Spinal lipoma misinterpreted as a meningomyelocele on antenatal MRI scan in a baby girl

Clinical Significance of Prenatal and Postnatal Heavily T2-Weighted Magnetic Resonance Images in Patients with Myelomeningocele

PURPOSE

To compare the utility and limitations of prenatal magnetic resonance (MR) imaging using half-Fourier acquisition single-shot turbo spin-echo (HASTE) with postnatal heavily T2-weighted imaging (hT2WI) for the evaluation of central nervous system abnormalities associated with myelomeningocele (MMC).

METHODS

Sixteen patients with MMC who had undergone pre- and postnatal MR imaging were included in this study. MR imaging, including HASTE, was undertaken in the 3rd trimester, and hT2WI was performed immediately after delivery. The precision with which each could distinguish MMC, hindbrain herniation and ventriculomegaly was compared retrospectively.

RESULTS

The skin defects and MMC sacs were clearly visible on prenatal HASTE images, although it was difficult to identify precisely the level of MMC compared with postnatal hT2WI, in which the detailed anatomical relationships of the spinal cord, neural placode and ventral nerve roots were evident in every case. Hindbrain herniation could be visualized on prenatal HASTE images, although its severity was difficult to evaluate because of the small size of the structures and neck flexion; again, the resolution was superior on postnatal hT2WI. For hydrocephalus, there were no significant differences in the diagnostic precision and ability to grade the severity between pre- and postnatal imaging.

CONCLUSION

Prenatal HASTE imaging permits the diagnosis and understanding of the gross anatomy of MMC and associated hindbrain herniation and ventriculomegaly, but postnatal hT2WI is superior for evaluating detailed anatomy.

Comparison of prenatal and postnatal MRI findings in the evaluation of intrauterine CNS anomalies requiring postnatal neurosurgical treatment

AIM

To assess the diagnostic capability of fetal magnetic resonance imaging (MRI) in children suspected antenatally to harbor central nervous system (CNS) defects that require immediate postnatal neurosurgical treatment.

MATERIALS AND METHODS

Between 2003 and 2005, 13 fetal MRI scans were performed in mothers suspected to have fetuses with congenital CNS defects that would require surgery soon after birth. Comparisons between antenatal and postnatal scans were made with emphasis on diagnostic accuracy of antenatal examinations.

RESULTS

All mothers were scanned using heavily T2-weighted fat-saturated sequences, allowing rapid acquisitions to avoid movement artefacts. Imaging quality was satisfactory in all patients. Diagnoses made antenatally were: myelomeningocele in seven, meningocele in one, diastematomyelia in one, occipital meningocele in one, and isolated hydrocephalus in three children. Of the seven children with antenatal diagnosis of myelomeningocele, one proved to have spinal lipoma postnatally. The patient who antenatally was diagnosed with meningocele proved to have spinal lipoma postnatally. These two were early antenatal MR scans. Antenatal diagnosis of hydrocephalus was made in five of the six confirmed myelomeningocele patients, which was verified postnatally. Antenatal diagnosis of Chiari II malformation was made in all six confirmed myelomeningocele patients. The antenatal diagnoses of occipital meningo-encephalocele and isolated hydrocephalus were verified postnatally. Antenatal diagnosis of diastematomyelia was not verified postnatally.

CONCLUSION

Fetal MRI scanning is an effective, noninvasive method of assessing in-utero CNS abnormalities. The diagnostic accuracy has improved to allow prediction of clinical outcome and counseling for possible treatment, but is not perfect yet to allow counseling for termination of pregnancy.

Fetal surgery for neural tube defects

Open spina bifida remains a major source of disability despite an overall decrease in incidence. It is frequently diagnosed prenatally and can thus - potentially - be treated by fetal surgery. Animal studies and preliminary human studies strongly suggest that at least a portion of the neurological abnormalities seen in these patients are secondary, and occur in mid-gestation. It is estimated that approximately 400 fetal operations have now been performed for myelomeningocele world wide. Despite this large experience, the technique remains of unproven benefit. Preliminary results suggest that fetal surgery results in reversal of hindbrain herniation (the Chiari II malformation), a decrease in shunt-dependent hydrocephalus, and possibly improvement in leg function, but these findings might be explained by selection bias and changing management indications. A randomized prospective trial (the MOMS trial) is currently being conducted by three centers in the United States, and is estimated to be completed in 2009.