Crohn’s disease is a chronic idiopathic inflammatory bowel disease characterized by segmental, discontinuous inflammation of the gastrointestinal tract. Unlike ulcerative colitis, which progresses continuously from the rectum to the cecum, Crohn’s disease can affect any part of the gastrointestinal tract, with a predilection for the terminal ileum and proximal colon. Typical symptoms include chronic diarrhea and recurrent abdominal pain, though some patients first present with complications or extraintestinal manifestations [1]. Anemia and elevated C-reactive protein may be observed [2]. Fecal calprotectin is a valuable marker for differentiating Crohn’s disease from irritable bowel syndrome  and for assessing disease activity, flare-ups, and treatment response [3].

Crohn's disease arises from a complex interaction of genetic, immunological, and environmental factors. Genetic predisposition plays a significant role, with numerous genes influencing immune function and gut barrier integrity increasing susceptibility. However, genes alone aren't sufficient; the immune system malfunctions, with an overactive response in the gut leading to chronic inflammation. This dysregulated immunity is likely triggered by environmental factors like smoking (a major risk factor), infections, and potentially diet, though the specifics are still being researched [4].

Crohn's disease pathology progresses through distinct stages. Initially, inflammation is confined to the mucosa, characterized by neutrophilic cryptitis, lymphoid hyperplasia, lymphedema, and superficial aphthoid ulcers. As the disease advances, inflammation extends through the entire bowel wall, creating deep, linear, longitudinally and circumferentially spreading ulcers, which can penetrate and lead to fistula formation. Chronic inflammation also affects the mesentery, eventually resulting in fibrosis and the development of strictures. While this describes a typical progression, the course of Crohn's disease can be variable, and not all patients will experience every stage in this linear fashion [4].

Crohn's disease often presents with extra-intestinal manifestations (EIMs) affecting various organs. Approximately 25–40% of individuals with inflammatory bowel disease (IBD) experience EIMs, commonly involving the joints (arthritis), skin (erythema nodosum and pyderma gangrenosum), eyes (uveitis and episcleritis), liver (hepatobiliary inflammatory disorders), and bones (osteoporosis). These manifestations can significantly impact a patient's quality of life and may require specialized treatment [5].

Common complications include strictures, fistulas, and abscesses, and imaging is crucial for effective management. The choice between US and CT can significantly impact treatment decisions, as each modality has unique strengths depending on the type of complication. However, in many cases, using both methods together enhances diagnostic accuracy by increasing the specificity of the findings.