Presentation
Reduced fetal cranial biometry
Patient Data
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There is delay of cerebral sulcation for gestational age. There is underdeveloped Sylvian operculisation. The parieto-occipital and calcarine sulci are not seen and would be expected at this stage, particularly in as there is no evidence of ventricular enlargement to account for their absence. In addition, the normal zonal anatomy of the cerebral hemispheres is difficult to identify and this does not appear to be due to motion degradation.
Frontooccipital cerebral hemispheric measurement is below the lower limit of the normal range.
The corpus callosum is present. No abnormality of the cerebellum, brainstem or orbits. No evidence of intraventricular hemorrhage.
Importantly, there is a normal appearance of the ganglionic eminences, which would typiically be enlarged in conditions producing lissencephaly, such as LIS1 gene mutation, dystroglycanopathies, tubulinopathies and mutations of the RELN and ARX genes.
MRI followup was recommended at this stage, to determine whether there was a persistent lag of sulcal development.
Amniocentesis: Normal microarray and negative CMV PCR.
Negative TORCH screen.
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Biometry:
Brain BPD 53 mm 5th - 10th centile
Brain FOD 63 mm < 3rd centile
Bone FOD 77 mm 10th centile
Vermis height 15 mm 50th centile
Vermis AP 9 mm 25th centile
Transverse cerebellar diameter: 31 mm 50th centile
Sulcal development and brain growth have progressed, and this is not consistent with lissencephaly. However, there is persistent substantially reduced hemispheric biometry and consistently normal cerebellar biometry.
In addition, somewhat atypical sulcal development is noted with a convex rather than flat appearance of the insular cortex bilaterally, and lack of visualization of the callosal sulcus and superior temporal sulcus, for which there should be at least early evidence by this gestational age.
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Biometry:
Brain BPD 60 mm <3rd centile for gestational age
Brain FOD 73 mm <3rd centile for gestational age
Bone FOD 83 mm <3rd centile for gestational age
Corpus callosum length 28 mm <3rd centile for gestational age
Vermis height 18 mm 50th centile
Vermis AP 9.8 mm 25th centile
Transverse cerebellar diameter: 40 mm 50th centile.
AP diameter of the pons: 11 mm 50th percentile
As on the previous examinations, there is a substantial disparity between the cerebellar / brainstem biometry and hemispheric biometry with the hemispheres and calvarial dimensions now lying below the 3rd percentile while posterior fossa structures are appropriately grown and on the 50th percentile.
Primary and secondary sulcation are grossly normal.
Postnatal clinical progress: At 6 weeks postnatal the baby’s head circumference was below the first centile for age, and she was failing to fix and follow on visual testing.
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Subtle finding of a simplified gyral pattern. Review the image comparing this case to an age matched normal brain: gyri are present but shallower than normal. The cortex is not thickened and the brain otherwise structurally normal.
Persistent hyperplastic primary vitreous is noted bilaterally, with retinal detachment also suspected on the left. This was not detectable on the prenatal MRI, even in retrospect.
PHPV was confirmed at opthalmologic review and patient underwent a vitrectomy. Adequate development was noted at the 4 month pediatric review.
Case Discussion
Microcephaly with a simplified gyral pattern. This imaging series demonstrates delayed but progressive cerebral development. Small head size became evident progressively on pre-natal imaging, and the head circumference <3SD postnatally confirms the diagnosis of microcephaly.
There were no associated cerebral abnormalities in this case, however microcephaly may be associated with cortical malformations, dysgenesis of corpus callosum and dysplasia or hypoplasia of the brainstem and cerebellum.
Interestingly, the associated bilateral persistent hyperplastic primary vitreous was only evident on the post-natal MRI.