Ultrasound Imaging of the Biliary Tract 395 hile harmonic imaging definitely improves detection, spatial com- pounding remains optional on an individual case basis Other stones such as soft pigment stones may not shadow with any technique. Soft pigment stones are less echogenic than the more cor terol gallstones and may simulate soft tissue asses. Pigmented stones are commonly associated with recurrent pyogenic cholangiohepatitis and are nore often seen in the bile ducts than in the gall bladder. Because of their lack of shadowing, they may be misinterpreted as sludge or debris and result in a false negative examination False positive Us diagnosis of gallstones may oc- cur secondary to side lobe artifacts that can generate Fig 3. Acute cholecystitis. This patient presented with echoes appearing to arise within the gallbladder lu- RUQ pain and had a positive se men but actually te from the wall or outside sign. Longitudinal ultrasound shows stones (arrows) the wall (1 . Similarly, gas in adjacent bowel can cre and diffuse gallbladder wall thickening (cursors) ate a brightly echogenic mass-like area with poste- measuring 5 mm (From Harrow A. The gallbladder rior shadowing which appears to be within the and biliary tree. In: Dogra V, Rubens D, editors. Ultra- gallbladder lumen because of a partial volume art fact and thereby mimics gallstones(Fig. 1A). A cal- p. 113-29: with permission.) cium bile salt precipitate may form in patients taking the antibiotic ceftriaxone and may mimic finding, because numerous other etiologies such gallstones on sonographic examination. These pre- as hepatic congestion or edema, congestive heart e anter patient failure, or hypoproteinemia(often associated with Other fluid-containing structures such as the renal disease or hepatic dysfunction)can cause duodenum,gastric antrum,colon, hematomas, pan- thickening of the gallbladder wall. Adenomyomato- creatic pseudocysts(Fig. 2), or even dilated vascular sis and cancer of the gall bladder also may result in collaterals may be mistaken for the gallbladder on thickening of the gallbladder wall (3).A thickened US examination, especially if the gallbladder is gallbladder wall also can occur in association with out of its normal position or is small and con- viral infections and adjacent inflammatory condi tracted. Mistaking these structures for the gallblad- tions, including hepatitis, peptic ulcer disease der may result in missing pathology in the true (Fig. 4), pancreatitis, perihepatitis(Fitz-Hugh- gallbladder or a false-positive diagnosis of gallblad- Curtis syndrome), and pyelonephritis(Fig. 5).In der disease(ie, obstructed gallbladder or acalculous patients who have thickening of the gallbladder cholecystitis) wall caused by etiologies other than acute cholecys- titis, the gallbladder often is nondistended, imply Gallbladder wall thickening ng a nonobstructive(non-biliary) cause of wall cystic flt thickening(Fig. 6) Thickened gallbladder wall demonstrating a stri Gallbladder wall thickening is defined as a wall ated appearance with alternating hyper- and hypo- diameter greater than 3 mm and is present in echoic layers in the setting of acute cholecystitis is 50%of patients who have acute cholecystitis strongly associated gangrenous cholecystitis [101 (Fig. 3)|1 However, this is a very non-specific However, striations in the gallbladder wall without Fig. 2. Pseudo gallbladders. (A) Transverse image in the right upper gallbladder" does not extend anteriorly and that the aorta (a)is immediately adjacent. B)(Left) CT image of the same area as in(a)showed a fluid-contain ing structure with similar attenuation to blood in the aorta(A). This was a retroperitoneal hematoma in an anti- coagulated patient. B)(Right) The true gallbladder(GB)is lateral to the aorta and extends anteriorly. (o)(Left) Fluid and debris-containing structure believed to represent an abnormal gallbladder(GB)in this patient who had RUQ pain (Right) The true gallbladder(arrows) is compressed and displaced by the adjacent mass, a pan creatic pseudocyst. (D)CT of the pancreatic pseudocyst(P) displacing the gallbladder(arrows).(From Rubens D. Hepatobiliary imaging and its pitfalls. Radiol Clin North Am 2004: 42: 257-78: with permission.from the stones themselves. So, while harmonic imaging definitely improves detection, spatial com￾pounding remains optional on an individual case basis. Other stones such as soft pigment stones may not shadow with any technique. Soft pigment stones are less echogenic than the more common choles￾terol gallstones and may simulate soft tissue masses. Pigmented stones are commonly associated with recurrent pyogenic cholangiohepatitis and are more often seen in the bile ducts than in the gall￾bladder. Because of their lack of shadowing, they may be misinterpreted as sludge or debris and result in a false negative examination. False positive US diagnosis of gallstones may oc￾cur secondary to side lobe artifacts that can generate echoes appearing to arise within the gallbladder lu￾men but actually originate from the wall or outside the wall [1]. Similarly, gas in adjacent bowel can cre￾ate a brightly echogenic mass-like area with poste￾rior shadowing, which appears to be within the gallbladder lumen because of a partial volume arti￾fact and thereby mimics gallstones (Fig. 1A). A cal￾cium bile salt precipitate may form in patients taking the antibiotic ceftriaxone and may mimic gallstones on sonographic examination. These pre￾cipitates resolve after the patient ends therapy. Other fluid-containing structures such as the duodenum, gastric antrum, colon, hematomas, pan￾creatic pseudocysts (Fig. 2), or even dilated vascular collaterals may be mistaken for the gallbladder on US examination, especially if the gallbladder is out of its normal position or is small and con￾tracted. Mistaking these structures for the gallblad￾der may result in missing pathology in the true gallbladder or a false-positive diagnosis of gallblad￾der disease (ie, obstructed gallbladder or acalculous cholecystitis). Gallbladder wall thickening and pericholecystic fluid Gallbladder wall thickening is defined as a wall diameter greater than 3 mm and is present in 50% of patients who have acute cholecystitis (Fig. 3) [1]. However, this is a very non-specific finding, because numerous other etiologies such as hepatic congestion or edema, congestive heart failure, or hypoproteinemia (often associated with renal disease or hepatic dysfunction) can cause thickening of the gallbladder wall. Adenomyomato￾sis and cancer of the gall bladder also may result in thickening of the gallbladder wall [3]. A thickened gallbladder wall also can occur in association with viral infections and adjacent inflammatory condi￾tions, including hepatitis, peptic ulcer disease (Fig. 4), pancreatitis, perihepatitis (Fitz-Hugh￾Curtis syndrome), and pyelonephritis (Fig. 5). In patients who have thickening of the gallbladder wall caused by etiologies other than acute cholecys￾titis, the gallbladder often is nondistended, imply￾ing a nonobstructive (non-biliary) cause of wall thickening (Fig. 6). A thickened gallbladder wall demonstrating a stri￾ated appearance with alternating hyper- and hypo￾echoic layers in the setting of acute cholecystitis is strongly associated gangrenous cholecystitis [10]. However, striations in the gallbladder wall without Fig. 2. Pseudo gallbladders. (A) Transverse image in the right upper quadrant (RUQ) with structure identified as the gallbladder (arrows) containing debris (asterisk). Note that the ‘‘gallbladder’’ does not extend anteriorly and that the aorta (A) is immediately adjacent. (B) (Left) CT image of the same area as in (A) showed a fluid-contain￾ing structure with similar attenuation to blood in the aorta (A). This was a retroperitoneal hematoma in an anti￾coagulated patient. (B) (Right) The true gallbladder (GB) is lateral to the aorta and extends anteriorly. (C) (Left) Fluid and debris-containing structure believed to represent an abnormal gallbladder (GB) in this patient who had RUQ pain. (Right) The true gallbladder (arrows) is compressed and displaced by the adjacent mass, a pan￾creatic pseudocyst. (D) CT of the pancreatic pseudocyst (P) displacing the gallbladder (arrows). (From Rubens D. Hepatobiliary imaging and its pitfalls. Radiol Clin North Am 2004;42:257–78; with permission.) : Fig. 3. Acute cholecystitis. This patient presented with RUQ pain and had a positive sonographic Murphy sign. Longitudinal ultrasound shows stones (arrows) and diffuse gallbladder wall thickening (cursors) measuring 5 mm. (From Harrow A. The gallbladder and biliary tree. In: Dogra V, Rubens D, editors. Ultra￾sound secrets. Philadelphia: Hanley and Belfus; 2004. p. 113–29; with permission.) Ultrasound Imaging of the Biliary Tract 395