Poststenotic dilatation.

Partial narrowing of arteries produces poststenotic dilatation. This appears as a dilation of the vessel wall 1 to 3 centimeters distal to the area of a partial stenosis. When a stenotic band is placed in dogs, poststenotic dilatation develops rapidly, often within eight to ten days. Moderate stenoses that produce a bruit and thrill are effective in eliciting poststenotic dilatation, whereas very tight and very mild stenoses usually are ineffective. Thus, development of poststenotic dilatation requires the presence of flow disturbances sufficient to produce an audible bruit and a palpable thrill. Although the exact flow disturbance is uncertain, statis, increased lateral pressure, cavitation, abnormal shear stresses and turbulence all have been postulated to be the cause of poststenotic dilatation. Of these, experimental studies support abnormal shear stresses and turbulence as the most likely causes. Whatever the flow disturbance, it must make the wall vibrate to produce poststenotic dilatation. Vibrations are thought to produce alterations in wall elastin and possibly in vascular smooth muscle tone. This leads to dilatation of the vessel. If the dilatation is slight, removal of the stenosis may cause reversal of poststenotic dilatation with recovery beginning within hours of correction of the stenosis. If the dilated area is enlarged to twice normal diameter, it may exhibit permanent aneurysmal changes and, therefore, requires resections with reanastomosis. Arteries that are dilated to as little as one-third more than normal size may contain areas of ulceration with overlying thrombus. These vessels also may require resection with reanastomosis.