The natural history of ventriculomegaly and tonsillar herniation in children with posterior fossa tumours - An MRI study

Objective: Posterior fossa tumours in children predispose to hydrocephalus, although the natural history is unclear and the need for drainage of the ventricles is controversial. We report on the natural history of ventriculomegaly and tonsillar herniation, as seen on serial MRI scans in children with posterior fossa tumours. Results: Eighty-nine children with posterior fossa tumours were reviewed retrospectively. Overall, 18 (20%) patients required permanent cerebrospinal fluid (CSF) drainage in the form of a ventriculoperitoneal shunt (n = 15) or third ventriculostomy (n = 3). On pre-operative MRI scan, the ventricular size was assessed by measurement of the ventricular index (VI) and 59 patients (66%) had a VI greater than 0.4. There was a progressive decrease in the mean VI from pre-operative to post-operative MRI scans and beyond 3-9 months after surgery, the mean VI was less than 0.4 (p = 0.0001). Patients requiring permanent CSF drainage had a greater VI pre-operatively and at 3-9 months post-operatively (p < 0.05). On pre-operative MRI scan, 75 patients (84%) had greater than 5 mm herniation of the cerebellar tonsils below the level of the foramen magnum. There was a progressive decrease in the mean tonsillar herniation from pre-operative to post-operative MRI scans, with time (p = 0.0001), although this did not relate to the need for CSF drainage. On multivariate analysis, the need for permanent CSF drainage was associated with pre- and intral-operative CSF drainage (odds ratio = 23.3; p = 0.0001) and incomplete surgical excision of tumour (odds ratio = 7.7; p = 0.006). Conclusions: Hydrocephalus and tonsillar herniation are common in children with posterior fossa tumours, although post-operatively there is a natural tendency for it to resolve and only a fifth of the patients needed permanent CSF drainage. We recommend selective drainage of CSF in children with posterior fossa tumours. Patients at risk are those with severe symptoms at presentation, needing perioperative CSF drainage and those with subtotal resection of tumour. Copyright (C) 2003 S. Karger AG, Basel.