Comprehensive assessment of ulcerative colitis with high-resolution water enema multidetector CT colonography

Clinical History

A 54-year-old female patient with known ulcerative colitis, currently undergoing medical treatment, was referred for radiological investigation and colorectal cancer screening, following incomplete follow-up optical colonoscopy because of left colon rigidity and poor patient tolerance. Endoscopy reported superficial mucosal changes consistent with the disease, plus pseudopolyps in the explored descending colon.

Imaging Findings

During consultation with the patient and referring clinician, the attending radiologist proposed contrast-enhanced water enema multidetector CT colonography (WE-MDCT) to obtain a comprehensive evaluation of endoluminal, mural, and pericolonic changes.
After standard bowel cleansing preparation (3 liters polyethylene-glycol solution the day before), WE-MDCT was performed with pharmacological hypotonization (20mg intravenous N-butyl-scopolamine), instillation of 1, 5 liters warm tap water through a rectal tube, volumetric acquisition with the patient supine starting 75 seconds after 120 ml contrast medium injection.
Multiplanar reformatted CT images depicted extensive longitudinal inflammatory involvement of the rigid, poorly distended descending colon, showing moderate, enhancing circumferential wall thickening. Furthermore, some millimetric endoluminal projections corresponding to endoscopic finding of pseudopolyps were identifiable. Ancillary inflammatory findings included proliferating pericolonic fat with hypervascularity (comb sign) and tiny lymphnodes. The well-distended recto-sigmoid, transverse and right colon did not show appreciable mural thickening, stenosis or endoluminal vegetations. Extraluminal abnormalities and complications were confidently excluded.

Discussion

Ulcerative Colitis (UC) is a life-long, relapsing and remitting chronic inflammatory disease, whose precise aetiology is unknown. Pathologically, UC is characterized by extensive ulceration and diffuse non-granulomatous mucosal inflammation that usually begins in the rectum and variably extends proximally along the large bowel. Colonoscopy represents the reference standard for the UC assessment as it allows direct visualization and biopsy of mucosal changes, that are needed for assessing disease extent, severity, activity, and post-treatment, as well as to screen for colorectal carcinoma [1].
Experiences using virtual CT-colonography (CTC) with air or CO2 insufflation to assess inflammatory bowel diseases yielded conflicting results, with unsatisfactory visualization of mucosal abnormalities and a potential, increased risk of perforation because of the fragile, inflamed colonic walls [2, 3].
Currently, water enema multidetector CT (WE-MDCT) with retrograde colonic distension using water and intravenous contrast administration is increasingly proposed as the best imaging technique in patients with suspected or proven colorectal cancer, as it provides excellent visualization of the enhanced bowel wall, and good contrast to the hypodense lumen and pericolonic fat. Reported advantages of WE-MDCT over air CTC include no risk of perforation, optimal patient tolerance, short learning curve without need for complex postprocessing, presurgical multiplanar visualization with submillimeter spatial resolution, high accuracy for assessment of both mural colonic diseases and associated extramural findings and complications [4, 5].
As this case exemplifies, in patients with incomplete colonoscopy WE-MDCT can prove very useful as a complementary technique to assess inflammatory colitis, as it can assess site and extent of colorectal involvement, rigid bowel segments, mural thickening and enhancement related to inflammatory activity, and the presence of endoluminal pseudopolyps [6, 7].
Despite UC being a primarily mucosal disease, bowel wall thickening is a common CT feature. In subacute and chronic phases, mural thickening, colon shortening and luminal narrowing result from submucosal fat deposition and transmural fibrosis, producing a “fat halo” appearance. Conversely, acute phases show mural thickening with stratified appearance due to mucosal hyperenhancement (corresponding to endoscopic erosion and ulceration changes), and oedematous submucosa: these features plus mesenteric hyperemia, pericolonic fat stranding and lymphadenopathies are positively associated with endoscopic activity, whereas only the degree of wall thickening measured on WE-MDCT significantly correlates with histologic severity [7]. Notably, in well-distended colonic segments with thin walls and preserved haustra, early superficial and flat mucosal abnormalities cannot be excluded, since they are below the high resolution power of the CT technique [6].

Differential Diagnosis List

Final Diagnosis

Ulcerative colitis with substenotic descending colon.

URL:	https://www.eurorad.org/case/10189
DOI:	10.1594/EURORAD/CASE.10189
ISSN:	1563-4086