Volume 11 Issue 1 (February) - Australasian Society for Ultrasound ...

Fetal intracranial abnormalities in the third trimester – MRI as a useful diagnostic tool
the cyst is lined by white matter. This case highlights the
limitations of USS and MRI prenatally, and demonstrates
how it may not be possible to make a definitive diagnosis
until after birth.
In the case of massive subarachnoid haemorrhage, the
resulting compression of the fetal brain made ultrasound
assessment of CNS anatomy difficult, and MRI was performed
to ascertain whether the haemorrhage was the
primary event responsible for the rapidly enlarging head
size, or whether the bleed was secondary to some other
underlying abnormality such as a tumour. The antenatal
MRI images were subsequently reviewed by paediatric
radiologists and neurosurgeons, and the area of haemorrhage
(which was subsequently confirmed on post-mortem
examination) was mistakenly reported as an intracranial
tumour. This case demonstrates the advantages of real time
imaging and dynamic assessment achieved with ultrasound,
and the importance of combining information obtained from
all imaging modalities to increase diagnostic accuracy.
In summary, fetal MRI has been reported as a valuable diagnostic
aid when investigating intracranial pathology, and it had
a major impact on the decision making processes and eventual
pregnancy outcomes in all three cases we have reported. Fetal
MRI has only recently been undertaken in our institution and
perhaps this at least partially accounts for why there was a
minor diagnostic discrepancy in one case (schizencephaly) and
misdiagnosis in another (intracranial haemorrhage).
Acknowledgements
The authors gratefully acknowledge the assistance of
the medical imaging department at Nepean Hospital and
Professor Albert Lam at Westmead Children’s hospital.
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ASUM Ultrasound Bulletin 2008 February 11 (1)