Contrast-Enhanced Ultrasound (CEUS) in Pancreatic Diseases
18 Contrast-Enhanced Ultrasound (CEUS) in Pancreatic Diseases
18.1 General Remarks
Ultrasound (US) is well suited in patients with suspected acute or chronic pancreatitis, as well as in solid or cystic benign and malignant lesions. The following paragraphs will discuss some diagnostic aspects on how to use contrast agents, but will not cover pancreatic diseases in general.
18.2 Examination Technique
The diagnostic value depends on scanning conditions, the skill of the operator, and the US device that is available. The examination usually starts with a wideband convex probe. Under good scanning conditions a linear probe can be helpful in imaging the echostructure of the glandule. Besides a careful examination of the pancreas and parapancreatic tissue, a special focus on the adjacent vessels, liver, biliary system, and spleen is needed as well. Presence of fluid collections, ascites or pleural effusion and the knowledge about possible routes of abscess formation in acute pancreatitis is mandatory.
The contrast agent is injected intravenously as a bolus followed by a 10 mL saline flush. The optimal dose depends on scanning conditions, probe, contrast mode, and US device. It ranges in most cases between 1 and 2.4 mL. The examination should be recorded digitally and start just before the enhancement of the aorta and superior mesenteric artery (SMA) for about 30 s, and after 1 to 2 minutes for a couple of seconds, thus avoiding a bubble destruction (pseudo washout).
18.3 Acute Pancreatitis
With an incidence of 13 to 45 per 100,000, acute pancreatitis is one of the most frequent gastrointestinal causes for hospital admission.2 – 5 The diagnosis is made clinically (acute onset of persistent severe epigastric pain, often radiating to the back, more than three times increase of lipase/amylase) and by characteristic imaging findings.4 , 5 The prognosis depends on parenchymal changes like edema, parapancreatic fluid collections, and even gas. The volume of pancreatic necrosis should be estimated (< 30% and > 30%). The number of extrapancreatic complications correlates to the mortality and morbidity.6 , 7
Conventional US including color Doppler may often be the first line imaging technique but will in most cases be followed or substituted by computed tomography (CT). CT is currently the gold standard for diagnosis and staging of acute pancreatitis. If the pancreatic region is clearly visible on US, CEUS can be used in the follow-up of acute pancreatitis after CT staging in order to reduce the number of CT examinations.5 Using ultrasound contrast agent necrotic pancreatitis and peripancreatic fluid can reliably be diagnosed (Fig. 18.1, Fig. 18.2). Nevertheless, CT is still superior to CEUS in the diagnostic management of acute pancreatitis. Proving a biliary cause is still the most important role of US.
Fig. 18.1 (a, b) Acute episode of a chronic pancreatitis. (a) Inhomogeneous echotexture with tiny calcifications on B-mode image. (b) Contrast image detects a focal necrosis (green arrow) and peripancreatic fluid (blue arrow).
Fig. 18.2 (a, b) Back pain in a 45-year-old female with acute pancreatitis. (a) B-mode study shows an enlarged organ with a homogeneous echotexture. (b) Necrosis of the pancreatic head, neck, and part of body (no contrast uptake), not seen on B-mode image.
18.4 Pancreatic Masses
18.4.1 Solid Pancreatic Tumors
CEUS can also contribute in characterizing cystic and solid pancreatic tumors. In about 90% of cases ductal adenocarcinoma will show a hypovascularized lesion on all CEUS cases.3 A meta-analysis concluded that CEUS is a reliable modality for the differential diagnosis of pancreatic adenocarcinoma in patients with pancreatic mass lesions.3 The presence of a hypoenhanced lesion is a sensitive predictor of pancreatic ductal adenocarcinoma (Fig. 18.3).3 , 6 – 9
Fig. 18.3 (a) Ductal adenocarcinoma of the pancreatic tail. (b) Contrast image after 16 s.
CEUS can demonstrate the relationship between the tumor and neighboring peripancreatic vessels much better than conventional US.10 – 13
In contrast, neuroendocrine tumors are markedly hypervascularized (Fig. 18.4, Fig. 18.5).14 Pancreatic metastases from hypervascular primary tumors—like renal cell carcinoma or melanoma—may also show a hypervascularity during the arterial wash-in phase (Fig. 18.6).
Fig. 18.4 (a–c) Neuroendocrine tumor of the pancreatic tail in an obese 53-year-old patient, showing echo-poor lesion on B-mode (a) and hyperenhanced tumor in the arterial phase (green arrow) (b). (c) Ultrasound (US)-guided fine-needle aspiration biopsy (FNAB) proved the lesion’s character (blue arrow).
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