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

CSF made inside the brain has to get back into the blood somehow, and that job belongs to small finger-like projections of the arachnoid membrane called arachnoid villi. The question asks which venous sinus they mainly poke into.

1. Superior sagittal sinus: this sinus runs along the top midline of the skull, right next to the subarachnoid space over the brain's surface. Arachnoid villi cluster here in the largest numbers, especially in its side pouches called venous lacunae, making it the main drainage route for CSF.
2. Inferior sagittal sinus: sits deep along the free edge of the falx cerebri and carries much less CSF drainage, with few villi present.
3. Straight sinus: mainly drains deep venous blood from structures like the great cerebral vein, not a major site for arachnoid villi.
4. Transverse sinus: carries blood onward toward the internal jugular vein but is not where villi concentrate.

Since the space above the brain sits closest to the superior sagittal sinus, that is where most of the CSF drains through the arachnoid villi.

Let's summarize:

• Arachnoid villi are one-way channels that drain CSF into venous blood.
• They are densest along the superior sagittal sinus, the sinus closest to the CSF-filled space over the brain.

So the correct answer is the superior sagittal sinus.