Homolateral hemiparesis as an early sign of cerebellar mass effect.

A patient with Wallenberg's syndrome and an inferior cerebellar infarction developed progressive hemiplegia ipsilateral to the infarction as cerebellar edema emerged. An MRI showed diagonal displacement of the medulla with impaction of the pyramids against the clivus; the hemiplegia resolved after posterior fossa decompression. In the pathologic specimen, the pyramids were flattened and showed small subpial ischemic lesions. Progressive ipsilateral hemiparesis in the setting of cerebellar infarction is an early sign of posterior fossa mass effect similar to the Kernohan's notch phenomenon.

Flaccid quadriplegia from tonsillar herniation in pneumococcal meningitis.

A young woman with fulminant pyogenic meningitis became quadriplegic, areflexic and flaccid due to herniation of the cerebellar tonsils and compression of the upper cervical cord. This state of spinal shock was associated with absent F-waves. Intracranial pressure was greatly elevated and there was an uncertain relationship of tonsillar descent to a preceding lumbar puncture. Partial recovery occurred over 2 years. Tonsillar herniation can cause flaccid quadriplegia that may be mistaken for critical illness polyneuropathy. This case demonstrates cervicomedullary infarction from compression, a mechanism that is more likely than the sometimes proposed infectious vasculitis of the upper cord.