0.001). TV/AC was significantly lower in IUGR with abnormal umbilical FVW compared with both constitutional SGA (p = 0.01) and IUGR with normal umbilical FVW (p = 0.01).

CONCLUSIONS

The differences in TV/AC between constitutional SGA and IUGR with abnormal umbilical FVW suggest that, in the latter, a specific 'trigger' might compromise trophoblastic invasion and thymic development; however, some kind of alteration of the immune system might occur in all SGA fetuses.

The thymic-thoracic ratio in fetal heart defects: a simple way to identify fetuses at high risk for microdeletion 22q11

OBJECTIVES

To establish reference ranges for the fetal thymic-thoracic ratio (TT-ratio) and to compare results with those from fetuses with congenital heart defects (CHD) with and without microdeletion 22q11 (del.22q11), a condition known to be associated with a hypoplastic thymus.

METHODS

TT-ratio was defined as the quotient of the anteroposterior thymic to the intrathoracic mediastinal diameters measured in the three vessels and trachea view. This ratio was measured in a prospective cross-sectional study of 302 normal healthy fetuses between 15 and 39 weeks' gestation. The study group comprised two groups: one group (CHDn) consisted of 90 fetuses with CHD and a normal karyotype with no del.22q11 and the other group (CHD(22)) included 20 fetuses with CHD and a normal karyotype but with proven del.22q11.

RESULTS

The TT-ratio of the normal fetuses did not show any statistically significant change during gestation, with a mean value of 0.44. The values of all 90 fetuses of the CHDn group were within the normal range and no different from normal fetuses. However, 19 of the 20 (95%) fetuses in the CHD(22) group had a significantly smaller TT-ratio (P < 0.001) compared with both the CHDn group and the normal fetuses, having a mean value of 0.25.

CONCLUSIONS

The TT-ratio is reliable and easy to obtain during fetal echocardiography. Fetuses with CHD and a low TT-ratio can be considered at high risk of having microdeletion del.22q11.