Cardiovascular system · Head and neck
Confluence of sinuses !
The confluence of sinuses, at the back of the skull, is where the main vein channels draining the brain meet before flowing to each side.
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What it is
The meeting point of the dural sinuses at the back of the head.
What it does
Where the superior sagittal, straight and transverse sinuses join.
Key facts
- Drains
- Superior sagittal and straight sinuses (and the occipital sinus)
- Into
- Both transverse sinuses (the right usually larger)
Relations
- Above
- Occipital lobes either side of the falx cerebri; the superior sagittal sinus enters from above
- Below
- Cerebellar hemispheres either side of the falx cerebelli; the occipital sinus enters from below
- In front
- Straight sinus, arriving along the junction of the falx cerebri and tentorium with the deep venous blood of the great cerebral vein
- Lateral
- Transverse sinuses leaving on both sides in the attached edge of the tentorium, toward the sigmoid sinus and internal jugular vein
- Behind
- Inner surface of the occipital bone at the internal occipital protuberance
How to find it
The external occipital protuberance (inion) is felt as the bony bump in the midline at the back of the head; the confluence lies just deep to it. Burr holes and suboccipital approaches are planned to stay clear of this point.
On imaging
CT or MR venography shows the confluence and whether both transverse sinuses fill; thrombosis gives a filling defect or an empty delta sign here. Normal arachnoid granulations and slow flow in a non-dominant transverse sinus can mimic clot.
Clinical notes
- Depressed occipital fractures over the confluence are handled cautiously, because lifting the fragment can tear the sinuses and cause major bleeding
- Venous sinus thrombosis reaching the confluence impairs drainage of both hemispheres: headache, papilloedema, seizures and venous infarcts
- Meningiomas near the confluence are planned around which sinuses are dominant and still open, since sacrificing a dominant one can cause venous infarction
Anatomical variants
- Drainage patterns vary: symmetric, right-dominant (the commonest), split into two channels, or with one transverse sinus hypoplastic
- The occipital sinus can be large in infants and may drain directly toward the sigmoid sinus or the vertebral venous plexus
Memory aid
Its old name, torcular Herophili, means the wine press of Herophilus: the place where the streams of venous blood are squeezed together.
Test yourself
Think of the answer, then tap the question to see it.
Which surface landmark marks the confluence of sinuses?
The external occipital protuberance (inion): the confluence lies just deep to it, against the internal occipital protuberance.
Which sinuses join at the confluence of sinuses?
The superior sagittal and straight sinuses (and the occipital sinus) drain in, and both transverse sinuses leave it, the right usually larger.
Why is a depressed occipital fracture over the confluence of sinuses handled cautiously?
Lifting the fragment can tear the sinuses and cause major bleeding.
How does the position of the confluence of sinuses differ in Dandy–Walker malformation and Chiari II malformation?
It is high in Dandy–Walker malformation (raised tentorium) and low in Chiari II malformation, with a small posterior fossa.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- confluens sinuum TA2 4852
- Official Spanish (DeCS)
- Confluencia de los senos
- English (TA2)
- Confluence of sinuses
- Also called
- torcular of Herophilus
Sources: Terminologia Anatomica (TA2); Neuroanatomy, Dural Venous Sinuses; Neuroanatomy, Superior Sagittal Sinus.
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Representative model, for educational purposes only.