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.
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 confluens sinuum produces bilateral transverse sinus obstruction with severe raised intracranial pressure, bilateral posterior cortical venous infarcts, and haemorrhagic transformation requiring anticoagulation and in severe cases decompressive craniectomy; it carries a worse prognosis than unilateral transverse sinus thrombosis.
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