The sigmoid sinus is a paired intracranial venous channel. It arises from the transverse sinus at the level where the transverse sinus leaves the tentorium cerebelli. The sigmoid sinus courses along the floor of the posterior cranial fossa to enter the jugular foramen. It drains into the jugular bulb via which it connects with the internal jugular vein.
Throughout its course, the sigmoid sinus receives tributaries that connect it to the pericranial veins. These tributaries include the mastoid and (posterior) condylar emissary veins. Additionally, the sigmoid sinus receives tributaries that drain the blood from the medulla oblongata, pons and cerebellum.
This article will discuss the anatomy and function of the sigmoid sinus.
|Mastoid emissary veins, condylar emissary veins, inferior cerebellar veins
|Internal jugular vein
|Transverse sinus, cerebellum, pons, medulla oblongata
Origin and course
The sigmoid sinus is a paired intracranial vessel. It begins as a continuation of the transverse sinus around the opening on the tentorium cerebelli. From here, it descends downward, forming an S-shaped curve in a groove on the mastoid process of temporal bone. This groove is called the groove for sigmoid sinus. It then courses over the jugular process of the occipital bone to emerge posterior to the jugular foramen. When it reaches the foramen, the sigmoid sinus is situated at the posterolateral part of the foramen with a meningeal branch of the occipital artery.
The sigmoid sinus terminates by an expansion known as the jugular bulb. This bulb is a junction between the sigmoid sinus and the internal jugular vein. Along its course, the sigmoid sinus receives a number of tributaries. Keep in mind that the venous system of the brain is largely variable and the tributaries of the sigmoid sinus are no exception. Some of the most common tributaries include the following vessels:
- Mastoid emissary veins in the mastoid foramen that connect the sigmoid sinus with the posterior auricular or occipital veins.
- Condylar emissary vein that runs between the sigmoid sinus and veins in the suboccipital triangle through the (posterior) condylar canal.
- Venous plexus of the hypoglossal canal, which is sometimes only a single vein that runs between the sigmoid sinus and the internal jugular vein.
- Inferior cerebellar veins, that drain the inferior portion of the cerebellum.
- Small unnamed tributaries from the pons and medulla.
The main function of the sigmoid sinus is to conduct blood from the transverse sinus to the internal jugular vein. Along the way, the sigmoid sinus receives tributaries that collect blood from the pericranial veins, and in some cases from pons, medulla oblongata and cerebellum.
The course of the sigmoid sinus is very variable and of major clinical importance since the neurosurgical approaches to the posterior fossa of the skull are classified according to the position of the sinus; retrosigmoid surgeries are performed behind the sinus, while the presigmoid are performed in front of it.
Explore the anatomy of the dural venous sinuses using the videos, articles, labeled illustrations and quizzes in the following study unit:
Sigmoid sinus diverticulum
The sigmoid sinus diverticulum is a rare vascular anomaly. It is an outpouching (diverticulum) of the wall of the sigmoid sinus. The diverticulum often has a tendency to grow and protrude into the mastoid process. The most common symptom of this condition is pulsatile tinnitus (noise or ringing) in the ear on the side of the anomaly.
The diagnosis is most commonly established by cerebral angiography. The treatment can be achieved with surgical procedures, usually via the endovascular coiling.
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