Unilateral atrophy of a cerebellar hemisphere occurring as a sequela of ischemic or destructive injury of the contralateral cerebral hemisphere is uncommon in children ⁽²³⁾. These findings are often found in children with a history of extreme prematurity, perinatal intracranial hemorrhage, and recurrent seizures. The most likely mechanism is transneuronal hypometabolism associated with interruption of the cerebropontine-cerebellar pathway. The immature cerebellum is presumably dependent on the trans-synaptic excitatory pathways for normal growth and development. Another possible cause of cerebellar atrophy is seizure-related trans-synaptic excitotoxic cell damage. MRI shows sequela of neonatal intracranial hemorrhage with atrophy of the contralateral cerebellar hemisphere (Figure 9).

Figure 9. A 19-year-old female with crossed cerebellar atrophy and history of recurrent seizures and perinatal intracranial hemorrhage.

A. T2WI shows right cerebral atrophy with ventricular dilatation representing a sequela of perinatal intracranial hemorrhage.

B. T2WI through posterior fossa shows atrophy of contralateral cerebellar hemisphere. Wallerian degeneration of ipsilateral brain stem is also seen (arrow).