Today in class we had a question about hydrocephalus in dwarfism. There are lots of articles and websites that mention the fact that you see hydrocephalus in dwarfism (especially achondroplasia, the most common type of dwarfism). It took a bit of searching to find the actual cause of the hydrocephalus, though. It turns out that in achondroplasia, the skull develops abnormally, and the foramen magnum is abnormally narrow (or stenotic), which may restrict the CSF flow at that point. Here’s a drawing to help you visualize the location of the foramen magnum in relation to the brainstem and ventricles:
Despite the misspelling of “magnum” the drawing is pretty accurate. You can see how having a tighter enclosure around the spinal cord/brainstem at that level would obstruct the flow of CSF, leading to hydrocephalus. This type of hydrocephalus doesn’t fall perfectly into the “noncommunicating” category (since the block isn’t truly inside the ventricular system), but it’s closer to noncommunicating than it is to communicating (in which the block is totally outside the ventricular system, the most common place being the meninges).
I hope that helps and doesn’t confuse things even further! Let me know if you have questions.