title: [The crescent and the periluminal halo: two computer tomography signs of aortic aneurysm with risk of rupture?].
abstract: OBJECTIVE
  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).
  
  
  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.
authors.affiliation: Istituto di Scienze Radiologiche, Facoltà di Medicina, Università Federico II, Napoli.
authors.forename: O
authors.initials: O
authors.lastname: Catalano
authors.forename: B
authors.initials: B
authors.lastname: Cusati
authors.forename: A
authors.initials: A
authors.lastname: Rotondo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000150:complications / Q000000981:diagnostic imaging*; D001019:Aortic Rupture / Q000000981:diagnostic imaging / Q000453:epidemiology; D006801:Humans; D008875:Middle Aged; D012307:Risk Factors; D014057:Tomography, X-Ray Computed
vernacular_title: La semiluna e l'alone periluminale: due segni con Tomografia Computerizzata di aneurisma aortico a rischio di rottura?