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

Fetal intracranial abnormalities in the third trimester – MRI as a useful diagnostic tool
Fig. 13: Coronal postnatal MRI demonstrating left sided open-lipped
schizencephaly.
Fig.14: Axial postnatal MRI demonstrating left sided cystic mass.
Fig.15: Coronal postnatal MRI demonstrating cystic mass posteriorly.
performed and reported a normal 46XY (male) karyotype
and negative PCR for CMV and toxoplasmosis. Due to the
difficulties with visualising intracranial structures and in
order to determine whether there was any other underlying
aetiology, a fetal brain MRI was performed. The MRI
images were reviewed by both paediatric radiological and
neurosurgical teams and the appearances were felt to be
consistent with a large, inoperable intracranial tumour, with
the unlikely possibility of this being a bleed per se (Figs 18,
19, 20).
Following multidisciplinary discussion and counselling,
planned preterm delivery by caesarean section was
performed in view of the rapidly enlarging head size, with
subsequent palliative care of the neonate. A live male infant
weighing 3280 g was delivered at 31 weeks 5 days gestation
with subsequent peaceful demise at 3 hours, 32 minutes of
age. Head circumference at birth was 48.5 cm, with no other
dysmorphic features noted on external examination.
Postmortem examination was carried out with findings
of severe hydrocephalus with a large subarachnoid haemorrhagic
mass adjacent to the falx cerebri in the region of the
sagittal sinus posteriorly.
Discussion
Compared to USS, MRI techniques have less spatial resolution,
lack real time imaging capabilities, are costly and
less versatile 2 . However, the advantages of MRI are that
it provides a larger diagnostic window allowing total fetal
Fig. 16: Prenatal USS demonstrating large intracranial mass with fine low
level echoes suggestive of a haemorrhage.
Fig. 17: Colour Doppler USS demonstrating no flow within the mass.
imaging with excellent resolution of tissue composition. It
provides visualisation of a precise anatomical plane, allows
easy interpretation of several planes and permits computeraided
reconstruction of multiple planes following a single
study 2 including three-dimensional modelling of the fetal
brain in utero 3 . MRI does not use ionising radiation and at
present, there is no evidence that short term exposure to
electromagnetic fields harms developing fetuses 4,5 .
In using MRI to assess CNS abnormalities of the fetus,
many of the technical artefacts of sound wave transmission
ASUM Ultrasound Bulletin 2008 February 11 (1)