superior sagittal sinus

ANATOMY - Location: Midline, in the superior (convex) border of the falx cerebri, in a groove along the inner surface of the skull. It begins near the crista galli (foramen cecum) and runs posteriorly to the internal occipital protuberance. - Cross-section: Triangular. It is lined by endothelium and has no valves. - Tributaries: Superior cerebral veins (bridging veins), diploic and meningeal veins, and emissary veins (connect to scalp veins). Parietal emissary veins link it to the extracranial venous system. - Lateral lacunae: Venous spaces along its sides that contain arachnoid granulations (villi). - Drainage: At the internal occipital protuberance it forms the confluence of sinuses (torcula) with the straight sinus. Flow then goes to the right and left transverse sinuses, then the sigmoid sinuses, then the internal jugular veins (via the jugular foramen). Usually the SSS drains mainly into the right transverse sinus. - Related sinuses: The inferior sagittal sinus (in the free edge of the falx) joins the great cerebral vein of Galen to form the straight sinus.

FUNCTION - Arachnoid granulations project into the SSS and lateral lacunae. They are the main site of CSF reabsorption into venous blood. CSF flows from the subarachnoid space into the SSS down a pressure gradient.

CLINICAL SIGNIFICANCE 1. Cerebral venous sinus thrombosis (CVST) - The SSS is the most commonly involved sinus, along with the transverse sinus. - Risk factors: Hypercoagulable states (pregnancy/postpartum, oral contraceptives, factor V Leiden, prothrombin gene mutation, protein C/S or antithrombin deficiency, antiphospholipid syndrome, malignancy, nephrotic syndrome, PNH), dehydration, infection, head trauma, and vaccine-induced immune thrombotic thrombocytopenia (VITT). - Presentation: Headache (most common), seizures, focal deficits (often bilateral leg weakness with parasagittal involvement), papilledema and signs of raised ICP, and altered mental status. - Pathophysiology: Venous outflow obstruction raises venous pressure, which causes vasogenic and cytotoxic edema, venous (often hemorrhagic) infarcts that do not respect arterial territories, and decreased CSF absorption (raised ICP, similar to pseudotumor cerebri). - Diagnosis: Non-contrast CT may show a hyperdense sinus (dense triangle/cord sign). CT venography or MR venography is the diagnostic test of choice. CT with contrast may show the "empty delta sign". - Treatment: Anticoagulation (heparin, then warfarin or a DOAC), even with hemorrhagic infarct. Endovascular thrombectomy is an option for refractory cases. Treat seizures and raised ICP.

2. Traumatic injury and bleeding - Bridging veins cross the subarachnoid and subdural space to drain into the SSS. Tearing of these veins (acceleration/deceleration injury, elderly, alcoholics, infants/shaken baby) causes a subdural hematoma, which is crescent-shaped and crosses suture lines. - Skull fractures or penetrating trauma over the vertex can lacerate the SSS and cause an epidural hematoma, which is lens-shaped (biconvex) and does not cross sutures. Middle meningeal artery injury is the classic cause of epidural hematoma, but venous sinus injury can also cause it.

3. Infection spread - Valveless emissary veins connect scalp and face veins to the dural sinuses. Infections can spread intracranially, causing meningitis or septic sinus thrombosis. The "danger triangle of the face" classically involves the cavernous sinus, but scalp infections can spread to the SSS.

4. Meningioma - Parasagittal meningiomas arise from arachnoid cap cells near the SSS. They can invade the sinus and cause contralateral leg weakness or spasticity (the motor cortex leg area is in the paracentral lobule), seizures, and headache. Histology shows psammoma bodies and whorled cells.

5. Other - Hydrocephalus: Obstruction of CSF reabsorption at the arachnoid granulations causes communicating hydrocephalus. - Infants: The open anterior fontanelle overlies the SSS. The SSS can be used for blood draws in emergencies (rare), but there is a risk of thrombosis and hemorrhage.

HIGH-YIELD PEARLS - Dural venous sinuses are valveless, and their endothelium-lined channels lie between the periosteal and meningeal layers of the dura. - CSF is reabsorbed at the arachnoid granulations into the SSS. - Flow: SSS → confluence of sinuses → transverse → sigmoid → internal jugular vein. - CVST: Treat with anticoagulation even when hemorrhage is present, and use MR venography for diagnosis.