Definition

Marie Joubert described the syndrome in 1968 [18] -69 [19] . It is a rare developmental defect of the cerebellar vermis, with autosomal recessive inheritance. The phenotype is highly variable and may include episodic hyperpnea, abnormal eye movements, hypotonia, ataxia, developmental delay, and mental retardation

Etiology

Unknown.

Prenatal diagnosis

The first ultrasonic diagnosis was made by Campbell in 1984 [20] . The following findings have been found in fetus with Joubert syndrome [21] , [22] :

1. vermian agenesis
2. abnormal cerebellar shape
3. hydrocephalus
4. renal anomalies
5. nuchal lucency [23]

Interestingly there is another report of a fetus in which the vermis was considered abnormal, had a normal postnatal examination and the diagnosis was only made later22 .

These are 9 images from 2 midtrimester exams (3 weeks apart) on a little baby boy. The spine was normal. The fetus was then referred elsewhere where he was considered normal. A CT at birth was also read as normal.

Findings

The images demonstrated a small degree of ventriculomegaly and an abnormal posterior fossa. The first six images do not demonstrate the vermis. Instead there is a great big cleft in between lateral lobes of the cerebellum.

 Image 7 demonstrates a small amount of ventriculomegaly but also notice the appearance of the cerebellum: the "buttock sign" 

            3. Picture 8: mild ventriculomegaly

            4. Picture 9 shows  the cavum of the septi pellucidi, thus excluding dysgenesis of the corpus callosum.

A CT done after birth was read as normal. However, when the child was one year old, a geneticist put together the clinical findings of this baby and obtained a MRI:

Several axial views that demonstrate the absence of the vermis and the “molar tooth” sign (see below)

Coronal views with absence of the vermis and demonstration of the corpus callosum

Sagittal views with absence of the vermis and demonstration of the corpus callosum