The meninges are important supporting structures, which surround the brain within the skull. The outermost layer of the meninges is referred to as the dura mater. This layer lines the inner surface of the skull and has an important circulatory function. The dura mater is further divided into an outer and inner layer known as the periosteal layer and the meningeal layer, respectively.
Between these two layers are channels known as the dural venous sinuses, which drain blood from the brain and cranial bones. One of these sinuses is referred to as the straight sinus. This article will talk about the anatomy of the straight sinus, followed by any relevant clinical information.
The inferior sagittal sinus and the great cerebral vein (great vein of Galen) join together to form the straight sinus, which is 50 mm in length on average. This sinus also receives veins from the occipital lobes and the superior surface of the cerebellum. It is located between the two dural layers at the junction of the tentorium cerebelli and the falx cerebri, which are folds of the dura mater.
The straight sinus ends at the internal occipital protuberance, a bony landmark on the cranium, and empties into the transverse sinus contributing to the formation of the confluence of sinuses. This is a dilatation of the venous channel at the level of the internal occipital protuberance, where the superior sagittal, straight, occipital and right/left transverse sinuses converge. After the confluence of sinuses, the transverse sinuses become sigmoid sinuses (right/left) that open into the bulb of the internal jugular vein.
Cerebral venous sinus thrombosis
Cerebral venous sinus thrombosis (CVST) is a disease that affects young to middle-aged people and can involve any of the sinuses. The straight sinus is uncommonly affected in this disease but when it is, it tends to be associated with a poor outcome. CVST can present with:
- paresis (weakness of voluntary movement)
- impaired consciousness
- occlusion of the sinus
- papilloedema - swelling of the optic disc due to increased intracranial pressure
Treatment involves anticoagulant drugs and thrombolysis. The outcome of CVST can vary from complete recovery to permanent neurological deficits.
A meningioma, a benign tumour of the meninges, can arise from the straight sinus, resulting in its occlusion. Straight sinus meningiomas are rare and usually grow unilaterally. Symptoms include:
- visual disturbances
- hearing loss
- memory loss
These tumours are usually removed supratentorially, approaching from above the tumour in order to have better visualisation. However, they may be removed using an infratentorial approach, from below the tumour, or use a combination of a supratentorial and infratentorial approach.
Thrombophlebitis, venous inflammation, is another condition that can occlude the straight sinus.