Transverse and Sigmoid Sinuses
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Direct answer
Blood leaving the back of the cranial cavity travels the posterolateral attached margin of the tentorium cerebelli in the transverse sinus, then curves down the S-shaped groove on the inner surface of the mastoid part of the temporal bone as the sigmoid sinus, to end in the jugular foramen as the superior bulb of the internal jugular vein. The right transverse sinus is usually the continuation of the superior sagittal sinus and is hence the larger channel. Its intimate posterior relation to the mastoid antrum is why middle-ear infection can thrombose this sinus, a complication every MBBS examiner probes.
What you must remember
- The transverse sinus begins at the internal occipital protuberance and runs forward in the tentorial margin, grooving the occipital and parietal bones, then turns downward as the sigmoid sinus at the superior border of the petrous temporal bone.
- The sigmoid sinus grooves the posterior surface of the petrous temporal bone, separated from the mastoid antrum and air cells by a thin plate of bone.
- It ends at the jugular foramen, forming the superior jugular bulb; cranial nerves nine, ten and eleven leave through the middle part of the same foramen in front of it.
- The right sinus is typically larger because it continues the superior sagittal sinus; the left continues the straight sinus.
- The mastoid emissary vein links it to the posterior auricular vein, so thrombosis produces postauricular pain and oedema — Griesinger's sign.
- A perisinus abscess sits between the sinus and the mastoid bone; Citelli's triangle is a surgical landmark used to locate the sinus during mastoidectomy.
- Tributaries include the superior petrosal sinus, cerebellar veins, diploic veins and emissary veins from the occipital region.
Working through mastoiditis that goes on to sinus thrombosis
Picture a nine-year-old with untreated otitis media who develops postauricular swelling, tenderness over the mastoid, a protruding ear and spiking fevers, and two days later becomes drowsy with papilloedema. Follow the anatomy of the spread. Pus in the mastoid antrum lies millimetres from the sigmoid sinus, separated only by compact bone; osteitis or thrombophlebitis across this plate seeds the sinus lumen. The clot occludes venous outflow, so intracranial pressure rises and optic discs swell, while infected emboli can propagate to the transverse sinus or discharge septic emboli to the lungs.
The clinical signs map directly onto tributaries and relations. Occlusion of the mastoid emissary vein gives the postauricular oedema of Griesinger's sign. If the clot extends to the jugular bulb, the glossopharyngeal, vagus and accessory nerves in the adjacent compartment complain — hoarseness, dysphagia and weakness of the sternocleidomastoid and trapezius, the jugular foramen syndrome of Vernet. Confirmation is with MR or CT venography; management per current practice combines intravenous antibiotics for the otitis, drainage of the mastoid by cortical mastoidectomy, and anticoagulation decisions individualised by the neurosurgical team.
Where students slip
Two confusions recur in vivas. First, candidates place the transverse sinus "in the occipital bone only" and forget that the groove crosses the posteroinferior angle of the parietal bone before the sinus hooks under the petrous temporal bone to become sigmoid — the transition point is a favourite spot question. Second, they mix up the contents of the jugular foramen compartments: the sigmoid sinus becomes the superior bulb in the posterolateral (pars vascular) compartment alongside the internal jugular vein's origin, while the pars nervosa in front carries the ninth, tenth and eleventh nerves with the inferior petrosal sinus most anteromedially. A candidate who can draw the foramen in cross-section, naming sinus, nerves and the inferior petrosal sinus, effectively closes the topic.
Frequently asked questions
Where exactly does the transverse sinus become the sigmoid sinus?
At the point where the transverse sinus leaves the tentorial margin and turns downward behind the petrous temporal bone, crossing from the occipital and parietal grooves into the S-shaped mastoid groove.
Which structures accompany the sigmoid sinus at the jugular foramen?
The ninth, tenth and eleventh cranial nerves in the anteromedial compartment, with the inferior petrosal sinus; the sinus itself dilates as the superior jugular bulb posterolaterally.
What is Griesinger's sign and why does it occur?
Oedema and pain over the mastoid, arising because thrombosis of the sigmoid sinus blocks the mastoid emissary vein that drains to the posterior auricular veins.
Why does middle-ear infection threaten this sinus?
The mastoid antrum and air cells lie directly in front of the sigmoid groove, separated only by a thin bony plate, so infection crosses by osteitis or thrombophlebitis.
Which sinus is usually larger, and why?
The right, because in most people it is the direct continuation of the superior sagittal sinus, while the left continues the straight sinus.