Intraductal papillary mucinous neoplasm of the intrahepatic bile ducts: a case report and literature review

Background: Intraductal papillary mucinous neoplasm of the bile ducts (IPMN-B) is a rare malignant tumor originated from the epithelium of the bile duct. It can secrete a large amount of mucin to cause biliary obstruction. This disease has just been recognized in recent years. Case presentation: We found a 60-year-old woman with intermittent right upper abdominal pain. Imaging examination showed that the left intrahepatic bile duct was dilated with a solid mass. We had left hepatectomy. During the operation, there was colloidal mucus in the bile duct. There was a papillary mass on the wall of the bile duct. -to have developed into invasive adenocarcinoma. At a postoperative 6 months follow-up, the patient had no recurrence and is in good conditions. Conclusion: In our case, IPMN-B has underwent a malignant transformation at the early stage. Therefore, we think that surgical resection should be done as early as possible after the diagnosis of IPMN-B, so as to get a favorable prognosis.

Contrast-enhanced computed tomography revealed a tumor in the dilated left intrahepatic bile duct.
The lesions in the hepatic artery phase and portal vein phase are all moderately enhanced. The hepatic artery phase lesions are enhanced more than the liver parenchyma, showing a slightly higher density lesions; the portal vein phase lesions are inferior to the liver parenchyma, showing a relatively low density lesion. Magnetic resonance imaging and magnetic resonance cholangiopancreatography showed significant dilation of the peripheral biliary ducts in the left lobe of the liver and an 1.9 × 1.5 cm tumor in ducts. The right intrahepatic bile duct and extrahepatic bile duct are normal (Fig. 1).
On intraoperative inspection, we found that the thick jelly-like substance was flowing out of the intrahepatic bile duct, and a mass of about 2 × 2 cm in size was seen in the left hepatic duct, which was papillary and had a soft pedicle. Because of it was suspected malignancy, we made a decision to perform a left hepatectomy. Pathology reports from the postoperative specimens were intraductal papillary neoplasm with high-grade intraepithelial neoplasia, part of invasive mucinous adenocarcinoma. Immunohistochemistry showed that CK19 was strongly positive in tumor tissue.
Other positive markers are CK8/18, CK19, CAM5.2 and CK, partially positive for the CEA. The proliferative index based on Ki-67 staining was 30%. The tumor cells were negative for CK7, CDX-2, CK20, AFP, GCDFP-15, CA125 and P53. The patient had an uneventful recovery and was discharged from the hospital 14 days later. No recurrence was found after 6 months of follow-up (Fig. 2).

Discussion And Conclusion
The definition of intraductal papillary mucinous neoplasm of the bile ducts (IPMN-B) is derived from intraductal papillary mucinous neoplasm of the panceas (IPMN-P). Both the bile duct and the pancreatic duct originated from the foregut mesoderm in embryology, which made IPMN-B and IPMN-P have many similar characteristics. They can both secrete mucus and cause corresponding blockages in the ducts. Most importantly, they are precancerous lesions [3]. In recent years, IPMN-P has been gradually recognized, but the understanding of IPMN-B is just the beginning.
IPMN-B is rare in western countries, mainly in China, Japan, South Korea and other Asian countries, there is no big data to provide the incidence in the population. The age of onset of this disease is 55-65 years, and there is no significant difference in incidence between men and women [4,5].The pathogenesis of the disease is not clear. But some scholars think that chronic inflammation of stones, clonorchis sinensis and chronic inflammation of bile duct may increase the risk of the disease [6, 7].
The clinical manifestations of B are atypical and non-specific. In the early stage, it only showed intermittent upper abdominal pain. As the disease progresses, the tumors increase and mucus secretion can cause fever, jaundice, and even secondary pancreatitis. In addition, about 10% of patients are asymptomatic [8,9].
As far as the current understanding of IPMN-B is concerned, it is still difficult to make a clear diagnosis before surgery. In laboratory tests, it is often found that abnormal liver function indexes and elevated CA-199 are caused by obstruction of the bile duct. Among them, the increase of CA-199 could not identify its benign and malignan [10]. Imaging tests also lack specificity for the diagnosis of IPMN-B. is currently the most accurate method for diagnosing benign and malignant tumors and determining whether they are metastatic. Ikeno et al. comparative study found that the preoperative PET-CT can differentiate non-invasive IPMN-B from invasive IPMN-B [12]. Eendoscopic retrograde cholangiopancreatography (ERCP) can detect mucus adherence and outflow at the duodenal papilla opening in some patients, and biliary filling defects can be found by angiography. Biopsy can be taken in some patients with choledochoscope, which is a clear diagnosis method, but because of its technical difficulty large and easy to induce iatrogenic pancreatitis, and less clinical application.
According to its pathological features, IPMN-B can be divided into four types: pancreaticobiliary duct type, gastric type, intestinal type, and eosinophilic type [13]. According to the degree of atypia, it can be divided into: low or medium grade intraepithelial tumors, high grade intraepithelial tumors, related invasive cancers [14]. Therefore, IPMN-B is considered to be an important precursors for the  15]. Lymph node metastasis of IPMN-B is rare, so it is still controversial whether to perform regional lymph node dissection. However, for tumors in the hilar and lower bile ducts, Jarnagin et al. recommend regional lymph node dissection [15]. For patients who cannot undergo radical surgical resection, biliary drainage or stent placement in the bile duct should be performed to control biliary infections, improve liver function, and reduce the incidence of complications.Studies show aggressive surgical treatment,the 1-, 5-and 10-year survival rates for patient with M-IPNB were 96%, 84% and 81% [8].
In conclusion, as a rare biliary tract tumor, IPMN-B is still unknown. For elderly patients, imaging studies suggest that patients with bile duct wall masses and bile duct dilatations need to be alert to the possibility of this disease. For early radical resection of this disease, good prognosis can be obtained by removing biliary obstruction.  Surgery photos: a There was a papillary mass (approximately 2 × 2 cm) in the left hepatic duct (black arrowhead). Pathological findings. b, c In the duct, the tumors are arranged in papillary shape, and the fibrous vascular axis can be seen in the center (HE, a,b × 40). d, e

Declarations
The tumor presented adenoid structure, partially fused and infiltrated the surrounding liver tissue (HE, d × 40, e × 100). f Immunohistochemistry showed that CK19 was strongly positive in tumor tissue (f × 100).