Differentiation of chronic total occlusion and subtotal occlusion of the femoropopliteal artery-role of retrograde flow sign and collateral circulation on CT angiography images

Differentiating total from subtotal arterial occlusion in lower extremities by using reverse attenuation gradient sign in CT angiography

OBJECTIVES

To investigate the use of reverse attenuation gradient sign (RAGS) in CT angiography (CTA) to differentiate total from subtotal occlusion in lower extremities which poses different challenges for the procedure and carries different prognoses.

METHODS

Eighty patients with 91 lesions in the lower extremities were divided into total occlusion (TO) group and subtotal occlusion (SO) group confirmed by digital subtraction angiography. The CT numbers of vascular lumen at the end of lesion (proximal, P) and at the first entrance (distal, D) of the lateral branch were measured and their difference (CT(PD) = CT(P) - CT(D)) of each lesion was calculated. The CT number gradient (G(DP) = 2 * CT(PD)/[CT(P) + CT(D)]) was calculated by dividing the CT number difference by the average CT number of the two points. The existence of RAGS where the CT number at the distal point is higher than that at the proximal point (CT(PD) and G(PD) < 0) was determined and the diagnostic efficacy of using RAGS in CTA for differentiating total from subtotal occlusive lesions in lower extremities was calculated.

RESULTS

The SO group had higher CT numbers than the TO group (p < 0.001). More importantly, the SO group had positive CT number gradient (G(PD) > 0), while the gradient was negative (G(PD) < 0) in the TO group. The specificity and sensitivity of using RAGS (G(PD) < 0) in images for diagnosing TO of lower extremity were 97.6% and 92.0%, respectively, and 87.8% and 88.0% using the standard CTA images.

CONCLUSION

The use of RAGS in CTA images has high diagnostic accuracy to differentiate TO from SO in lower extremities.

KEY POINTS

• Total occlusions often exhibit higher CT number at distal point than at proximal point to the occlusion. • The reverse attenuation gradient sign (RAGS) may be determined using the CT number measurements between the proximal and distal points after occlusion. • RAGS can be used to improve the diagnostic efficiency in CTA to differentiate between total and subtotal occlusions of lower extremity arteries.