Fetal Situs, Isomerism, Heterotaxy Syndrome: Diagnostic Evaluation and Implication for Postnatal Management

Abstract

A hallmark of vertebrate anatomy is asymmetry of structures, especially internal organs, on the left and right side of the body. Heterotaxy syndrome is the combination of correct-sided, and incorrect-sided organs. The establishment of the left-right axis is an early event in vertebrate embryogenesis. Failure to establish this axis has numerous consequences for later development and can result in a wide range of potential defects. Congenital heart disease is among the more frequent and serious problems. Heterotaxy syndrome is diagnosed prenatally with increasing frequency due to improved screening practices. The key to proper management of fetal heterotaxy syndrome is reliable determination of left and right in the fetus, a thorough understanding of associated defects and comprehensive imaging.

Fetal cardiac abnormalities: Genetic etiologies to be considered

“…Arrhythmia is rare (1.3%). Abnormal stomach position (54.5%), abnormal liver position (45.9%), and intestinal malrotation (27.1%) are common …”

“…As with right isomerism, abnormal stomach position (59.4%), abnormal liver position (32.5%), and intestinal malrotation in 14.2% are common. Hydrops can develop (11.8%), and there are increased rates of fetal death because of the atrioventricular block and sinus node dysfunction . Death during or after surgery occurs in 26.8% of prenatal cases …”

“…In left isomerism, bradyarrhythmia is the only predictor of fetal death, although in newborns, this rhythm does not predict a poor prognosis. Overall, the more important predictors for postnatal death are the presence of pulmonary vein stenosis and noncardiac anomalies …”

“…The inheritance is heterogeneous: most cases are multifactorial. However, molecular diagnosis and familial cases were identified more often than in other cardiac malformations; and single‐gene disorders with autosomal recessive, dominant, and X‐linked inheritance are reported (Table ) …”

“…Abnormal stomach position (54.5%), abnormal liver position (45.9%), and intestinal malrotation (27.1%) are common. 198,200 In the fetus with LAI, cardiac anomalies include AVSD in 59.3%,…”