The confluence of sinuses (torcular Herophili) is the dilated junction on the internal occipital protuberance where the superior sagittal sinus, the straight sinus, the two transverse sinuses, and the occipital sinus converge. It is asymmetric in most individuals, with the right transverse sinus typically dominant (receiving the superior sagittal sinus) and the left transverse sinus receiving predominantly the straight sinus.
| Origin | Meeting point of the superior sagittal, straight and occipital sinuses at the internal occipital protuberance |
|---|---|
| Course | A dilated venous junction that drains laterally into the right and left transverse sinuses |
| Branches |
The confluence of sinuses is the surgical landmark in the suboccipital and posterior fossa approaches where the transverse and superior sagittal sinus terminations must be avoided during craniotomy. Thrombosis at the confluence produces the most severe form of cerebral venous sinus thrombosis, with bilateral transverse sinus occlusion causing raised intracranial pressure, bilateral cortical venous infarcts, and potentially fatal cerebral oedema. MRI venography demonstrates flow voids at the confluence; normal right-left asymmetry must not be mistaken for thrombosis.
Thrombosis of the confluence obstructs both transverse sinuses, causing severe raised intracranial pressure and bilateral venous infarcts; it needs anticoagulation and sometimes decompressive craniectomy, and has a worse outlook than unilateral transverse sinus thrombosis.
An abnormal arterial connection into the confluence and transverse sinuses causes pulsatile tinnitus, headache and raised intracranial pressure, with a bleeding risk if it drains back into cortical veins; endovascular embolisation aims to close the fistula while keeping the sinuses open.
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