usg pancreas

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Ultrasonography of the Pancreas Giulia A. Zamboni, MD*, Maria Chiara Ambrosetti, MD, Mirko DOnofrio, MD, Roberto Pozzi Mucelli, MD Although the pancreas is often thought of as an organ that is difficult to explore using ultrasound (US), due to its deep retroperitoneal location, with the appropriate technique it can be studied successfully in most patients. US can provide information that is useful for diagnosis of patho- logic conditions, especially with the use of harmonic imaging, color-Doppler, and contrast agent administration. EXAMINATION TECHNIQUES To improve visualization of the pancreas, the ultra- sound (US) examination is usually performed after at least 6 hours of fasting. In this way, the presence of bowel gas is limited, the stomach is empty of food, and the entire organ can be visualized. Nevertheless, technical success is also dependent on the skill and persistence of the examiner. 1 US should be performed routinely along multiple scan planes, including transverse, longitudinal, and angled oblique, to visualize the entire organ: the head with the uncinate process, the body, and the tail. These multiple scan planes should allow examination of the entire pancreas in at least 2 views. When needed, the spleen can be used as an acoustic window to visualize the pancreatic tail. When visualization of the pancreas is limited, it is possible to use other scanning techniques, such as moving the transducer and applying compres- sion to displace bowel gas, filling the stomach with water, examining the patient in suspended inspiration or expiration, and changing the patient to a decubitus position. Conventional gray-scale US with multifrequency transducers is usually the first step when examining the pancreas, selecting the best frequency for each depth. Usually, convex probes are used, with frequencies ranging between 3 and 5 MHz. Doppler frequency must be set to record flows from deep abdominal vessels (1–4 MHz). Lower Doppler frequencies allow better penetration and are used to evaluate the peripancreatic vessels, whereas higher Doppler frequencies are useful for evalu- ating slower flows in thin patients whose pancreas is more superficial. 2 Tissue Harmonic Imaging The routine examination technique should include the use of tissue harmonic imaging (THI), which can improve visualization of the pancreas by increasing the signal-to-noise ratio and reducing the reverberation artifacts from the body wall, especially when studying large patients or deep structures. Shapiro and colleagues 3 demonstrated that harmonic imaging had better penetration detail and overall image quality than conventional US. In a prospective study on 107 patients, Hohl and colleagues 4 demonstrated that sensitivity for the detection of pancreatic lesions with THI using the phase inversion technique was higher than for conventional B-mode US. Color-Doppler and Power-Doppler Ultrasound Doppler ultrasound is another fundamental part of the conventional US examination for evaluating the peripancreatic vessels (portal vein, superior Disclosures: G.A.Z., M.C.A., and R.P.M. have no disclosures. M.D. was an Advisory Board member, Siemens Healthcare (2010). Istituto di Radiologia, Policlinico GB Rossi, Azienda Ospedaliera Universitaria Integrata Verona, P.le LA Scuro 10, 37134 Verona, Italy * Corresponding author. E-mail address: [email protected] KEYWORDS Ultrasonography Pancreatic ultrasound Pancreatic diseases Contrast-enhanced ultrasonography Radiol Clin N Am - (2012) -- doi:10.1016/j.rcl.2012.03.010 0033-8389/12/$ – see front matter Ó 2012 Elsevier Inc. All rights reserved. radiologic.theclinics.com

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Page 1: Usg Pancreas

Ultrasonographyof the Pancreas

Giulia A. Zamboni, MD*, Maria Chiara Ambrosetti, MD,Mirko D’Onofrio, MD, Roberto Pozzi Mucelli, MD

KEYWORDS

� Ultrasonography � Pancreatic ultrasound� Pancreatic diseases � Contrast-enhanced ultrasonography

Although the pancreas is often thought of as anorgan that is difficult to explore using ultrasound(US), due to its deep retroperitoneal location,with the appropriate technique it can be studiedsuccessfully in most patients. US can provideinformation that is useful for diagnosis of patho-logic conditions, especially with the use ofharmonic imaging, color-Doppler, and contrastagent administration.

EXAMINATION TECHNIQUES

To improve visualization of the pancreas, the ultra-sound (US) examination is usually performed afterat least 6 hours of fasting. In this way, the presenceof bowel gas is limited, the stomach is empty offood, and the entire organ can be visualized.Nevertheless, technical success is also dependenton the skill and persistence of the examiner.1

US should be performed routinely along multiplescan planes, including transverse, longitudinal,and angled oblique, to visualize the entire organ:the head with the uncinate process, the body,and the tail. These multiple scan planes shouldallow examination of the entire pancreas in at least2 views. When needed, the spleen can be used asan acoustic window to visualize the pancreatic tail.

When visualization of the pancreas is limited, it ispossible to use other scanning techniques, suchas moving the transducer and applying compres-sion to displace bowel gas, filling the stomachwith water, examining the patient in suspendedinspiration or expiration, and changing the patientto a decubitus position.

Disclosures: G.A.Z., M.C.A., and R.P.M. have no disclosuHealthcare (2010).Istituto di Radiologia, Policlinico GB Rossi, Azienda Ospe10, 37134 Verona, Italy* Corresponding author.E-mail address: [email protected]

Radiol Clin N Am - (2012) -–-doi:10.1016/j.rcl.2012.03.0100033-8389/12/$ – see front matter � 2012 Elsevier Inc. All

Conventional gray-scale US with multifrequencytransducers is usually the first stepwhenexaminingthe pancreas, selecting the best frequency for eachdepth. Usually, convex probes are used, withfrequencies rangingbetween 3and5MHz.Dopplerfrequency must be set to record flows from deepabdominal vessels (1–4 MHz). Lower Dopplerfrequencies allow better penetration and are usedto evaluate the peripancreatic vessels, whereashigher Doppler frequencies are useful for evalu-ating slower flows in thin patients whose pancreasis more superficial.2

Tissue Harmonic Imaging

The routine examination technique should includethe use of tissue harmonic imaging (THI), whichcan improve visualization of the pancreas byincreasing the signal-to-noise ratio and reducingthe reverberation artifacts from the body wall,especially when studying large patients or deepstructures. Shapiro and colleagues3 demonstratedthat harmonic imaging had better penetrationdetail and overall image quality than conventionalUS. In a prospective study on 107 patients, Hohland colleagues4 demonstrated that sensitivity forthe detection of pancreatic lesions with THI usingthe phase inversion technique was higher thanfor conventional B-mode US.

Color-Doppler and Power-Doppler Ultrasound

Doppler ultrasound is another fundamental part ofthe conventional US examination for evaluatingthe peripancreatic vessels (portal vein, superior

res. M.D. was an Advisory Board member, Siemens

daliera Universitaria Integrata Verona, P.le LA Scuro

rights reserved. radiologic.th

eclinics.com

Page 2: Usg Pancreas

Zamboni et al2

mesenteric artery and vein, splenic artery and vein,aorta and inferior vena cava). Doppler imagingallows the visualization of smaller peripancreaticand intrapancreatic vessels, and at the sametime the assessment of patency and characteris-tics of blood flow.2

The normal color-Doppler and pulsed-Dopplerfeatures of peripancreatic vessels in healthysubjects are well known5: the mean flow velocityis about 103 � 18 cm/s in the celiac trunk, 78 �16 cm/s in the hepatic artery, 85 � 18 cm/s in thesplenic artery, 100 � 22 cm/s in the superiormesenteric artery,2 and 12 to 20 cm/s in the portalvein.2 The resistance index in the superior mesen-teric artery is general higher than in the other arterialvessels.2

Box 1What to look for in pancreatic US

� Size

� Contour

� Texture

� Echogenicity

� Main pancreatic duct

� Common bile duct

� Major peripancreatic vessels (portal vein,superior mesenteric artery and vein, splenicartery and vein, aorta and inferior vena cava)

Contrast-Enhanced Ultrasound

Contrast-enhancedultrasound (CEUS)withsecond-generation contrast agents is not currently ap-proved by the Food and Drug Administration forthe study of solid abdominal organs in the UnitedStates, but is used in many other countries forthe study of the pancreas and other abdominalorgans.CEUS with second-generation contrast agents

(Sonovue, Bracco, Milan, Italy; Sonazoid, GEHealth care, Oslo, Norway; Optison, GE Healthcare, NJ, USA; Definity, LantheusMedical Imaging,MA, USA) and the use of contrast-specific US tech-niques allows a continuous dynamic observation ofpancreatic parenchymography. CEUS can, there-fore, beused for a better identificationof pancreaticlesions as compared with conventional US and forcharacterization and staging of focal lesionsalready identified at US.6

The technique of CEUS of the pancreas shouldvary according to the clinical indication.6 Thepatient should be in the position that provides thebest visualization of the area of interest in thepancreas, most commonly the supine position.Harmonic microbubble (MB)-specific imagingwith a low acoustic US pressure (mechanical index<0.2) is required for a dynamic CEUS examination:with specific US software, the background tissuesignals are canceled and only the signals relatedthe responses of the MBs are visualized. In ourinstitution, we routinely administer a 2.4-mL intra-venousbolus of second-generation contrast agent,constituted of sulfur hexafluoride–filled MBs witha phospholipid peripheral shell (SonoVue, Bracco)followed by a 5-mL saline flush. The enhancementis evaluated in real time, maintaining the samescanning frame rate as in the previous conventionalgray-scale examination. The dynamic continuousobservation of the contrast-enhanced phases

(arterial, portal/venous, and late phases) startsimmediately after the contrast agent injection.7 Stillimages or clips are saved according to the radiolo-gist’s preferences; however,most often still imagesare saved for the baseline and delayed parts of theexamination, whereas clips are saved for the earlyarterial and parenchymographic phases (startingfrom the arrival of the contrast in the aorta).In our institution, the most common indication is

characterization and staging of focal lesions: thelesion must be examined in the arterial, pancreatic,and venous contrast-enhanced phases. The rela-tionshipwith the peripancreatic vesselsmust be as-sessed. With second-generation agents, after thestudy of the pancreas, the liver can be studied inthe delayed “sinusoidal” phase to exclude the pres-ence of liver metastases8; for the study of the liver,the left lateral decubitus position may be useful.When the objective is detection or study of

a small pancreatic lesion, often the case for endo-crine tumors, 2 boluses of contrast agent can beused, each of 2.4 mL, to be able to explore allthe portions of the pancreas in the arterial phase.6

Also, the use of a high–acoustic pressure flash,which almost completely eliminates saturation ofthe area immediately adjacent to the parenchymaalready studied by disrupting the MBs, canprovide another pure arterial phase.The complete examination of the pancreas

(Box 1) should include the evaluation of size,contour, and texture of the gland, and the echopattern of the head, body, and tail (Fig. 1). Themain pancreatic duct and the common bile ductmust be identified, as well as the major peri-pancreatic vessels, such as the portal vein, supe-rior mesenteric artery and vein, splenic artery andvein, and aorta and inferior vena cava.

NORMAL ANATOMY

The pancreas is located at the level of the first orsecond lumbar vertebra in the retroperitoneal

Page 3: Usg Pancreas

Fig. 2. Mild acute pancreatitis: the transverse conven-tional US image depicts the pancreas slightlyenlarged, with a heterogeneous texture.

Fig. 1. Tranverse conventional US image of a normalpancreas in a young adult: the pancreas appears isoe-choic to the normal liver parenchyma.

Ultrasonography (US) of the Pancreas 3

space, and its position can vary with respiration.The pancreas is usually divided into the head,with the uncinate process posteriorly and inferi-orly, neck, body, and tail. The normal pancreaticparenchyma usually has a homogeneous textureand is isoechoic or hyperechoic to the normal liverparenchyma. With age, fatty replacement of thepancreas (pancreatic lipomatosis) is common,and the parenchyma may appear as echogenicas the adjacent retroperitoneal fat in up to 35%of cases.9

The main pancreatic duct normally measuresbetween 95 and 250 mm in length. The diameteris greatest in the head (3–4 mm), and tapers inthe body (2–3 mm) and tail (1–2 mm).10

Box 2Focal acute pancreatitis

� Homogeneously hypoechoic segmental en-largement of the pancreas (differential diag-nosis with neoplasms).

� Color-Doppler: increased signal owing tohyperemia.

� CEUS: the inflamed parenchyma shows in-creased parenchymography, as opposed toductal adenocarcinoma,which appears hypo-vascular.

INFLAMMATORY DISEASEAcute Pancreatitis

Acute pancreatitis is an acute inflammatoryprocess of the pancreas; the diagnosis is usuallybased on elevated serum amylase and lipaselevels and clinical findings. Although computedtomography (CT) is the imaging modality of choicein patients with suspicion of acute pancreatitis, USis often the first examination performed in patientswith acute abdominal pain. US can also help inidentifying the presence of biliary stones; there-fore, allowing a diagnosis of biliary pancreatitis.

Most commonly, patients with mild acutepancreatitis will show normal findings at US.When the disease is more severe, the pancreasbecomes enlarged and hypoechoic to the normalliver, with a heterogeneous texture as a result ofedema (Fig. 2).

Pancreatitis can involve the entire gland or onlya portion. Diffuse acute pancreatitis is usuallyeasily recognized, without problems in differentialdiagnosis. Focal acute pancreatitis, appearing as

a homogeneously hypoechoic segmental enlarge-ment of the pancreas, can be difficult to differen-tiate from a neoplasm. Color-Doppler can aid inthe differential diagnosis, showing increasedsignal owing to hyperemia. CEUS can also beuseful in the differential diagnosis between focalpancreatitis and pancreatic cancer: the inflamedparenchyma shows increased parenchymogra-phy, different from a neoplastic lesion (Box 2).6

US can also detect the complications of acutepancreatitis, and guide treatment. Complicationsinclude acute fluid collections, abscesses, pseu-docysts, infected necrosis, and hemorrhage. Themost common complications are acute fluidcollections, seen in up to 50% of patients, andare most commonly localized within the anteriorpararenal space and in the lesser sac.11

Pseudocysts are delayed complications ofacute pancreatitis (typically after 4 weeks ofsymptom onset).12 Pseudocysts can contain inclu-sions that can hinder the sonographic distinctionfrom cystic tumors, especially mucinous cystade-noma. CEUS can aid in this differential diagnosisbecause the endoluminal debris is not vascular-ized and will appear completely and homoge-neously anechoic at CEUS (Box 3, Fig. 3).6

Page 4: Usg Pancreas

Box 3US evaluation of complications of acutepancreatitis

Pseudocyst

� Thick wall

� Possible endoluminal debris, anechoic atCEUS (differential diagnosis with mucinouscystic tumors)

Infected pseudocyst (abscess)

� US: anechoic or inhomogeneously isoechoicor hypoechoic

� CEUS: avascular content

Box 4US features of chronic pancreatitis

� Calcifications

� Duct dilation

� Atrophy and alterations in size

� Irregular contours

� Hyperechoic parenchyma owing to fattydeposition and fibrosis

Zamboni et al4

Other delayed complications that can developweeks after the onset of pancreatitis are infectedpseudocysts (abscesses) (ie, collections of puru-lent material in or around the pancreas). Infectedpseudocysts at US are anechoic or heteroge-neously isoechoic or hypoechoic because ofbright echoes from pus, debris, or gas bubbles.13

Pancreatic abscesses require drainage, eitherpercutaneous drainage, often US guided, orsurgical or endoscopic intervention.

Chronic Pancreatitis

Chronic pancreatitis is an inflammatory process inwhich the pancreatic parenchyma is replaced byfibrous tissue. The diagnosis is based on clinicalfindings, laboratory evaluation, and imaging find-ings: these imaging findings are readily recognizedin the advanced phases of the disease, but areoften subtle in the early phases.1 US is able toidentify the fine alterations in the parenchymaechotexture that can present in the early stagesof the disease, which can be important for thediagnosis (Box 4); however, especially in the earlystages of the disease, the texture of the paren-chyma can be normal in up to 40% of cases.14–16

Fig. 3. Pseudocyst: small cystic lesion in the pancreatic heCEUS shows the absence of enhancing septations or nodu

With advanced disease, atrophy and alterationsin size occur, which are the most easily identifiedfindings. The organ has irregular contour and theparenchyma becomes hyperechoic owing to fattyinfiltration and fibrosis1,10: this sign is sensitivebut nonspecific.The most typical imaging findings for the diag-

nosis of chronic pancreatitis are intraductal calcifi-cations and pancreatic duct dilation (Fig. 4).According to the Japan Pancreas Society, the

presence of calcifications is the most importantand pathognomonic diagnostic criterion forchronic pancreatitis.17 At US, calcifications appearas hyperechoic foci with posterior shadowing,a feature that smaller calcifications may lack.Calcifications are better demonstrated with har-monic imaging.Dilatation of the main pancreatic duct (ie,

caliber >3 mm) can be easily identified at US inpatients with chronic pancreatitis and has 60%to 70% sensitivity and 80% to 90% specificity forthe diagnosis.1,18 Main pancreatic duct dilatationis a specific but not sensitive sign for the diagnosisof chronic pancreatitis: Bolondi and colleagues18

reported that the main pancreatic duct was dilatedin 52.3% of patients with chronic pancreatitis.Although identifying alterations of the contour ofthe main pancreatic duct may be difficult, the pres-ence of irregularly dilated portions of the duct istypical of the more advanced stages of chronicpancreatitis.

ad with anechoic content and well-defined wall (A).les (arrow in B).

Page 5: Usg Pancreas

Fig. 4. Chronic pancreatitis: Conventional US showsthe pancreatic head, heterogeneously hypoechoicwith a multiple hyperechoic parenchymal calcifica-tions. The main pancreatic duct is dilated (betweencalipers).

Ultrasonography (US) of the Pancreas 5

Mass-forming pancreatitis is usually observed inpatientswith a history of chronic pancreatitis.19 Thedifferential diagnosis with adenocarcinomamay bechallenging because the lesions can present withvery similar US features, as well as similar symp-toms and signs (Table 1). In most cases, mass-forming pancreatitis appears as a hypoechoicmass with enlargement of a limited portion of theorgan, most commonly the head. The presence ofsmall calcifications may suggest the diagnosis,10

but contrast-enhanced examinations and biopsyare necessary for the diagnosis. CEUS can aid inthe differential diagnosis, because although ductaladenocarcinoma is hypoechoic in all contrasto-graphic phases, mass-forming pancreatitis shows“parenchymographic” enhancement similar to thesurrounding parenchyma in all the phases (Fig. 5).This enhancement has an intensity that is inverselycorrelated with the length of the inflammatoryprocess: the longer the inflammatory process, theless intense the enhancement.20

Autoimmune chronic pancreatitis is character-ized by periductal fibrosis, with lymphocytic infiltra-tion and evolution to fibrosis.21 The process can bediffuse or focal, depending on extension of thedisease. US findings are characteristic in thediffuse form: the pancreas is enlarged with the

Table 1US differential diagnosis between mass-forming pan

Mass-Forming Pancreatitis

US Hypoechoic mass

Calcifications Pathognomonic

Ductal dilatation Present

CEUS Enhancement similar to adjacnormal parenchyma

typical “sausage”-like morphology, with markedlyhypoechoic parenchyma, and the main pancreaticduct is compressed by the surrounding paren-chyma.21 At CEUS, the parenchyma involved byautoimmune pancreatitis shows a moderate tomarked enhancement in the early contrast-enhanced phases,22 followed by washout.

SOLID TUMORSDuctal Adenocarcinoma

The aims of imaging in pancreatic neoplasms aredetection and staging to ensure proper manage-ment for the patient. US is often the first examina-tion for the initial evaluation of the pancreas.1

Ductal adenocarcinoma represents up to 90% ofall tumors of the exocrine pancreas. At US, adeno-carcinoma typically appears as a solid hypoechoiclesion with ill-defined margins that alter the glandcontours or, when the mass is small, is completelysurrounded by parenchyma.

Masses in the pancreatic head cause ductalobstruction, with secondary dilatation of thecommon bile duct and the pancreatic duct, theso-called “double-duct sign”; however, thesefeatures can also be frequently seen in chronicpancreatitis. In the more aggressive tumors, theimbalance between growth rate and angiogenesismay cause necrosis.6

As observed at contrast-enhanced CT andmagnetic resonance (MR) imaging, during CEUS,ductal adenocarcinoma shows poor enhancementin all contrast-enhancement phases and appearshypoechoic compared with the adjacent nor-mal parenchyma. Contrast medium administrationenables better evaluation of themargins and size ofthe lesion and its relationship with peripancreaticarterial and venous vessels for local staging(Box 5, Fig. 6).6 By using second-generationcontrast agents, after studying the pancreas inthe first dynamic phases, it is possible to scan theliver in the delayed phase to detect the presenceof metastases.

creatitis and adenocarcinoma

Adenocarcinoma

Hypoechoic mass

Absent

Present

ent Hypovascular compared with adjacentnormal parenchyma

Page 6: Usg Pancreas

Fig. 5. Mass-forming pancreatitis. (A) Transverse conventional US shows the pancreatic head, enlarged and hypo-echoic. (B) After contrast-agent administration, the parenchyma in the head (asterisk) shows “parenchymo-graphic” enhancement, appearing isoechoic to the rest of the organ.

Zamboni et al6

Endocrine Tumors

Pancreatic endocrine tumors arise from the neuro-endocrine cells of the pancreas; these tumors areclassified as functional or hyperfunctioning versusnonfunctional or nonhyperfunctioning based onthe presence of clinical symptoms related tohormone overproduction by the tumor. Usually,hyperfunctioning endocrine tumors, the mostcommon of which are insulinomas and gastrino-mas, are small at the time of diagnosis, whereasnonhyperfunctioning tumors are frequently largeat detection and more often malignant.23 Endo-crine tumors are hypervascular, which influencesthe imaging features (Box 6).12 Color- andpower-Doppler US can show a “spot pattern”within endocrine tumors, from small vessels thathave flow visible at Doppler: this feature, however,can be absent in small tumors or in tumors witha poorly developed vascular network.24

CEUS features are dependent on the size andvascularity of the tumor. Most often these lesionsenhance rapidly and intensely in the earlycontrast-enhanced phases and retain the MBs inthe late phase.24

In a minority of cases, however, the presence ofdense and hyalinized stroma inside the lesion can

Box 5US features of pancreatic adenocarcinoma

� Solid hypoechoic mass with ill-definedmargins

� Possible areas of necrosis (rare)

� CEUS: hypoenhancing mass; better evalua-tion of margins and relationship with vesselsfor local staging.

cause hypovascularity of endocrine tumors.24

Nevertheless, it has been reported that a clearenhancement during CEUS can be seen in somepancreatic endocrine tumors that appear hypo-dense on multidetector CT24: this is probablybecause of the high resolution power of state-of-the-art US imaging, combined with the size andblood-pool distribution of MB contrast agents,along with the advantage of continuous observa-tion of the arrival of the contrast agent. CEUScan, therefore, improve the identification and char-acterization of endocrine tumors,24,25 and furtheraid in their locoregional and hepatic staging(Fig. 7).24

CYSTIC PANCREATIC TUMORS

Cystic tumors represent 10% to 15% of all pancre-atic tumors; serous and mucinous subtypes arethe most common cystic neoplasms of thepancreas (Table 2).

Serous Cystadenoma

Serous cystadenoma (SCA) is a benign lesion witha strong female predilection, usually seen inpatients older than 60 years. SCA is generallycharacterized by tiny cysts (smaller than 2 cm indiameter) and is most commonly located in thehead of the pancreas.12

The content of the cysts appears anechoic atUS; however, when the cysts are extremely small,the lesion may appear solid on US and CT. Acentral scar may be present in up to 15% of thecases, appearing as a central solid hyperechoicportion of the tumor, sometimes with calcifica-tions. US can show the microcystic appearanceof the tumor. US features of SCA that are typi-cal and often diagnostic include sharp lobulated

Page 7: Usg Pancreas

Fig. 6. Ductal adenocarcinoma. (A) Sagittal US image shows a large hypoechoic solid mass in the pancreatic headencasing the gastroduodenal artery (arrowhead). Axial (B) and sagittal (C) CEUS shows that the mass is hypovas-cular and confirms vascular encasement.

Ultrasonography (US) of the Pancreas 7

margins, thin wall, and internal septations that areradially arranged and converge to a central scar(Fig. 8). CEUS can demonstrate the enhancementof intralesional septations revealing the microcys-tic nature of the lesion even in lesions that mightappear solid at baseline US.6

Mucin-Producing Tumors

Mucin-producing tumors of the pancreas arisefrom the peripheral ducts (mucinous cystictumors) or from the main pancreatic duct and itsside branches (intraductal papillary mucinousneoplasms [IPMNs]).26

Mucinous cystic tumors are most common inwomen 40 to 60 years of age, are malignant orpotentially malignant lesions, and most commonlyare observed in the body or tail of the pancreas.27

Mucinous cystic tumors are located peripher-ally in the parenchyma and show cysts that arefewer in number and larger in size than thoseobserved in SCA. At US, mucinous cysticneoplasms appear round or ovoid-shaped, andare made up of unilocular or multilocular cystswith thick walls. Mucinous cystadenoma mayhave calcifications in the wall and/or septations,parietal nodules, and papillary vegetations. Thevisualization of the wall and inclusions may beimpaired because of the mucinous content of

Box 6US features of endocrine tumors

� US: solid hypoechoic/isoechoic, well-definedmass

� Color- and power-Doppler US: “spot” pattern

� CEUS: rapid and intense enhancement in thearterial phase with retention of MBs in thelate phase

the cysts, which demonstrates fine echoes atUS. For these reasons, harmonic imaging isused to allow better evaluation of the walls, septa-tions, nodules, and papillary vegetations.28 Also,contrast administration may significantly improvethe US identification of the parietal nodules andsepta, and can aid in differentiating these lesionsfrom pseudocysts (Fig. 9).6

IPMNs are tumors that induce dilation of themain pancreatic duct and/or side branches, orresult in formation of cysts because of proliferationof ductal epithelium and excessive mucin produc-tion. IPMNs are classified on the basis of their siteof involvement into main duct type, branch ducttype, or a combination of the two.29 In the mainduct type, dilatation of the main pancreatic ductis visible at US (Fig. 10).

Especially for the ductectatic mucin-hyperse-creting type of the branch duct IPMNs, it can bedifficult to differentiate mucin from solid portionsof the tumor. Therefore, harmonic imaging maybe used to better identify the fluid components.

With CEUS, intraductal papillary tumoral vege-tations may be more visible because they enhancein the dynamic phase, especially in the papillary-villous variant20; however, US may not easilydemonstrate the communication between sidebranch lesions and the main pancreatic duct.30

ACOUSTIC RADIATION FORCE IMPULSE

The assessment of the viscoelastic properties oftissues with US has gained increasing interest inrecent years. Many types of software have beenproposed for US tissue-strain analysis performedunder compression, such as Hitachi Real-timeTissue Elastography (HI-RTE, Hitachi MedicalSystems Europe, Zurich, Switzerland), eSie Touch(Siemens, Erlangen, Germany), or Elasticity Imag-ing (Siemens), or without compression, such as

Page 8: Usg Pancreas

Fig. 7. Pancreatic endocrine tumor: small hypoechoic solid mass in the pancreatic body (A, between calipers).CEUS shows strong enhancement in the arterial phase (B, arrowhead) and MB retention in the delayed phase(C, arrowhead).

Zamboni et al8

acoustic radiation force impulse (ARFI) imagingand its new implementations, Virtual Touch tissueimaging (Siemens) and Virtual Touch tissue quan-tification (Siemens).ARFI imaging is a new US imaging modality that

evaluates the stiffness of deep tissues by short-duration acoustic radiation forces that producelocalized displacements in a “pushed” region ofinterest (ROI). Through the use of acoustic pushpulses to generate shear waves on a fixed target,

Table 2Clinical and US features of cystic lesions of the panc

SCA MCN

Location Head Body, ta

Age Older than 60 years 40–60 ye

Sex Female Female

b-mode Microcystic appearanceLobulated margins

Internal septa arrangedradially and convergingon the central scar

Round oUniloculcysts

THI — Better ewalls,and pa

Duct dilation Absent Absent

Cyst features Small and multipleAnechoic content

Larger aContentThick waCalcificathe se

Parietalpapilla

CEUS Enhancement of thinintralesional septa

Enhancenodul

Abbreviations: CEUS, contrast-enhanced ultrasound; IPMN, incystic neoplasm; SCA, serous cystadenoma; THI, tissue harmon

ROI qualitative visual and quantitative valuemeasurements can be obtained (Fig. 11). VirtualTouch tissue quantification provides numericalmeasurements (wave-velocity values) of tissuestiffness at a precise image-based anatomic loca-tion. The normal values of shear-wave speed fornormal liver, gallbladder, pancreas, spleen, andkidneys have been defined.31 A recent study as-sessed the role of ARFI in the characterization ofpancreatic cystic lesions, suggesting a potential

reas

IPMN

il Ubiquitous

ars Older

Indifferent

r ovoid-shapedar or multilocular

Dilatation of the mainpancreatic duct and/or itsside branches orformation of cysts

valuation of thesepta, nodules,pillary vegetations

Identify the fluid portionsof IPMN

Present in the main ducttype

nd fewerwith fine echoesllstions on the wall orptanodules andry vegetations

ment of parietales and thick septa

Enhancement ofvegetations

traductal papillary mucinous neoplasm; MCN, mucinousic imaging.

Page 9: Usg Pancreas

Fig. 8. Serous cystadenoma: conventional US shows a cystic lesion with sharp lobulated margins and internal sep-tations that converge radially (arrowheads in A). CEUS demonstrates enhancement of thin intralesional septa-tions (arrow in B).

Ultrasonography (US) of the Pancreas 9

new approach for a noninvasive analysis of thefluid content.32

INTRAOPERATIVE ULTRASOUND

Intraoperative ultrasound (IOUS) can guaranteehigh-resolution B-mode imaging of the pancreasand liver. Image quality is improved by placingthe probe either directly on the surface of theorgan or with a minimal fluid interface, avoidingany interference by the abdominal wall or thegas-filled bowel.

Several investigators have reported that sensi-tivity of IOUS in the detection of carcinomas is92.3% to 100.0% and that its use can modify thesurgical treatment in up to 67.0% of cases.33–36

This imaging technique is especially useful forselected cases when preoperative studies indicatepossible vascular invasion by the pancreatic massor possible hepatic involvement.

Pancreatic IOUS can have a clinical role in lesionidentification and/or in lesion staging. In the firstscenario, IOUS is used for lesion detection; forexample, a hyperfunctioning endocrine tumor notidentified at preoperative imaging. For lesionstaging and operative guidance, the examinationrequires an evaluation of the relationship of the

Fig. 9. Mucinous cystadenoma: large cystic lesion with thicat conventional US (A). Harmonic imaging allows better vshows enhancement of the thick wall and septations (arro

lesion with the main pancreatic duct and theassessment of resectability from the major peri-pancreatic vessels.

INTERVENTIONAL ULTRASOUND

The use of Interventional ultrasound for the diag-nosis and therapy of some pancreatic pathologieshas definitely modified diagnostic and therapeuticmanagement. Percutaneous US-guided proce-dures are widely used because of the possibilityfor continuous monitoring, the high spatial resolu-tion, availability, and the low cost of this technique.For US-guided procedures, the entry points to thepancreas can be selected freely because of thepossibility of scanning along oblique planes.37

Percutaneous Diagnostic Procedures

The accuracy of US-guided percutaneous diag-nostic biopsy procedures can vary according tothe site of the lesion. Brandt and colleagues38 re-ported a 93% to 94% accuracy for body-taillesions and a slightly lower accuracy for headlesions (83%–84%).39 In a more recent series of545 diagnostic fine-needle aspirations (FNAs) ofpancreatic lesions, 63% of which were located in

k walls and septations, the content shows fine echoesisualization of the posterior wall of the cyst (B). CEUSwheads in C) and of parietal nodule (arrow in C).

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Fig. 10. Main duct IPMN: segmental dilatation of the main pancreatic duct in the body-tail (A), the duct contentshows fine echoes owing to the presence of mucin. CEUS reveals enhancement of papillary parietal vegetations(arrowhead in B).

Zamboni et al10

the head or uncinate process, we obtaineda 99.4% sensitivity, 100.0% specificity, 99.4%accuracy, and a 1.5% incidence of minor compli-cations.40 Indeed, US guidance for percutaneousdiagnostic procedures has a low reported inci-dence of complications, ranging from 1.5% to5.0%.40,41

The safest and most commonly used entry pointfor FNA and biopsy is the left upper quadrant, leftof the midline, which allows avoidance of majorvessels. The angle of the needle track will vary de-pending on the location of the lesion in thepancreas.40 The safest entry point and track areselected to avoid passage into hollow organs.Although transgastric passage is not absolutelycontraindicated, transcolonic passage alwaysshould be avoided.For interventional procedures, 2 types of probes

are commonly used: probes with lateral support,

Fig. 11. Acoustic radiation force impulse (ARFI)imaging of the normal pancreatic body, with VirtualTouch tissue quantification providing a numericalmeasurement (wave-velocity value) of the stiffnessof the parenchyma.

and probes with noncontinuous crystals andcentral support. The use of a lateral-support probewill allow only oblique needle tracks, whereasa central support probe will allow both verticaland oblique tracks. In our institution, we routinelyuse probes ranging in frequency from 2.5 to 5.0MHz with a laterally mounted guide kit (Fig. 12).Color-Doppler images are fundamental for identi-fying major blood vessels and excluding themfrom the needle track.

Percutaneous Therapeutic Procedures

The other major use of US-guidance is for the posi-tioning of percutaneous drainage catheters. USguidance can guarantee a direct access route tothe pancreas, avoiding involvement of the neigh-boring structures, such as vessels, and allows effi-cient treatment of infected pancreatic necrosis or

Fig. 12. Transverse US image shows a hypoechoic massin the pancreatic head (arrowhead). A probe withlateral support is used, providing the oblique needletrack shown. The needle tip (arrow) can be seen insidethe lesion.

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Ultrasonography (US) of the Pancreas 11

pseudocysts. During the procedure, a fluid samplecan be obtained to assess the presence ofamylase, which proves a communication with themain pancreatic duct.

SUMMARY

With the appropriate technique, US can provideuseful information on the pancreas and its dis-eases in most patients. US can also be used toguide diagnostic and therapeutic procedures andfor intraoperative guidance.

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