Ping Li, Liang Zhu, Xuan Wang, Huadan Xue＊,Xin Wu, Zhengyu Jin

1Department of Radiology, 2Department of Gastroenterology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences &Peking Union Medical College, Beijing 100730, China

Key words: choledochocele; gastrointestinal imaging; multi-detector computed tomography;endoscopic retrograde cholangiopancreatography; magnetic resonance imaging;magnetic resonance cholangiopancreatography

Abstract Choledochocele is a congenital abnormality of the biliary system, which characterized by a cystic dilatation of intramural segment of the distal common bile duct. Choledochocele manifests as cystic lesions in the duodenal lumen and resembles duodenal duplication cysts in imaging. We reported a patient with choledochocele.Magnetic resonance cholangiopancreatography showed a thin-walled sac in the duodenal cavity and a fine tubular structure connecting with the end of the common bile duct. Magnetic resonance cholangiopancreatography is a noninvasive and convenient technique in the diagnosis of choledochocele.

CHOLEDOCHAL cysts (CCs) are congenital abnormality of the biliary system. It is characterized by cystic dilatation of intrahepatic duct and extrahepatic biliary tree individually or both.1According to the modified Todani system, CCs are classified into categories I-V. Type III is a rare form of CCs,also called choledochocele, which comprises only 4%-6%of all reported cases.2It appears as a cystic dilatation of intramural segment of distal common bile duct protruding into duodenal lumen. Choledochocele has distinctive anatomic features and a lower risk of malignancy than other types.3-4The clinical presentations and imaging findings of choledochocele resemble duodenal duplication cysts (DDCs), making their differential diagnosis difficult.5Imaging examinations play an important role in the initial diagnosis, differential diagnosis, surgical planning and long term surveillance of CCs.6The purpose of this study was to demonstrate the importance of magnetic resonance cholangiopancreatography(MRCP) and biliary specific contrast agents in the diagnosis of bile duct cyst.

CASE DESCRIPTION

A 42-year-old man was admitted to the Peking Union Medical College Hospital on October 29, 2015 for having been suffering from abdominal pain over one year. There was no significant medical history or family history. Physical examination did not show obvious abnormality. Laboratory data including complete blood count, urinalysis and blood biochemistry were within the normal limits.

In order to confirm the diagnosis, he underwent a series of imaging examinations. Ultrasonography did not show significantly positive signs. After symptomatic treatment, abdominal pain still appeared intermittently. Next, the patient underwent gastroscopy and endoscopic ultrasonography to make a definitive diagnosis. The results revealed a parenteral cystic lesion in the descending section of the duodenum. It was deemed as a duodenal diverticulum (Fig. 1). The upper gastrointestinal barium study displayed a round filling defect in the second portion of the duodenum (Fig.2). Therefore we excluded the diagnosis of duodenal diverticulum. Abdomen CT revealed a thin-walled cystic mass without nodules causing mild duodenal dilatation and multiple stones in the duodenum (Fig. 3).We considered it as a type Ⅲ CC or a DDC. In order to confirm the relationship between the cystic lesion and the intestine, MRCP was performed with pineapple juice (PJ). PJ can significantly reduce the liquid in the intestinal cavity itself on T2 signal (Fig. 4).MRCP demonstrated the cystic lesion had no communication with the duodenal lumen. But this modality could not clearly identify its communication with the bile duct. During follow-up dynamic contrast enhancement (DCE)-MRI with specific liver intake contrast agent revealed a slender tube connecting the lower common bile duct with the cystic lesion (Fig. 4).Finally the patient was diagnosed with choledochocele based on imaging findings.

Figure 1. Endoscopy (A) revealed a parenteral cystic lesion (star) in the descending duodenum. Endoscopic ultrasonography (B) showed a cystic lesion in the duodenal lumen with many stones (star).

The operation was carried out. The diagnosis was confirmed by pathological findings. He was discharged on postoperative day 10 with good health condition.

DISCuSSION

Type Ⅲ cyst is a rare type of CCs, characterized by a cystic dilatation of the bile duct terminal bulging into duodenal lumen.6-7It is similar to DDCs, which also present as cystic structures and typically protrude into the second or third portion of the duodenum.8DDCs are extremely rare6,9and account for 5% of all gastrointestinal duplications.10DDCs are usually located in the mesenteric side and share their circumference with the intestine. They have a muscle coat and may or may not communicate with the gut lumen. Both CCs and DDCs can communicate with the bile duct. Except for connecting with the bile duct, DDCs can communicate with the pancreaticobiliary duct, especially with the pancreatic duct. They have much in common about clinical manifestations and imaging findings.11

Figure 2. The upper gastrointestinal barium study displayed a round filling defect (arrow) in the second portion of the duodenum.

Figure 3. Axial (A) and coronal (B) CT scan images of the abdomen revealing a cystic mass with multiple stones in the duodenum lumen (arrow). Coronal CT scan (B) showing a thin-walled cystic lesion (arrow) without nodules accompanied with mild duodenal dilatation.

Figure 4. Magnetic resonance cholangiopancreatography (MRCP) (A-C) and dynamic contrast enhancement (DCE)-MRI(D-F) images.

It is difficult to distinguish them using preoperative diagnostic procedures. The key to differentiating them is to determine the relationship between the lesions and the lumen as well as bile duct. Cholangiography and upper gastrointestinal barium studies have been proposed to differentiate them. Choledochocele could be filled with contrast during cholangiography but not be filled during barium studies, whereas DDCs could not be filled when scanned with both studies.12It may be sufficient to identify larger lesions with the two methods, but for smaller lesions the sensitivity and specificity of the two techniques are low. In addition, cholangiography is invasive. Recently the commonly used imaging techniques are ultrasonography,CT, MRCP and endoscopic retrograde cholangiopancreatography (ERCP) to verify CCs. Ultrasonography is economic, convenient and widely used, but it’s extremely susceptible to interference of bowel gas.Multi-detector computed tomography (MDCT) is very helpful in surgical planning, especially in the accurate delineation of extent of the dilated bile ducts. MDCT can also identify cyst wall thickening and intracystic masses that develop secondary to malignancy. But it’s difficult to display the relationship between cystic lesions and the bile ducts, duodenal lumen. MRCP and DCE-MRI well settle these problems with PJ and hepatocyte-specific contrast agent. PJ has shorter T1 and T2 than other juices. After oral PJ, fluid pre-existing in the lumen is suppressed, but liquid in the cystic cavity is still bright on T2WI.13It can clearly show the relationship of the cystic lesion with the lumen. The liver specific contrast agent excreted by the bile duct can clearly show the relationship between the cystic lesion and bile ducts. Despite ERCP remains the most widely used diagnostic tool for identification of choledochocele, with a reported diagnostic sensitivity of 97%,5it is invasive and the patients are difficult to tolerate. Nevertheless MRI is safe, non-invasive and no ionizing radiation. Furthermore, MRI does not carry the risks of ERCP including cholangitis, duodenal perforation, hemorrhage and pancreatitis. MRCP has distinct advantages to assess cyst lesions, size, site and shape of bile duct dilatation.14The image quality of MRCP is more susceptible to motion artifacts than ERCP, which can be compensated by breath-hold sequences and respiratory triggered scanning.15Sacher et al14identified that MRCP has a 96%-100% detection rate for CCs, which making it the best choice for preoperative evaluation. MRI can entirely replace ERCP in assessing the relationship between the cystic lesion and bile duct, making guidance for surgical planning. This may benefit from PJ and liver specific contrast agent. It may be achieved in all patients with choledochocele who cannot be verified by ERCP.After a series of tests, the patient was diagnosed as type Ⅲ choledochal cyst by MRCP, and MRI with adminstration of the specific contrast agent of biliary tract confirmed the diagnosis. MRCP is noninvasive and convenient in the diagnosis of choledochocele.

Conflicts of interest statement

The authors have no conflicts of interest to disclose.