Teaching Case

20-year-old pregnant woman. Intrauterine MRI

An obstetric ultrasound examination at the 24th week of gestation revealed enlarged lateral ventricles, and a small posterior fossa in association with lumbosacral meningocele. The woman was referred for intrauterine MRI. On MRI, the HASTE (half-Fourier single-shot turbo spin echo) was used to obtain images of the fetus in three imaging planes. Total acquisition time was 33 seconds (11 sec for each). Slice thickness was 4 mm.

Fetal central nervous system, especially the brain, can be examined by newer fast imaging sequences including the HASTE sequence, providing high-quality images. In the current fetus lateral ventricles were dilated associated with prominent dilatation of the occipital horns (sometimes referred to as colpocephaly), and the posterior fossa was small. A lumbosacral meningocele was shown. These features were consistent with Chiari II malformation. The pregnancy was terminated, and the diagnosis was confirmed. Chiari II malformation is a severe and complex anomaly. Current hypotheses on pathogenesis of Chiari II malformation stress the role of myelomeninigocele and consequent CSF leaking on the origin of cerebellar squeezing, as in all the Chiari II patients there is meningomyelocele, usually in the lumbar spine (without meningomyelocele an alternative diagnosis such as rhombencephalosynapsis could be considered). It should be remembered that there is possibility of fetal surgery for meningomyelocele to prevent the formation of cerebellar herniation.