La semiluna e l'alone periluminale: Due segni con Tomografia Computerizzata di aneurisma aortico a rischio di rottura?

Purpose: To assess the prevalence, significance, and practical value of two recently described CT signs of instable aneurysm: The crescent sign (a curvilinear high-attenuating density within the thrombus) and the periluminal halo (a low-attenuating internal layer of the thrombus around the patent lumen). Material and methods: Among the CT examination performed in the last 5 years, we retrospectively selected the nonruptured aneurysms with a diameter exceeding 4 cm (no. = 93, average diameter 5.1 cm, unenhanced images in 28 cases and enhanced in 84) and the ruptured aneurysms (no. = 16, average diameter 6.7 cm, unenhanced images in 9 cases and enhanced in 9). We studied the prevalence of the crescent and halo sign, their relationship with the aneurysm diameter, and the effect of contrast enhancement Results: The crescent sign was identified with a statistically significant prevalence in ruptured (37.5% of cases) over asymptomatic aneurysms (5.5%); the halo, instead, had the same frequency in the 2 groups (12.5% and 9.5%, respectively). Both signs were more frequent in bigger aneurysms and were recognizable without differences in unenhanced and enhanced images. Conclusions: The crescent sign, though not exclusive of aneurysmal rupture, indicates instability and its detection should lead to careful follow-up or surgical repair. The halo seems to have no real value as risk factor.