Sonography of chronic pancreatitis

Morphologic alterations detectable by US in CP may be schematically classified as: (1) size increase or decrease; (2) variations in shape with particular regard to contour irregularities; (3) changes in the parenchymal echo-texture; (4) presence of calcifications; (5) dilatation of the MPD; (6) presence of fluid collections; (7) dilatation of the biliary tree; and (8) obstruction of the portal venous system. These findings are associated in various combinations and occur with differing frequencies. Changes in pancreatic size may be found in many physiologic and pathologic conditions other than CP. The pancreas is usually larger during and shortly after acute relapses, whereas gland atrophy occurs in more advanced cases. A diagnosis of CP cannot generally be made only on the basis of a diffuse enlargement of the gland without changes in the echo-texture or in the MPD. Abnormalities of the parenchymal echo-texture are relatively sensitive but nonspecific for the diagnosis of CP. Calcifications can often be missed by US, and CT is clearly superior. Dilatation of the MPD is the most reliable sign of pancreatic disease. In CP, it generally has irregular walls, which is a distinctive finding that aids in differentiation of MPD dilatation occurring in pancreatic cancer. Changes in the MPD that are not visible under basal conditions may become evident under maximal hormonal (secretin) stimulation. Cysts and pseudocysts complicating the course of CP may present various shapes, contain necrotic debris, and even show a completely solid pattern. Dilatation of the CBD may also be seen as a consequence of a stricture of the intrapancreatic portion of the duct. Other complications, such as obstruction of the portal venous system, ascites, and pleural effusion, occur more rarely and are easily visualized by US. Despite the great technologic improvement of US in recent years, there is still general agreement that the US diagnosis of CP remains difficult owing to the polymorphism of anatomic changes and the relatively high incidence of false-negative results in early stages of the disease. It is, however, accepted that in clinical practice US currently is the first diagnostic step when CP is suspected.