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British Journal of Radiology (2003) 76, 857-865
© 2003 British Institute of Radiology
doi: 10.1259/bjr/16642775
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Review article

State-of-the-art imaging of pancreatic neoplasms

M K Kalra, MD, DNB, M M Maher, MD, FFR (RCSI), FRCR, P R Mueller, MD and S Saini, MD

Department of Abdominal Imaging and Intervention, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA

Correspondence: Dr Sanjay Saini


   Abstract
Top
 Abstract
Introduction
 Imaging techniques and protocols
 Imaging features of pancreatic...
 References
 
Pancreatic imaging with multidetector CT allows multiphase acquisition of thin slices in a single breath-hold and is especially valuable in obtaining isotropic three-dimensional reformations that improves our ability to provide accurate pre-operative vascular mapping. Advanced MR technology allows faster imaging of pancreas, thus facilitating MR cholangiopancreatography. Use of tissue-specific MR contrast agents, endoscopic ultrasound and PET in pancreatic imaging has evolved considerably. This review article discusses the role of CT, MR, endoscopic ultrasound and PET imaging in pancreas.


   Introduction
Top
 Abstract
 Introduction
Imaging techniques and protocols
 Imaging features of pancreatic...
 References
 
Current state-of-the-art cross-sectional imaging techniques are invaluable in early diagnosis and accurate staging of pancreatic malignancies. CT and ultrasound (US) are the most commonly utilized imaging modalities for evaluation of pancreatic pathologies. Multislice CT is regarded as the most efficient modality for imaging pancreatic neoplasms [1, 2]. Development of faster MRI systems with improved contrast and temporal resolution, and tissue-specific contrast agents such as mangafodipir trisodium, have significantly enhanced the role of MR in imaging of pancreatic neoplasms. It is particularly useful as a "problem solving" adjunct to CT and US in imaging pancreatic neoplasms. In addition, endoscopic ultrasound (EUS) and positron emission tomography (PET) in pancreatic malignancy have developed considerably as complimentary diagnostic modalities. The present review article describes the present state of CT, MRI, EUS and PET in imaging of pancreatic tumours.


   Imaging techniques and protocols
Top
 Abstract
 Introduction
 Imaging techniques and protocols
Imaging features of pancreatic...
 References
 
CT
Multidetector CT technology takes advantage of sufficiently reduced image acquisition time for multiphasic thin slice acquisitions of the pancreas and liver in a single breath-hold with superior contrast bolus utilization. Generally, dual phase imaging in arterial and portal venous phases is used for evaluating suspected pancreatic neoplasms and depicting peripancreatic/peritumoural vascular anatomy. For dual phase imaging in arterial and portal venous phases for evaluating pancreatic neoplasms, 150 ml of non-ionic contrast media (300 mg ml-1) is injected at 5 cm3 s-1 and images are acquired following delays of approximately 45 s and 70 s for arterial and portal venous phases, respectively [3]. Contiguous thin sections are obtained using protocols dependent on machine manufacturer, to enable overlapping reconstruction. Arterial phase CT imaging with thin overlapping slices can on occasion be important in the detection of hypervascular primary tumours and metastases.

Multiplanar three-dimensional reconstruction techniques including volume rendering, maximum intensity projection and shaded surface display provide comprehensive information about the relationships and possible involvement of vascular structures in pancreatic neoplasms, and the degree and level of dilatation of pancreatic and biliary ducts [4]. While axial source images depict the involvement of the superior mesenteric vein, sagittal reformats are best for demonstrating superior mesenteric artery involvement. Coronal reformats help in demonstrating local extension to the stomach and duodenum [5, 6]. Standard oral contrast media for pre-operative assessment of pancreatic neoplasm and peripancreatic vasculature is unnecessary. Instead, a negative oral contrast agent such as water provides optimum visualization of the duodenal ampulla and duodenal–pancreatic interface, aiding detection of duodenal/paraduodenal tumour invasion and terminal bile duct calculus [7, 8].

MRI
State-of-the-art MRI of pancreatic neoplasms is optimally performed with 1.5 Tesla gradient systems using phased-array torso coils to improve the signal-to-noise ratio, optimized with thin slice profiles and small fields of view [9]. Breath-hold acquisitions are obtained with fast spin echo (FSE) or gradient echo (GRE) sequences and echo planar imaging. A moderately T2 weighted FSE and single shot fast spin echo (SSFSE) should be obtained, followed by T1 weighted in-phase GRE and T1 weighted opposed-phase GRE. To evaluate cystic lesions of the pancreas, coronal and axial magnetic resonance cholangiopancreatography (MRCP) with SSFSE are usually obtained. Fat-suppressed, three-dimensional spoiled GRE sequences after the administration of gadolinium-DTPA are obtained in arterial, portal and delayed phases.

For detection of islet cell tumours, T1 weighted fat suppressed images are acquired in arterial phase (30–40 s), portal phase (70–80 s) and equilibrium phase (180 s), following the administration of intravenous gadolinium. Tissue-specific contrast agents, such as mangafodipir trisodium may be used to aid detection of subtle pancreatic neoplasms in equivocal cases. The mechanism of action of mangafodipir trisodium is that normal pancreatic parenchyma enhances following administration and becomes hyperintense on T1 weighted images whereas neoplasms do not enhance [10]. Fat-suppressed, high-resolution T1 weighted sequence acquired 10 min after administration of mangafodipir trisodium (5 µmol kg-1 body weight) in a slow bolus over 1–2 min may be of value in the detection of small pancreatic masses.

MRCP techniques with a single breath-hold, using thick (2–5 cm) sections can provide excellent selective displays of the whole extrahepatic biliary tract and pancreatic duct without respiratory artefact and few susceptibility artefacts. Some authors have stressed the value of secretin administration in improving pancreatic ductal details in MRCP [11, 12]. The basis of secretin-enhanced MRCP is that the exogenous administration of secretin stimulates the secretion of pancreatic juice, which consequently increases the volume of stationary fluid in the pancreatic ducts. Secretin (1 ml per 10 kg body weight) administration 10–15 min prior to MRCP, improves pancreatic duct and side-branch delineation as well as potentially permitting the evaluation of pancreatic flow dynamics and the assessment of pancreatic exocrine function.


   Imaging features of pancreatic neoplasms
Top
 Abstract
 Introduction
 Imaging techniques and protocols
 Imaging features of pancreatic...
References
 
Pancreatic adenocarcinoma
Each year there are 185 000 new cases of pancreatic adenocarcinoma worldwide, making it the 13th most common cause of cancer and 8th most common cause of cancer mortality [13]. About 90% of pancreatic tumours are ductal adenocarcinomas, whereas neuroendocrine tumours and acinar cell carcinomas constitute about 2–5% of all pancreatic tumours. The differential diagnosis of pancreatic tumours has been summarized in Table 1Go. The major objective of imaging pancreatic malignancies is their detection and staging, to determine the appropriate management and ultimately the prognosis of the disease.


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  		Table 1. Classification of pancreatic tumours

 
Significant improvements in pancreatic cancer staging with multislice CT and the use of interactive multiplanar reconstructions has been reported [14]. Often, pancreatic adenocarcinomas appear as masses distorting the contour of the gland with associated findings such as dilated pancreatic and common bile ducts, atrophy of the gland, vascular invasion and metastases to regional nodes, liver and the peritoneal cavity [15]. On an unenhanced CT, pancreatic adenocarcinomas are generally isoattenuating to normal pancreatic parenchyma, unless extensive necrosis or cystic change is present. On dynamic contrast enhanced CT, most adenocarcinomas are hypoenhancing with respect to the surrounding normal parenchyma, aiding detection of small and subtle tumours not producing a visible mass or distorting the contour [16]. Tumour resectability is determined by the extent of loco-regional spread. The features that may preclude a curative surgical resection include:
  1. invasion of the portal vein, superior mesenteric artery and vein, common hepatic artery and proper hepatic artery (Figure 1Go)
  2. involvement of the neural plexus around the coeliac axis or the superior mesenteric artery
  3. invasion of contiguous structures such as the stomach, colon, spleen, left adrenal, kidney, or spine
  4. the presence of metastases to the liver and peritoneum



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  		Figure 1. (a) Dynamic contrast enhanced axial CT image of a 55-year-old man with known pancreatic adenocarcinoma. A hypodense, mildly enhancing mass is seen in the pancreatic head and neck involving the common bile duct and proximal portal vein. Note the filling defect in superior mesenteric vein suggests vein thrombosis (large arrow) and retrocaval lymphadenopathy (small arrow). (b) Coronal reformation of the axial source image demonstrates the vascular relation of the mass. Narrowing of the proximal portal vein is exquisitely demonstrated on this three-dimensional rendering (arrows).

 
Spiral CT has been reported to have a positive predictive value of 100%, negative predictive value of 56%, and 70% overall accuracy for unresectable pancreatic carcinoma. The use of thin-slice helical CT and 3D CT angiography improves delineation of small vessel involvement [17, 18], tumour encasement is suggested by narrowing or obliteration of vascular lumen. Grading of vessel circumference contact represents the best tool in determining venous involvement, but shape deformation and dilatation of collateral veins are also important signs [19]. Increased attenuation of the normal perivascular fat has been described as "perivascular cuffing", a sign that correlates with vascular invasion and suggests unresectability. In addition, obliteration of the fat planes around the superior mesenteric and coeliac arteries raises suspicion of coeliac plexus involvement [5, 6, 17, 18]. Identification of enlarged nodes around the coeliac, superior mesenteric artery or para-aortic chains suggest lymphatic involvement. However, as normal size peripancreatic nodes can harbour small foci of malignancy, nodal staging of early pancreatic cancer is not accurate with CT.

T1 weighted spin echo MRI with and without fat suppression and immediate post-gadolinium spoiled gradient echo (SGE) sequences have been found to be superior to spiral CT imaging for detecting small lesions. Due to their scirrhous character from dense fibrotic tissue, pancreatic adenocarcinomas are generally slightly hypointense relative to pancreas on T2 weighted images but are difficult to visualize unless there is substantial necrosis [20]. Being relatively hypovascular, pancreatic adenocarcinomas enhance to a lesser extent than normal pancreatic tissue on early post-contrast images and appear distinctly hypointense to the maximally enhanced pancreas during the arterial phase of dynamic contrast enhancement. A thin rim of greater enhancing pancreatic tissue is often observed in pancreatic cancers and may help to establish the focal nature of the disease process. T1 weighted spin-echo MRI has been reported to be superior to dynamic contrast-enhanced CT imaging for the determination of vascular encasement. Gadolinium-enhanced T1 weighted SGE images are extremely useful for evaluating arterial and venous patency [9]. Three-dimensional (3D) contrast-enhanced dynamic MR angiography with fat suppression helps in delineating regional vascular encasement or occlusion as well as regional vascular anatomy [2]. Recently, Lopez Hanninen et al have reported positive and negative predictive values for cancer non-resectability of unenhanced and contrast-enhanced MR of 90% and 83%, respectively, and the accuracy, sensitivity, and specificity were 85%, 69%, and 95%, respectively [21]. A recent retrospective study has reported that in patients with a suspicion of pancreatic cancer, gadolinium should be used for performance of a contrast-enhanced MR angiography at the expense of a dynamic MR examination [22].

The characteristic features of pancreatic head adenocarcinoma on MRCP include encasement and obstruction of the pancreatic duct or bile duct. In pancreatic head carcinoma, dilatation of both biliary and pancreatic ducts ("double duct sign") occurs in 77% of cases, biliary duct dilatation occurs alone in 9% and pancreatic duct dilatation alone in 12% [12, 23]. MRCP readily demonstrates this "double duct" pattern of obstruction, which is strongly suggestive of a pancreatic or ampullary carcinoma [23]. In conjunction with abdominal MRI, MRCP helps in the detection of pancreatic malignancies and in establishing resectability as well as preventing unnecessary pre-operative endoscopic retrograde cholangiopancreatography (ERCP) and stenting. In addition, MRCP is helpful in planning percutaneous biliary drainage and radiation therapy [12]. Greater detail of the intrahepatic biliary tract provided by MRCP also facilitates planning of peripheral access to transhepatic biliary drainage.

Metastases to peripancreatic, para-aortic mesenteric and coeliac lymph nodes are well depicted on T2 weighted fat suppressed spin echo and gadolinium enhanced T1 weighted fat-suppressed images. However, detection of small peripancreatic lymph nodes can be difficult on MRI. In addition, contrast-enhanced MR with gadolinium DTPA has greater accuracy in the detection and characterization of liver metastasis compared with helical CT [2, 9, 15, 24]. Similarly, T1 weighted fat suppressed contrast-enhanced MR images appear to be superior to CT for visualization of peritoneal implants [9]. Normal pancreatic tissue becomes hyperintense on T1 weighted images after the intravenous administration of tissue specific MR contrast agent, mangafodipir trisodium. As pancreatic adenocarcinomas do not take up manganese, they are well delineated in the background of enhancing normal pancreatic parenchyma on T1 weighted fat suppressed images [25] with a significant increase in contrast-to-noise ratio reported in patients with focal pancreatic lesions with mangafodipir-enhanced MRI [20]. Romijn and colleagues have reported that mangafodipir enhanced MRI provides better delineation of the pancreatic tumour but does not significantly improve the detection rate and staging accuracy of focal pancreatic lesions over MRI without this contrast medium [25]. Some studies have shown that mangafodipir enhanced MRI may be helpful in the setting of suspected pancreatic neoplasm when CT is equivocal [26–28]. However, further studies are required to establish the exact role of mangafodipir in the evaluation of pancreatic cancer and differentiation from benign pancreatic pathology.

EUS is an imaging procedure that can display small pancreatic lesions undetectable by CT and MRI. In addition, EUS can also localize lymph node metastases and/or vascular tumour infiltration with high sensitivity [29]. The major limitations of the technique are operator dependence and a limited field of visualization for detecting metastatic spread to the liver and peritoneum. EUS guided fine needle aspiration biopsy has been reported to have a high sensitivity (93%) and specificity (100%) when used in patients with masses in whom pancreatic cancer is suspected but prior biopsies have been negative [30].

PET is complementary to cross-sectional imaging techniques such as CT and MRI in patients with suspected pancreatic carcinoma at initial presentation and allows detection of unsuspected distant metastases [31]. PET is especially helpful in evaluation of loco-regional tumour recurrence, distant metastases and in cases with an equivocal diagnosis on CT/MRI. A recent study of malignant pancreatic neoplasms has reported superior specificity and positive predictive values of FDG-PET in comparison with CT and MR imaging, in detecting metastatic disease [32]. In patients with suspected recurrent pancreatic carcinoma, PET can localize the disease when abdominal CT is equivocal as a result of post-therapy anatomic alteration [33]. Absence of FDG uptake at 1 month following chemotherapy for pancreatic cancer has been reported to be an indicator of improved overall survival [34].

Differentiation of pancreatic malignancy from focal pancreatitis involving the pancreatic head, though critical, is often difficult [35]. Despite diminished signal intensity in chronic pancreatitis relative to the normal pancreatic parenchyma on T1 weighted images, there is considerable overlap of signal characteristics and contrast enhancement patterns with pancreatic malignancies [35]. Following secretin administration, MRCP may help in demonstrating an associated stricture of the pancreatic duct and altered filling dynamics of pancreatic fluid, which are generally absent in pancreatic malignancy [11]. In addition, a positive duct-penetrating sign on MRCP seen as a smoothly stenotic or normal main pancreatic duct penetrating through the apparent tumour may be useful in the distinction from pancreatic malignancies [36]. Differentiation between pseudotumourous lesions in chronic pancreatitis and pancreatic carcinoma may be difficult due to similar mild contrast enhancement of these focal lesions [36]. In these circumstances, mangafodipir enhanced MRI may improve the detection rate and characterization of focal pancreatic lesions because of better delineation of the abnormal area [37].

Pancreatic neuroendocrine tumours
Pancreatic islet cell tumours or neuroendocrine tumours are believed to originate from the neuroendocrine cells of the pancreas. These tumours present with different manifestations depending on production of hormonally active peptides (functioning tumours) or non-production (non-functioning tumours). Insulinomas and gastrinomas are the most common functioning islet cell tumours and are generally small at the time of detection. Other functioning and non-functioning pancreatic neuroendocrine tumours such as glucagonomas, somatostatinomas, VIPomas (secreting vasoactive intestinal polypeptide) and GRFomas (secreting growth hormone-releasing factor) are frequently large at diagnosis and are often malignant [38].

Functioning neuroendocrine tumours
In comparison with insulinomas, which are usually benign and solitary, gastrinomas are more commonly malignant and multiple. They require meticulous CT imaging technique with careful multiphase dynamic acquisition with thinner slices. These tumours are hypervascular and are best detected in the arterial phase with thin slices (1.25–1.5 mm). Typically they are usually isolated to the "gastrinoma triangle" whose vertices are the cystic duct confluence, the junction of the pancreatic neck and body, and the junction of the second and third portions of duodenum. Occasionally, primary gastrinomas are impossible to find and functioning tumour is only found in lymph nodes following pancreatic and duodenal resection. On T1 weighted fat suppressed images, these lesions are hypointense to pancreatic parenchyma. The T1 and T2 relaxation times of these tumours are long relative to the normal pancreas (Figure 2Go). Due to the longer relaxation time, these tumours exhibit high signal intensity relative to the normal pancreas on T2 weighted images, facilitating the detection of small tumours. Consequently, fast spin echo techniques reduce the T1 "contamination" of the T2 weighted sequence and accentuate the high signal from the tumour [39]. The most optimal sequences for imaging of pancreatic neuroendocrine tumour include T2 weighted fast spin echo, fat suppressed T1 weighted spin echo and gradient echo, and dynamic contrast enhanced FLASH (fast low angle shot) imaging [40–44]. Being hypervascular, these tumours frequently demonstrate homogeneous or ring enhancement during the arterial phase of contrast enhanced dynamic MR imaging [38].



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  		Figure 2. (a) 57-year-old man with biopsy proven pancreatic neuroendocrine tumour (insulinoma). Axial T1 weighted image shows a well-defined hypointense mass in the pancreatic head. (b) T2 weighted image shows a typical high signal intensity mass (arrow) relative to the normal pancreatic parenchyma.

 
On EUS, most pancreatic neuroendocrine tumours are hypoechoic, homogeneous, and have distinct margins. Anderson et al have reported an overall sensitivity of 93% and 95% specificity of EUS in the detection and characterization of pancreatic neuroendocrine tumours [45]. EUS can demonstrate the size and shape of the tumours, as well as their relationship to adjacent structures such as the pancreatic duct, bile duct and large vessels [46]. Anderson's results support the use of EUS as the primary diagnostic modality in the evaluation and management of patients with neuroendocrine tumours. Ahlström and colleagues have reported application of 11C-L-dihydroxyphenylalanine (L-DOPA) and 11C-5-hydroxytryptophan (5-HTP) as labelled radiopharmaceutical agents to detect endocrine pancreatic tumours with PET [47]. They found PET to be a valuable complement to CT in demonstration of functional pancreatic endocrine tumours. Blind distal pancreatectomy has been advocated for occult insulinomas not detected on imaging studies or during abdominal exploration. However, use of pre-operative imaging studies, most notably calcium-stimulated arteriography and intraoperative ultrasound permits detection of virtually all insulinomas, including reoperated cases [48].

Intraoperative ultrasound is performed using a near-field real-time high-resolution 7.5 MHz to 10 MHz transducer [49, 50]. After exposing the pancreas, to facilitate palpation of the body and tail, the inferior border of the pancreas is divided, and the spleen and pancreatic tail are elevated out of the retroperitoneum. Usually, an islet cell tumour is felt as a firm nodule within the softer pancreatic parenchyma [50]. Following palpation, intraoperative US of the pancreas is performed in the longitudinal plane by passing the probe from the pancreatic head, across the body, and to the tail. Several parallel passes of pancreas are essential for a thorough examination. Insulinomas usually appear as sonolucent mass lesions seen in both transverse and longitudinal imaging planes. Guided biopsies are performed on all abnormal lesions identified by palpation or intraoperative US. In the pancreatic head, suspected tumours are enucleated, whereas in the pancreatic body and tail, enucleation is performed unless tumours are adjacent to the pancreatic duct, in which case they are resected by a distal pancreatectomy.

Non-functioning neuroendocrine tumours
Unlike functioning tumours, the non-functioning pancreatic neuroendocrine tumours are usually larger at presentation. The typical characteristics of these lesions include hypervascularity and calcifications. These features are uncommon in pancreatic ductal adenocarcinoma and should raise the suspicion of non-functioning islet cell tumour. Morphologically, the non-functioning large tumours are less likely to encase adjacent vascular structures and rarely show central necrosis. In patients with non-functioning pancreatic neuroendocrine tumours, a hypoechoic mass with an irregular central echogenic area on EUS or complete obstruction of the main pancreatic duct on ERCP suggests malignancy [52].

Cystic pancreatic tumours
The differential diagnosis of cystic pancreatic lesions has been summarized in Table 2Go [51]. The most common types of cystic neoplasms of pancreas include serous and mucinous tumours and intraductal papillary mucinous tumour.


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  		Table 2. Differential diagnosis of cystic pancreatic lesions

 
Serous tumours are benign and typically contain greater than six cysts which are smaller than 20 mm and have a central stellate scar. Usually, they are composed of innumerable small cysts, the vast majority of which vary from less than 1 mm to 2 cm in size. These tumours have a strong female predilection (male:female=3.2:9.2) and typically occur between ages of 34 years and 88 years. Accurate imaging diagnosis and differentiation from mucinous cystic tumours is crucial to avoid aggressive surgical intervention in an asymptomatic serous cystadenoma, which has low malignant potential [53]. On unenhanced CT, serous adenomas appear as hypodense masses that frequently show central calcification. Contrast enhancement of the septations results in a honeycombing appearance due to the presence of tiny cysts. In addition, a characteristic central fibrotic scar may be appreciated on contrast enhanced CT scan. On MR, it appears as a well-defined cystic lesion that does not show invasion of fat or adjacent organs. On T2 weighted images, the small cysts and intervening septations may appear like a cluster of small grape-like hyperintense cysts, best depicted on breathing independent single shot echo train spin echo sequence (for example single shot fast spin echo or half Fourier acquisition snap shot turbo spin echo). Post-contrast MRI shows minimal enhancement of tumour septae. Occasionally, delayed enhancement of the central scar may be noted.

Mucinous cystic neoplasms are most often located in the body or tail of the pancreas. These tumours have a strong female predilection and are more sinister neoplasms with malignant potential [54]. They reveal cysts that are less numerous and larger in size (average diameter=12 cm) than are typically observed with serous cystadenoma. Their external surface is smooth, and they are composed of unilocular or multilocular large (>2–4 cm) cysts with thicker wall. On CT, mucinous cystic neoplasms appear as round to ovoid, externally smooth, near-water-density cystic lesions [55]. Amorphous calcification, septations and solid excrescences may be seen. Contrast enhanced CT demonstrates the enhancement of cystic walls and thin, straight or curvilinear septations. Higher inherent soft-tissue contrast of MRI allows better differentiation between serous and mucinous cystadenomas [56]. Mucin produced by these tumours may result in high signal intensity on T1 weighted and T2 weighted images of the primary tumour. If present, liver metastases frequently follow the appearance of the primary tumour on T1, T2 and contrast enhanced images. Thick irregular septae and solid portions or papillary excrescences may be seen on gadolinium enhanced T1 weighted fat-suppressed images or contrast enhanced CT in patients with mucinous cystadenocarcinoma (Figure 3Go). Mucinous cystadenoma and cystadenocarcinoma do not have central scars.



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  		Figure 3. (a) Axial post-contrast CT image of a 70-year-old woman with mucinous cystadenocarcinoma. A large well-defined cystic mass with focal calcification (arrow) and thick irregular wall is seen in the distal pancreatic body. (b) Axial CT image acquired at a slightly caudal position reveals a large eccentric mural nodule (arrow) typical of a malignant cystic neoplasm.

 
Intraductal papillary mucinous tumour (IPMT) is the preferred term to describe a spectrum of proliferation of the pancreatic ductal epithelium with production of excessive amounts of mucin and progressive dilatation of the main pancreatic duct or cystic dilatation of the branch ducts [57]. It is characterized by the presence of cystic dilation of the branches of the pancreatic duct in the uncinate process (branch duct type) (Figure 4Go), diffuse or segmental dilatation of the main pancreatic duct (main duct type), or dilatation of the main duct and the branch ducts (combined type) [58, 59]. It is associated with parenchymal atrophy especially in more advanced cases. Intraductal fungating lesions or mucin deposits may cause small intraductal areas with solid signal intensity seen on MRI. MRCP can demonstrate the dilated ducts as hyperintense collections that are not frequently conspicuous on ERCP [11]. The branch duct mucinous tumour is characterized by cystic ectasia of the branch ducts, forming a mass with lobulated contours that usually involves the uncinate process. MRCP may demonstrate a grape-like appearance of the lesion and its wide communication with the main pancreatic duct (Figure 4Go). Rarely, ectasia of a single duct communicating with the main pancreatic duct through a long pedicle may be seen.



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  		Figure 4. (a) Coronal heavily T2 weighted image of 62-year-old woman showing a lobulated cystic mass (arrow) in the uncinate process of pancreas suggestive of branch duct type intraductal papillary mucinous tumour. (b) Three-dimensional thick slab, heavily T2 weighted magnetic resonance cholangiopancreatography image shows a "grape-like" lobulated cystic mass (large arrow) in relation with the uncinate portion of main pancreatic duct (small arrow). The common bile duct appears normal (curved arrow).

 
FDG PET has been reported to be more accurate than CT in identifying malignant pancreatic cystic lesions and in the pre-operative evaluation of patients with pancreatic cystic lesions. A positive result on 18-FDG PET strongly suggests malignancy. On the other hand, a negative result suggests a benign tumour that may be treated with limited resection or, in selected high-risk patients, with biopsy, follow-up, or both [29].

Lymphoma
Pancreatic lymphoma is almost invariably of the non-Hodgkin's B cell type and is usually associated with peripancreatic and retroperitoneal lymphadenopathy or splenic, hepatic, renal, and epidural space lesions. The presence of intact fat planes between the nodes and the pancreas and anterior displacement of the pancreas help in distinguishing peripancreatic lymphadenopathy from a primary pancreatic tumour. Diffuse pancreatic enlargement often noted in pancreatic lymphoma may be due to diffuse pancreatic tumour, tumour induced pancreatitis, or pancreatitis associated with tumour lysis from chemotherapy. The enlarged pancreas is usually homogeneous and has relatively low attenuation on unenhanced CT without ductal obstruction, although pancreatic ductal obstruction may rarely be associated with pancreatic lymphoma (Figure 5Go). MRI demonstrates diffuse or focal pancreatic enlargement that is isointense to normal pancreatic parenchyma on both T1 and T2 images [9].



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  		Figure 5. Axial post-contrast CT image of a 76-year-old man with biopsy proven pancreatic lymphoma. A large non-enhancing, hypodense mass is seen in the pancreatic head engulfing the common bile duct (arrowhead) and superior mesenteric vessels (small arrows). Focal lymphomatous deposits are seen as subtle hypodense lesions in the right kidney (large arrows).

 
Pancreatic metastases
The most common primary tumours that metastasize to the pancreas are from lung, breast, kidney and melanoma [60]. Three distinct patterns of pancreatic involvement may be noted, namely; localized, multifocal or diffuse enlargement. Pancreatic metastases should be suspected in the presence of multiple pancreatic masses in a patient with a known primary carcinoma. On CT, most pancreatic metastases are hypodense and show variable contrast enhancement. On MRI, the majority of pancreatic metastases appear hypointense on T1 weighted images and hyperintense on T2 weighted images [9]. Contrast-enhanced CT and MR may be useful in the evaluation of pancreatic metastases by showing features such as increased vascularity in the presence of a hypervascular primary malignancy. Hypervascular metastases are seen commonly with renal cell carcinoma and melanoma.

Received for publication September 19, 2002. Revision received June 7, 2003. Accepted for publication August 20, 2003.


   References
Top
 Abstract
 Introduction
 Imaging techniques and protocols
 Imaging features of pancreatic...
 References
 

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