Standards of the Polish Ultrasound Society - update. Pancreas examination.

Ultrasound examination of the pancreas constitutes an integral part of the abdominal ultrasound. It is mostly indicated to diagnose pain in the epigastrium, discomfort and jaundice as well as to monitor the patients with acute pancreatitis. The assessment of this organ in an ultrasound examination may be problematic due to its anatomical location and the fact that it might be covered by gastric and duodenal contents as well as due to a number of possible pathological changes, including inflammation and benign or malignant neoplasms, which require differentiation. The basis for establishing a correct diagnosis is the knowledge of the examination technique, correct pancreas structure and images of individual pathologies. This paper presents the standards of ultrasound examination published in 2011 and updated with the current knowledge. The following are discussed: preparation of the patient for the examination, abnormal lesions in the pancreas, acute pancreatitis, chronic pancreatitis, cystic lesions (benign and malignant cysts) and solid focal lesions. Ultrasound is also used to guide the drainage of fluid cisterns, abscesses and cysts. The prime role in the diagnosis and treatment of selected diseases of the upper gastrointestinal tract and parenchymal organs of the abdomen belongs to endosonography of the upper gastrointestinal tract, with the possibility to conduct a fine needle aspiration biopsy, and intraoperative or laparoscopic ultrasound.

Ultrasound examination (US) is an initial imaging examination performed in the diagnosis of pancreatic pathologies, which frequently dictates subsequent diagnostic steps(.

According to the ultrasound standards of the Polish Ultrasound Society, the pancreas in adult patients is examined through the abdominal integuments with the use of a sector, convex-type transducer with the frequency of 3.5 MHz(. The image should be generated in as many lines as possible (128 transmit/receive channels are recommended), the grey scale applied should be greater than 256 shades and the number of foci used to generate the image should not be lower than 4. Due to the fact that the pancreas is located at various depths depending on the person (slender or obese patient), it is essential to adjust the focal zone of the transducer. The ultrasound scanner should be equipped with software to calculate the surface area and volume of the tested body, in color and power Doppler option as well as in harmonic imaging option. The supplementary procedures include: endosonography (EUS), intraoperative sonography and fineneedle aspiration biopsy (FNAB) through the integuments or EUS(.

Preparation for examination

The prime obstacle in ultrasound assessment of the pancreas is gas accumulating in the alimentary tract. In order to optimize the examination conditions, the patient should avoid distending and heavy food for two days prior to the examination. The test is usually performed in the morning with the fasting patient. Otherwise it is recommended to refrain from ingesting solid food and drinking carbonated drinks for 6 hours prior to the examination. It is recommended to take gas-reducing pharmacological agents(.

Examination technique

The pancreas is examined in transverse, longitudinal and oblique planes. It is also recommended to make use of the acoustic window of the liver, i.e. an examination through the left liver lobe, as well as to visualize the pancreas in both left and right lateral positions of the patient and after a deep inspiration. If the pancreatic duct has been visualized, its diameter and course should be measured(. The size, shape, outlines and echostructure of the normal pancreas might vary depending on, e.g., patient's stature, age and the volume of the adipose tissue between the organ's lobules(.

The upper limit of the normal size in the AP aspect of the head of the pancreas is up to 3.4 cm, the body – 2.9 cm, and the tail – 3.2 cm. The length of the organ ranges from 12 to 20 cm. Its echogenicity is usually slightly higher than the echogenicity of the liver, but may also be normo- or hyperechoic. The echostructure is most frequently homogeneous. Finally, the diameter of the normal pancreatic duct should not exceed 3 mm(.

Pathological lesions in the pancreas may be diffuse or focal. In the examination, their localization in relation to individual anatomic elements of the pancreas needs to be determined as well as their dimensions, echogenicity in relation to the unaltered pancreatic parenchyma and echostructure. The assessment of the outer outlines of the pancreas is also important. An integral element of the pancreas ultrasound is the assessment of the retroperitoneal space in terms of local lymph nodes as well as the visualization of the peripancreatic vessels to diagnose their adherence or infiltration(.

Characteristics of abnormal pancreatic lesions

Acute pancreatitis (AP)

The golden standard in the diagnosis of AP is computed tomography (CT). US examination, due to its non-invasive character, is of fundamental significance in monitoring the patient's condition(.

Moreover, ultrasound examination is performed in order to(:

specify possible coexistence of cholecystolithiasis and, above all, choledocolithiasis (determining the indication for early endoscopic sphincterotomy);

diagnose hypoechoic lesions, at the monitoring stage, which might correspond to areas of necrosis (fig. 1);

Fig. 1

Acute pancreatitis. Non-homogeneous, hypoechoic area in the body/tail projection attests to extensive necrosis

visualize other fluid cisterns in the region of the peritoneal cavity, in the pleural cavities and mediastinum, i.e. cysts, abscesses and phlegmon (figs. 2, 3);

Fig. 2

Acute pancreatitis. Large cyst with necrotic tissue

Fig. 3

Large abscess in the projection of the tail. Complicated acute pancreatitis

determine the indications for a surgical intervention;

diagnose vascular complications including thrombosis, mainly involving the portal vessels, and pancreatic pseudoaneurysms.

Interventional sonography allows for the performance of percutaneous biopsy, US-guided puncture and drainage procedures, endoscopic necrosectomy and drainage with the use of EUS or laparoscopic ultrasound.

Chronic pancreatitis (ChP)

Beside CT, sonography constitutes the major imaging examination in the diagnosis of ChP. Endoscopic retrograde cholangiopancreatography (ERCP) is applied more and more rarely, mainly as part of the interventional procedure (sphincterotomy). In the course of ChP, US examination reveals morphological changes such as atrophy, fibrosis or calcifications, which lead to pancreatic failure.

Typical features of ChP include(:

altered echogenicity of the pancreas – in the majority of cases the lesions are hyperechoic and more often diffuse than focal;

focal hyperechoic echoes corresponding to fibrous changes;

calcifications in the pancreatic parenchyma, in the walls of the pancreatic ducts;

pseudocysts in various localizations;

altered size of the pancreas – in certain cases the surface of the pancreas is, sometimes fragmentarily, enlarged due to accompanying proliferative reaction; atrophy and scarring of the parenchyma lead to the reduction of the size of the pancreas; the diameter, however, is frequently dependent on the width of the Wirsung's duct (fig. 5);

Fig. 5

Chronic pancreatitis. Wirsung's duct dilatation in the body of the pancreas, parenchymal atrophy, degenerative changes

abnormal presentation of the main pancreatic ducts (dilated lumina, irregular course, calcified concrements) (fig. 6);

Fig. 6

Chronic pancreatitis. Dilated Wirsung's duct with irregular course and large calcified concrements. Fibrous lesions in the parenchyma

pancreatic pseudoaneurysm (fig. 7);

Fig. 7

Power Doppler sonography. Pancreatic pseudoaneurysm. The aneurysm of the gastroduodenal artery in the course of ChP

inflammatory tumor often encompassing the head of the pancreas (fig. 8);

Fig. 8

Large hyperechoic inflammatory tumor of the head of the pancreas with a non-homogeneous structure. Wirsung's duct dilated peripherally due to obstruction

ascites and fluid in the pleural cavity (mainly in the left one).

Inflammatory tumors require the differentiation from neoplastic lesions(. Within the inflammatory tumor, degenerative lesions are frequently observed in the form of cysts, focal areas of fibrosis and calcifications. If solid tissues are predominant and degenerative features are not evident, a malignant lesion should be suspected and further tests should be suggested in the description of the examination. EUS, which allows for a good visualization of the lesion and performance of the biopsy, constitutes a recommended diagnostic method(. It is currently believed that contemporary EUS is more accurate than ERCP in the assessment of early inflammatory lesions in the course of ChP.

The autoimmune form of ChP, however, is characterized by intensified peripancreatic inflammatory reaction with consequential fibrosis. In the US examination, focal or diffuse enlargement of the pancreas and the reduction of the gland's echogenicity are observed. Calcifications or fluid cisterns, however, are not detected(.

Intraoperative sonography is valuable for the assessment of the course of the pancreatic duct, in the identification of the calculi which cause obstruction and in monitoring of their removal(.

Cystic focal lesions of the pancreas

Benign cysts

Pancreatic cysts are usually a consequence of acute or chronic pancreatitis. We distinguish retention and necrotic cysts, which possess a capsule, and pseudocysts, which are outcomes of ChP(. On US examination, their size needs to be determined, which constitutes a criterion for the qualification to the treatment. The cysts with the diameters exceeding 5–6 cm, especially symptomatic ones, constitute an indication for interventional treatment(. The most common procedure is the EUS-guided drainage(. Doppler sonography, in turn, is an examination which improves the safety of the procedures performed both in the examination through abdominal integuments and in EUS as well as in intraoperative assessment(. The procedure also allows for a differentiation of rare cases of pancreatic pseudoaneurysms which are a complication of ChP and, sometimes, AP.

Neoplastic cystic tumors

Neoplastic cystic tumors account for 2–4% of all cystic lesions of the pancreas(.

Serous cystic tumors are well-vascularized, contain numerous slight cysts, often include central scars and calcifications in their area. The cysts may have a grape-like appearance and may contain septations (fig. 4). This type of tumors shows very low malignancy potential.

Fig. 4

Color Doppler sonography. Serous cystadenoma in the head of the pancreas showing poor signs of flow. “Honeycomb” structure with cystic areas and central scar

Mucinous cystic tumors occur more frequently. They are characterized by irregularly thickened walls, dense contents, solid intramural nodules and peripheral calcifications. Most of such lesions are malignant. Apart from transabdominal ultrasound, it is also recommended to perform EUS and intraoperative US.

Moreover, the presence of intraductal papillary mucinous neoplasm (IPMN) is manifested by the detection of a cystic dilatation of the pancreatic duct and intraductal papillary projections(. In the diagnosis, the following tests are performed: US and EUS examination including the US/EUS-guided FNAB, cytological and biochemical tests of the cystic fluid, mucin content tests when mucus-secreting tumors are suspected as well as neoplastic markers (CEA and more rarely – CA 19-9) mainly in the case of lesions exceeding 4–5 cm(. Intraoperative sonography aids in determining the differences in the structure of cystic, solid-cystic and solid lesions in the pancreas and in its surroundings(.

Solid focal lesions of the pancreas

The accuracy of US examinations in differential diagnosis of solid lesions in the pancreas is relatively low. It constitutes 50–70%. In order to improve the examination results, currently, the following techniques are used: EUS, US/EUS-guided FNAB, contrast-enhanced US, 3D US and 3D Doppler examination, elastography as well as intraoperative and laparoscopic ultrasound(.

Adenocarcinoma

Adenocarcinoma is the most common pancreatic malignant neoplasm and accounts for 70–85% of all solid lesions in the pancreas(. The lesion is hypoechoic in relation to normal pancreatic parenchyma or of mixed echogenicity and irregular borders. In 60–65% of the cases of pancreatic carcinomas, the lesions are localized in the head causing secondary dilatation of the pancreatic and common bile ducts(. The purpose of US examination is to determine the localization of the tumor in relation to individual anatomical elements of the gland as well as to specify its size and degree of advancement (infiltration in the adjacent structures, including vessels, involvement of the lymph nodes). It is crucial to distinguish adenocarcinomas from other pancreatic lesions, frequently inflammatory or post-inflammatory ones, and to specify the degree of advancement (figs. 9, 10)(. The method of choice in determining the tumor advancement with simultaneous assessment of the peripancreatic lymph nodes, vessels and other abdominal organs in search for metastases, is CT. Ultrasound is considered a supplementary technique.

Fig. 9

Power Doppler sonography. Pancreatic carcinoma. Hypoechoic 2 cm tumor of the head of the pancreas (on the border of T1/T2). The tumor is enclosed in the pancreatic parenchyma and does not infiltrate the mesenteric-portal confluence

Fig. 10

Power Doppler sonography. Pancreatic carcinoma. Hypoechoic tumor of the head of the pancreas with the dimensions of 3×4 cm. The lesion on the long axis adheres to the vessels of the mesenteric-portal confluence

Determining the localization of the carcinoma is of considerable significance when decisions concerning surgical treatment are to be made. The lesions situated in the region of the body of the pancreas are localized to the left of the mesenteric vessels and to the right of the aorta. In many cases they considerably infiltrate the extraperitoneal space, aorta and nerve plexus, which prevents the resection of the tumor together with the pancreas. Carcinoma of the head of the pancreas which infiltrates the vessels of mesenteric-portal confluence is considered a non-resectable lesion(. It is important to assess the size of the tumor. Its largest dimension or two objectively largest values obtained in two different planes should be provided. This decides about the T feature (T1–T4) according to the clinical assessment of the extent of the carcinoma progression by TNM-AJCC(. In the assessment of slight nodular lesions and in the diagnosis of surrounding enlarged lymph nodes, EUS is a valuable modality(.

In the US examination, it is important to assess the surrounding peripancreatic lymph nodes (N feature of TNM classification), both superior and inferior ones, lymph nodes in the region of the pylorus and splenic hilum as well as those located further along the superior mesenteric artery, hepatic artery and coeliac trunk(. The presence of enlarged lymph nodes portends an unfavorable prognosis.

A subsequent element of diagnosis is the assessment of the vessels in terms of possible infiltration(. The purpose of Doppler examination is to determine the relationship between the pancreatic tumor and major coeliac arteries (coeliac trunk, superior mesenteric, common hepatic, splenic and gastroduodenal) and veins (portal vein, portal drainage and superior mesenteric vein) (figs. 11, 12)(. The sensitivity of the method in the diagnosis of infiltration constitutes 60–80% and specificity 90–95%(. Good outcomes are obtained with the use of EUS(.

Fig. 11

Color Doppler sonography. Pancreatic carcinoma. 3 cm tumor (T2) closely adjoining to the region of the mesentericportal confluence

Fig. 12

3D power Doppler sonography. Examination with the volume transducer (convex). The same tumor as in fig. 11. The examination revealed angular infiltration of the fragment of the mesenteric-portal confluence

Supplementary US-guided diagnostic procedures and US examination techniques

US-guided biopsy

The procedure is conducted with transabdominal US or EUS monitoring. It is performed intraoperatively and by means of a laparoscope(. An important indication to perform it is the application of the combination therapy, i.e. neoadjuvant and induction therapy as well as intraoperative radiotherapy, which require the confirmation of carcinoma. A positive biopsy, which indicates the presence of pancreatic carcinoma, enables to select the surgical procedure. In patients, who do not qualify for a resection due to the presence of inoperative tumors, FNAB enables to make a relatively rapid decision concerning the palliative treatment mainly with the use of minimally invasive methods(.

Contrast agents

Contrast enhanced ultrasound examinations (CEUS) are helpful in determining the character of pancreatic focal lesions( – in the diagnosis of slight nodular lesions and those with ambiguous etiology. CEUS allows for the differentiation between poorly vascularized forms of pancreatic carcinomas and neuroendocrine tumors, which are highly vascularized, as well as metastatic lesions and inflammatory changes. The suspicion of neoplastic cystic tumors is an indication for the examination. CEUS allows for a good visualization of the “honeycomb” image and of inner neoplastic septations in the cyst (serous tumors) as well as intramural nodules (mucinous cystic tumors)(. The fluid foci, including necrotic areas, do not undergo contrast enhancement. CEUS is more and more frequently performed with the use of EUS(.

Elastography

Elastography may be used in transcutaneous sonography and has recently started to be used in EUS(. The sensitivity and specificity of this method in the differentiation of benign and malignant lesions reach even 90%.

Intraoperative and endoscopic sonography

Intraoperative and endoscopic ultrasound is commonly used in referral centers which perform complex surgical procedures involving parenchymal organs of the abdomen, also in pancreatic pathologies. It is used primarily for the differentiation between focal lesions, mainly pancreatic ductal carcinoma, inflammatory lesions, neuroendocrine and cystic tumors as well as secondary lesions (lymphoma, granulomatosis and metastases of the renal carcinoma, melanoma, colonic carcinoma, breast and lung carcinomas as well as sarcoma)(. It enables to assess the progression of the neoplastic tumor of the pancreas and determine the range of resection(. At present, it is recommended to extend the examination to include Doppler imaging (fig. 13). Thanks to laparoscopic sonography, it is possible to visualize metastatic lesions in the peritoneal space and superficial lesions in the liver. The application of laparoscopic ultrasound with FNAB raises the efficacy of the examination up to 88%(.

Fig. 13

Intraoperative US, power Doppler. Carcinoma of the uncinate process (Tu) adhering to the superior mesenteric vein (vms). Normal lobulated tissue in the region of unaltered head of the pancreas (Pc)

Examination results

The examination description should include the patient's personal details, date of examination, name of the facility in which the examination was performed, name of the US scanner as well as the frequency of the transducer. If normal pancreas has been visualized, it should be indicated in the result. If, however, an irregularity has been found, the description should contain information concerning the anomalies in terms of: the size of the pancreas and its outer outlines, changes in the echostructure, homogeneity of the structure and echogenicity.

In the case of pathological findings, the following aspects should be specified: their localization (including, e.g. in ChP, secondary lesions in the region of the organ and distant ones in the peritoneal cavity and retroperitoneal space), number, size, echogenicity and echostructure, outlines, focal or diffuse character and their relation to adjacent peripancreatic vessels.

The width of the common bile duct and gallbladder should be measured.

The description should be ended with a conclusion (normal pancreas, inflammatory lesions, proliferative lesions, others) and, if indicated, the suggestion of a subsequent diagnostic examination/examinations.

If difficulties in the US assessment of the pancreas occur (e.g. the gland covered by gas), such information should be included in the description.

The photographic documentation of abnormal morphological changes should be enclosed and the description should indicate the number of the attached photographs. The description needs to be confirmed with a stamp and signature of the examiner.