Intraductal papillary mucinous tumor of the bile ducts is characterized by innumerable frondlike infoldings of proliferated columnar epithelial cells and slender fibrovascular stalks that are supported by connective tissue from the lamina propria [1, 2]. At histopathologic analysis it may present as adenocarcinoma, adenoma, dyspalsia or as a mixed form .
Papillary cholangiocarcinoma rappresents 3–5% of the reported cholangiocarcinomas .
Papillary adenocarcinoma is a low-grade malignancy that grows slowly and tends to spread along the mucosal surface and invading the ductal wall in the late phase of the development [1, 2, 7].
Papillomatosis represents a known condition where tumors are multiple and extend along bile ducts [1, 2].
Intraductal papillary tumor produces a variable amount of mucin that may be retained in the lesion. Some tumors produce a large amount of mucin that is discharged into the bile ducts and may intermittently and partially impede the flow of bile juice, causing obstructive jaundice, sometimes complicated by cholangitis or stone formation. Endoscopy may show mucin draining from the papilla of Vater. This condition is diagnostic of a mucin-producing tumor of the bile or pancreatic ducts. When the mucin flow obstructs the duodenal papilla, both proximal and distal to the tumor bile ducts become diffusely dilated. So dilatation can be caused by the presence of the lesion as by the mucin excretion. Dilatation may affect only the segmental or lobar bile ducts or the entire biliary tree depending on the location of the cause. Moreover, the dilatation in bile ducts containing tumor may be disproportionate with that in the surrounding biliary tree [1, 2].
The clinical manifestations are consisting in upper abdominal pain, episodic biliary pain, fever and jaundice. These symptoms are related to the recurrent obstruction of the bile ducts .
The imaging techniques used for the study of papillary bile ducts neoplasms include ultrasonography (US), CT, endoscopic retrograde cholangiopancreatography (ERCP) and MR cholangiopancreatography that reveal bile ducts dilatation with or without visible intraductal papillary lesion [1, 2, 8].
Bile ducts that contain a mucinous intraductal papillary tumor may dilate diffusely or focally like an aneurysm and this presentation, such as the disproportionate lobar dilatation of the bile ducts where the tumor is localized than the ducts in the controlateral lobe, are considered a characteristic sign of the presence of an intraductal papillary mucinous tumor. So the involved bile ducts may dilate aneurysmlike, whereas others diffusely and proportionally [1, 2].
Despite the study of Lim et al., where imaging techniques showed the presence of bile duct dilatation in all 15 patients, our case was not associated to bile duct dilatation, probably because the tumor was localized peripherically.
At US papillary tumor can appear as an echogenic mass. The echogenicity is similar to that of the liver and there is no acoustic shadow. In our case, the lesion appeared hypoechogenic in the presence of surrounding steatosis. On CT the neoplasm presents as intraluminal soft-tissue mass enhancing or nonenhancing depending on whether the tumor is connected to the wall or not. When it is fixed, it shows confined within the ducts and preserves the bile ducts wall integrity. Moreover, the tumor can present as asymmetric enhanced thickening of the bile duct wall [2, 8]. Besides, the tumor may not be depicted when it is small and isoattenuating to the adjacent hepatic tissue or when the complex orientation of the dilated ducts obscures the mass .
Yoon et al, describing the CT findings in 15 patients affected by malignant papillary neoplasms of intrahepatic bile ducts, reported that most of the tumors were hypo- or isoattenuating on contrast-enhanced CT. Conversely, CT could reveal an intraductal hypoattenuating mass associated with markedly dilated intra- and extrahepatic bile ducts in the three patients with mucin-hypersecreting papillary cholangiocarcinoma .
In this case, the appearance of a mass showing hypovascular with the enhanced rim in later phases, suggesting the presence of a capsule, could invite to include the hepatocellular carcinoma with atypical features in the differential diagnosis. Early stages like a dysplastic nodule with focal degenerated areas was a inconsistent hypothesis because the focal hypervascular degenerated areas did not show in the arterial phase. The low attenuation of the lesion in the arterial and venous portal sequences and the elongated morphology, as in our case, could suggest the presence of a peripheral cholangiocarcinoma but, on the contrary, the late intralesional enhancement was poor . Because a definitive diagnosis, based on imaging appearance of the lesion, was impossible in our case, we decided to perform a hystopathological investigation but the biopsies were inconclusive. So, the definitive diagnosis was made on surgical resected material.
The use of ERCP is recommended to detect the presence and the location of the suspected neoplasm and to reveal the presence and the quantity of mucin draining from duodenal papilla. Moreover, ERCP permits biopsy performation . This last procedure could not be performed in our case because the tumor was peripherical.
On ERCP the lesion appears as filling defect representing papillary tumor or as fine irregularities of the bile duct wall with a velvety or serrated contour.
On US mucin is echo-free but may appear as a echogenic focus; on CT it is water-attenuating.
Instead, ERCP may show small or large, elongated or amorphous filling defects caused by mucin presence in the dilated ducts.
Various conditions present as filling defects in the dilated ducts and include air bubbles, stones, blood clots, and intraluminal tumors [2, 10, 11].
However, the papillary tumors of the bile ducts are characterized by the inconsistency and changeability of the imaging findings. Moreover, there can be differences between the radiologic and surgical presentation, and both these can differ from the pathologic findings but when intraductal masses are seen with localized dilatation of the intrahepatic bile ducts, papillary tumor of the bile ducts should be included in the differential diagnosis. Otherwise, the diagnosis may be made on the basis of histopathologic examination, as in our case [6, 8].