2.2. Definition and measures

SIVAD patients were divided into two groups: asymptomatic (incidental findings) or symptomatic (absence of explanations other than dissection-related). The symptomatic group was divided into nonoperative and endovascular groups (no patients had undergone surgery), based on the treatment received. Patient characteristics, incidence, vascular risk factors, medical histories, follow-up duration, length of hospital stay, change of symptoms, treatment strategies and morphology of the dissection in the CE-CT images and morphological changes were analyzed and compared between groups. Further, we classified the five types based on the CE-CT images (Fig. 1): type I (patent true and false lumen revealing entry and re-entry sites); type II (blind pouch of false lumen); type III (partial thrombosis false lumen); type IV (completely thrombosis false lumen); type V (completely thrombosis lumen).

Drawings illustrate the five types classification based on the abdominal contrast-enhanced computed-tomography for spontaneous isolated visceral artery dissection. Type I: patent true and false lumen revealing entry and re-entry sites; type II: blind pouch of false lumen; type III: partial thrombosis false lumen; type IV: completely thrombosis false lumen; type V: completely thrombosis lumen.