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Congress: ECR25
Poster Number: C-18574
Type: Poster: EPOS Radiologist (educational)
DOI: 10.26044/ecr2025/C-18574
Authorblock: S. Barbarino, M. Adorna, D. Antoci, G. A. Meli, E. David, P. V. Foti, S. Palmucci, A. Basile; Catania/IT
Disclosures:
Sebastiano Barbarino: Nothing to disclose
Miriam Adorna: Nothing to disclose
Davide Antoci: Nothing to disclose
Gaetano Alfio Meli: Nothing to disclose
Emanuele David: Nothing to disclose
Pietro Valerio Foti: Nothing to disclose
Stefano Palmucci: Nothing to disclose
Antonio Basile: Nothing to disclose
Keywords: Abdomen, Colon, Gastrointestinal tract, CT, Ultrasound, Diagnostic procedure, Abscess, Fistula, Inflammation
Findings and procedure details

Ultrasound (US) is a valuable non-invasive, radiation-free, and readily accessible imaging modality that plays a crucial role in the initial assessment and follow-up of Crohn's disease activity. Its affordability and portability make it particularly useful for frequent monitoring [6, 7]. In active Crohn's disease, US can reveal characteristic features such as small bowel wall thickening, often exceeding 3mm, and increased bowel wall hyperemia, which can be visualized using color Doppler ultrasound.

Fig 1: Bowel Wall Thickening seen in US in active Crohn’s disease
The presence of free intraperitoneal fluid, indicative of inflammation or complications, can also be detected [8,9].
Fig 2: US Signs of Active Crohn’s Disease in the bowel loops, with dilatation of loops, thickening of the wall and fluid collections
Fig 3: An example of inflamed bowel loops in US
US is particularly adept at evaluating superficial complications. For instance, in the context of abscess formation, US typically demonstrates an irregular, hypoechoic or echo-poor fluid collection. This collection may contain varying amounts of internal echogenic material, representing debris or gas, and characteristically exhibits posterior acoustic enhancement.
Fig 4: US signs of an hypoechoic spherical collection of echogenic fluid compatible with an abscess in a patient with active disease
While color Doppler often shows an absence of internal flow within the abscess cavity itself, power Doppler may reveal increased peripheral vascularity surrounding the abscess, reflecting the inflammatory response. US can also visualize fistula formation, appearing as a linear, anechoic tract extending from an affected bowel loop to another structure, which could be another part of the bowel, the skin, or other organs. These tracts often contain scattered hyperechoic puncta, representing air within the fistula, which can produce inhomogeneous posterior acoustic shadowing [7].
Fig 5: An example of enteroenteric fistula seen in US: linear, anechoic tract extending from an affected bowel loop to another
Furthermore, US can assess luminal stenosis, showing segmental bowel wall thickening, a reduction or absence of peristalsis in the affected segment, and narrowing or even obliteration of the bowel lumen. A dilated bowel segment, typically greater than 2.5 cm, may be observed proximal to the stenosis, indicating a partial obstruction [10] However, US has inherent limitations. Its ability to visualize deeper intra-abdominal structures can be compromised by factors such as patient body habitus, the presence of bowel gas, and the operator's skill. The subjective nature of US interpretation can also lead to variability in assessing the full extent of disease complications, making it less reliable than CT in some situations [6-7] .

Computed Tomography (CT), with its superior spatial resolution, excels in the comprehensive evaluation of Crohn's disease and is particularly well-suited for identifying severe and deep-seated complications. In the acute phase of Crohn's disease, CT findings can include mural hyperenhancement, reflecting increased blood flow to the inflamed bowel wall, submucosal fat deposition, which appears as low-density areas within the bowel wall, and bowel wall thickening, often most prominent in the terminal ileum. Engorgement of the vasa recta (the "comb sign"), along with perienteric fat stranding, are other findings indicating inflammation in the surrounding mesentery [11,12,14].

Fig 6: Different CT signs of active disease: the submucosal fat sign, the comb sign and bowel wall enhancement
CT plays a crucial role in the detailed assessment of several key complications. For strictures, CT provides excellent three-dimensional visualization, allowing for precise characterization of the narrowing and often revealing upstream dilatation of the bowel lumen.
Fig 7: CT Evaluation of a stenotic bowel loop with associated signs of active disease (comb sign), MPR reconstruction help to assess the stenotic segment in its full length
For complex fistulas, CT is the preferred imaging modality, enabling detailed mapping of the fistulous tracts and clearly demonstrating their connections to other organs or structures [13-14].
Fig 8: Entero-enteric fistula, comparison between US and CT
Fig 9: CT Evaluation of different perianal fistulas in the same patient: MPR reconstruction images are helpful for the correct visualization of the full extension of the complications
CT is also highly sensitive for detecting deep intra-abdominal abscesses, accurately delineating their size, location, and relationship to adjacent organs and tissues [14-15].
Fig 10: CT assessment of an abscess formation nearby an inflamed bowel loop in active Crohn’s disease
Fig 11: An association of an abscess and a entero-cutaneous fistula in a patient with a recurrence: CT examples
Fig 12: CT assessment of periumbilical enterocutaneous fistula and abscess formation
Moreover, CT can provide valuable information regarding perianal disease, hepatobiliary involvement, and extraintestinal manifestations of Crohn's disease [16].
Fig 13: CT images of a perianal fistula and inflamed bowel loops in a patient with a flare-up
Fig 14: Perianal abscess: a CT evaluation
Due to its comprehensive evaluation capabilities, CT is essential in the assessment of Crohn's disease complications, especially in emergency settings. However, the use of ionizing radiation limits its role in long-term, repeated monitoring. Ultimately, the decision to use US or CT depends on the specific clinical scenario, the patient's individual characteristics, and the expertise of the interpreting physician [11-15].
GALLERY