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EDUCATION EXHIBIT |
1 Department of Radiology, University of Bern, Inselspital Bern, Switzerland
IPMN is now a well-recognized category of pancreatic neoplasms. IPMNs are characterized by the intraductal, often papillary proliferation of neoplastic mucinous cells, which lead to cystic dilatation of the pancreatic ducts (1,2). Patients with IPMN are usually elderly with a slight male predominance. Symptoms are nonspecific (only one-third of patients are symptomatic), and in most cases, IPMNs are discovered incidentally during work-up for other diseases (3). There is a spectrum of cyst and papilla formation, so that some masses are predominantly cystic or exclusively papillary. Larger, more complex lesions or those with abundant papilla formation (mural nodules) are more likely to harbor carcinoma (1,2).
On the basis of the degree of cytoarchitectural atypia at microscopic examination, IPMNs are classified as adenoma, borderline, carcinoma in situ, and invasive. On the basis of the location, IPMNs are classified into two, actually three types: the branch duct type (small tumors, commonly adenomas, relatively low incidence of carcinoma); the main duct type (more proliferative, larger, complex tumors with atypia); and the mixed type, which includes features of both other types (1,4,5). Pathologically, main duct type proliferation has substantial potential for progression into aggressive disease (ie, invasive carcinoma). Therefore, this classification, if used carefully, appears to be useful in the preoperative management of cases and determining those that can be followed up more conservatively. Thus, imaging techniques that allow definition and classification of IPMNs could be useful tools for prognostication and placement of patients into appropriate treatment categories (1,3,5–7).
Early studies (8) demonstrated the potential of CT (conventional and spiral), endoscopic retrograde pancreatography, and endoscopic US in distinguishing between invasive and noninvasive IPMNs, with overall accuracies of 76%, 79%, and 76%, respectively. Obviously, a noninvasive imaging technique that has sensitivity and specificity similar to those of endoscopic visualization (by means of sonography or retrograde pancreatography) of the dilated ductal system, filled with mucus, demonstrating the extent of disease in the main or side branch ducts and revealing the presence of mural nodules, could result in accurate staging. On the other hand, retrograde pancreatography with brush cytologic analysis demonstrates malignancy infrequently in IPMNs, unlike in other pancreatic malignancies (1,9).
With the introduction of multidetector CT, improvements in evaluation of the pancreas have occurred. The speed of multidetector CT and the flexibility in regard to thinner sections allow better detection and characterization of pancreatic lesions.
Moreover, thinner collimation and multiplanar reformation of multidetector CT images allow acquisition of adequate information concerning pancreatic duct anatomy. As shown by Itoh et al (10) using four-section multidetector CT, with 0.5-mm-thick axial images there is a significant improvement in pancreatic duct delineation, with the aim of detecting cystic changes and neoplasms of pancreatic duct origin.
The excellent article by Kawamoto et al (11) in this issue of RadioGraphics supports earlier observations that CT could be an important diagnostic tool for identifying and staging IPMNs, as well as differentiating this entity from pancreatic diseases that demonstrate dilatation of the pancreatic duct or cystic changes, such as chronic pancreatitis and pancreatic cystic masses.
Since pathologic-radiologic correlation of the macroscopic morphologic duct changes is the key to identifying and classifying the disease, 0.5-mm-thick reconstructed images are essential. Because the presence of a communication between the cystic lesion and the main pancreatic duct is one of the most reliable findings for the diagnosis of IPMN, demonstration of this connection by means of imaging is the key radiologic feature. Previous studies demonstrated the potential of MR imaging and MR cholangiopancreatography to depict the connection between the cystic lesion and the pancreatic duct (12). However, CT—and nowadays multidetector CT—remains the most commonly employed imaging technique for the evaluation of pancreatic neoplasms. The development of 16-section multidetector CT scanners allows acquisition of isotropic volume imaging data for the pancreas in daily practice.
Kawamoto et al (11) nicely present the diagnostic capability of multidetector CT to depict IPMNs, demonstrating the connection between the cystic lesions and the pancreatic duct, and to provide information regarding multifocal involvement and the presence of large mural nodules or solid masses, therefore increasing the sensitivity and specificity of multidetector CT in diagnosing malignancy, enabling classification of patients into appropriate treatment categories.
A current publication in European Radiology (13) has revealed similar findings, demonstrating the diagnostic value of multiplanar reformatted images in multisection CT in cases of branch duct type IPMNs. However, in that study, four-detector-row CT was used.
The usefulness of high-resolution reformatted images as shown in the preceding RadioGraphics article is relevant. The ability to differentiate between branch duct type and main duct type lesions enables surgeons and gastroenterologists to classify patients and decide about taking a surgical or conservative approach (9,14,15). Preoperative definition of the extent of ductal involvement with multidetector CT enables surgeons to effectively plan the surgical procedure, although the planned surgical resection could be modified by intraoperative frozen section analysis to yield negative margins (11). Therefore, if preoperative multidetector CT staging does not support the diagnosis of aggressive disease, a less invasive surgical procedure is planned; preserving a part of the pancreas yields better long-term survival, if the intraoperative findings confirm the diagnosis.
The use of high-resolution axial, multiplanar reformatted, and three-dimensional reformatted images, as demonstrated by Kawamoto et al (11) using 16-section multidetector CT, improves diagnostic performance and enables depiction of the connection between the cystic lesions of IPMN and the pancreatic duct. Additional features of IPMNs such as multifocal involvement, the presence of a large mural nodule or solid mass, large size of the mass, and common bile duct obstruction are nicely demonstrated as well. Therefore, radiologists should be aware of IPMNs, specifically in cases of older patients, with or without a history of pancreatitis, if cystic lesions in the pancreas or dilatation of the pancreatic duct is seen. Multiplanar reformation is essential to achieve the correct diagnosis and differentiate it from other cystic pancreatic entities. Collaboration with the surgeon would be an additional benefit for the patient in terms of predicting malignancy and performing more aggressive treatment or performing conservative follow-up in cases of nonsuspicious IPMN lesions.
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