MRI diagnosis of acute sigmoid colon diverticulitis in a young patient

Clinical History

We present a young man with known diverticulosis of the large bowel, who developed an acute abdomen. The clinical suspicion of acute diverticulitis was investigated with magnetic resonance imaging (MRI).

Imaging Findings

A young man complained of recurrent episodes of colicky abdominal pain and diarrhoea during the last 3 months, with presence of some blood and mucus in his stools. Under the clinical suspicion of chronic inflammatory bowel disease, he underwent ileo-colonoscopy with diagnosis of diverticular disease of the large bowel mainly involving the sigmoid colon.
After 6 more weeks he experienced a severe, sudden bout of lower abdominal pain with fever; physical examination discovered signs of peritonism with positive Blumberg sign, and marked tenderness at palpation in the pelvic region. Laboratory tests confirmed acute systemic inflammation with raised ESR and CRP levels.
The presumptive clinical diagnosis of acute diverticulitis, in consideration of his young age, was investigated with MRI. Unenhanced MRI documented diffuse involvement of the sigmoid colon by wall thickening with multiple small diverticula and a pericolonic mass. After intravenous gadolinium, marked enhancement consistent with active inflammation was seen in the thickened sigmoid walls, the perivisceral fat planes and the adjacent fascia; the pericolonic soft-tissue mass showed peripheral, abscess-like enhancement.
The patient underwent emergency surgery with a presumptive diagnosis of acute diverticulitis; at exploration a thickened, acutely inflamed sigmoid colon was found and resected.
Pathology reported a 12-cm large bowel segment with opaque serosal surface, multiple diverticula with histological signs of acute diverticulitis, and marked perivisceral inflammatory changes with some reactive lymph nodes.

Discussion

Radiologic imaging plays a paramount role in the Emergency Department for triage of patients with acute abdominal pain. A reliable, reproducible and rapid diagnosis is needed for selection of patients who need urgent surgery, since clinical evaluation is often inaccurate. The cost-effectiveness of CT for acute abdomen evaluation is widely recognized; mainly thanks to its widespread availability and speed, CT is the imaging modality of choice.

Diverticular disease is very common, especially in older people, and a significant proportion of affected patients will develop acute diverticulitis, with high misdiagnosis rates on clinical grounds.
In the past, diagnosis of diverticulitis relied on physical and laboratory findings, and colon contrast enema was the standard imaging method. Indirect signs including stenosis, lumen dislocation and sometimes extraluminal iodinated contrast extravasation allowed a variable, often insensitive diagnosis.
Currently CT, usually performed on multidetector scanners with multiplanar reformations, is the mainstay for the diagnosis of colonic diverticulitis. CT findings include colonic hyper-segmentation due to spasm, wall thickening and diverticula, hyperdensity of the perivisceral fat due to hypervascularization and/or oedema; in complicated diverticulitis, the perivisceral inflammation progresses to phlegmon and abscess formation, rarely to intraperitoneal perforation or fistulization.
Alternative conditions that clinically mimic diverticulitis and may be diagnosed with CT include colon carcinoma, faecal impaction, bowel ischemia, ovarian masses, renal colic or pyelonephritis.
The impact of CT in patients with acute diverticulitis has been well documented, with high performance for detection of severe forms with greater chances of medical treatment failure.

As this case exemplifies, MRI is a promising alternative to CT for diagnostic assessment of acute abdomen, and a particularly attractive imaging modality in patients for whom the risk of radiation is a major concern, such as children and pregnant women, or with contraindication to iodinated contrast agent due to previous allergic reactions or impaired renal function. MRI advantages include its high native soft tissue contrast, lack of ionizing radiation and the excellent safety profile of gadolinium-based contrast agents; direct multiplanar acquisition with MRI competes with MDCT reformations.
Reported experiences with MRI are still scarce, mostly limited to pregnant patients with conditions such as choledocholithiasis and gallbladder disease, appendicitis, adnexal torsion, tubo-ovarian abscess, endometriosis, Crohn ileitis and perianal fistulas.
Disadvantages of MRI include its limited availability, high cost, generally lengthy examination times, the need of trained radiographers and radiologists, lower spatial and temporal resolution compared with those of CT, and the incompatibility of MRI magnet with the equipment used for intensive care. Moreover, MRI in acute care setting requires technical and logistical effort, since imaging protocols have to be adapted to the constraints of uncooperative patients, with minimization of the duration of sequence acquisition, and strategies to reduce breath and motion-related artifacts. Improved MRI sequences include free-breathing T1- and T2-weighted, and volumetric isotropic post-contrast acquisitions allowing coverage of the abdomen or pelvic region in less than 30 seconds, and confident evaluation of the urinary tract, of areas of haemorrhage, inflammation and abscess formation.

Differential Diagnosis List

Final Diagnosis

Acute sigmoid colon diverticulitis

URL:	https://www.eurorad.org/case/8636
DOI:	10.1594/EURORAD/CASE.8636
ISSN:	1563-4086