Three-phase Dynamic CT Findings of Liver Abscess:Related Factors with Multiple Layering Enhancement Pattern

ABSTRACT

PURPOSE: To determine the number of multiple alternating layers of liver abscess, and changes in this number, as revealed by spiral CT, and to ascertain which factors are related to changes occurring during the three phases of this modality. MATERIALS AND METHODS: Using three-phase spiral CT imaging we studied 26 cases of liver abscess (pyogenic:amebicm=23:3). The number of layers comprising the abscess, as seen on postcontrast CT scans, was determined during the arterial (30sec), portal (70sec), and delayed (220sec) phase, and all cases were assigned to one of two groups according to changes in the number of layers observed during the three phases. With regard to underlying disease, the two groups were compared in terms of the presence of abscess and of diabetes mellitus,CT interval (time from onset of symptoms to CT scanning), microbial agent (pyogenic vs. amebic), and the largest diameter of abscess as revealed by CT. RESULTS: Except in one case, three or four alternating layers [in 13(50%) and 7(27%) cases, respectively] were seen only during the arterial and portal phase. During each of the three phases-and especially the delayed phase, where it was present in 25 of cases (96%)-two alternating layers (2:2:2) was the most common pattern, with a 3:3:3 pattern occurring in one case. All 12 cases (46%) in the unchanging-layer group showed one of these two patterns. All changing-layer group cases (14;54%) demonstrated three or four layers during the arterial and portal phase but only two during the delayed phase. The CT interval was the only significantly different factor between the two groups. During the first week, the number of cases in the unchanging-layer group was much higher than in the changing-layer group (86%,14%), but during the second week this situation reversed (25%, 75%). CONCLUSION: Our study reveals that on three-phase dynamic CT images, a characteristic enhancement feature of liver abscesses is three or four layers during the arterial and portal phases, with reduction to two layers during the delayed phase. This change, as revealed by spiral CT, is rare during the week following the onset of symptoms, but common during the second week.