When atherosclerotic plaques develop, the cross-sectional area of the artery at that point often increases to accommodate the plaque without any reduction in lumen size. In consequence the angiogram does not detect a high proportion of atherosclerotic plaques. The increase in size of the artery (compensatory dilatation-arterial remodelling) varies widely in degree between different plaques even in the same artery. Dilatation of a degree to prevent any loss of lumen size is regarded as adequate compensatory dilatation. In contrast, other plaques are associated with no or minimal increase in the vessel cross-sectional area and a reduction in lumen size in present (inadequate compensation). High-grade stenosis is in particular associated with a total failure of remodelling. Such plaques may have had a rapid growth phase, out-pacing the ability of the medial smooth muscle cells to undergo a rearrangement. The phenomenon of remodelling has important consequences for pathologists who use the traditional method of comparing the lumen size relative to the cross-sectional area of the vessel at the site of a plaque to measure stenosis. The area of the vessel at this point may be anything up to 60% above its size before the plaque developed. An error is introduced which on average overestimates diameter stenosis by 30% when compared to an angiographic equivalent method in which the lumen size at the lesion is compared to the lumen size at an adjacent segment of artery without a plaque.