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80 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder Figure 4.6 Axial contrast-enhanced CT shows acute cholecystitis with evidence of calculi and gallbladder wall thickening greater than 3mm. Figure 4.7 Axial contrast-enhanced CT shows gangrenous cholecystitis with massive distension and gallbladder wall thickening greater than 3mm. gradient echo images with fat suppression are commonly used to define the extent of invasion into the liver, pancreas, or duodenum [39]. On PET or PET/CT scan, gallbladder cancer shows up as specific FDG accumulation in the gallbladder area with pos-sible extension into the liver. Advanced tumors may impose as large FDG-positive mass with infiltration into the liver or adjacent abdominal organs (Plate 1, facing p. 84). PET and PET/CT scan have a high sensitivity to detect gallbladder can- cer regardless of the primary or recurrent nature of the tumor (Table 4.1). Although the study population is relatively small, the three series which use PET scans to detect gallbladder cancer report a sensitivity of 75 to 80% and a specificity of 87 to 82% [40–42]. Furthermore, the PET scan proved to be an accurate method to differentiate benign disease such as cho-lecystitis, gallstone disease, and cholesterol polyp from gall-bladder cancer [40,42]. Our experience in Zürich with the integrated PET/CT scanner even demonstrated a sensitivity Chapter 4: Noninvasive imaging of the biliary system 81 (A) (B) (C) (D) Figure 4.8 Coronal T2-weighted (A), unenhanced axial T1-weighted (B), and gadolinium-enhanced axial T1-weighted (C) images in a patient with acute cholecystitis. Note the wall thickening and the pericholecystic fluid (arrows). Edema within the pericholecystic fat is best appreciated on MRCP image(D). of 100% witha high median maximum standardized uptake value (SUVmax) of 9.9 [43]. We also found PET/CT very help-ful in detecting distant metastases which were not visible by standard imaging. Bile ducts The intrahepatic bile ducts may not be visualized by ultra-sound when they are normal in caliber. When dilated, they often have a “tram track” appearance because the biliary rad-icals parallel the portal veins. Color Doppler ultrasound is helpful in discerning which tubular structure is the bile duct (Fig. 4.10, Plate 2, facing p. 84). When they are markedly di-lated, the ducts can be quite tortuous. The wall of the bile duct is normally very thin, measuring less than 1 mm. CT has the advantage of high spatial resolution, which allows depiction of both the lumen and the wall of the bile ducts, but has the disadvantage of imaging only in the axial plane. Thisis offset by multidetector helical CT with which a high-quality volu-metric data set can be acquired and then rendered or dis-played in a multiplanar or three-dimensional fashion. CT is very sensitive to ductal dilatation and on occasion even non-dilated bile and pancreatic ducts can be visualized. The de- piction of ductal structures is markedly reduced, however, 82 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder (A) Figure 4.9 Axial unenhanced(A)and contrast-enhanced(B) CT images show carcinoma of the gallbladder. While this tumor is hardly visualized on unenhanced imaging(A), it shows subtle perfusion (B) after contrast administration(B). when intravenous iodinated contrast material is not used. Furthermore, CT cholangiography can also be performed noninvasively by acquiring a thin-section spiral CT within the first hour after the intravenous administration of 20mL of iodipamide meglumine 52% (Cholografin; Bracco Diag-nostics, Princeton, NJ) diluted in 80mL of normal saline via a 30-min infusion [44,45]. This data set can be reconstructed in three dimensions to evaluate the bile ducts in a fashion similar to direct cholangiography or MR cholangiography (MRC) (Fig. 4.11). Unfortunately, there must be reasonable liver function in order for the ducts to be adequately opacified. Like MRI of the intrahepatic and extrahepatic bile ducts, MRC relies on heavily T2-weighted sequences on which sta-tionary fluid within the ducts is of very high signal intensity relative to the adjacent liver [46–49] (Fig. 4.12). Gradient-echo sequences were originally used to produce these images but more recently fast spinecho sequences have been shown to yield better visualization of the ducts without long breath holds or magnetic susceptibility artifacts [50]. The data ob- Chapter 4: Noninvasive imaging of the biliary system 83 (A) (B) Figure 4.10 Grey-scale(A)and color Doppler(B)ultrasound of a patient with intrahepatic biliary ductal dilatation. Color Doppler ultrasound is particularly helpful in discerning which tubular structure is the bile duct. (See also Plate 2, facing p. 84). Figure 4.11 Three-dimensional CT cholangiogram obtained 25min after the intravenous administration of a biliary secreted contrast agent. This method offers excellent delineation ofthe segmental biliary branches. (Courtesy of F. Yang, M. D. and SG Ruehm, M.D., University Hospitals of Essen, Germany.) tained from these sequences can be manipulated on a com-puter workstation and displayed like the images obtained in an ERCP. In addition, it is also possible to obtain physiological information on the gallbladder ejection fraction utilizing cholecystokinin-stimulated magnetic resonance cholangi-ography [51]. Currently, even nondistended second order biliary branches are seen on a regular basis on MRC, inde-pendent of the patient’s liver function (Fig. 4.12). Choledocholithiasis Ultrasound is usually the initial imaging choice in patients with jaundice todetermine the integrity of the bile ducts. Al- though ultrasound does not reliably visualize the bile ducts at their extremes (i.e. the peripheral intrahepatic ducts at one end and the distal common bile duct at the other), the central intrahepatic ducts and especially the common hepatic duct are well visualized. Either CT orMRI betterdelineate the ex-treme portions of the ductal system. The normal common he-patic duct courses just anterior to the main portal vein and measures 5 to 6 mm in diameter. A duct measuring more than 6 mm yet not obstructed is a condition seen in elderly patients, in a minority of patients following cholecystectomy, and in patients with previous long-standing ductal obstruc- tion. For elderly patients in particular, the upper limit of nor- 84 Section 2: Diagnostic and therapeutic approaches for the biliary tree and gallbladder mal in duct caliber can increase by 1 mm for every decade after the age of 60 (i.e. 7 mm after age 70, 8 mm after 80, and so on) [52]. Most patients with choledocholithiasis have di-lated ducts, and on occasion the calculi themselves will be visualized as echogenic intraluminal foci, with or without acoustical shadowing. In general, CT is very sensitive to dilatation of the biliary tree, including both intrahepatic and extrahepatic ducts. Al-though ultrasound is superior to CT for detecting stones in Figure 4.12 MRCP using a respiratory triggered three-dimensional T2-weighted data set in a patient postcholecystectomy. Arrow marks a duodenal diverticulum. Note the exquisite image quality with depiction of nondilated biliary segmental branches. the gallbladder, CT is superior to ultrasound for detecting stones in the bile ducts [53–55]. This is mainly because there is better visualization of the distal common bile duct by CT and the level of dilatation or obstruction is better depicted. Even when a stone is not readily apparent, the diagnosis may be entertained when there is no evidence of a mass at the level of obstruction. However, this combination of findings is not specific for choledocholithiasis, because both a benign stric-ture and ampullary stenosis may have a similar appearance. There is some evidencethat a preliminary CT prior to the ad-ministration of either oral or intravenous contrast material may increase the sensitivity for detecting stones [56]. In general, ERCP remains the technique of choice when evaluating patients with a high probability of having com-mon bile duct stones, as the diagnosis can be made and then treatment applied in the same setting [57]. However, in cer-tain clinical settings—for example where ERCP is contrain-dicated or there is a moderate to low probability of common bile ducts stones—MRC is the imaging modality of choice [57]. MRC has greater than 90% sensitivity and specificity in the detection of choledocholithiasis [58–62]. These percent-ages are superior to both ultrasound and CT. With MRC, cal-culi are seen as low-signal intensity defects within high-signal intensity bile (Fig. 4.13). It must be remembered, however, that both air bubbles and blood clots can have a similar low-signal intensity appearance. Cholangitis Inflammation of the bile ducts is caused by a number of conditions including infection, such as acute suppurative cholangitis, recurrent pyogenic cholangitis, or sclerosing (A) (B) Figure 4.13 MRCP using a respiratory triggered three-dimensional T2-weighted data set in a patient with calculi in the distal common bile duct. Maximum intensity projection (MIP)(A)and source image(B)show intraluminal filling defects within the distal common bile duct. ... - tailieumienphi.vn
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