INTRODUCTION:

Imaging=20 of the pancreatic tumors is challenging because of its anatomical = location in=20 the retro peritoneum and its intricate relationship with major vessels = and the=20 bowel. The incidence is 2 per cent of all cancers and is the fourth = leading=20 cause of cancer related deaths.¹The five-year survival rate = of=20 pancreatic carcinoma is 15 per cent when it is confined to the pancreas = and=20 falls to 6.8 per cent with peripancreatic invasion and 1.8 per cent with = distant=20 metastasis. ² Thus preoperative diagnosis and staging of = tumors is=20 very important.

Classical=20 presentation of pancreatic cancer is pain abdomen, weight loss and = obstructive=20 jaundice. Ultrasonography is the initial method of investigation to = assess if=20 there is obstruction in the intrahepatic or extrahepatic portions of the = biliary=20 tree and if it extrahepatic, whether it is intrapancreatic or = suprapancreatic.=20 Further evaluation is obtained with CT, MRI, endoscopic retrograde=20 cholangiopancreatography (ERCP), endoscopic ultrasound and=20 PET.

PANCREATIC=20 NEOPLASMS

Malignant=20 neoplasms of the pancreas are classified according to the cells of = origin as=20 ductal cell, acinar cell and uncertain histogenesis like=20 pancreaticoblastoma. But = common=20 types of neoplasms are:

Ductal=20 adenocarcinoma=20
Cystic=20 pancreatic neoplasms

- =20 Mucinous=20 macrocystic neoplasms

- =20 Serous=20 microcystic neoplasms

Intraductal=20 papillary mucinous tumors=20
Solid=20 and papillary mucinous tumors=20
Metastatic=20

=20

IMAGING

PLAIN=20 FILMS

= Plain=20 films are obtained in patients with suspected pancreatic tumors to = exclude other=20 conditions such as obstruction or perforation but some times oblique = views are=20 often helpful in patients with chronic pancreatitis and rarely cystic = neoplasms=20 to detect calcification that may be obscured by the spine on AP=20 views.³

CONTRAST=20 STUDIES

In=20 present day practice, barium studies have become less important in = evaluation of=20 pancreatic tumors. However the following areas should be examined = carefully in a=20 patient with suspected pancreatic carcinoma. The greater curvature of = the=20 gastric antrum and the medial aspect of the descending duodenum can be = involved=20 by lesions arising in the pancreatic head and neck. The posterior = gastric wall,=20 the distal duodenum and the DJ junction can be abnormal with lesions of = the=20 pancreatic tail and body. Barium enema examination may show = abnormalities of the=20 colon (transverse) or the splenic flexure involvement by the disease via = transverse mesocolon or phrenico- colic ligament=20 respectively.³

ULTRASOUND

It=20 is safe, non invasive, inexpensive and a fast method of evaluating = pancreatic=20 tumors. Ultrasound examination of the pancreas is best performed on = fasting=20 patient to reduce the amount of gas and food in the overlying bowel. = Real time=20 equipment with curvilinear transducer of frequency 5 to 8 MHz is = essential.=20 Ultrasound of the pancreas should be performed with the patient supine = and the=20 transducer turned into a modified transverse plane angled cephalad = towards the=20 spleen. With meticulous technique and special attention to details, even = a small=20 tumor of the pancreas can be picked up. Several maneuvers can improve=20 sonographic visualization.⁴

Having=20 the patient drink 4 to 6 cups of water, which will provide a = sonographic=20 window for improved visualization of the body and = tail.=20
Deep=20 inspiration/ erect position causes the liver to move inferiorly over = the=20 pancreas and displace gas filled bowel loops caudally thus giving a = good=20 sonographic window=20
Gentle=20 pressure on the transducer is also helpful in displacing overlying = bowel gas.=20 By turning the patient to the right posterior oblique position, gas in = the=20 antrum and duodenum rise to the fundus and the body of the stomach and = thus=20 improves visualization.=20
IV=20 injection of 0.3 mg of glucagon stops peristalsis for several minutes = and=20 improves water retention by the stomach and duodenum =
Metoclopramide=20 and secretin can be used to eliminate gas from the surrounding bowel = but these=20 pharmacological methods are not generally employed because they are = time=20 consuming and are expensive.

Color=20 Doppler allows quick differentiation of vascular from non-vascular = structure and=20 aids in staging of pancreatic carcinoma. Use of intravenous ultrasound = contrast=20 material in Doppler examination of the pancreas improves the = visualization of=20 vessels.

COMPUTED=20 TOMOGRAPHY

It=20 is the modality of choice in suspected pancreatic neoplasms. Improvement = in CT=20 technology during the past decade with fast image acquisition and = improved=20 spatial resolution has increased the accuracy of CT for lesion detection = and=20 characterization.

Techniques

The=20 patient is made to drink approximately 500 to 1000 ml of water one hour = before=20 the scan. Another 300 to 500 ml of water is administered orally = immediately=20 before the scan. An unenhanced scan is performed from the level of the = diaphragm=20 to the iliac crest using a 5 mm slice thickness at 2mm collimation and=20 increment. Then biphasic contrast scanning is obtained after a rapid = injection=20 of a large bolus of intravenous contrast (100 =96 150 ml at 4 -5 ml/ = sec). The=20 arterial phase begins approximately 35 to 50 sec after the beginning of = the=20 injection of the contrast agent and is used to maximize the enhancement = of the=20 pancreatic parenchyma and to improve the contrast between the tumor and = normal=20 parenchymal tissue. The portal venous phase obtained 60 =96 70 seconds = after the=20 beginning of the intravenous contrast injection and this phase is used = to=20 visualize liver metastasis and tumor involvement of portal venous = structure.=20 Besides a rapid injection rate, thin section imaging with a slice = thickness of 1=20 mm is also very important in detection and staging of pancreatic cancer=20 particularly in the case of small tumors in which volume averaging may=20 obscure.⁵ Recent advances in real time 3D volume rendering = are=20 helpful in diagnosing and staging pancreatic cancers and in = communicating=20 findings to clinicians.

MR=20 IMAGING

MRI=20 offers several advantages for imaging pancreatic tumors. MRI has = inherently=20 better soft tissue contrast without the administration of intravenous = contrast=20 material and ability to acquire images directly in multiple planes. MRI = can be=20 performed in patients with a history of allergy to iodinated contrast = agents and=20 in patients with renal insufficiency. MRI of the upper abdomen is best = performed=20 with either a phased array torso coil or body coil, former preferred for = enhancing tumor visualization as it increases signal to noise ratio and = allows=20 thinner slice section. Typical examination protocols=20 include

- =20 T1=20 weighted images (breath hold spoiled gradient or spin=20 echo)

- =20 T2=20 weighted fat suppressed images (fast spin echo)

- =20 T1=20 weighted fat suppressed images (breath hold spoiled gradient or spin=20 echo)

- =20 Dynamically=20 enhanced 2D or 3D breath hold spin echo images

These=20 may be followed by T1 weighted pin echo images wither with or without = fat=20 suppression. ⁶

ERCP

Until=20 recently, ERCP has been the dominant technique both for diagnostic = evaluation of=20 the biliary tree and pancreatic duct and for therapeutic interventions. = Now ERCP=20 remains the best choice for intervention in the biliary tree and the = pancreatic=20 duct, both for histological examination of regions of stenosis or = obstruction=20 (i.e. by obtaining brushings) and for placement of stents to treat = ductal=20 abnormalities as it is associated with incomplete examinations and post=20 procedure pancreatitis

MRCP

It=20 is a non-invasive method of evaluating the site and severity of biliary=20 obstruction and ductal abnormalities. Typical MRCP protocol includes = heavily T2=20 weighted sequences that depict the biliary tract and the main pancreatic = duct as=20 high signal intensity structures. Basically we acquire multiple thin = slab images=20 of the pancreatico biliary tract at section thickness typically ranging = from 2=20 to 5 mm in the coronal plane and at a variety of angles to optimally = depict the=20 ductal system. These thin slab images manipulated with MIP and MPR = techniques to=20 generate 3D images. ⁷ Thick slab sections (typically 30 =96 = 50 mm)=20 provide an overview of the biliary and the pancreatic ductal systems. = With=20 current techniques, MRCP identifies not only the dilated ducts located = proximal=20 to the obstruction, but also the narrowed ducts encased by the=20 tumor.

ENDOSCOPIC=20 ULTRASOUND

It=20 is used for detection of small tumors of the pancreas and periampullary = region=20 and for guidance of fine needle aspiration thus helping in the = detection,=20 characterization and staging of pancreatic tumors. EUS uses a high = frequency=20 probe (7.5 to 12 MHz) manipulated via an endoscope to provide real time = imaging.=20 Major limitation is the small field of view. ⁸

PET

Fluorine-=20 18 labeled 2 fluoro 2 deoxy D glucose ( FDG) PET scans can noninvasively = assess=20 metabolic activity in tumors. Principle is based on the observation that = tumor=20 cells tend to take up more glucose than the normal tissue. Images are = obtained=20 between 40 and 180 minutes after injection. Emission and transmission = scans are=20 usually performed. Uptake values are interpreted by quantitative=20 methods.⁹.=20

IMAGING=20 FINDING OF PANCREATIC TUMORS

DUCTAL=20 ADENOCARCINOMA: -

Adenocarcinoam=20 is the most common (90-95%) of all pancreatic neoplasms. Affects = patients=20 between 60-80yr of age with slight female predominance. Risk factors = include=20 cigarette smoking, diabetes mellitus, chronic pancreatitis, syndromes = like Peutz=20 =96 Jeghers syndrome, hereditary nonpolyposis colon cancer, familial = atypical=20 multiple mole melanoma syndrome and hereditary breast ovarian cancer = syndrome.=20 Pancreatic head is the most commonly affected, followed by body and=20 tail.

On USG,=20 ductal adenocarcinoma appears relatively hypoechoic compared to the = normal=20 pancreatic parenchyma. Doppler ultrasound can be helpful in the = evaluation of=20 vascular involvement. On CECT, these tumors appear as ill-defined focal=20 hypodense mass during parenchymal phase. Small tumors may show secondary = signs=20 suggestive of mass include dilated CBD and main pancreatic duct (double = duct=20 sign), dilated main pancreatic duct in the body or the tail without = involving in=20 the head or neck and an abrupt termination of either CBD or pancreatic = duct. MRI=20 shows low signal intensity mass on T1W fat suppressed images, gadolinium = enhanced T1w images and T2W images.

Criteria=20 for resectability:

The=20 absence of local peripancreatic extension and distant metastases is the = criteria=20 for resectability. Most common causes of tumor unresectability are = 1)tumor=20 diameter of 5cm or more; 2) extrapancreatic invasion of adjacent = tissuesand=20 organs with exception of the duodenum; 3)occlusion, stenosis, or = enhancement of=20 vessels including the portal venous system, superior mesenteric artery, = and=20 major branches of celiac trunk; 4) distant nodal metastases; and 5) = hematogenous=20 metastases.(liver, adrenals, bones, lungs and = pleura)

CYSTIC=20 NEOPLASM OF PANCREAS

Rare=20 type of pancreatic tumors, divided in to two main groups, mucinous = macrocystic=20 neoplasm and serous microcystic neoplasm. Mucinous type re most common = among=20 cystic neoplasms and these are reclassified in to 2 groups, mucinous = cystic=20 neoplasms and intraductal papillary mucinous tumors=20 (IPMT).

Mucinous=20 cystic neoplasms=20 commonly seen in women in their fourth to sixth decades of life. Plain=20 radiograph demonstrates intralesional calcification. Sonography shows = large=20 cystic cavities (2-19cm) with internal septations and nodular, papillary = excrescence. CT demonstrates cystic mass with enhancing walls and = internal=20 septations that may be thin or focally thickened focal calcification or = mural=20 papillary projections. On MRImaging these cystic spaces have signal = intensity=20 depending on protein content of the mucin and usually appears low signal = intensity on T1w and high signal intensity on T2w. Walls of the cyst and = septations enhances after intravenous gadoloinum=20 injection.

Serous=20 microcystic neoplasms are=20 benign lesion with female predominance occurring in middle aged and = elderly=20 patients, having mild predilection to pancreatic head. Plain radiogram = shows=20 central foci of calcification. Sonography demonstrates multiple tiny = cysts=20 (<2cm); tumor may appear as a homogenous hyperechoic solid = encapsulated mass=20 having central calcification. On CT, lesions are well-defined hypodense, = encapsulated lobulated masses with central calcification. Contrast study = shows=20 diffuse homogenous enhancement or only localized enhancement of the = solid=20 portions of the tumor and its radiating fibrotic bands. Angiography = demonstrates=20 high vascularity with an extensive capillary network seen within the=20 septa.

IPMT are=20 mainly divided into main duct and branch duct type. Main duct type = tumors cause=20 diffuse or segmental ductal dilatation. Branch tumors commonly involve = the=20 uncinate process resulting in focal dilatation of affected branches = giving=20 appearance of =93bunch of grapes=94 with mild or diffuse dilatation of = the main=20 duct. The key to diagnosis is the demonstration of a communication = between the=20 cystic structure and the main pancreatic duct. ERCP is the gold standard = to=20 establish the diagnosis of IPMT. CT findings suggestive of malignancy = include=20 the presence of a solid mass, dilatation of the main duct to greater = than 10mm,=20 diffuse or multifocal involvement and attenuating or calcified = intraluminal=20 contents.

ISLET=20 CELL TUMOR

Islet=20 cell tumor are rare tumors of neuroendocrine origin, most commonly = arising in=20 the pancreatic bod and tail. Depending on hormone production they are = classified=20 as functioning neuroendocrine tumors or nonfunctioning neuroendocrine = tumors.=20 Functioning neuroendocrine tumors areclassified according to the type of = hormones they produce into insulinoma, gastrinoma, Vipoma, glucogonoma,=20 somatostatinoma and corticotropinoma. Insulinomas are most common = neuroendocrine=20 tumors, followed by gastrinoma and vipoma. Functioning tumors are = usually small=20 in size and difficult to identify with current imaging techniques = therefore=20 diagnosis is always established on biochemical basis. Nonfunctioning = tumors=20 remain clinically silent and typically present when they have reached a = large=20 size or are metastatic. On CT, these tumors appear hyperdence lesions = compared=20 with the surrounding pancreatic parenchyma, some times may also appear = as=20 hypodense lesions. Pattern may range from small, solid and homgenous = masses to a=20 large, heterogenous pattern with areas of cystic degeneration and area = of=20 necrosis or calcification. On MRI, Islet cell tumors show low signal = intensity=20 on T1w images and high signal intensity on T2w. EUS typically shows a = single=20 nodule or multiple well defined hypoechoic nodules however illdefined,=20 hyperechoic tumors with cystic area and calcification may be seen.=20

SOLID=20 AND PAPILLARY EPITHELIAL TUMORS

Another=20 rare type of pancreatic tumors, occurring mainly in young women in = second and=20 third decades of life. They often grows to a large size (8-10cm) and = commonly=20 seen in the pancreatic tail. On imaging studies they appear as a well = defined=20 heterogenous large masses of variable internal architecture depending on = the=20 degree of intralesional hemorrhage and necrosis surrounded by a thick = capsule=20 which enhances on contrast administration.

LYMPHOMA:

Primary=20 involvement of pancreas is uncommon however wide spread nonhodgkin = lymphoma can=20 involve as one or more soft tissue lesions which shows little contrast=20 enhancement.

METASTASIS:

Most=20 common tumors metastasize to pancreas are Renal cell carcinoma, = bronchgenic=20 carcinoma, breast carcinoma, soft tissue sarcoma, colonic carcinoma, = melanoma.=20 They can involve any apart of pancreatic tissue or can involve=20 diffusely.

SUMMARY

Diagnostic=20 imaging has a very important role to play in the diagnosis and staging = of wide=20 range of pancreatic tumours. Ultrasonography is the initial method of=20 investigation followed by CT for further characterization and staging. = MR=20 Imaging utilized as problem solving tool. Newer techniques such as MDCT = with=20 advanced post processing tools, 3D breath hold dynamic MRI, MRCP, PET = should aid=20 in early detection of small tumours.

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