Falsely Claiming Use of NASCET Percentage Stenosis Method

Abstract

We read with interest the report of Dr Anzidei and colleagues (1), which appeared in the May 2009 issue of Radiology, in which they compared steady-state contrast agent–enhanced magnetic resonance (MR) imaging with digital subtraction angiography (DSA) for the imaging of internal carotid artery (ICA) stenosis. This is an important contribution. Stenosis degrees were peripheral to this report, yet they were included. North American Symptomatic Carotid Endarterectomy Trial (NASCET) percentage stenosis methods (2–4) are referenced, with the explanation that percentage stenosis was used as a denominator beyond the bulb, where the walls are parallel, and was not The chief neuroradiology investigator (A.J.F.) for NASCET measured thousands of ICAs (2–4) in a consistent way as a balance to other inconsistent measurements (4,8–10). Yet, the so-called NASCET method for carotid stenosis calculation failed to enlist sufficient compliance. This is because many investigators choose ratio denominators from ICA locations that are too proximal, where the bulb is still tapering, contrary to the NASCET criteria to measure “where walls are parallel.” NASCET researchers never measured near occlusions, as it is fallacious and requires near occlusion interpretation before measuring. However, Dr Anzidei and colleagues ignore this in figure 1 (1). Researchers in scores of studies have also claimed to use NASCET criteria for percentage stenosis, yet the values they have produced have little relationship to NASCET. However, all of these investigators associate their findings with NASCET outcomes, with potentially many more surgeries resulting from overstated percentage stenosis. Radiologists are culpable for sending patients for surgery or stent placement on the basis of incorrect NASCET measurements and for the associated costs and risks. The ICA bulb is an anatomic aberration (2,4), which is larger than its outflow ICA. NASCET investigators adopted its method to provide the basis for a consistent measurement of percentage ICA stenosis, yet compliance with this method seems to be poor, with many authors using their own pseudo-NASCET methods. If the percentage stenosis denominator were eliminated and investigators and clinicians were to use the actual stenosis measurement in millimeters (7,13), now that it can easily be obtained, these ratio pitfalls that have been muddying things for years would be removed. References