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Known Venous Problems (CCSVI related) 

A basic understanding of the human vascular system is crucial to understanding the impact that CCSVI can have on the body. In an optimally working vascular system, oxygen-rich blood is delivered to the organs from the heart and lungs through arteries, and oxygen-depleted (deoxygenated) blood is returned to the cardiopulmonary system through veins. In CCSVI, blockages or other abnormalities in the vessels carrying blood away from the central nervous system (CNS) impede the flow of deoxygenated blood back to the heart. As a result, circulation times are slowed, and blood can reverse course (or reflux) and flow back toward the CNS, potentially damaging the tissues surrounding the veins.

The venous system is highly complex, varying substantially from one person to another (unlike, for example, the arterial system, which is generally more consistent across individuals). Moreover, the venous system often provides multiple drainage pathways, further complicating the designation of what is and is not “normal” for any given individual.

Nonetheless, while we are still very early in our understanding of venous hemodynamics, by comparing the veins of healthy individuals with those who have CCSVI, an initial set of venous abnormalities associated with CCSVI have been identified and categorized. The most common venous obstructions include:

Stenosis

"Stenosis” is the abnormal narrowing of a blood vessel. This may also include crimping, flattening, collapsing, or other similar malformations which reduce blood flow through the vessel. In CCSVI, stenosis is typically seen in the internal jugular, azygos, vertebral, lumbar, renal and/or other major venous pathways draining deoxygenated blood from the brain and spinal cord. While even healthy veins can display some narrowing, the veins of CCSVI patients exhibit extreme narrowing, often more than 50%. Stenosis is most commonly found in the Internal Jugular Veins, and the Azygos vein.

At present, the origin of some kinds of stenoses are unknown. Veins are naturally more elastic than arteries and may flatten or collapse when unused.  They can be “unused” at times because blood drainage varies across different veins when a person is in different positions. For example, blood from the brain drains primarily through the jugulars when a person is supine, but largely through the deep cerebral veins when a person is sitting. In CCSVI, veins may remain flattened or collapsed when they should be transporting blood.

Stenoses (more than one stenosis) can disrupt blood flow, increasing venous blood circulation times (also called mean transit times) and, in some cases, causing reflux, which is a key indicator of CCSVI. Stenosis can occur anywhere along the length of a blood vessel. Specific types of stenosis include:

  • Annulus - A ring, ring-like, or circular stricture (blockage) found inside the vein.
  • Twisting of the Jugular and/or Azygos Veins - A twist, cork-screwed, or similar malformation in a segment of a vein. These twists and malformations impede the normal flow of blood, potentially leading to CCSVI.
  • Osseous Occlusion of the Jugular and/or Azygos Veins- A stenosis caused by a bony structure (for example, an arachnoid granulation) impinging on a blood vessel, potentially causing CCSVI.

 

Venous Developmental Abnormalities

Hypoplasia, agenesis, and atresia all refer to veins that are either not fully opened (atresia), not fully formed (hypoplasia), or almost entirely missing (agenesis). In particular, CCSVI diagnosis has identified cases of incompletely formed jugular veins, including situations where the jugular is almost completely missing, as well as stunted or only minimally developed veins in the azygos system.  These overt abnormalities, which are generally considered congenital/developmental, can contribute to CCSVI.

Valve Abnormalities

Veins have one-way flaps called “venous valves” that prevent blood from flowing backwards through the vein. CCSVI diagnosis has identified cases where valves are reversed, incomplete, or abnormally located. These valve abnormalities may inadvertently allow blood to flow backwards through the vein, and can lead to the reflux of blood back into the CNS, which is a hallmark of CCSVI.

Substitute Circles – Collaterals and Shunts

When stenoses or blockages in the main pathways draining blood from the brain and spine occur, the venous system appears to partially adapt or respond by generating alternate pathways through which blood flow and pressure can be alleviated. These alternative pathways, called “substitute circles,” partially bypass large venous obstructions by branching out from a main vein prior to an obstruction and reconnecting to other non-stenosed vein segments elsewhere in the venous system.

The two most common types of alternate pathways are called “collaterals” and “shunts.” Collaterals, seen here, are networks of small veins that appear to splinter off from a larger vein near the stenosis. Shunts also serve to bypass stenoses, but shunts are often longer single vein segments as opposed to the profusion of smaller, more spidery, collaterals.

Remarkably, during CCSVI Treatment, veins comprising these substitute circles can often be seen to drain and empty when a stenosis has been cleared. The substitute circles often seem to “disappear” because shunted blood is no longer flowing through them. Images showing collateral veins can be seen here.

While collaterals and shunts protect against excessive cerebrospinal hypertension, they may allow less blood flow than non-stenosed vein segments, and have been linked to both increased mean transit times and venous reflux.

Other Venous Abnormalities

A wide assortment of less common abnormalities has also been seen in CCSVI patients. These include abnormally located membranes (called “septums”) in the veins, web-like structures blocking the veins, and problems at the point of confluence between blood vessels.

Summary

The precise anatomy of veins around the CNS is extremely complex and much more variable from patient to patient than the anatomy of arteries. Further, our understanding of venous hemodynamics is still at an early stage. While a variety of venous abnormalities may contribute to CCSVI, it is imperative to remember that CCSVI refers to the reflux of deoxygenated blood back into the central nervous system, and to decreased mean transit times for blood flow through the CNS, and not to any specific abnormality in venous anatomy.  It is entirely possible for an individual to have a venous anomaly that does not cause flow reflux or significant changes in mean transit times, and thus does not indicate CCSVI.



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