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

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CASE STUDY ASUM Ultrasound Bulletin February 2008; 11 (1): 30–35 Fetal intracranial abnormalities in the third trimester – MRI as a useful diagnostic tool Jacqueline Cartmill 1 , Ann Quinton 1 , Michael Peek 2 1 Nepean Centre for Perinatal Care and Research, Level 5 South Block, Nepean Hospital, Penrith, New South Wales 2750, Australia. 2 The University of Sydney, Nepean Centre for Perinatal Care and Research, Level 5 South Block, Nepean Hospital, Penrith, New South Wales 2050, Australia. Correspondence to Mrs Ann Quinton. Email aquinton@med.usyd.edu.au. Fig 1: Sagittal transvaginal (TV) fetal brain USS at 26 weeks 6 days demonstrating anechoic space posteriorly. Fig. 3: Axial TV USS demonstrating preserved falx and difficulty in visualising brain structures due to USS reverberation at 30 weeks gestation. Introduction Ultrasound has many advantages as an imaging modality as it is relatively inexpensive, does not use ionising radiation, and high resolution images are obtained allowing dynamic real time assessment. It is widely employed in prenatal diagnosis and the assessment of fetal anomalies, however, sonographic evaluation of the fetal central nervous system (CNS) can be hindered by the non-specific appearance of some abnormalities, and by technical factors such as maternal obesity and advanced gestational age 1 . Developments in the field of magnetic resonance imaging (MRI), particularly the use of ultra fast image acquisition which minimises fetal motion artefact, have led to its use as a non-invasive, complementary technique in situations where Fig. 2: Axial TV USS demonstrating bilateral anechoic areas posteriorly and preserved frontal brain structures at 30 weeks gestation. the extent of the fetal intracranial anomaly cannot be accurately determined on ultrasound scan (USS). We report three cases of fetal intracranial abnormalities detected late in pregnancy where sonographic visualisation of the structural anatomy of the CNS in the third trimester was found to be inconclusive, and MRI was then used in an attempt to clarify the diagnosis. Case 1 – Hydranencephaly A 41-year-old woman in her second pregnancy, booked late for antenatal care and had a routine fetal anatomy scan performed at 26 weeks 6 days gestation. An intra-cranial abnormality was strongly suspected, although structures were difficult to visualise, even with transvaginal scanning, due to fetal position and gestational age (Figs. 1, 2, 3). Amniocentesis was performed and reported a normal 46XY (male) karyotype and negative polymerase chain reaction (PCR) for cytomegalovirus (CMV) and toxoplasmosis. A fetal MRI was performed, which demonstrated absence of normal cortical mantle apart from a thin rim of tissue in the inferior aspect of the frontal lobe and the inferomedial aspect of the temporal lobes. The thalami, falx, cerebellum and brainstem appeared to be intact. These findings were consistent with hydranencephaly (Figs. 4, 5, 6). Following multidisciplinary discussion regarding the poor prognosis, the patient requested termination of pregnancy. Fetocide was carried out with intracardiac potassium chloride injection at 30 weeks gestation, followed by induction of labour. A stillborn male infant was delivered weighing 1240 g. Postmortem examination confirmed the diagnosis of hydranencephaly. 0 ASUM Ultrasound Bulletin 2008 February 11 (1)
Fetal intracranial abnormalities in the third trimester – MRI as a useful diagnostic tool Fig. 4: Prenatal axial MRI of fetal brain demonstrating hydranencephaly. Fig. 5: Prenatal coronal MRI demonstrating hydranencephaly. Fig. 6: Prenatal sagittal MRI demonstrating hydranencephaly. Note preservation of inferior aspect of frontal lobe and infero-medial aspect of temporal lobes of brain. Fig. 7: USS demonstrating mild lateral ventriculomegaly. Fig. 8: Coronal USS demonstrating absent left cerebral cortex. Fig. 9: Axial USS demonstrating absent left cerebral cortex. Case 2 – Schizencephaly A 16-year-old female in her first pregnancy, presented late for antenatal care. A routine fetal anatomy scan performed at 29 weeks 2 days gestation demonstrated apparent absence of the cerebral cortex on the left side of the fetal brain, with mild right-sided lateral ventriculomegaly (12 mm) (Figs. 7, 8, 9). Amniocentesis was performed and reported a normal 46XY (male) karyotype, and ASUM Ultrasound Bulletin 2008 February 11 (1)
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