CT Enterography score: a potential predictor for severity assessment of active ulcerative colitis

Ulcerative colitis (UC) is a chronic non-specific inflammatory bowel disease (IBD) characterized by diffuse inflammation of bowel mucosa and a relapsing disease course. UC mainly affects the rectum and sigmoid colon, but may involve the entire colon and terminal ileum [1‐3]. As UC is a chronic condition, management of these patients requires prolonged treatment and regular follow-up throughout the course of the disease. Accurate evaluation of UC is a crucial component of therapeutic decision-making [4, 5]. However, owing to the non-specific symptoms, assessment of UC typically requires a combination of colonoscopic, histological and radiological examinations in addition to clinical examination [6].

Modified Mayo score is used frequently for assessment of UC activity [7], mainly depending on patient’s symptoms and colonoscopy. Colonoscopy affords direct visualization of the colonic mucosa and has been the preferred method for defining the extent and site of inflammation, and to obtain biopsy specimen [8]. However, colonoscopy does not provide information on extra-intestinal manifestations and complications of UC. Moreover, in severe cases of UC, colonoscopy is contraindicated due to the risk of perforation or exacerbation of disease activity [9]. At present, computed tomography enterography (CTE), with its high contrast resolution and rapid images capability, allows evaluation of intramural and extra-intestinal involvement of UC and complications such as fistula, abdominal abscess or cellulitis. CTE is now widely used to diagnose and monitor inflammatory bowel disease (IBD), including UC [10, 11].

Establishment of a quick and accurate method to predict the severity of UC is an important goal for improving management of patients in future. Depending on the symptom, endoscopy and histology findings to predict the severity of UC is quite complex and time-consuming. Several studies have suggested the utility of CTE for assessment of severity of UC and a positive association of CTE findings with clinical and colonoscopic findings has been demonstrated [11]. Thus, identification of a CTE score system to assess and predict the severity of active UC is possible. However, to the best of our knowledge, no previous studies have investigated the utility of CTE score in predicting the severity of UC.

In this retrospective study, we assessed the individual CTE features in different severity of active UC, established a new CTE score system for UC, and analyzed the correlation between cumulative CTE score and modified Mayo score, so as to investigate the possibility of CTE score system as a predictor in assessing the severity of active UC.

The symptoms of active UC include persistent or recurrent episodes of diarrhea, intestinal bleeding with abdominal pain, tenesmus and different levels of systemic symptoms [2]. Repeated bouts of inflammation lead to chronic active UC, and increase the grade of activity [11]. Based on the extent of involvement and degree of inflammatory activity, the active inflammatory severity of UC was divided into mild, moderate and severe disease.

In patients with UC, an exhaustive evaluation of disease extent and activity is crucial for therapeutic decision-making [17‐19]. Therapeutic planning and follow-up is related to disease severity [10]. Modified Mayo score comprised of four categories (stool frequency, rectal bleeding, endoscopic appearance and physician assessment) is common used to evaluate severity of active UC [2, 20]. Nevertheless, these are indirect indices, mainly relying on self-assessment of symptoms by the patient [21]. Moreover, endoscopy can not provide information on bowel wall, extraintestinal manifestations and complications of UC [22].

CTE with increased speed and resolution, allows for comprehensive assessment of the bowel wall and extra-intestinal manifestations and becomes a useful compliment to endoscopy [23‐25]. A few studies have focused on the accuracy of CTE for the detection of UC. Johnson et al. [26] reported that an overall sensitivity of 74% for the detection of IBD (either Crohn or UC), and sensitivity was 93% for the detection of moderate and severe disease in well-distended colons and specificity was 91%. Andersen et al. [27] reported a moderate correlation of the loss of haustration, rigid bowel wall, and bowel thickness with severity of UC. Our study and previous studies showed that CTE was highly correlated with colonoscopic findings in assessment the extent of UC. Consequently, CTE is an ideal method and has great potential in evaluation for UC even at earlier occasion.

CTE spectrum are correlated closely with pathological findings and has the ability to reflect the pathological changes of UC. Pathologically, the early stages of UC are characterized by mucosal hyperplasia, increased mucosal vascularity, congestion and edema, which present as mucosal hyperenhancement and bowel wall thickening on CTE. With progression of disease course, the disease is characterized by multiple mucosal erosions or ulcers, which may manifest as mucosal bubbles in interrupted mucous. With further development of UC, the disease is characterized by edema, congestion, and inflammatory cells infiltration of submucosa, and hyperplasia and chronic fatty deposits of muscular layer. On CT, these changes appear as mural stratification and loss of haustration. In addition, luminal narrowing due to hyperplasia and fibrosis of muscularis mucosa occurs along with enlarged mesenteric lymph nodes and engorged mesenteric vessels due to chronic inflammation. Also, perirectal stranding is hallmark of chronic disease [11, 27, 28]. These pathological characteristics allow an objective assessment which reflects the severity of UC.

In our study, the spectrum of CTE findings in the three groups was difference. Bowel wall thickening and mucosal hyperenhancement were the essential characters and almost observed in all the cases. However, mucosal bubbles were more frequently observed in the moderate group as compared to that in the mild group. Mural stratification, loss of haustration and enlarged mesenteric lymph nodes in the severe group were significantly higher than that in the moderate group. Compared with the mild group, patients in the severe group were more likely to show mucosal bubbles, loss of haustration, engorged mesenteric vessels and enlarged mesenteric lymph nodes. Thus, increasing severity of UC demonstrated various CTE findings, reflecting the corresponding severity of intestinal inflammation. In mild UC, the intestinal inflammatory was mainly located in the mucosa and submucosa. In more severe disease, the inflammation spread from mucosa and submucosa to the whole intestinal wall, including ulceration and edema [27]. Small and tiny ulcerations are hard to detect by CTE. Mucosal bubbles represents obvious ulcer indicating more serious inflammatory activity. Mural stratification and loss of haustration indicated the UC involving the whole intestinal wall suggesting the severe disease. However, no statistically significant difference was found between the three groups with respect to luminal narrowing, perirectal stranding and pseudopolyp. Because these three signs may be more related to disease duration and individual differences rather than the disease severity [29].

Due to the correlation between the extent of UC and the clinical manifestations, the wider the extent of UC is, the worse are the symptoms. Due to this, the extent of UC was added to the CTE score system. A synthesis of all CTE features provides for a quantitative score system to evaluate the severity of UC. Our results showed a statistically significant difference in the CTE scores between the three groups. Moreover, the CTE score strongly correlated with modified Mayo score (r = 0.835). With aggravation of the disease course, CTE score increased significantly. Patel et al... [11], reported a weak correlation between the composite CT severity score and clinical assessment (r = 0.45), while bowel thickening, mucosal hyperenhancement, and mural stratification each individually showed a moderately positive association with clinical severity (r = 0.58; 0.57; 0.68). One possible reason is that our sample size is relatively large, and the modified Mayo scoring system (including colonoscopy) was used to evaluate active UC. Moreover, compared with the study of Patel et al [11], we developed a more comprehensive CTE score system in which CTE features correlated with disease severity as reflected in the extent of UC, mucosal bubbles, luminal narrowing and loss of haustration. Finally, we used plenty of low-density contrast media to expand the colon and the small intestine. The intraintestinal CT characteristics of UC such as mucosal bubbles, mural stratification, mural hyperenhancement may be displayed clearly with use of such agents, as opposed to high-density contrast media.

Accurate prediction of severity of active UC using a convenient method is necessary for management. Current methods (depending on the symptom, endoscopy and histology findings) to predict the severity of UC have some limitations. CTE provides more valuable information for judgment of active UC severity and maybe predict the severity. To our best knowledge, there are few studies using CTE score to predict severity of UC. In our study, based on ROC analysis, the CTE score system has the potential ability of predicting severity of UC. Our study showed CTE score was better for predicting moderate and severe disease of active UC with a CTE score cut-off value of 9.5 with high specificity. But there was no optimal cut-off value for predicting mild and moderate UC. This is probably due to the selection bias for the relative small number of mild UC. Another possible reason is there are more overlapping CTE findings between mild and moderate UC. Moreover, the CTE features are easier to identify with increasing inflammation degree. Even so, patients with UC whose CTE score more than 9.5 should be considered as having moderate or severe inflammatory severity. It is strongly recommended that such patients should be hospitalized.

Consequently, CTE enabled a comprehensively assessment of UC, helped determine the optimal treatment strategy and, to some extent, made up for the limitations of the conventional CT, as development of new signs on CTE, such as mucosal bubbles and loss of haustration showed a correlation with pathological changes of UC. These advantages are of clinic relevance in the diagnosis and classification of UC. Thus, CTE can be a reliable examination method that helps in systematic evaluation of the severity of UC.

There are some limitations in our study. Firstly, the score given to each characteristic should ideally be derived based on regression analysis. However, for our study, the sample size is relative small. Most of the cases are severe groups (41.3%, 19/46) and selection bias can not be avoided. Thus, we did not use regression analysis in building CTE score system. Secondly, this CTE score system cannot be reliably used as a predictor of the outcomes of UC; however, it remains a very interesting subject to investigate. These need a further study enrolling a larger number of patients from multiple centers.

CTE enables assessment of extraintestinal manifestations and complications of UC. And, CTE score system provides a quantitative basis for accurate assessment of the severity of UC. Thus, CTE is a valuable supplement to the traditional methods such as colonoscopy and clinical assessment. It can be used as a potential predictor of severity assessment of active UC, help determine therapeutic strategy, and predict prognosis.