Suspected acute diverticulitis
Author: Charles Allison, MB ChB
Diverticulitis is an inflammation of a diverticulum caused by an initial obstruction and then infection of the diverticulum. This results in spread of the inflammation to the tissues surrounding the bowel. Clinical presentation is with abdominal pain usually in the left lower quadrant associated with fever.
WHAT STUDY? CT is the modality of choice for acute LLQ pain. Contrast enema or ultrasound are suitable alternatives.
CT is the investigation of choice in most cases, with the exception of young women of childbearing age, in whom ultrasound is preferred. Oral and intravenous contrast is preferred, but not essential if there is a contraindication. Administration of rectal contrast may be considered in such cases and may slightly improve sensitivity by dilating the colon. The reported sensitivity of CT for diagnosing acute diverticulitis is 79-99%. CT is excellent for detection of complications of diverticulitis including abscess and fistula formation; furthermore, it may detect non-colonic causes of RLQ pain that would be missed with contrast enema.
Contrast enema with plain radiography was previously the diagnostic test of choice for diagnosing diverticulitis before the advent of CT; it is still a good alternative with a sensitivity of 50-90% for diverticulitis. It is safe in patients with acute pain and no signs of perforation. Barium is preferred to water-soluble contrast, though water-soluble is less damaging to the peritoneum than barium should a perforation be present. Double contrast (involving administration of contrast then insufflation of air) is preferred to single contrast enemas.
Graded compression abdominal ultrasound is the investigation of choice in pregnant patients with suspected diverticulitis. Ultrasound is relatively inexpensive and non-invasive but there is some heterogeneity in sensitivity related to operator skill.
CT scanning is very fast and provides information on a wide spectrum of bowel, genitourinary and gynecological pathologies. It allows determination of disease extent and complications in diverticulitis, hence guiding management; this may not be possible with contrast enema. CT also has a role in surgery–sparing treatment of abscesses, through guiding percutaneous drainage. CT can often not differentiate between acute diverticulitis and a perforated colon carcinoma; as such follow up colonoscopy or contrast enema is usually recommended after the diverticulitis has resolved. It is less invasive than contrast enema but more expensive and involves a much larger dose of radiation.
Contrast enema is inexpensive and provides excellent views of the colonic wall, making it a good choice for suspected diverticulitis. It is also good for identifying colon carcinoma, which can be confused for diverticulitis on CT. As such, it is often used as a follow-up examination after diverticulitis has resolved, or in patients with more chronic symptoms or altered bowel habit. Patients with recurrent diverticulitis who present with the same symptoms are also good candidates for contrast enema, since it avoids the repeated high radiation doses of abdominal CT scanning.
Ultrasound is relatively inexpensive and non-invasive but may be somewhat operator dependent. It is slightly less good than CT for detecting diverticulitis, with reported sensitivity and specificity of 77-98% and 80-99% respectively. Abdominal ultrasound may be limited by patient factors such as excessive size or presence of bowel gas obscuring the image.
WHEN? Imaging should be performed at time of presentation if the diagnosis is in question in order to expedite management.
HOW TO ORDER?
It is important to reference the symptom or the sign as the clinical indication and not the diagnosis.
ie Patient with “LLQ pain” is acceptable, whereas R/O diverticulitis is not acceptable.
Optimal ordering would list symptoms/signs as well as the putative diagnosis being investigated: “LLQ pain, fever r/o diverticulitis”. This allows the radiologist to suggest alternative imaging strategies if a suboptimal approach has been ordered.
CT preparation depends on the use of contrast. For renal stones no contrast in required and the patient may be scanned immediately. Administration of oral contrast required drinking or NG administration of 30cc gastrograffin diluted in 900cc water to ensure it adequately coats the length of the bowel. Intravenous contrast in given in the scanner and may be timed to highlight the arterial or venous supply to a specific organ. The patient’s allergies, medications and renal function need to be identified before hand as the contrast is iodine based and carried risk of precipitating renal failure in at risk patients (diabetic, on metformin etc). The study itself takes about 1 minute once the patient is on the table
The patient should be fasting for 4 hours before an ultrasound examination; the procedure takes about 30 minutes.
CLINICAL RED FLAGS:
Acute deterioration with generalized abdominal pain, guarding and rebound and hypotension suggests perforation of a diverticulum. Although uncommon, it carries a high morality of around 5%, increasing to around 30% if there is feculent peritonitis. Appropriate management includes fluid resuscitation, broad spectrum antibiotics and prompt surgical exploration.
ACR Appropriateness Criteria
Frequency, sensitivity and specificity of individual signs of diverticulitis on thin section helical CT with colonic contrast material: experience with 312 cases – Kircher M, Rhea J, Kihiczak D, Novelline R
AJR 2002; 178(6): 1313-18