Vasculature - Venous Drainage Flashcards
What three main structures drain blood from the head and neck?
1) Dural venous sinuses - drains blood from the brain and the meninges
2) Veins of their arterial face and scalp counterpart - these empty into the internal and external jugular veins.
3) Venous drainage of the neck - carried out by anterior jugular veins.
External jugular vein
Drains the majority of the external face.
Formed by the union of two veins:
1) Posterior auricular vein - drains area of the scalp posterior and superior to the outer ear.
2) Retromandibular vein (posterior branch) - itself formed by the maxillary and superficial temporal veins. which drain the face.
These two veins form posterior to the angle of mandible and inferior to the outer ear.
It then descends down the neck with the superificial fascia of the neck, runs anteriorly to the sternocleidomastoid, crossing in an oblique, posterior and inferior direction.
At the root of the neck, it then passes under the clavicle and drains into the subclavian vein.
The EJV receives a few veins - posterior external jugular, transverse cervical and suprascapular.
Clinical relevance - severance of the external jugular vein
It has a relatively superficial course down the neck, so can be prone to damage.
If slashed by a knife, the lumen is held open by investing fascia.
Air will be drawn into the vein, producing cyanosis, and can stop blood flow to the right atrium. This is a medical emergency, managed by pressure to the wound - stopping the bleeding, and the entry of air.
Anterior jugular veins
These veins vary from person to person. They are paired veins that drain the anterior aspect of the neck. Often they will communicated with the jugular venous arch.
They will descends down the midline of the neck and drain into the subclavian veins.
Internal jugular veins
Begins in the cranial cavity and as a continuation of the sigmoid sinus. Initially the IJV is dilated - this is known as the superior bulb. It exits the skull via the jugular foramen.
It then descends the neck within the carotid sheath, deep to the sternocleidomastoid and lateral to the common carotid artery.
At the base of the neck, posterior to the sternal end of the clavicle, the IJV combines with the subclavian vein to form the brachiocephalic vein. Immediately prior to this, the vein dilates to form the inferior bulb. It has a valve to stop backwards blood-flow.
During its descent. the IVJ receives blood from: the facial, lingual, occipital, superior and middle thyroid veins. These veins drain blood from the anterior face, trachea, thyroid, oesophagus, larynx, and muscles of the neck.
Clinical relevance - JVP
In clinical practice, the JVP can be observed for pulsations - the nature of which can provide the estimation of the right atrial pressure.
When the heart contracts, a pressure wave is passed upwards, which can be observed. There are no valves in the brachiocephalic and subclavian veins - so the pulsations are a fairly accurate indication of the right atrial pressure.
Dural venous sinuses
Dural venous sinuses are the spaces between the periosteal and menigeal dura mater, which are lined with endothelial cells. They ultimately drain into the IVJ.
Clinical relevance - cavernous sinuses
They are located at the lateral aspect of the body of sphenoid bone. The sinus receives blood from the superior and inferior opthalmic veins, the middle superficial cerebral veins and the sphenoparietal dural venous sinus.
Located within the internal carotid artery is the carotid artery, which crosses the sinus. This allows for cooling of the blood before it reaches the brain.
The abducens nerve also crosses the sinus with the ICA.
In the lateral aspect of the cavernous sinus is the following nerves:
1) Oculomotor nerve
2) Trochlear nerve
3) Ophthalmic nerve
4) Maxillary nerve
If the cavernous sinus is infected, these nerves are at risk of damage. The facial vein is connected to cavernous sinus via the superior ophthalmic vein. The facial vein is valveless - blood can reverse direction and flow from the vein to the cavenous sinus, providing a potential route of infection.
