Abstract
ObjectivesThe 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 designA 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. Results38 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). ConclusionsMRI 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.
Highlights
The fetal thymus is a primary lymphoid organ involved in the development and differentiation of T-cells as part of the fetal immune system [1]
The fetal thymus has been demonstrated to involute in response to intrauterine infection in pregnancies affected by preterm premature rupture of membranes (PPROM) [2,3]
These findings suggest that the fetal thymus gland may be
Summary
The fetal thymus is a primary lymphoid organ involved in the development and differentiation of T-cells as part of the fetal immune system [1]. The fetal thymus has been demonstrated to involute in response to intrauterine infection in pregnancies affected by preterm premature rupture of membranes (PPROM) [2,3]. These findings suggest that the fetal thymus gland may be. ⇑ Corresponding author at: Department of Women and Children’s Health, King’s an early, non-invasive indicator of fetal compartment infection in high-risk pregnancies. There is no direct, non-invasive method to identify fetal compartment infection and clinical markers, including elevated maternal temperature, maternal and fetal tachycardia and uterine tenderness, are used in conjunction with raised maternal inflammatory markers to make this diagnosis [2,4].
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