The sigmoid sinus is a venous blood channel inside the skull that drains blood from the brain towards the neck. This term describes part of the venous system in the head, which plays an important role in carrying away oxygen-poor blood.
Structure and position in the skull
Inside the human head, there are several venous channels called the sinus durae matris. The sigmoid sinus is one of the largest of these and runs in an S-shaped curve, which is exactly where its name comes from, as "sigmoid" refers to this curved shape, similar to the letter S. It sits in the back part of the skull, more precisely along the base of the skull, and runs from the posterior cranial fossa to the jugular foramen. There, it connects to the internal jugular vein, which carries the blood further towards the heart.
Function of the sigmoid sinus
The main job of the sigmoid sinus is to collect used blood from the brain, the meninges, and parts of the skull, and drain it away. Together with other sinuses, such as the transverse sinus, which connects to it, the sigmoid sinus forms a kind of collection point for venous blood. Without this drainage, blood would build up in the head, which would have serious consequences. The sigmoid sinus keeps the pressure in the brain balanced and ensures that blood reliably returns to the heart.
When does the term appear?
The sigmoid sinus is often mentioned in medical reports or during imaging examinations. Particularly in scans of the head using MRI or CT, the course, patency, or specific features of this venous vessel may be described. The term is also frequently used in reports about operations or procedures on the skull, as the sigmoid sinus lies close to important structures. Changes or particular features noted are usually purely descriptive and do not necessarily indicate a disease.
Important notes for your report
When the sigmoid sinus is mentioned in a doctor's letter or report, it is in most cases an anatomical description. For example, it may state that the sigmoid sinus is "freely patent" or "unremarkable". This means there are no abnormalities. Only rarely is there any indication of changes such as thrombosis or inflammation. In such cases, however, the report would usually make a clear reference to a specific condition.
Distinguishing from diseases
The sigmoid sinus itself is not a disease but a normal anatomical vessel. Diseases can affect this area, for example through a condition called sinus venous thrombosis, where a blood clot forms in the venous system of the skull. However, such diagnoses are always explicitly named as such and come with additional information and symptoms. As a general rule, the simple mention of the sigmoid sinus in a report is no cause for concern.
In summary
The sigmoid sinus is a natural part of the venous system in the head. It ensures the safe drainage of blood from the brain and is described in medical texts mostly as part of normal anatomy. Abnormalities in this area are rare and are usually clearly identified as such. In the vast majority of cases, the mention of the sigmoid sinus in a report simply means that this vessel was examined or assessed.
