[LEFT]: The midbrain has a deep interpeduncular cistern, and the superior cerebellar peduncles are very prominent and elongated, making the brainstem at this level look like a molar tooth. This is a classic finding in Joubert syndrome.
[RIGHT]: A comparison "normal" midbrain. However, this patient's brain is not normal at all. Can you find the abnormalities?
Answer
Compare the left and right temporal lobes in [RIGHT] to the [LEFT] image. Look at how many more gyri and sulci there are in the [LEFT] image. The [RIGHT] patient has a diffuse pachygyria (abnormally reduced brain gyrations). Both Joubert syndrome and pachygyria arise from failure of neurons to migrate, although the genes involved and underlying mechanism are different between the two. (NB: Pachygyria is just a descriptive term for less than normal number of gyri, which can be from a large number of causes mostly having to do with abnormal neuron migration.)
