Contrast-Enhanced Ultrasound (CEUS) in Intestinal Diseases
17 Contrast-Enhanced Ultrasound (CEUS) in Intestinal Diseases
17.1 General Remarks
For diagnosis, degree of inflammation, and follow-up in inflammatory bowel disease, ultrasound (US) is an ideal cross-sectional imaging technique to detect and characterize the diseased intestinal segment. US and contrast-enhanced ultrasound (CEUS) are in most cases a reliable tool for diagnosing strictures, abscesses, and fistulas as complications especially in inflammatory bowel disease. Sometimes ischemia and infarction may also be diagnosed by using US along with a contrast agent. In case of bowel cancer and tumor infiltration like Non-Hodgkin diseases, including extended regional tumor infiltration of adjacent tissue, metastases and lymph nodes- contrast should be applied.
17.2 Examination Technique
Imaging of the bowel wall and local lymph nodes requires at least a 5-MHz linear probe, a sensitive color Doppler, and contrast setting with a high spatial and time resolution. The use of elastography for evaluating the stiffness of the bowel wall has been recommended by a European guideline.1
Fasting for > 6 hours is recommended before measuring splanchnic blood flow. Color Doppler imaging should be used to evaluate the vessels supplying the bowel wall and vascularization of the pathologic bowel wall.
A peak systolic velocity of between 80 and 220 cm/s of the superior mesenteric artery (SMA), and a resistive index between 0.80 and 0.89 should be considered normal.1 An angle of insonation below 60 degrees may sometimes be difficult to obtain. In order to image the perfused vessel lumen morphologically, B-flow may be helpful (Fig. 17.1a–c).2 , 3
Fig. 17.1 (a) Celiac axis compression syndrome (Dunbar syndrome, compression by median arcuate ligament2 , 3) imaged by B-flow and ( c) pulsed wave (PW) Doppler during inspiration and (b) expiration. All images are based on B-flow, b and c are Duplex images superimposed on B-flow.
Before using US contrast agent (CA), the operator should be familiar with the US device, especially its probes and the dose of US CA, which depends on the contrast setting. For linear probes—as a general rule—the contrast dose should be doubled. In case the bowel segment of interest already shows an increased vascularity on color Doppler imaging, the dose can be reduced to 1.5-fold. The local pressure on the probe should be as low as reasonable to avoid a flow reduction of small vessels. So the operators’ experience and skill and the performance of the US equipment influence the sensitivity and specificity greatly, especially when using US CA in bowel diseases.
CEUS is indicated in the following clinical situations4:
•Estimation of the activity of inflammatory bowel disease
•Distinguishing between fibrous and inflammatory strictures in Crohn’s disease.
•Characterization of suspected abscesses.
•Confirming and following the route of fistulas.
17.3 Pathologic Findings
17.3.1 Diverticulitis
A diverticulum is a mucosal herniation through the intestinal muscle wall. Diverticulosis can often be detected by US; only at deep location like in the aboral sigma US may miss diverticula and consequently diverticulitis especially in obese patients. The positive and negative predictive values for the clinical diagnosis of colonic diverticulitis were 0.65 and 0.98 respectively. Clinical diagnosis without imaging reaches sensitivities of between 64% and 71 %.1 , 2 “Qualified abdominal ultrasound” should be used as the primary cross-sectional imaging procedure for the initial and follow-up diagnostic workup of acute diverticulitis. Local pain will guide the operator to the diseased segment. Wall thickening of the colon with preservation of the US layer structure represents inflamed colon wall. Following the course of the neck, the supplying vessels can be detected by using color Doppler (Fig. 17.2a,b).
From clinical and disease management perspective (conservative, interventional, and surgical treatment), the German guidelines have suggested a new disease classification for diverticulitis.5 They take clinical parameters and imaging findings into consideration, and put US in the first place for patients’ diagnostic management and decision-making.
Fig. 17.2 (a) B-mode image of a sigma diverticulum. (b) Color Doppler demonstrates the vessels close to its neck (base of the diverticulum).
Diverticulitis is suspected in case of lower left quadrant abdominal pain and tenderness associated with fever and raised white blood cell (WBC) and/or C-reactive protein (CRP). Acute diverticulitis is conveniently divided into uncomplicated—without involvement of the surrounding fatty tissue (type 1a)—and complicated diverticulitis, from phlegmonous diverticulitis (type 1b) to micro- and macro-abscesses (type 2a, type 2b), perforation, and peritonitis (type 2c). (see Fig. 17.3 and Fig. 17.4a–c).
Sensitivities of 1.00 and 0.98, respectively, and a diagnostic specificity of 1.00 for both US and computed tomography (CT) investigative modalities were found.6 In more advanced stages of diverticulitis the involved diverticula may be dissolved by phlegmonous inflammation and gangrene so the diverticula cannot be imaged.7 Another limiting factor may be obesity, with baseline US being less sensitive in comparison to contrast-enhanced CT while US tends to be superior to CT in not too obese patients.
Fig. 17.3 Symptomatic diverticulitis with fever. (a) Echo-poor thickening of a posterior sigma segment with a pericolic inflammatory edema. (b) Contrast-enhanced ultrasound (CEUS) demonstrated a small intramural sigma abscess and pericolic inflammatory edema.
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