A 1-year-old female presented with dysmorphic facies, hypotonia, and developmental delay.

Sagittal T1w MRI brain showing
a large posterior fossa hypointense lesion
with cerebellar hypoplasia
Axial T1w image showing the
anterior extent of the lesion and a positive
“molar tooth sign”
Axial T2w image showing
a positive “molar tooth sign”


Joubert syndrome.


Joubert syndrome is a genetic disorder characterized by the absence or underdevelopment of the
cerebellar vermis and malformation of the brain stem. Because of the lack of normal decussation of
the superior cerebellar fiber tracts, the mid-brain gives the characteristic “molar tooth sign”.
Patients usually present with ataxia, hypotonia, nystagmus, dysmorphic facies, and developmental


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