Curved Planar Reformatted CT Angiography: Utility for the Evaluation of Aneurysms at the Carotid Siphon

I read with interest the article by Ochi et al (1) and can confirm that the technique they describe is accurate in the detection and delineation of aneurysms of the terminal internal carotid artery. It is a technique that we have been employing within the Institute of Neurological Sciences in Glasgow since 1988 that evolved to an examination of patients with isolated CN III palsy, with the goal of obviating the need for invasive angiography (2). The original method used overlapping single slices and a straight parasagittal oblique plane planned from the coronal reformation with standard Philips software. In 1990 when the Elscint Elite CT ws installed, true curved planar reformations (CPR) were introduced, producing a curved parasagittal oblique from the coronal arterial projection, as described by Ochi et al. We reported 36 patients prospectively studied with isolated CN III palsy: 17 aneurysms were found in 13 patients, all causative aneurysms were detected, and all normal vessels and aneurysms were confirmed with arterial angiography. Another article followed on the comparison between 3D CT and CPR (3), and our conclusions are similar to those described by Ochi et al; that is that CPR is superior to 3D CT for the detection and delineation of aneurysms even with cine loop rotations of the 3D data. This led us to replace conventional angiography with CT angiography and CPR by 1990 for the primary investigation of patients with CN III palsy. The technique is robust, and its efficacy is attested to by a recent follow-up article of 100 consecutive patients with CN III palsy investigated by CT angiography (4) in whom all causative aneurysms were detected and follow-up showed no cases had been missed. Those palsies caused by local tumors were also diagnosed from the source images as the scanning of parameters (120 Kv 400 mas per single slice) allowed analysis of the soft tissues and vessels, unlike to low-helical CT angiographic technique of Ochi et al.