Basilar venous plexus

At a glance

English

Basilar venous plexus

Latin (TA2)

Plexus venosus basilaris

System

Vein

Region

Whole body

Side

Single, on the midline

About the basilar venous plexus

The basilar venous plexus, sometimes called the basilar or transverse sinus, is the largest of the venous networks at the base of the skull. Instead of a single tube it is a set of interlacing channels lying between the two layers of the dura mater on the clivus, the sloping surface formed by the back of the sphenoid body and the front, basilar portion of the occipital bone. It sits directly behind the dorsum sellae and in front of the brainstem, with the basilar artery and the pons lying just behind it beyond the dura.

Its chief job is to join the venous sinuses of the two sides across the midline. Laterally it opens into the inferior petrosal sinus of each side, and towards the front it connects with the back ends of both cavernous sinuses. Below, it continues through the region of the foramen magnum into the anterior internal vertebral venous plexus, the valveless veins inside the vertebral canal.

That last connection is the one that matters most. Because neither the plexus nor the vertebral veins have valves, blood can move in either direction depending on pressure, for example during coughing or straining. The plexus thus forms part of a continuous low-resistance route between the veins inside the skull and those along the spine. This route is thought to help explain how tumours of the trunk can spread to the vertebrae and the skull without passing through the lungs.

In skull-base surgery approaching the clivus, through the nose and sphenoid or from the side, the plexus can bleed briskly and has to be controlled. Its channels can also become enlarged in dural arteriovenous fistulas of this region. On imaging with contrast, the plexus appears as a thin enhancing band lining the back of the clivus.

Course and drainage

Begins at

Collects blood between the dural layers on the clivus and from the cavernous sinuses at its front.

Drains into

Drains laterally into both inferior petrosal sinuses and downwards into the anterior internal vertebral venous plexus.

Drains

Links the venous sinuses of the two sides at the skull base and joins the intracranial veins to the vertebral venous system.