18F-FDG-PET and other imaging modalities in the diagnosis and management of inflammatory bowel disease.

Am J Nucl Med Mol Imaging 2024;14(5):295-305 www.ajnmmi.us /ISSN:2160-8407/ajnmmi0156310 Review Article 18F-FDG-PET and other imaging modalities in the diagnosis and management of inflammatory bowel disease Abhijit Bhattaru1,2, Anish Pundyavana1,2, William Raynor1, Sree Chinta1,2, Thomas J Werner1, Abass Alavi1 Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, The United States; 2Department of Medicine, Rutgers New Jersey Medical School, Newark, New Jersey, The United States 1 Received March 3, 2024; Accepted August 22, 2024; Epub October 15, 2024; Published October 30, 2024 Abstract: Inflammatory bowel disease (IBD), which encompasses ulcerative colitis (UC) and Crohn’s disease (CD), is a chronic inflammatory condition of the gastrointestinal (GI) tract that presents complex diagnostic and management challenges. Early detection and treatment of IBD is paramount, as IBD can present with serious complications, including bowel perforation, arthritis, and colorectal cancer. Most forms of diagnosis and therapeutic management, like ileocolonoscopy and upper endoscopy are highly invasive and require extensive preparation at great discomfort to patients. 18F-fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) imaging can be a potential solution to the current limitations in imaging for IBD. This review explores the utility and limitations of various imaging modalities used to detect and manage IBD including ileocolonoscopy, magnetic resonance enterography (MRE), gastrointestinal ultrasound (IUS), and 18F-FDG-PET/computed tomography (18F-FDG-PET/CT) and magnetic resonance imaging (18F-FDG-PET/MR). This review has an emphasis on PET imaging and highlights its benefits in detection, management, and monitoring therapeutic response of UC and CD. Keywords: 18F-FDG-PET, IBD, non-invasive imaging, ulcerative colitis, Crohn’s disease Introduction Inflammatory bowel disease (IBD) manifests as inflammation of the digestive tract and consists of two main types: Crohn’s disease (CD) which affects the gastrointestinal tract from the mouth to the anus and ulcerative colitis (UC) which is primarily restricted to the large intestine and rectum [1]. These disorders are characterized by abdominal pain, vomiting, weight loss, fever, and inflammatory bowel syndrome, among other symptoms [2-4]. Although CD and UC are somewhat similar, there are distinguishing factors in presentation. CD associated inflammation affects the full thickness of the bowel, while UC commonly affects the innermost layers, the mucosa and submucosa; inflammation in CD can occur in non-contiguous patches or “skip lesions”, while inflammation in UC tends to be contiguous [5]. Due to these patterns of inflammation and areas of the gastrointestinal tract that are involved, the two disorders can be distinguished symptomatically. CD patients more commonly suffer from malnutrition, and in severe cases may suffer from intestinal abscesses and fistulas, while UC patients usually suffer from bloody diarrhea [6, 7]. The pathogenesis of IBD has not been clearly attributed to any single cause but rather associations have been found between incidence of disease and the presence of various gut microbiota, mutations associated with immune system dysregulation, as well as environmental factors [8-10]. The lack of a cure for CD and UC ensues from the incomplete understanding of the pathogenesis of IBD, yet there are common treatments that have varying degrees of success in achieving remissions such as enteric-coated budesonide for CD and aminosalicylates for UC; immunomodulators and antiTNFα inhibitors are implemented in the treatment plan when remission is not sustained [11, 12]. Despite incomplete knowledge of IBD manifestations in various patient populations, diagnostic modalities have seen promising improvements and innovations in recent years. The purpose of these techniques is primarily to properly diagnose patients in cases of suspected IBD and record disease progression, including extraintestinal manifestations [13]. Ileocolonoscopy and upper endoscopy with biopsy have been considered the golden standard of differentially diagnosing CD versus UC because they allow for direct visualization of various parts of the gastrointestinal tract, leading to proper diagnosis in over 75% of cases because different patterns of inflammation can be differentiated histopathologically, and because of what traditionally have been considered endoscopic-specific features [14-18]. In UC, these features are mucosal erythema, mucosal edema, and mucosal friability, while in CD they are aphthous ulcers, discontinuous longitudinal ulcers, and cobblestone appearance in the mucosa [19, 20]. Beyond diagnosis, ileocolonoscopy and upper endoscopy have been identified as particularly apt for detecting mucosal healing [21-23]. Capsule endoscopy (CE) has emerged as an effective and less invasive substitute to ileocolonoscopy [24, 25]. MRI has the advantage of not exposing patients to radiation, which allows for motion-free, high resolution images of the body [26, 27]. While MRI has high accuracy with respect to grading frank disease, it has been found to https://doi.org/10.62347/YXQT2560 18F-FDG-PET in IBD overstage disease activity in 38% of patients in remission [28]. MR enterography (MRE) has the disadvantages of high cost, reduced availability, and considerable duration compared to other radiographic techniques [29]. Dynamic contrast enhanced- and diffusion weighted MRI have been found to correlate with histopathological scores of surgical specimens in CD patients in addition to providing additional information beyond that of regular MRI [30]. Similar to MRI, ultrasound (US) has the advantage of not exposing patients to radiation, and also requires minimal bowel preparation [31, 32]. US has some additional unique advantages that help with monitoring of IBD complications. First, US can be used as a staging test to monitor patient’s active disease status [33]. Additionally, it provides faster assessment of systemic complications such as fistulas seen in CD, and it is more comfortable for patients who have serial assessment. US has demonstrated greater utility in CD rather than UC [34]. Currently, the usage of US in assessment and management of IBD is dwarfed by more favored structural imaging methodologies, but there is a strong motivation for clinicians to increasingly use US for monitoring IBD [35]. Considering the approximately 600,000 patients each with CD and UC along with the peak incidence years of CD and UC overlapping with the pediatric patient age range, diagnostic measures must take into account the tendencies of younger patients [36-40]. Another important consideration is a diagnostic technique that is apt for frequent application in terms of low cost, time effectiveness, and minimal radiation exposure because of the cumulative 67%-83% relapse rate 10 years after initial diagnosis and high documented remiss (...truncated)