dural venous sinus

**Structure:** Dural venous sinuses are trabeculated, valveless, endothelium-lined channels with no smooth muscle in their walls, so they cannot constrict. They lie between the periosteal (outer) and meningeal (inner) dural layers. Cerebral veins, diploic veins, and emissary veins drain into them. CSF is reabsorbed into the superior sagittal sinus via arachnoid granulations.

**Major sinuses and flow:** - *Superior sagittal sinus:* runs along the convex edge of the falx cerebri. It receives CSF through arachnoid granulations and drains into the confluence of sinuses. - *Inferior sagittal sinus:* runs along the free edge of the falx cerebri. It joins the great cerebral vein of Galen to form the straight sinus. - *Straight sinus:* runs along the junction of the falx cerebri and tentorium cerebelli and drains to the confluence of sinuses. - *Confluence of sinuses (torcular Herophili):* receives the superior sagittal and straight sinuses and drains into the transverse sinuses. - *Transverse sinuses:* run in the posterolateral tentorium cerebelli and drain into the sigmoid sinuses. - *Sigmoid sinuses:* S-shaped, and continue as the internal jugular vein through the jugular foramen. This foramen also carries CN IX, X, and XI. - *Cavernous sinuses:* paired, on either side of the sella turcica. They drain into the superior and inferior petrosal sinuses. - *Superior petrosal sinus:* drains to the transverse sinus. - *Inferior petrosal sinus:* drains to the internal jugular vein. - *Others:* sphenoparietal, occipital, and basilar sinuses.

**Cavernous sinus (high-yield):** - *Contents in the lateral wall:* CN III, IV, V1, and V2. - *Contents passing through the sinus:* CN VI and the internal carotid artery with its sympathetic plexus. CN VI is the most commonly affected nerve because it lies free within the sinus. - *Connections:* it receives the superior and inferior ophthalmic veins, the sphenoparietal sinus, and the superficial middle cerebral vein. It communicates with the contralateral sinus through intercavernous sinuses. - *Infection route:* the face drains via the angular vein and ophthalmic veins, which are valveless, into the cavernous sinus. Infection of the "danger triangle" of the face can therefore spread to the sinus. - *Septic cavernous sinus thrombosis:* typically from S. aureus. It presents with fever, headache, periorbital edema, chemosis, proptosis, and ophthalmoplegia (CN VI palsy first), with V1/V2 sensory loss. Bilateral spread is common because of the intercavernous connections. Treat with IV antibiotics. Anticoagulation is controversial. - *Other lesions:* carotid-cavernous fistula (pulsatile proptosis, orbital bruit), pituitary adenoma extension, and aneurysm of the cavernous ICA.

**Cerebral venous sinus thrombosis (CVST):** - *Risk factors:* hypercoagulable states (pregnancy/postpartum, oral contraceptives, factor V Leiden, prothrombin mutation, antiphospholipid syndrome, malignancy, nephrotic syndrome, PNH), infection (mastoiditis, sinusitis), and dehydration. - *Most common sites:* superior sagittal and transverse sinuses. - *Presentation:* headache, seizures, papilledema, and focal deficits. Venous infarcts do not follow arterial territories, and they are often hemorrhagic. - *Diagnosis:* MR or CT venography. Non-contrast CT may show the "dense triangle/cord sign." Contrast CT may show the "empty delta sign." - *Treatment:* anticoagulation (heparin, then warfarin or a DOAC), even when hemorrhage is present. Endovascular thrombectomy is reserved for deterioration.

**Other associations:** - *Subdural hematoma:* tearing of bridging veins that cross from the cortex to the superior sagittal sinus. This is common in the elderly, alcoholics, and shaken-baby syndrome. - *Idiopathic intracranial hypertension:* often has transverse sinus stenosis. - *Mastoiditis:* can spread to the sigmoid sinus, causing thrombosis (Gradenigo syndrome involves the petrous apex and CN VI). - *Venous vs arterial:* sinuses lie in dura, whereas the epidural space contains meningeal arteries (the middle meningeal artery causes epidural hematoma).