Which of the following is NOT a mechanism by which hydrocephalus can develop?

• A. Increased CSF production
• B. Impaired CSF flow
• C. Impaired CSF reabsorption
• D. Increased CSF absorption

Answer: (D)

Hydrocephalus happens when CSF dynamics become imbalanced—production, flow, and absorption all have to be in harmony. Overproduction of CSF can cause it, though it’s rare (think choroid plexus tumors producing excess CSF). Obstruction to CSF flow leads to accumulation upstream, creating noncommunicating hydrocephalus. When CSF isn’t absorbed properly, such as with impaired function of the arachnoid granulations, CSF builds up in the ventricles, causing communicating hydrocephalus. Increasing CSF absorption, on the other hand, would help clear CSF from the ventricles rather than cause its buildup. So, enhanced absorption is not a mechanism by which hydrocephalus develops.