A New Draining or Emissary Vein Originating from Terminal Segment of Sigmoid Venous Sinus?

Abstract

The venous efflux from cerebral dural venous sinus into
the extracranial venous drainage is predominantly based
on sigmoid venous sinus draining into the internal jugular vein. In the fetal stage, the rapid growth of cerebral
hemispheres leads to an enlargement of transverse
venous sinuses in somewhat disproportionate manner to
growth of sigmoid venous sinus and internal jugular
vein. Therefore, emissary veins are necessary to ensure
adequate efflux pathways for intracranial venous drainage. A variable number of emissary veins may persist
after the fetal stage [2–4]. Some of the important emissary veins include the mastoid emissary vein [2,3] that
connect the transverse sinus with the posterior auricular
or occipital veins, and the anterior and posterior condyA.A lateral projection of cerebral angiogram demonstrating the new vein in the venous phase (dashed
arrows). Notice the narrow internal jugular vein anterior to the new vein.
lar veins that connect the terminal sigmoid venous sinus
with suboccipital cavernous sinus and internal vertebral
venous plexus [3,4]. In our observation, there is another
vein that connects the terminal sigmoid venous sinus
with the ipsilateral external jugular vein. The vein
appears to originate at the horizontal section of the terminal segment of sigmoid venous sinus as it enters the
internal jugular vein (see Figure). This vein appears to
exit from a dorsal foramen within the wall of the jugular
foramen. The vein can be prominent even in the presence of a large patent internal jugular vein and posterior
condylar vein (see Figure). Occasionally, individuals
with such a vein report tinnitus which may be self-limiting. The vein may also become noticeable after internal
jugular vein thrombosis or fibrosis subsequent to intravascular catheter placement(s). The prevalence and
physiological importance of this vein requires further
study. Further studies also need to delineate whether the