Imaging in the presence of meroanencephaly

Abstract

Meroanencephaly occurs when there is an incomplete open median calvarial defect. This condition, which is in the spectrum of anencephaly, results in ectopic brain without skin covering and a normal foramen magnum. We present a rare case of a female fetus with meroanencephaly referred to our institution at 24 weeks and imaged with both prenatal ultrasound and MRI, demonstrating an open neural tube defect in the high parietal area and lack of visualization of the supratentorial ventricular system. Postnatal the child survived and went on to require antibiotic therapy and closure of the defect without cerebral spinal fluid diversion but demonstrates severe permanent neurologic deficits.

Keywords: Anencephaly spectrum; Fetal MRI; Meroanencephaly; Neural tube defect.

Fig. 1

Meroanencephaly with imaging in a female fetus at 24 weeks and 6 days. A: Sagittal ultrasound demonstrates a defect in the calvarium with herniation of dysmorphic tissue through the defect (arrow). No skin covering suggested. B: Sagittal T2-SSFSE image from fetal MRI demonstrates similar findings of midline calvarial defect, herniation of disorganized tissue (arrow) and no apparent skin covering. C: Axial T2-SSFSE image from fetal MRI shows lack of lateral ventricles, germinal matrix and sulcation.

Fig. 2

Postnatal imaging of meroanencephaly of same patient from Figure 1 at 10 days of life. A: Sagittal T1 image shows median calvarial defect in area of posterior fontanelle with herniation of disorganized tissue and CSF (solid arrow). High signal material outlining defect (dotted arrows) were dressings over the open tissue. The brainstem is stretched and pulled into the defect with the curved arrow representing the midbrain. The posterior fossa is distorted but there is normal development of the cerebellum and lower brainstem. B: Axial T2-FSE MRI again demonstrates lack of ventricular system with complete effacement of the extra-axial CSF spaces and disorganized supratentorial brain.

Fig. 3

Prenatal and Postnatal Meroanencephaly. A: Sagittal T2-SSFP image from prenatal MRI at 29 weeks and 6 days in a female fetus showing midline parietal calvarial defect with herniation of dysmorphic tissue without skin covering (arrow). Notice lack of midline anatomy or visualized ventricles. B: Postnatal T2-FSE MRI of the same patient on day of life 1 showing similar findings with arrow again denoting open neural tube defect.