Gas distribution in intraabdominal and pelvic abscesses on CT is associated with drainability

Intraabdominal and pelvic abscesses are treated by percutaneous image-guided drainage, under sedation or general anesthesia. This study attempts to determine if the CT features of gas distribution are associated with "drainability." Our premise was that gas may be trapped deep in a collection as bubbles, if the material is thick. Gas may rise to the surface if the material is thin, forming either an air-fluid level or superficial bubbles.

Patients with intraabdominal and pelvic abscesses were identified by the interventional radiology database, after research ethics board approval. Patients without prior CT were excluded. The imaging and clinical records were analyzed retrospectively. Intracollection gas distribution was recorded as superficial bubbles, deep bubbles, or air-fluid levels. Collections were classified accordingly: type 1, air-fluid levels; type 2, superficial or deep bubbles and air-fluid levels; type 3, superficial bubbles; type 4, deep bubbles; and type 5, no gas.

One hundred five abscesses were examined in 61 patients, ranging in age from 2-17 years. Eight of 8 of type 1, 16 of 16 of type 2, 19 of 21 of type 3, 8 of 13 of type 4, and 43 of 47 of type 5 were drainable. The abscesses of all patients with an air-fluid level were drainable. Of abscesses with deep bubbles, 61.5% were drainable, versus 90.5% of those with superficial bubbles. Of those with superficial gas (superficial bubbles or air-fluid levels), 95.6% were drainable. In comparison with superficial gas, abscesses with deep trapped gas were associated with a longer duration of drainage, longer hospital stay, lower percentage of successful drainage, and higher percentage of residual collections. The difference is significant for drainability (p = 0.0048; p = 0.0331 after statistical adjustment for multiple testing).

Distribution of gas in an intraabdominal or pelvic abscess is associated with drainability. Abscesses with superficial gas (superficial bubbles or air-fluid levels) have a greater chance of being drained successfully than do abscesses with deep trapped gas.