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cbd anatomy radiology

MRI/MRCP is less frequently indicated in evaluation of hemobilia due to lengthier examination times and suboptimal evaluation of the peripheral vasculature, but can effectively demonstrate blood products within the biliary system. Hemorrhagic bile appears as increased signal on T1-weighted MRI and decreased signal on T2-weighted MR. Blood products within the biliary system usually appear as filling defects on MRCP. Once the site of bleeding is identified, the site can be embolized in the interventional fluoroscopy suite using either microcoils or liquid embolic agents (Figure 6). 34 Surgical intervention is often unnecessary, as success of endovascular management at experienced centers approaches 100%. 36 Depending on the patient’s situation, percutaneous biliary drainage may also be necessary for successful drainage of biliary obstruction from intraluminal blood products.

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MRI imaging characteristics of ascending cholangitis include central intrahepatic biliary dilation with smooth ductal wall thickening and enhancement. Associated parenchymal inflammatory changes include patchy or peribiliary parenchymal enhancement (most apparent on arterial phase postcontrast imaging) and geographic, wedge-shape T2-hyperintense segments of inflamed tissue around the involved bile ducts (Figure 3). In acute suppurative cholangitis, dilated bile ducts filled with echogenic purulent material are observed on ultrasound; dense biliary contents are seen on CT. 10 Biliary contents will appear low signal relative to liver on T2-weighted MRI and intermediate signal on T1-weighted MRI. 15 A uni- or multiloculated collection with capsular or rim enhancement is characteristic for abscess formation on CT and MRI; coalescence of adjacent abscesses may result in a cluster sign. 16

Choledochojejunostomy, in which the donor CBD is anastomosed directly to the recipient jejunum, is usually performed in patients with pre-existing biliary disease such as primary sclerosing cholangitis, prior history of biliary surgery, or when a size mismatch exists between donor and recipient ducts. Post-transplant bile duct leaks may be due to ischemia, relative downstream obstruction, sphincter of Oddi hypertension, or from T-tube removal, and most commonly occur at the biliary-enteric anastomosis or T-tube exit site. Leaks may manifest as extravasation of contrast material from the T-tube site into the peritoneal cavity on direct cholangiography, or as single or multiple bilomas. 41

Biliary leaks after liver transplant

Biliary complications can result from either traumatic or iatrogenic bile duct injury and encompass a spectrum of often coexisting entities, including retained stones, hemorrhage, hemobilia, bile leaks, bile duct ligation and strictures.

CT is useful for evaluation of biliary ductal dilatation and the measurements used in CT are applicable, but it is only moderately sensitive for detection of choledocholithiasis (with reported sensitivities between 25-90%). Only 20% of stones are high attenuation and up to 24% are isoattenuating to the surrounding bile (Figure 1). 7,8 Narrow window settings and coronal reconstructions may help accentuate the stone from adjacent bile or soft tissue. 9

Biliary tract injury is a rare complication of abdominal trauma, with a reported prevalence of 2.8–7.4% in patients sustaining blunt hepatic injury. 17,18 Injuries to the extrahepatic bile ducts usually result from acute deceleration and tend to occur at sites of anatomic fixation, such as the intrapancreatic portion of the CBD. Injuries to the intrahepatic bile ducts may be seen in the setting of parenchymal liver injury.

Biliary obstruction, stasis, and infection

Ultrasound is primarily utilized for follow-up of findings such as bilomas, but can be used to screen for the presence or absence of perihepatic and intrahepatic fluid collections, and ascites. 19,21

MRCP with hepatobiliary contrast agents such as gadoxetate disodium (Eovist; Bayer Healthcare Pharmaceuticals, Berlin, Germany) can provide useful functional and anatomic information and in many cases may supersede both scintigraphy (through superior anatomic detail and spatial resolution) and ERCP (by demonstrating peripheral sites of leakage that do not opacify by retrograde injection) in the dynamic evaluation of biliary injury. Delayed hepatocyte phase T1-weighted MR imaging may allow improved characterization of biliary anatomy by providing a higher signal-to-noise ratio in the bile duct than can be achieved with conventional T2-weighted MR imaging. 25 Extravasation of contrast material in the liver, perihepatic space, peritoneum, or pleural cavity is indicative of bile leak. Pooling of contrast material within an intrahepatic or perihepatic fluid collection implies direct communication with the biliary tree. 26

Biliary anatomy and its common and uncommon variations are of considerable clinical significance when performing living donor transplantation, radiological interventions in hepatobiliary system, laparoscopic cholecystectomy, and liver resection (hepatectomy, segmentectomy). Because of increasing trend found in the number of liver transplant surgeries being performed, magnetic resonance cholangiopancreatography (MRCP) has become the modality of choice for noninvasive evaluation of abnormalities of the biliary tract. The purpose of this study is to describe the anatomic variations of the intrahepatic and extrahepatic biliary tree.

Introduction

MRCP is performed by using a respiratory-triggered high-spatial-resolution isotropic 3D fast-recovery FSE sequence with parallel imaging in axial and oblique coronal planes, which provides high signal-to noise ratio and excellent spatial resolution (1-mm isotropic voxels) in a relatively short acquisition time (repetition time- one respiratory cycle, echo time- 700 ms, echo space- 8.5 ms, matrix- 320 × 256, section thickness- 1.4 mm, zero-fill interpolation to 0.7, 40-70 sections, receiver bandwidth- 25 kHz, acquisition time- 3-7 min, array spatial sensitivity encoding factor two, actual voxel dimensions (mm) isotropic at 1.4 _ 1.4 _ 1.4 interpolated to 0.7 _ 0.7 _ 0.7). In addition, 2D half-Fourier single-shot FSE sequence is implemented in thick-slab and multi-section modes (image acquisition parameters: Relaxation time- 2.800 ms, effective TE- 750 ms, image matrix- 384 × 256, field of view- 200 × 200 mm, refocusing flip angle- 180°). The resulting images are displayed as projection images of the biliary tree after a 7.13 s acquisition time. Maximum intensity projection (MIP) algorithm is used to produce a 3D cholangiogram from 3D FSE images.

Discussion

Intrahepatic and extrahepatic bile duct variations are commonly seen. Normal biliary anatomy is seen in only 58% of the population. There are various techniques available for the visualization of biliary tree. Intravenous cholangiography often does not opacify the intra- and extrahepatic biliary tree and rarely allows a detailed visualization of the duct bifurcation. Endoscopic retrograde cholangiopancreatography (ERCP), although very accurate, is an invasive method for imaging the biliary tree. Intraoperative cholangiography is also highly accurate; however, it is an invasive procedure and its routine use remains controversial. Magnetic resonance cholangiopancreatography (MRCP) is an excellent non-invasive imaging technique for visualization of detailed biliary anatomy. High-resolution cross-sectional, two-dimensional (2D) and three-dimensional (3D) projection images provide excellent detailed anatomy which is comparable to ERCP and intraoperative cholangiograms. In this article, we will discuss the different patterns of right and left hepatic duct variations and variations in cystic duct anatomy. We will also highlight the clinical significance of these anatomic variations.