Figure 1. Normal sulcation. (a) T2 and T1-weighted axial images at 22 weeks gestational age (GA). Note the wide, shallow appearance of the primitive Sylvian fissures. The germinal matrix is visible alongside the atria of the lateral ventricles as a thin band of T1 high and T2 low signal. A broader band of similar signal is seen spreading through frontal white matter between frontal horns and cortex. This is thought to represent migrating cells (arrows). (b) Sagittal T2-weighted image. By 27 weeks GA the parieto-occipital fissure (dashed arrow), calcarine (long arrow) and cingulate (short arrows) sulci are visible.

Figure 2. Normal sulcation. (a) Coronal images at 25 and 30 weeks (same patient). The Sylvian fissures gradually narrow during the third trimester as the opercula form. By 30 weeks the superior temporal sulci (horizontal arrow) have formed. The collateral sulci (vertical arrow) are also visible, above which the hippocampi have started to rotate. (b) Axial images at 23 and 27 weeks. The cerebral cortex at the vertex is featureless in this 23-week-old foetus, but in a different patient the central sulcus is clearly shown at 27 weeks (arrow). (c) Sulcation in a different patient is much more advanced by 35 weeks with development of secondary and tertiary sulci, although still not as complex as at term (see Fig. 15b).

Figure 3. Occipital cephalocoele. Sagittal and axial foetal images at 24 weeks (top row) and a few days after delivery at term (bottom row). There is a superficial soft-tissue mass in the occipital region (long arrows). The brain is normally formed apart from hypoplastic inferior vermian lobules (short arrow). The sagittal postnatal image shows the midline communication through the vault in a typical location just below the venous confluence (dashed arrow). Note adjacent to this is a small, birth-related tentorial subdural haemorrhage (hyperintense on T1). The cephalocoele is clearly shown on the axial image. It consists of a small CSF containing sac and some amorphous soft tissue.

Figure 4. Dandy–Walker malformation. Sagittal and coronal images at 22 weeks. The posterior fossa is enlarged and the tentorium elevated by cystic expansion of the fourth ventricle. There is a very hypoplastic, upwardly rotated vermis (short arrow). A meningeal sac bulges through a defect in the occipital bone just below the venous confluence (long arrow). This is an occipital meningocoele. The coronal image confirms the vermis is predominantly absent and the fourth ventricle enlarged. The atria of the lateral ventricles are also increased in size.

Figure 5. Cerebellar hypoplasia at 33 weeks in a child with trisomy 18. Axial, sagittal and paired coronal images. The cerebellum has formed but is small and consequently the cisterna magna is prominent (arrow). There is no supratentorial malformation, but the subarachnoid space is prominent for gestational age. On the coronal images note the associated bladder outflow obstruction and hydroceles (arrow).

Figure 6. Agenesis of the corpus callosum. (a) Normal corpus callosum at 25 weeks (arrow). (b) Sagittal image at 21 weeks and (c) coronal image at 23 weeks in different patients show absent corpus callosum. The characteristic lateral convexity of the frontal horns shown on the coronal image is the reverse of normal (see Fig. 2a for comparison).

Figure 7. Dysgenesis of the corpus callosum and subependymal heterotopia at 23 weeks. Post mortem confirmed the MRI findings. Axial, coronal and sagittal images. The atria of the lateral ventricles are widened and have irregular margins due to subependymal heterotopia (arrows). Normal germinal matrix does not protrude into the ventricular lumen. The sagittal image shows anteriorly that the corpus callosum has formed (long arrows), but posteriorly that the splenium is absent (short arrow; compare with normal example Fig. 6a).

Figure 8. Two examples of extensive hypoxic ischaemic injury, confirmed at post mortem. (a) Sagittal and coronal T2-weighted images at 22 weeks. The coronal image shows extensive areas of focal cerebral atrophy in both cerebral hemispheres. There is T2 shortening (darker areas) suggesting blood products from haemorrhagic transformation of infarcts. The corpus callosum is absent (compare with Fig. 6). (b) Axial T2-weighted image at 24 weeks shows widespread cortical thinning with ventriculomegaly. Note the round mass arising from over the caudate nucleus and projecting into the lateral ventricle. The coronal T1-weighted image shows the mass to return a high signal confirming that it is a germinal matrix haemorrhage into the ventricle.

Figure 9. Cortical malformation at 24 weeks. Axial image shows abnormal asymmetrical cortical infolding (arrow). MRI and ultrasound also demonstrated agenesis of the corpus callosum (not shown). Both findings confirmed at post mortem.

Figure 10. Agenesis of the corpus callosum and septated interhemispheric cyst. Axial and coronal images at 22 weeks (top row) show absent corpus callosum and large interhemispheric cyst. Confirmed on postnatal MRI (bottom row). A septum is visible in the cyst on pre and postnatal axial images (long arrows). Note on the postnatal axial image the CSF-containing structure on the right is the cyst, not the right lateral ventricle. The coronal images show the ventricle is compressed and displaced below the cyst (arrows).

Figure 11. Septum pellucidum. (a) Cavum septi pellucidi et vergae at 35 weeks GA. This is more prominent than usual, particularly posteriorly, but it does not have any clinical significance. The septal leaves are separated by the cavum but are visible medial to the lateral walls of the ventricles. (b) Absent septum pellucidum with closed lip schizencephaly in the left frontal lobe (compare with normal right side). These are associated in the condition of septo-optic dysplasia. There is focal loss of normal cortical outline and grey–white differentiation in the left frontal lobe (arrows). The dysplastic grey matter lining the cleft causes a focal alteration in the shape of the left lateral ventricle.

Figure 12. Two examples of severe hydrocephalus. Sagittal image at 30 weeks (left). Aqueduct stenosis. First noted on ultrasound at 23 weeks. Initially referred for concerns about holoprosencephaly or hydranencephaly. Born at 37 weeks and VP shunt inserted. Normal development at 6 months. The image shows macrocephaly affecting posture. There is marked supratentorial hydrocephalus with severe thinning of the cerebral mantle. Note a small posterior fossa but no hindbrain ectopia. The aqueduct and fourth ventricle are not enlarged. Axial image at 22 weeks (right). Ultrasound showed severe hydrocephalus. Intraventricular CSF had a particulate appearance suggesting haemorrhage. MRI confirmed hydrocephalus and intraventricular haemorrhage. The ventricular CSF returned a lower signal than subarachnoid CSF (arrow) and there is a fluid–fluid level in the dependent ventricle with low signal precipitant (frontal lobes on left of image). The septum is no longer visible having been severely attenuated by ventricular enlargement.

Figure 13. Presumed hemimegalencephaly (not confirmed). An ultrasound image had shown a large head and dilated right lateral ventricle. On MRI at 23 weeks the right frontal lobe appears enlarged. The right frontal horn is also enlarged and shows the abnormally straight configuration characteristic of this condition.

Figure 14. Enlarging arachnoid cyst. Axial image at 22 weeks (left image) shows a right subtemporal arachnoid cyst. Follow-up axial and sagittal images at 30 weeks (middle and right) demonstrate expansion of the cyst. There is considerable enlargement of the right middle cranial fossa and remodelling of the temporal lobe.

Figure 15. Mild isolated ventriculomegaly. (a) The lateral ventricles appeared large on ultrasound (not shown) and measured 14 mm on this MRI at 27 weeks. (b) A follow-up postnatal MRI at 2 months of age was normal. The apparent ventriculomegaly had resolved. The child showed normal attainment of early developmental milestones. (c) Normal appearance of a different patient at 27 weeks for comparison.

Figure 16. In utero insult causing schizencephaly. Antenatal ultrasound at approx 20 weeks showed only bilateral posterior cerebral oedema (not included). Sagittal and coronal T2-weighted images at 22 weeks (top row) showed the development of atrophy at sites of oedema on earlier ultrasound. Full-thickness clefts have developed in both cerebral hemispheres (arrows). Sagittal T1 and axial T2 are shown from a follow-up MRI image at 3 weeks of age (bottom row). The lateral ventricle is recognizable on the sagittal image (arrow) but the thinned cerebral mantle has collapsed due to large overlying CSF collection. The axial image confirms very large extra-cerebral CSF spaces. There are bilateral clefts in the residual cerebral hemispheres (short arrows), lined by dysplastic cortex, which is also evident in adjacent brain (long arrow). The septum pellucidum is absent. This case demonstrates that not all cases of schizencephaly are genetic; some are acquired in utero. The primary insult could have been ischaemic, infective, or a combination. An even more severe insult might have caused more complete loss of the cerebral hemispheres and produced hydranencephaly.

Figure 17. Dural sinus malformation. A possible arachnoid cyst was seen at the ultrasound examination. A diagnosis of dural sinus malformation with thrombus was made at the MRI examination and confirmed at post mortem. Axial T2 and T1-weighted (top row), sagittal and coronal T2-weighted images (bottom row) at 22 weeks. The T2-weighted axial image shows a triangular extra-axial mass between the occipital lobes with a round area of low signal (also visible on sagittal image). The T1-weighted image shows a high signal confirming haematoma. The sagittal and coronal images show the mass conforms to the shape of the falx cerebri and is restrained by the tentorium cerebelli inferiorly indicating that it is intradural. Note: normal vessels do not show signal void on these sequences.