RADIOLOGY: GENITOURINARY: GU: Case# 32872: PERIDIVERTICULAR ABSCESS OF SIGMOID COLON, COMMUNICATION WITH BLADDER. 64 year old male with leukemia, now with pneumaturia. CT requested to R/O a bladder fistula. There is a 4.0 x 2.5 cm abscess cavity which abuts the left anterolateral wall of the bladder. It contains gas and fluid and communicates with adjacent sigmoid colon. There are inflammatory changes in the surrounding mesentery, and the wall of the sigmoid is thickened. There is a large amount of air within the bladder. Bone windows demonstrate a diffuse, mottled decrease in bone density, consistent with marrow placement by leukemia. CT has been shown to be capable of detecting the presence of diverticulitis, confirming the existence of fistulae, especially to the bladder, and in determining the presence and location of pericolic abscesses. The visualization of an inflammatory process in the pericolic fat is the primary diagnostic feature of diverticulitis. Most diverticula occur along the messenteric surface of the colon. Thus, perforation due to diverticulitis is initially confined to between the leaves of the mesocolon. CT is superior to barium enema in the documentation of this extraluminal disease. DIverticula are seen on CT as small rounded collections of air, feces, or contrast material outside of the lumen. Diverticulitis is also associated with thickening of the colon wall (>5mm). Other findings include pericolic inflammatory soft tissue mass often containing fluid, air, contrast, or fecal material; linear stranding densities in pericolic fat representing inflammatory changes; sinus tracts and fistulae to adjacent organs or skin represented by linear fluid or air connections. Diverticulitis can be associated with the formation of an extensive abscess. Bowel and urinary tract obstruction as a result of inflammation are not uncommon.