Transient ischemic attacks

Venous outflow from the brain

The drainage of venous blood from cerebral structures is a complex process based on the dural venous sinus system. The main trunk pathway for outflow is directed into the internal jugular vein (v. jugularis interna) system.

Blood from the convex (convexital) surface of the brain collects and flows from anterior to posterior along the superior sagittal sinus (sinus sagittalis superior), which topographically lies strictly along the midline along the attachment site of the cerebral falx (falx cerebri). In the posterior regions of the skull, where the cerebral falx transitions into the tentorium of the cerebellum (tentorium cerebelli), this sinus merges with the straight sinus (sinus rectus). The straight sinus itself also runs along the midline at the boundary of the falx and tentorium, being responsible for draining blood from deep brain structures.

Next, the flows from the superior sagittal and straight sinuses combine at the confluence of sinuses (the so-called torcular Herophili). It is worth noting that sinuses are often asymmetric, and the pathways of blood inflow into the confluence can vary. From the sinus confluence, venous blood is distributed into two transverse sinuses (sinus transversus), each of which then continues into the respective sigmoid sinus (sinus sigmoideus). Descending below the jugular foramen, the sigmoid sinus directly continues into the internal jugular vein.

In addition to the main pathway, alternative drainage options exist. Specifically, a certain portion of blood may be drained via the pterygoid venous plexus, entering the venous system of the facial skeleton (viscerocranium).

Topography and pathology of the cavernous sinus

The cavernous sinus (sinus cavernosus) is a vital collector at the base of the skull. It is localized inside a double fold of the dura mater and performs the function of draining venous blood from the basal regions of the brain. The main inflow into this sinus comes from the temporal lobe and orbital structures (via the superior and inferior ophthalmic veins).

Outflow from the cavernous sinus occurs in two main directions:

1. Via the superior and inferior petrosal sinuses (sinus petrosus superior et inferior), blood is directed into the sigmoid sinus.
2. Into the pterygoid venous plexus.

Clinical significance: Knowledge of cavernous sinus anatomy is critically important for diagnosing vascular pathologies. If an intracavernous (within the sinus itself) rupture of the internal carotid artery aneurysm occurs, a pathological increase in venous pressure arises. This leads to retrograde (reverse) blood flow through the orbital veins, which clinically manifests as the development of pronounced chemosis and exophthalmos.

Arterial system of the spinal cord

The vascular pattern of the spinal cord is not a set of isolated arteries, but rather a long chain of anastomoses. The basis of this network consists of three longitudinal trunk arteries connected by numerous plexuses.

The anterior spinal artery (a. spinalis anterior) is the single (unpaired) vessel descending along the anterior surface of the brain in the trough of the anterior median fissure (fissura mediana anterior). The vascular bed is formed by the inflow of segmental branches. It gives off penetrating vessels — the sulcocommissural arteries (aa. sulcocommissurales). They branch off opposite each segment, enter transversely into the median fissure and penetrate into the brain tissue, where each such artery strictly supplies only one half of the segment parenchyma. This anterior basin nourishes the anterior horns, the lateral and anterior spinothalamic tracts, as well as a part of the pyramidal tract (including the lateral corticospinal tract) — i.e., the ventral part of the gray matter and adjacent structures.

The posterior spinal arteries are the main longitudinally oriented paired vessels for the posterior half of the spinal cord. They descend between the posterior roots and lateral funiculi. Unlike the anterior system, their fusion from segmental arteries may remain incomplete in places. They supply blood to the posterior funiculi, posterior roots, and posterior horns.

The anterior and posterior trunk vessels are interconnected by radicular anastomoses.

Vascularization zones and blood supply features

In a cross-section of the spinal cord, three topographical blood supply zones are clearly differentiated:

• Zone of the anterior spinal artery: encompasses the central and anterior parts of the parenchyma (anterior horns, central gray matter, deep sections of the anterior and lateral funiculi).
• Zone of the posterior spinal artery: supplies the posterior part of the parenchyma (posterior horns and funiculi).
• Vasocoronary zone (sulcal-pial network): a superficial arterial network encircling the brain along the periphery and supplying the outer layers of white matter of the anterior and lateral funiculi.

In the proximal parts of the arterial system, there are numerous anastomoses, so stenosis or occlusion of a single artery at this level usually proceeds without clinical manifestations. However, in the peripheral parts, arteries become end branches. If embolic occlusion occurs within the spinal cord (e.g., at the level of the sulcocommissural artery), this inevitably leads to spinal cord infarction.

Regional features: In embryogenesis, blood supply comes from segmental arteries, but as maturation proceeds, most of them regress. Identifying preserved vessels in an adult is only possible via angiography. The remaining arteries are distributed by regions:

• Upper cervical region: the main inflow to the anterior spinal artery comes from the vertebral arteries (the contribution of one of them usually predominates).
• Lower cervical region: blood comes from the vertebral artery and cervical branches of the subclavian artery (costocervical or thyrocervical trunk).
• Thoracic and lumbar regions (below Th3): the source is aortic branches (thoracic and lumbar segmental arteries). They give rise to surviving spinal branches, each of which bifurcates into anterior and posterior branches penetrating the spinal canal together with the corresponding roots.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Topography of the cranial vault sinuses (superior and inferior sagittal sinuses)
• Topography of the cranial base sinuses (sphenoparietal and petrosal sinuses)
• Blood supply to the anterior and posterior funiculi of the spinal cord
• Formation of the spinal cord arterial network in embryogenesis
• The role of the pterygoid venous plexus in extracranial outflow

Other topics in the section "DeMyer's The Neurologic Examination" / "Duus' Topical Diagnosis in Neurology"

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