Ultrasound Imaging of the Biliary Tract 401 B Fig. 10. Emphysematous cholecystitis. (A) Transverse supine view of the gallbladder reveals nondependent echoes anteriorly (arrowheads), which cast a dense posterior shadow.( B)When viewed longitudinally from the flank, the dependent echogenic gallstones (arrows) can be seen. Note that the shadow cast by the gas in (A)is denser and sharper than that from the stones (B). bowel gas does not necessarily cast a"dirty" or reverber- cholecystitis in another patient Sagittal image of the gallbladder shows echoes anteriorly (arrow) that could be in either the lumen or the wall. (D)When the patient is turned into the upright position, the gas moves and breaks into bubbles (arrowhead), distinguishing it from mural air or calcium. 10A and B (From Rubens d Hepatobiliary imaging and its pitfalls. Radiol Clin North Am 2004: 42: 257-78: with permission the entire gallbladder wall is less common than focal adenoma and carcinoma On imaging alone, how or segmental diseases ever, it is impossible to identify coexistent dysplasia or carcinoma in situ within an adenoma, or to deter Benign neoplasms of the gallbladder mine whether a polypoid mass is benign or malig. nant (Fig. 17). The current surgical literature Adenomas are well-demarcated, polypoid gall- therefore recommends excision of polyps greater bladder lesions, usually less than 2 cm in size, than 1 cm in size in patients older than age 50 years and are rare compared cholesterol polyps or any polyp that is clearly growing, even if less than or polyps of adenomyomatous hyperplasia. They 1 cm124,2 are found in 0. 3% to 0.5% of cholecystectomy specimens and are usually solitary. They are class fied as tubular, papillary, or tubulopapillary, Malignant neoplasms of the gallbladder depending on their growth pattern. On Us they Gallbladder carcinoma represents 98% or more are typically echogenic when small, but become of all gallbladder malignancies; the rest are com more heterogeneous as they enlarge [19). Their prised of nonepithelial tumors arising from the premalignant potential is believed to be low, al- muscular or neurologic components of the wall, though this is somewhat controversial. There metastases or lymphoma(lymphoma)[26. The a much stronger relationship between chronic cho- median age at presentation is 72 years, with a 2: 1 lecystitis and gallbladder carcinoma than between female-to-male ratio [26 The major risk factor isthe entire gallbladder wall is less common than focal or segmental diseases. Benign neoplasms of the gallbladder Adenomas are well-demarcated, polypoid gall￾bladder lesions, usually less than 2 cm in size, and are rare compared with cholesterol polyps or polyps of adenomyomatous hyperplasia. They are found in 0.3% to 0.5% of cholecystectomy specimens and are usually solitary. They are classi- fied as tubular, papillary, or tubulopapillary, depending on their growth pattern. On US they are typically echogenic when small, but become more heterogeneous as they enlarge [19]. Their premalignant potential is believed to be low, al￾though this is somewhat controversial. There is a much stronger relationship between chronic cho￾lecystitis and gallbladder carcinoma than between adenoma and carcinoma. On imaging alone, how￾ever, it is impossible to identify coexistent dysplasia or carcinoma in situ within an adenoma, or to deter￾mine whether a polypoid mass is benign or malig￾nant (Fig. 17). The current surgical literature therefore recommends excision of polyps greater than 1 cm in size in patients older than age 50 years or any polyp that is clearly growing, even if less than 1 cm [24,25]. Malignant neoplasms of the gallbladder Gallbladder carcinoma represents 98% or more of all gallbladder malignancies; the rest are com￾prised of nonepithelial tumors arising from the muscular or neurologic components of the wall, metastases or lymphoma (lymphoma) [26]. The median age at presentation is 72 years, with a 2:1 female-to-male ratio [26]. The major risk factor is Fig. 10. Emphysematous cholecystitis. (A) Transverse supine view of the gallbladder reveals nondependent echoes anteriorly (arrowheads), which cast a dense posterior shadow. (B) When viewed longitudinally from the flank, the dependent echogenic gallstones (arrows) can be seen. Note that the shadow cast by the gas in (A) is denser and sharper than that from the stones (B). Bowel gas does not necessarily cast a ‘‘dirty’’ or reverber￾ant echo-filled shadow. The shadow thus cannot be used to distinguish gas from the stones. (C) Emphysematous cholecystitis in another patient. Sagittal image of the gallbladder shows echoes anteriorly (arrow) that could be in either the lumen or the wall. (D) When the patient is turned into the upright position, the gas moves and breaks into bubbles (arrowhead), distinguishing it from mural air or calcium. 10A and B (From Rubens D. Hepatobiliary imaging and its pitfalls. Radiol Clin North Am 2004;42:257–78; with permission.) Ultrasound Imaging of the Biliary Tract 401