Chronic uncal herniation secondary to posterior fossa shunting: case report and literature review.

INTRODUCTION: Chronic herniation syndromes other than tonsillar herniation are not well-recognized. Transtentorial uncal herniation in its chronic form has been reported in only few case reports (Horowitz et al., J Neuroimaging 12:78-79, 2002; Naidich et al., Radiology 158:431-434, 1986; Ng and Valiante, J Clin Neurosci 16:944, 2009; Ng and Valiante, J Clin Neurosci 16:984, 2009). We hereby illustrate a case with this rare finding, including MR imaging, and analyze this phenomenon. CASE REPORT: A 15-year-old girl had a resection of a cerebellar pilocytic astrocytoma at 5 years of age. Two months later, she underwent a cystoperitoneal shunt for persistent headache and pseudomeningocele, secondary to an enlarging cyst at the tumor bed. Subsequently, her shunt was upgraded to a more conservative valve following clinical evidence of over drainage. This was also associated with imaging compatible with bilateral uncal herniation. After the procedure, she had relief of symptoms.
CONCLUSION: We conclude that a negative pressure gradient in the posterior fossa, relative to the supratentorial compartment, is the etiology of the chronic uncal herniation in our patient. Comparing the case reports in the literature with our case, we postulate that chronic uncal herniation is a complication of shunting of a posterior fossa fluid cavity in children, many of them with Dandy-Walker syndrome and/or other cerebellar cystic formations. The treatment priority at presentation should be to rule out shunt malfunction. In the event of association with clinical over-drainage syndrome, there may be a role for changing the shunt system into a more conservative drainage combination.