Dural sinuses are formed between which layers?

• A. Pia mater and arachnoid
• B. Periosteal dura and meningeal dura
• C. Choroid plexus and dura
• D. Subarachnoid space and dura

Answer: (B)

Dural venous sinuses form in the gaps where the two layers of the dura mater separate—the periosteal (endosteal) dura lining the skull and the inner meningeal dura covering the brain. Normally these layers are fused, but where they split, endothelial-lined channels become sinuses that collect venous blood from the brain (and CSF via arachnoid granulations) and drain toward the internal jugular veins. The other structures mentioned aren’t sites of these sinuses: the delicate pia and arachnoid lie closer to brain tissue, the choroid plexus is inside the ventricles, and the subarachnoid space and dura are separated by arachnoid, not forming the sinus.