Purpose: Fourth ventricular outlet obstruction (FVOO) causes obstructive hydrocephalus. Often, despite high-quality MRI sequences, differentiation between FVOO and communicating (absorptive) hydrocephalus is not easy. We describe our initial experience with five children with suspected FVOO that underwent CT ventriculography (CTV) or cisternography (CTC), to assist with this difficult diagnosis.
Methods: Over 2.5 years, five children with suspected FVOO (5 months-7.5 years old) underwent CTV or CTC. Technical and clinical data were retrospectively collected.
Results: Four children had progressive macrocephaly, and one child had progressive ventriculomegaly. On CTV/CTC, four of five children showed communication between the ventricular system and spinal subarachnoid space or prepontine cistern, as evidenced by passage of contrast material. One child had a FVOO and therefore underwent an endoscopic third ventriculostomy, and is since, symptom and shunt free for 2.5 years.
Conclusion: CT ventriculography in infants, and CT cisternography in elder children, may assist to differentiate between FVOO and communicating hydrocephalus. The importance of these tests is for children with MRI suggestive of FVOO related hydrocephalus, but with no clear demonstration of the obstruction site. The implication of this differentiation may be for deciding between treatment of hydrocephalus with a ventriculoperitoneal shunt or with an endoscopic third ventriculostomy.