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This is an MRI of the brain in a one-week-old

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child that had an abnormal fetal

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MRI and fetal ultrasound,

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we can see massive enlargement of both lateral

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ventricles and the third ventricle.

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But if we go inferiorly,

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the fourth ventricle is nondilated.

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And further confirming our suspicion on the fetal MRI,

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we do not see a cerebellar vermis.

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We see midline continuity of

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the cerebellar hemispheres.

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Sagittal image again shows massive enlargement

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of the lateral ventricles,

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enlargement of the third ventricle,

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distension of the superior aspect of the

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aqueduct of sylvius, but tapering.

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The aqueduct of sylvius tapers,

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and we do not see any patency of

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that caudal to this point.

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This is, therefore, a congenital aqueductal stenosis

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with triventricular hydrocephalus.

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By triventricular,

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I mean the two lateral ventricles in the third ventricle,

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and the fourth ventricle is not dilated.

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Now, while the fourth ventricle is not dilated,

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it's not normal.

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It has an abnormal configuration.

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Now,

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that abnormal configuration is partially because

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these massively enlarged ventricles are distorting

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everything in the posterior cranial fossa.

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But if we look on this axial image,

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we can see the cerebellum in the fourth ventricle

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probably did not develop normally,

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but it's very difficult to tell for several reasons.

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To fully characterize it,

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it's helpful if the child is older,

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the brain is larger,

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and right now, the massively enlarged lateral

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ventricles are impairing our ability to understand

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the normal configuration of the

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postcranial fossa.

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Well, approximately a year later,

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an MRI was performed.

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We can see a ventriculostomy catheter in place.

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The ventricles have come down markedly in size,

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and now we can see there is no cerebellar vermis.

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The posterior margin of the cerebellar hemispheres

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forms this contiguous arc right here,

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continuity between the two cerebellar hemispheres.

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So, this is a case of rhombencephalosynapsis with

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additionally congenital aqueductal stenosis,

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possibly related to incomplete transverse

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migration of the intercolliculi,

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also referred to sometimes as

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mesencephalosynapsis.