Rhesus macaque as an animal model for posterior fossa syndrome following tumor resection.

BACKGROUND/AIMS Posterior fossa tumors are the most common brain tumors in children. Surgeons usually remove these tumors via a midline incision through the posterior vermis of the cerebellum. Though often effective, this surgery causes hypotonia, ataxia, oculomotor deficits, transient mutism, difficulty in swallowing and nausea. To date, there is no animal model that mimics these complications. We found that the rhesus macaque is a good model for the consequences of this surgery. METHODS We made a midline incision through the cerebellar vermis of one monkey to mimic the posterior fossa surgery. Then, we closely monitored the monkey for deficits following the surgery. RESULTS In the first few days, the monkey exhibited nausea, hypotonia, ataxia, difficulty in swallowing and an absence of vocalization. At 28 days, we recorded eye movements and found severe deficits in the accuracy of rapid eye movements and smooth pursuit of a target. Additionally, the animal had trouble fixating and a rightward-beating nystagmus. Oculomotor signs persisted until we sacrificed the animal 99 days after surgery, but the other effects resolved by 37 days. CONCLUSION Our surgery in a monkey caused the same postsurgical signs observed in humans. We expect to use this model to improve the posterior fossa surgery methods.