Intravascular Ultrasound in the diagnosis and treatment of chronic cerebrospinal venous insufficiency

Thrombus (Figure 7)

Thrombus is another echogenic material within the lumen. Clot tends to be thicker and amorphous and has a speckled and more brightly echogenic character. It is also inconstant in location and less reproducible.

Diffuse narrowings

Intravascular ultrasound is very useful in assessing and differentiating the many causes of long narrowed segments Diffuse luminal narrowing can be a phasic, inconstant phenomenon or it can be caused by compression syndromes, by hypoplasia, by intimal hyperplasia or by post-thrombotic recanalization. Each of these presents venographically as a narrow contrast column. Differentiating these problems is sometimes challenging but important as different treatment strategies are warranted. Treatments vary from doing nothing to stenting.

Inconstant narrowing (Figure 8)

Inconstant narrowings are a physiological effect frequently associated with fixed stenoses that are located more centrally in the vein. The dual outflow system of the cerebral venous system through the internal jugular veins and the vertebral veins and vertebral plexus allows the obstructed vein to decompress. Because of the compliance of the veins, the vein can collapse. Such collapse may be more pronounced due to pressure upon this vein by the internal or common carotid artery or compressed by muscles.

Venography, as a static sequence, does not allow dynamic imaging because of time constraints and radiation exposure. Imaging with IVUS is free from these impediments and allows one to place the transducer at the point of interest and perform a variety of maneuvers. Maneuvers that increase flow by activation of the thoracic pump, such as deep expiration, may increase flow through the vein. Changing neck position, such as flexion and extension, internal or external rotation may reduce flow by increasing the pressure on the IJV.

Other compressions are more significant and IVUS can plan an important role in their evaluation. The Nutcracker and the May-Thurner syndrome are clinically manifested obstruction of the left renal vein and left common iliac vein that are caused by compression of these veins between two structures. IVUS shows complete flattening of the vein, associated with a prominent hemiazygous, or renal vein or, is

Long luminal narrowings (Figure 9 )

Long luminal narrowings may be caused by hypoplasia, intimal hyperplasia, post-thrombotic recanalization, or perivenous inflammatory processes. Venographic appearance of these entities can be virtually indistinguishable. When the luminal diameter is completely collapsed, differentiation of these abnormalities can be impossible. While IVUS may have theoretical advantages over venography in evaluating some of these conditions, there is little data published in the literature on this subject in general and none as it relates to CCSVI or jugular veins.

However, IVUS has the potential to differentiate these problems, based upon the echogenicity of the offending pathology. Hypoplasia shows a narrow lumen but the echogenicity of the wall may be normal. In a recanalized vessel, IVUS may show intraluminal thrombus lining the interior of the vein. Thrombus is highly echogenic and often can be differentiated from the reflections of the wall itself. The echogenic areas may be interspersed with areas of diminished echogenicity. Echogenicity will be less for intimal hyperplasia than for thrombus lining the vessel wall. Perivenous inflammation may be detectable as separate from the vein itself.