• Aqueductal stenosis
• Chiari I malformation
• endoscopic third ventriculostomy
• hydrocephalus
• syringomyelia
• tonsillar herniation
• neurosurgery

The combination of Chiari I malformation (CM), tonsillar herniation (TH), syringomyelia (SM) and obstructive hydrocephalus (HCP) is a rare condition.1 Endoscopic third ventriculostomy (ETV) has been reported as therapy in a case of associated TH and HCP,2 and the resolution of combined CM and SM was first reported in 1996. Numerous publications postulate a developmental volume reduction of the posterior fossa as the cause of TH in CM type 1.1

By contrast, our MRI series illustrates the generation of a cerebellar herniation and formation of SM due to an untreated long-standing triventricular obstructive HCP.

There are only a few case reports or small series demonstrating the successful use of ETV in this syndrome pattern.2–4 The successful application of ETV, however, provides strong evidence for the primary role of HCP in the development of TH and SM.2

Our case underscores the primary role of a long-standing non-communicating HCP in the development of a TH and SM formation, which can subsequently be treated with ETV.