Cerebellar tonsillar herniation after weight loss in a patient with idiopathic intracranial hypertension.

Acquired cerebellar tonsillar herniation is a known complication of lumboperitoneal shunt (LPS) for any indication, including idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri.(1) While the underlying pathophysiology of IIH remains unknown, increasing body mass index is a clear risk factor for the development of IIH. We describe an obese patient with IIH unresponsive to LPS who developed symptoms of intracranial hypotension and cerebellar tonsillar herniation after bariatric surgery and a 50-kg weight loss.