Magnetic Resonance Imaging (MRI) Practice Test

Pathology associated with the dilation of the third ventricle while the fourth ventricle remains unaffected is likely related to which structure?

1. Cerebral aqueduct

2. Choroid plexus

3. Interventricular foramen

4. Corpus callosum

The correct answer is: Cerebral aqueduct

The dilation of the third ventricle while the fourth ventricle remains unaffected is typically indicative of an obstructive pathology that specifically affects the cerebral aqueduct, also known as the aqueduct of Sylvius. This structure connects the third ventricle to the fourth ventricle and is a key pathway for the flow of cerebrospinal fluid (CSF). When there is a blockage or obstruction at the level of the cerebral aqueduct, CSF cannot flow from the third to the fourth ventricle. As a result, fluid accumulates in the third ventricle, causing it to dilate, while the fourth ventricle may remain normal in size since the obstruction prevents any changes in pressure or fluid dynamics from being transmitted beyond that point. This condition is often seen in cases of aqueductal stenosis or in other conditions that compress or obstruct the aqueduct. The other structures listed are not directly involved in the flow between these two ventricles. The choroid plexus produces cerebrospinal fluid but does not regulate its flow; the interventricular foramen connects lateral ventricles to the third ventricle but does not impact the fourth; and the corpus callosum is a major white matter structure that connects