Unknown Case of the Month #113
The CT scan shows thickening and induration
of the sigmoid colon with a fistulous track extending to the bladder on the
right. A small amount of barium is seen in the base of the bladder, along
with air in the non-dependent portion.
secondary to diverticulitis
Colonic diverticuli are herniations of
mucosa and submucosa through the hypertrophied muscularis of the colonic
wall between the mesentery and lateral tenia at sites of vessel and nerve
entry secondary to increased muscular thickening (myotactic contractures)
and chronic increased intraluminal pressure. Between 5-10% of the US
population over the age of 45 years have diverticulosis, a prevalence that
increases to roughly 80% by the age of 85 years. Approximately 10-35% of
these patients will develop symptoms and 25% of those will require surgery.
Diverticulitis occurs when the narrow neck of the diverticulum becomes
occluded, leading to inflammation and localized perforation. 95% of cases of
diverticulitis involve the left colon, with less than 5% occurring on the
right. Patients present with left lower quadrant pain, fever and elevated
WBC. Bleeding may supervene and is more common on the right.
CT has become the diagnostic modality of
choice. The most common findings are bowel wall thickening, disproportionate
fat stranding and the presence of diverticuli. Other signs of diverticulitis
include: fascial thickening, free fluid, inflamed diverticula, engorged
mesenteric vessels, pneumoperitoneum (rare), arrowhead signs, phlegmons, and
intramural air. Abscess formation (30%) and the presence of mesenteric air
pockets >5mm are poor prognostic signs for non-operative treatment.
Intramural sinus tracts and fistula to adjacent organs (most commonly
involving the urinary bladder – 65% of all diverticular fistulas) may be
suggested on CT scans due to intravesical air, focal bladder wall
thickening, or extraluminal masses. Presenting symptoms include: recurrent
cystitis, fever, abdominal pain, pneumaturia, and fecaluria. If a
colovesicle fistula is suspected, the CT scan should be performed with bowel
contrast only (no IV contrast) and prior to bladder instrumentation in order
to maximize the chance of observing intravesicle air or contrast (urine
centrifugation may be helpful). Barium enemas have a sensitivity of only
Other causes of colovesicle fistulas
include: Chron’s disease (usually younger patients with ileovesical
fistulas), radiation therapy, pelvic surgery, foreign bodies and colon
cancer. Approximately 10% of sigmoid colon carcinomas will have associated
diverticular disease and the two may be occasionally difficult to
differentiate. Carcinoma causes a shorter irregular or eccentric stricture
with shouldered (apple core) ends, mucosal destruction, a relative paucity
of surrounding mesenteric fat stranding (vs. diverticulitis) and
Horton KM, Corl FM, Fishman EK. CT evaluation of the colon: inflammatory
disease. RadioGraphics 2000; 20:399-418.
Joseph RC, Amendola MA, Artze ME, et al. Genitourinary tract gas: imaging
evaluation. RadioGraphics 1996; 16:295-308.
Yu NC, Raman SS, Patel M, et al. Fistulas of the genitourinary tract: a
radiologic review. RadopGraphics 2004; 24:1331-1352.
Dr. Lawrence C. Swayne, Attending
Morristown Memorial Hospital