PancreasPathological conditions
Acute pancreatitis
The term acute pancreatitis implies primarily inflammation of the organ itself, but there are often associated secondary inflammatory changes in the surrounding tissues and organs. The complications of acute pancreatitis include necrosis of the pancreatic parenchyma, so-called necrotic or haemorrhagic pancreatitis, and cyst and abscess formation. Computed tomography, particularly contrast-enhanced CT, has proved to be of decisive importance in both the diagnosis of disease and the grading of its severity. The method is valuable for determining the correct course of management in the individual patient, and is therefore performed at an early stage. Other diagnostic methods do not have this decisive importance. Since patients with acute pancreatitis are often dehydrated, proper hydration is essential and intravenous fluids may be necessary to avoid contrast-induced renal damage.
The CT examination starts with an un-enhanced study of the upper abdomen in which the entire area from the dome of the diaphragm to the pelvic rim is sequentially examined by means of contiguous 5-10 mm slices. The configuration of the pancreas is noted and an evaluation made of the organ and its surrounding tissues (e.g. the mesentery), which includes observations concerning the presence of oedema, abscesses, cysts,
a
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Figure 43.
Contrast-enhanced CT of acute pancreatitis. (a) The pancreatic parenchyma (arrows) enhances with contrast material; the pancreas itself is slightly oedematous and it is also surrounded by oedema (e). In the body of the pancreas there is a low-density area of focal necrosis (*). These features are consistent with acute oedematous non-haemorrhagic pancreatitis, with preserved perfusion of the pancreatic parenchyma. Note also the low attenuation of the liver, indicating fatty degeneration. (b) Minimal contrast enhancement in the body of the pancreas (p), but no enhancement in the tail. The pancreas is swollen and surrounded by oedematous tissue (e). This finding is consistent with haemorrhagicnecrotic pancreatitis.
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etc. This preliminary study is us ed to determine the axial section which demonstrates the pancreas to best advantage and at this level a
dynamic contrast study is performed. This involves the exposure of that slice every 15th second during two minutes after injection of a contrast medium bolus. This gives an idea of the pattern of
perfusion of the pancreatic
parenchyma, and allows the distinction to be made between haemorrhagic-necrotic pancreatitis, in which contrast-enhancement of part or all of the pancreatic
parenchyma does not occur, and oedematous pancreatitis in which contrast-enhancement is pre served (Fig. 43). The severity of pancreatitis can in this way be estimated and graded, and secondary changes and complications evaluated.
Oral contrast medium is not used in
CT studies of acute pancreatitis so as not to interfere with density measurements of the organ.
Follow-up studies are performed at regular intervals depending upon the patient's progress.
 | Figure 44.
US of acute pancreatitis. The pancreas (arrows) is swollen and has a lower echogenicity than usual (compare with Fig. 41). Ventrally an echo-free pseudocyst (*), 5 cm in diameter, is seen. |
The value of ultrasonography in the assessment of acute pancreatitis is diminished by the gas- filled distended bowel oops that are so often present in this disease and US is inferior to
CT in its ability to provide comprehensive information on the remainder of the
abdomen and the retroperitoneal space (Fig. 44).
Chronic pancreatitis
Chronic pancreatitis is assessed by means of US, CT and ERCP. Ultrasound provides information concerning the size and parenchymal volume of the pancreas, the calibre of the pancreatic duct and the presence of cysts or other abnormal features (Fig. 44). On CT the parenchyma is displayed with great precision, the pancreatic duct is sometimes seen and any areas of calcification that may be present are better demonstrated than on either US or the plain film. Contrast enhancement often improves the quality of the imaging and allows more accurate distinction between various entities such as cysts, abscesses, oedema, fluid collections and adjacent bowel loops (Fig. 45). Knowledge concerning the anatomy of the ductal system is of importance in grading the changes of chronic pancreatitis and therefore influences clinical management decisions such as the choice of therapy and the nature of any operation that may be necessary. The ductal anatomy is best seen on ERCP, which is important in these selected cases. In chronic pancreatitis ductal changes such as dilatation, ectasia, local narrowing and possible communications with cysts are seen on ERCP (Fig.46), as well as any concretions that may be
 | Figure 45.
CT of chronic pancreatitis. Extensive calcification is seen in the body and the tail of the pancreas (arrows). In the liver parenchyma and hilum, dilated bile duets are seen, caused by obstructive changes in the pancreatic head. |
 | Figure 46.
ERCP in a case of chronic pancreatitis, showing a dilated pancreatic duet of varying calibre, and a local stricture (arrow). A pseudocyst is seen in the head of the pancreas (*). The distal part of the common bile duet (de) is narrowed and the proximal duet dilated. |
present. The changes are graded on an agreed scale from I to IV.
Pancreatic tumours
When a pancreatic tumour is suspected, the first imaging studies are undertaken with ultrasound. A tumour is seen as an area of abnormal echogenicity which is usually hypoechoic in relation to the surrounding parenchyma. A careful assessment is made of the tumour's location, its possible effect on the pancreatic and/or common bile ducts, its relationship to vascular structures and the extent to which it may be invading neighbouring organs (Fig. 47). Fine-needle biopsy of the tumour can also be performed under US-guidance. Computed tomography is often performed in addition to ultrasound because of the superior anatomical detail it affords; the same features are looked for on CT as are described above for US. Any extension into the surrounding areas is better shown on CT than US, as are metastatic deposits in, for instance, the regional lymph nodes (Fig. 48). The CT study should include iv-enhanced sequences, in order better to delineate the tumour; malignant tumours
 a | Figure 47.
US of the pancreas. A tumour (arrows) is seen on the transverse scans as a region with lower echogenicity than the surrounding parenchyma. (a) Small intrapancreatic tumour, diameter 2 cm. (b) Large tumour, obstructing the pancreatic duet (*). These features are consistent with the diagnosis of carcinoma of the pancreas. |
 b | |
 a | Figure 48.
Contrast-enhanced CT of a pancreatic carcinoma. (a) A low density, expanding lesion (arrow) is seen in the head of the pancreas. The tumour displaces the superior mesenteric vein (small arrow) anteriorly, white the superior mesenteric artery is intact. (b) The importance of a proper early timing of the CT study in relation to the contrast medium injection is demonstrated. A non-distorting tumour of less than 2 cm (arrow) is demonstrated, the only criterion for its detection being its decreased contrast enhancement in comparison with the surrounding pancreatic parenchyma. |
 b |
 | Figure 49.
An ERCP in a patient with carcinoma of the head of the pancreas shows total obstruction of the common bile duet (large arrowhead) and narrowing of the pancreatic duet (small arrowheads), this is the so-called double-duct sign. The proximal pancreatic duct is dilated because of the obstruction. |
enhance more slowly than normal
parenchyma, but this feature is mostly seen only during the first two minutes after contrast medium injection (see description of
CT technique above). Studies other than US and
CT are usually unnecessary. The smallest
tumour that can be detected with these methods is approximately 1-2 cm in diameter. In doubtful cases ERCP is performed, where the typical findings of ductal involvement are stricture or
obstruction with dilatation proximal to the
lesion (Fig. 49).
Endocrine tumours have been briefly considered above in the section on angiography.
Non-neoplastic lesions
Pseudocysts are not infrequently seen, occurring mostly as a complication of pancreatitis. They may or may not have a connection with the pancreatic duct; in the latter circumstance they may well be infected. Cysts are well shown on US, CT and MRI and appear as thin-walled, fluid-filled lesions. Abscesses also frequently arise as a complication of pancreatitis; they commonly have thick, uneven walls that exhibit contrast enhancement on CT while the centre has fluid characteristics across a wide range of viscosity.
In abdominal trauma the bowel loops are often distended and computed tomography (particularly contrast-enhanced CT) is therefore the method of choice when evaluating traumatic lesions. A disruption of the pancreas is then seen as a discontinuity in the pancreatic parenchyma.
Peripancreatic changes are also seen, and extravasation of intravascular contrast medium may very rarely be visualized in a patient with active haemorrhage. Under favourable circumstances information on the pancreas may also be obtained by US and further evaluation may require angiography.
David J. Allison and Carl-Gustaf Standertskjold-Nordenstam