Prenatal magnetic resonance imaging enhances fetal diagnosis

Ultrasound (US) evaluation of some fetal anomalies provides limited information. Anatomic details that affect prognosis and selection for fetal therapy, such as liver herniation and pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) and airway patency in giant neck masses, may be difficult to delineate using conventional sonographic methods. The authors evaluated the utility of prenatal magnetic resonance imaging (MRI) with new ultrafast imaging sequences in the diagnosis and management of fetal anomalies.

From April 1996 to April 1997 45 MRI scans were performed in 31 pregnant women with an US diagnosis of a fetal anomaly. The US diagnoses included CDH, giant neck masses, lung masses, abdominal and pelvic abnormalities, twin anomalies, and central nervous system (CNS) anomalies. The fetuses ranged in age from 18 to 39 weeks' gestation (mean, 28.7 weeks). Using a 1.5-T magnet, a variety of ultrafast imaging sequences were performed including fast gradient-echo, half-fourier single shot turbo spin-echo (Haste) and echo-planar imaging yielding images with T1 to T2 type weighting.

With CDH, MRI demonstrated liver herniation into the chest in 11 of 14 cases. In four cases, US findings had not been definitive. In two cases of CDH detected by MRI, the primary diagnosis by US had been congenital cystic adenomatoid malformation (CCAM). With lung masses, MRI accurately distinguished between CCAM and bronchopulmonary sequestration (BPS). For giant neck masses with potential airway obstruction, MRI scans permitted differentiation of teratoma from cystic hygroma and allowed delineation of fetal airway involvement. The accurate anatomic evaluation facilitated planning for the ex utero intrapartum treatment (EXIT) procedure, a technique for securing the airway while the term fetus is still on placental support. With huge abdominal masses such as enterogenous cyst and lymphangioma, MRI scanning clarified the diagnosis. Fourteen of the 31 (45%) patients underwent fetal treatment after US and MRI evaluation.

Prenatal MRI enhances fetal anatomic evaluation and facilitates perinatal management and family counseling. Ultrafast imaging sequence MRI is helpful to corroborate and refine US diagnoses. Fetal MRI is a valuable adjunct to US for prenatal diagnosis before fetal surgical intervention for selected life-threatening birth defects.