Aggressive screening of patients with blunt head and neck trauma identified an incidence of BCVI in 1.03% of blunt admissions. Early identification, which led to early treatment, significantly reduced stroke rates in patients with VAI, but provided no outcome improvement with CAI. More encompassing screening may be required to improve outcomes for patients with CAI. However, less-invasive diagnostic techniques (CTA and MRA) are inadequate for screening. Technological advances are necessary before abandonment of conventional angiography, which remains the standard for diagnosis.
A prospective study was performed in 340 obstetric sonograms to evaluate the sonographic characteristics of the fetal thymus. The thymus was identified as a homogeneous structure in the anterior fetal mediastinum in 251 cases (74%). The thymus was categorized as either hyperechoic, isoechoic, or hypoechoic relative to fetal lung. Seventy one of 115 cases (62%) prior to 27 weeks gestation were hyperechoic relative to fetal lung whereas T he normal thymus is relatively large at birth and is easily visible with a standard chest radiograph or computed tomography. 1 Although the appearance of the infant thymus has been described extensively using several imaging modalities including ultrasound, 2 .3 we know of no report describing the sonographic appearance of the fetal thymus. The purpose of this paper is to describe the sonographic appearance of the normal fetal thymus and to report our experience with imaging it.
METHODSWe prospectively evaluated the fetal thymus in 340 consecutive normal obstetric sonograms between 14 weeks gestation and term. Dating of each pregnancy was based on multiple fetal growth parameters, 4 earlier ultrasound if available, or reliable menstrual history. The frequency of sonographic visualization of the thymus was assessed. Only if well-defined borders could be seen be-
The sagittal sign for sonographic prediction of fetal gender in the early second trimester is described and its sensitivity and accuracy evaluated. One hundred eighty-four ultrasound examinations with gestational ages between 10 weeks and 20.5 weeks were performed in 165 patients over a three month period. Of the 165 patients included in this prospective study, the gender of the fetus in 105 patients was known as a result of amniocentesis or chorionic villus sampling. These 105 patients with known results were used to compare gender prediction based on conventional views with prediction based on the sagittal sign. The results of this study reveal the superiority of the sagittal view for predicting gender in the gestational age group of 14 weeks to 20.5 weeks.
To determine the embryonic size at which cardiac activity is always seen in a normal early pregnancy, 398 endovaginal sonograms were evaluated in which the gestational sac contained a yolk sac and/or embryo of less than or equal to 12 mm in crown-rump length (CRL). In the 99 sonograms in which there was a yolk sac but no identifiable embryo, cardiac activity was absent in 75; 58 of these pregnancies progressed normally. Of the 299 sonograms where there was an identifiable embryo with CRL less than or equal to 12 mm, cardiac activity was absent in 31; 29 of these were proven to be failed pregnancies. In two cases the pregnancy progressed normally; the CRL was 2 mm in one case and 4 mm in the other. We conclude that once an embryo is seen by endovaginal sonography, the absence of cardiac activity usually indicates embryonic demise. However, when cardiac activity is absent, one should refrain from definitively diagnosing embryonic demise, based on a single sonogram, if the CRL is less than 5 mm.
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