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Chủ Nhật, 12 tháng 8, 2012



On US examination, pancreatic pseudocysts appear as anechoic structures associated with acoustic enhancement, as demonstrated in the images below. Pseudocysts are well defined and round or oval, and they are contained within a smooth wall.

Intraoperative sonogram of a pancreatic pseudocyst.

Intraoperative sonogram demonstrates internal echoes in pancreatic pseudocyst fluid. This finding suggests presence of necrotic debris or possible pus.

An intraoperative sonogram is used to guide needle placement through the posterior wall of the stomach and into a pancreatic pseudocyst. Fluid is aspirated to delineate placement of the cystgastrostomy site and to sample the fluid within. The needle is clearly depicted as the bright echogenic line entering the fluid-filled cavity.

During the early phases of their development, pseudocysts can appear more complex, with varying degrees of internal echoes. Usually, this appearance results from the presence of necrotic pancreatic and peripancreatic debris and is more common in pseudocysts that form as a result of acute necrotizing pancreatitis than in other pseudocysts. The debris is cleared over time. The pseudocyst can appear more complex in 2 other instances: when hemorrhage occurs into the cyst or when infection of the cyst complicates the clinical course.

Color Doppler or duplex scanning should always be performed in cystic lesions to ensure that the lesion in question is not a giant pseudoaneurysm.

Degree of confidence

Sensitivity rates for US in the detection of pancreatic pseudocysts are 75-90%, according to Pitchumoni and Agarwal; therefore, US is slightly inferior to CT, which, as previously mentioned, has a sensitivity of 90-100%.[11]

US has several limitations, as compared with CT, in the initial diagnosis of a pseudocyst: the presence of overlying bowel gas decreases the sensitivity of US, and unlike CT, US examinations are highly operator dependent. However, CT scans provide more information regarding the surrounding viscera and vasculature.

False positives/negatives

No normal anatomic variants mimic the presence of a pseudocyst; however, other cystic pancreatic masses can be misinterpreted as pseudocysts. This observation is important, because as many as 10% of cystic pancreatic lesions are neoplasms; examples of these include serous and mucinous cystadenomas and mucinous cystadenocarcinomas. Clues to the diagnosis of a neoplastic cyst include a complex nature and the presence of internal septations, which can be extremely difficult to detect with US.
Brugge states that endoscopic US is helpful in the differentiation of pancreatic fluid collections.[12] Endoscopic US is more sensitive than transcutaneous US for demonstrating the internal architecture of the lesions.

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