Question

The arachnoid villi responsible for CSF absorption protrude mainly into the:

• A. Superior sagittal sinus
• B. Inferior sagittal sinus
• C. Straight sinus
• D. Transverse sinus

Hint:

Arachnoid villi cluster mainly along the superior sagittal sinus, the main CSF drainage route.

Answer 1

The Correct Option is A

Step 1: Recall what arachnoid villi do.
Arachnoid villi, and their larger clusters called arachnoid granulations, are small projections of the arachnoid membrane that push through the dura mater into the venous sinuses. They act as one-way valves that let cerebrospinal fluid (CSF) drain from the subarachnoid space into the venous blood.

Step 2: Recall where they are found in the largest numbers.
Arachnoid villi are scattered along several dural sinuses, but they are most numerous and most prominent along the superior sagittal sinus, especially near its lateral extensions called the venous lacunae, which run along the top of the brain in the midline.

Step 3: Explain why this location makes sense.
CSF flows from the ventricles into the subarachnoid space that surrounds the brain, and the space over the top of the cerebral hemispheres sits right next to the superior sagittal sinus. This makes the superior sagittal sinus the most convenient and most heavily used route for CSF to drain back into the bloodstream.

Step 4: Rule out the other options.
The inferior sagittal sinus, straight sinus, and transverse sinus do carry venous blood from the brain, but arachnoid villi are sparse along them compared with the dense concentration seen along the superior sagittal sinus.

Final Answer:
Arachnoid villi are most concentrated along, and drain CSF mainly into, the superior sagittal sinus.
\[ \boxed{\text{Superior sagittal sinus}} \]