The veins of the head and neck are important to understand for assessment of numerous pathologies, but are more variable than arteries in terms of size, course, and potential filling-defect fake-outs (although recall variability of the structure of the circle of Willis and many other embryologic arterial variants are possible). Like arteries, there are venous vascular (drainage) territories, but these are also more variable.

Intracranially, the major venous structures include dural venous sinuses, superficial/cortical veins, and deep veins. The dural venous sinuses are located within separated portions of the layers of the dura. The essential dural venous sinuses to learn include the superior sagittal (SSS), the inferior sagittal sinus (ISS), the straight, transverse, sigmoid, cavernous (CS), and inferior petrosal (IPS) sinuses.

The major cortical veins include the vein of Trolard, vein of Labbe, and the superficial middle cerebral vein. The major deep veins to learn include the internal cerebral vein, basal vein of Rosenthal, and vein of Galen.

There are two major drainage pathways from the head; the jugular (internal, external, and anterior) veins and the vertebral venous system. The IJVs are a continuation of the sigmoid sinuses, collecting blood from other tributaries including the IPS. The facial veins and the pterygoid venous plexus also drain via jugular veins. The external jugular veins form from a confluence of the posterior branch of the posterior facial (retromandibular) vein and the posterior auricular vein and courses superficial or lateral to the sternocleidomastoid muscles. The anterior jugular veins course superficially and anteriorly, medial to the sternocleidomastoid muscles.

The vertebral venous system begins predominantly as a collection from the anterior, lateral, and posterior condylar veins and other emissary veins at the skull base. An important relationship to skull base anatomy is the anterior condylar confluence (ACC) at the anterior margin of the hypoglossal canal and anterior condylar vein (hypoglossal venous plexus) within the hypoglossal canal. These drain into the internal or external vertebral plexus. The vertebral plexus and veins of the spine are detailed further in the next section on neurovascular anatomy of the spine.

References

Escott EJ, Branstetter BF. It's not a cervical lymph node, it's a vein: CT and MR imaging findings in the veins of the head and neck. Radiographics 2006;26:1501-1515

Sagittal 3D MIP MRA image demonstrates the major dural venous sinuses and select deep cerebral veins. The jugular bulb is a dilatation at the junction of the sigmoid sinus and IJV. The diminutive inferior sagittal sinus is not depicted. The occipital sinus is a common variant arising from the torcula.

There are several normal variants that may be pitfalls in venogram interpretation. Normal variant filling defects, especially arachnoid granulations, are common. The ISS is often so small that it is not seen or barely seen even on high resolution imaging-which should not be confused with thrombosis. There is a normal constriction near the confluence of the Vein of Galen and the straight sinus.

Several other variants may be associated with pulsatile tinnitus (high riding jugular bulb, dehiscience, diverticulum). As mentioned in the section on bones of the face/skull, the jugular foramen size is directly related with side of dominance.

Just as there are arterial territories in the brain, there are also venous drainage territories. These are lesser known for a few reasons including the fact venous infarcts are less common, venous drainage patterns are more variable, and infarcts conforming to entire defined 'territories' are particularly less common. Four main venous territories of the supratentorial brain have been described in the Anne Osborne book. These include a:

1. peripheral territory draining into the SSS or cortical veins to SSS

2. deep territory draining into the internal cerebral veins/vein of Galen to straight sinus

3. peri-Sylvian territory draining into the sphenoparietal sinus to cavernous sinus

4. posterolateral/temporoparietal territory draining into a vein of Labbe to transverse sinus

Reference

Osborn's Brain. Imaging, Pathology, and Anatomy. Chapter 9

According to the Monro-Kellie hypothesis, the volume of intracranial blood, brain, and CSF remains constant in the fused skull (as a first approximation). As such, changes in CSF volume has an effect on the volume of volume of blood (as the volume of brain is close to constant in the short term outside a major acute insult). This is directly visualized in lower pressure venous structures (but not so much arteries unless they are directly compressed). For example, the intracranial findings in spontaneous intracranial hypotension can be accounted for by the Monro-Kellie hypothesis and many relate to increased venous volume. These include distension of the dural venous sinuses (often assessed at the midpoint of the dominant transverse sinus), enhancement of the pachymeninges, and engorgement of the pituitary gland. Conversely, the transverse sinuses demonstrate smooth tapered narrowing laterally with idiopathic intracranial hypertension. Other key pathology includes the vein of Galen Malformation and dural venous sinus thrombosis.