Early First-Trimester Diagnosis of Iniencephaly at 10 Weeks of Gestation: Ultrasound and Pathologic Correlation

Abstract Iniencephaly is a rare and uniformly lethal neural tube defect characterized by fixed retroflexion of the fetal head, absence of the neck, and severe cervico-occipital malformations. Prenatal diagnosis is usually established in the late first or second trimester, with early first-trimester detection being uncommon. We report a case of iniencephaly diagnosed at 10 weeks 4 days of gestation during routine obstetric ultrasound. Sonographic findings included persistent fetal head hyperextension, nonvisualization of the cervicovertebral junction, absent neck, and abnormal configuration of posterior brain structures. The diagnosis was confirmed on gross examination following termination of pregnancy. This case highlights the importance of systematic evaluation of fetal head posture and craniocervical anatomy during early first-trimester ultrasound to facilitate timely diagnosis, counseling, and informed decision-making in lethal fetal anomalies.