Helical classification of type B aortic dissections.

Objective: Although anecdotal findings of spiraling aortic dissections have been reported, the mechanisms of dissection propagation are unclear; hence, we categorized type B dissection helicity and mechanistically explain distinct propagation patterns. Methods: From computed tomography of 102 patients, type B dissections were geometrically modeled from entry tear to renovisceral aorta and helical properties were quantified. Results: There were 4 distinct helical groups: right-hand chiral, left-hand chiral, mixed-chiral, and nonhelical. Right- and left-hand chiral cases exhibit true lumen blood supply to the celiac artery (CA) from the left side, whereas mixed-chiral and nonhelical cases supply the CA from the right, with only a few exceptions of CA ostial avulsion. Conclusions: Although left-hand chiral dissections make a gentle twist to have the true lumen supplying the CA from the left side, the right-hand cases must twist in the opposite direction much more dramatically to supply the CA also from the left. The prevalence of mixed-chiral cases suggests that chirality in the proximal descending thoracic aorta tends to reverse spiraling direction to supply the CA via the true lumen. This mechanistic description of dissection propagation improves the understanding of aortic dissection anatomy and pathophysiology, paving the way for better diagnostics and treatments.