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Reproductive/Endocrine Imaging

E2265. First Trimester Fetal Malformations: A Review of Sonographic Findings and Screening Evaluation

Josifoski D,  Rheinboldt M. Henry Ford Hospital, Detroit, MI

Address correspondence to M. Rheinboldt (mrheinbold@yahoo.com)

Background Information: Sonographic imaging of the uterus during the first trimester is widely performed, both in the emergent and outpatient settings, not only for confirmation of intrauterine pregnancy but also for the evaluation of abnormal bleeding or in the setting of pelvic pain. It is estimated that between 50% and 70% of fetuses that undergo spontaneous abortion harbor underlying genetic abnormalities. In this regard, there is growing awareness and attention paid to detecting a range of potential early anatomic malformations. Measurement of nuchal translucency between 11 and 14 weeks in conjunction with maternal serum panel testing is a widely used screen, not only for trisomy 21 but also other aneuploidies. Additionally, cardiac, neural, skeletal, genitourinary, and body wall defects may be detected, either in isolation or as harbingers of more complex multisystem malformations. Awareness of the potential gamut of imaging features as well as normal developmental appearances allows timely and appropriate referral for genetic testing and obstetric follow-up.

Educational Goals/Teaching Points: The goals of this exhibit are to present a review of potential structural abnormalities detectable in the first trimester as well as their prognostic implications and review normal imaging features, including early cranial development and expected ventricular size, timing and appearance of bladder and renal development, as well as physiologic midgut herniation, which may be potential confounders in imaging evaluation. We will discuss normal and pathologic biometrics and genetic implications regarding nuchal fold thickness and associated structural defects.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: First trimester detection of absent cranial ossification as part of the acrania and anencephaly spectrum may be problematic on midsagittal imaging; however, loss of frontal calvarial development is observable with careful attention on axial and coronal plane imaging. Though typically noted in second trimester screens, recognition of calvarial and brain maldevelopment in conjunction with spina bifida, namely the lemon and banana signs and ventriculomegaly is also possible in the late first trimester. Absent nasal bone ossification may be noted in up to 75% of trisomy 21 fetuses between 11–14 weeks. Nuchal increased translucency is observed not only in 75% of fetuses with trisomy 21 but also serves as a marker for other aneuploidies including trisomy 13 and 18 and Turners syndrome as well as other syndromic structural defects. Omphalocele and gastroschisis detection is difficult due to physiologic herniation of bowel between 8–10 weeks and is typically not made before 12 weeks; however, careful attention to hepatic and stomach bubble displacement may allow earlier omphalocele identification.

Conclusion: Both a thorough knowledge of and attention to the gamut of potentially detectable early fetal structural anomalies will allow timely and appropriate patient referral for high-risk screening.