A study of prenatal ultrasound and postnatal magnetic imaging in the diagnosis of central nervous system abnormalities.

Accurate prenatal diagnosis of central nervous system (CNS) abnormalities is essential in counselling parents, as they are the most common developmental abnormalities causing considerable mortality. Currently, the standard in prenatal imaging is ultrasound scanning (USS). The introduction of fast acquisition magnetic resonance imaging (MRI) has lead to increased diagnostic confidence and information available for parents. Frequently USS initially identifies CNS abnormalities as ventriculomegaly alone. However, it is known that ventriculomegaly is commonly associated with other CNS pathology, which may adversely affect the prognosis. As MRI has superior soft tissue resolution and can be used at any time postnatally, it is expected to identify disorders of myelination that may result from prenatal ventriculomegaly. This study will evaluate the role of MRI as a postnatal imaging tool in patients that had a prenatal USS diagnosis of isolated ventriculomegaly. This was a retrospective review of patient notes and scan reports. The postnatal MRI study group consisted of 9 patients that had been diagnosed initially with prenatal isolated ventriculomegaly on USS, and followed up with postnatal MRI (cases of spina bifida and Dandy-Walker malformations were excluded). Findings from the scan reports were recorded and analysed. Both MRI and prenatal USS gave the same information in 55.6 % of the patients. In the remaining 44.4 %, MRI added to the information provided by the prenatal USS. An interesting finding was that MRI missed a small fluid-filled cyst and an arachnoid cyst in 2 cases. 55.6 % of patients went on to develop other CNS abnormalities prenatally, whereas 33.3 % showed prenatal regression of VM with no other pathology. 11.1 % showed postnatal persistence of isolated VM. As USS has the advantage of being cheap and easy to perform, it will remain as the primary imaging tool in obstetric care. MRI can provide significant additional information that can affect parent counselling, prenatal intervention, and postnatal management. Postnatally, MRI can give some idea of prognosis by evaluating myelination patterns, which is not possible with USS.