Biliary Atresia Triangular Cord Sign

Fig. 11. Caroli disease on MRCP. Same case as demonstrated in Fig. 9. MRCP demonstrates diffuse, hyperintense, round and cystic lesions, distributed in both lobes of the liver, with a flower tree appearance communication between sacculi and bile ducts (Fig. 11), which is positively demonstrated with Gd-BOPTA and other hepatobiliary contrast agents if contrast material is present within the sacculi and bile ducts during the hepatobiliary phase after administration (Fig. 12).

Differential diagnoses of Caroli's disease include primary sclerosing cholangitis, recurrent pyogenic cholangitis, and polycystic liver disease. Primary sclerosing cholangitis and recurrent pyo-genic cholangitis may be associated with duct dilatation, stenosis, intrahepatic calculi, and malignancy. The ductal dilatation in primary sclerosing cholangitis is typically more isolated and fusiform than saccular (Fig. 13), and is not characteristic of Caroli's disease. Recurrent pyogenic cholangitis is the most difficult diagnosis to exclude because patients with pyogenic cholangitis present with sepsis and have intra- and extrahepatic biliary dilata-

tion. Saccular dilatation favors the diagnosis of Caroli's disease because it is not typical in recurrent pyogenic cholangitis. Hepatic cysts of poly-cystic liver disease do not communicate with the bile ducts (see Fig. 54, Chapter 4).

Biliary Atresia

Biliary atresia is an obliterative cholangiopathy that may affect not only the extrahepatic but also the intrahepatic bile duct system, with complete obliteration or discontinuity of the hepatic or common bile ducts at any point from the porta he-patis to the duodenum. Obstruction of bile flow leads to cholestasis, progressive fibrosis, and ultimately, cirrhosis. The disorder occurs once every 10,000-15,000 live births and is more common in girls than in boys [5]. It accounts for approximately one third of all cases of prolonged neonatal cholestatic jaundice (see Chapter 10,"MR Imaging of the Liver in Pediatric Patients", Section 10.5.2, "Biliary Atresia").

Although factors such as developmental malformation, perinatal viremia (cytomegalovirus, rubella, retroviruses), and toxicity of bile constituents have been implicated, the actual cause of biliary atresia remains unknown [9,22]. A single, unifying cause appears unlikely, and it seems more probable that there is etiologic heterogeneity that results in a progressive sclerosis; for example, an inflammatory process that affects the extrahepatic biliary tract leading to ductular luminal obliteration [5].

Biliary atresia occurs in two clinical forms, the embryonic or fetal type, and the perinatal type. The latter form is more frequent, and accounts for more than 60% of cases. The fetal variant may be associated with congenital malformations such as polysplenia, cardiovascular defects, abdominal situs inversus, intestinal malrotation, and anomalies of the portal vein and hepatic artery [22].

Nutcracker Syndrome Renal Vein

Fig. 12a, b. Caroli disease. On the unenhanced T1-weighted GRE image (a) the cystic sacculi are heterogeneously hypointense. On the T1-weighted GRE image (b) acquired during the hepatobiliary phase after the administration of Gd-BOPTA (0.1 mmol/kg BW) the cystic sacculi demonstrate an increase of signal intensity due to the presence of contrast agent within the cysts

Triangular Cord Biliary Atresia

Fig. 13a-c. Primary sclerosing cholangitis. T2-weighted images (a, b) show intrahepatic, fusiform, hyperintense, ductal dilatation (arrows associated with ductal stenosis (arrowheads). The intrahepatic ductal dilatation and stenosis are well depicted on the 3D-MRC image (c)

Fig. 13a-c. Primary sclerosing cholangitis. T2-weighted images (a, b) show intrahepatic, fusiform, hyperintense, ductal dilatation (arrows associated with ductal stenosis (arrowheads). The intrahepatic ductal dilatation and stenosis are well depicted on the 3D-MRC image (c)

Biliary atresia can be classified in three ways according to the site of the obstruction:

• type I, obstruction at the level of the common bile duct;

• type II, obstruction at the level of common hepatic duct;

• type III, obstruction at the level of the porta he-patis.

The latter type is considerably more frequent and accounts for more than 90% of cases [9].

The macroscopic aspect of the liver varies according to the stage of the disease. At first it enlarges and is dark green in color, becoming finely nodular as cirrhosis develops. In untreated cases cirrhosis may take between 1 and 6 months after birth to develop. Microscopically, cholestasis, periportal ductal proliferation, and the presence of bile plugs in cholangioles and interlobular bile ducts are apparent. Fibrosis is progressive with a periportal and perilobular distribution. Linkage of portal areas is frequent and secondary biliary cirrhosis is a possible development [5]. In biliary atresia the liver parenchyma can be normal in structure, or demonstrate signs of biliary cirrhosis with a prominent hepatic artery.

Signs on US that may be related to biliary atre-sia include the shape and contractility of the gallbladder and the presence of the "triangular cord".

In cases of biliary atresia, the gallbladder has a ghostlike appearance and these features have been described as the "gallbladder ghost triad" [25]. This consists of an atretic gallbladder of less than 1.9 cm in length, an absent or thinned smooth echogenic mucosal lining with indistinct walls, and a knobbly, irregular, or lobular contour (Fig. 14). A triangular- or tubular-shaped echogenic density on transverse or longitudinal scans represents a fibrous cone at the porta hepatis known as the triangular cord (Fig. 15). This focal hyperechogenici-ty associated with perivascular hyperechogenicity is related to progressive fibrosis and ductal sclerosis, and is very useful for the diagnosis of biliary atresia (Fig. 16) [12,32].

Although scintigraphy is not used routinely, Technetium TC 99m iminodiacetic acid derivatives are rapidly excreted from the blood by hepatocytes and excreted into the bowel through the biliary system. With biliary obstruction, this material accumulates in the liver and none appears in the bowel (Fig. 17). When employed for imaging of infants, phenobarbital should be given for five days before the study. This is because phenobarbital increases bilirubin conjugation and excretion and has a choleretic effect, and thus enhances and accelerates the uptake of iminodiacetic acid analogues by the liver [17].

Triangular Cord Sign Ultrasound
Fig. 14a, b. Biliary atresia. US scans of two different patientsatresia show different gallbladder shapes. In (a) a very small, atretic gallbladder (arrows is apparent, while in (b) an enlarged gallbladder (asterisk) with a thinned wall is seen
Triangular Cord
Fig. 15a, b. Biliary atresia. US scans show the triangular cord (arrowheads) as tubular (a) or triangular (b) hyperechoic tissue located at the porta hepatis
Triangular Cord Sign Ultrasound
Fig. 16a, b. Biliary atresia. On US B-mode (a) and color Doppler US (b) scans, perivascular hyperechogenicity (arrowheads) corresponding to progressive fibrosis is clearly seen

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Fig. 17. Biliary atresia on scintigraphy. On Technetium 99m iminodiacetic scintigraphy scans, TC 99m is progressively accumulated in the liver and does not appear in the bowel

Fig. 17. Biliary atresia on scintigraphy. On Technetium 99m iminodiacetic scintigraphy scans, TC 99m is progressively accumulated in the liver and does not appear in the bowel

On T2-weighted MR imaging, moderately high signal intensity along the portal tract that extends peripherally from the porta hepatis correlates with periductal edema and inflammatory cell infiltration. Although biliary atresia can be reliably diagnosed on the basis of the lack of visualization of either the common bile duct or the common hepatic duct, findings on MRC should still be interpreted in relation to clinical information [22,29, 52].

The prognosis of untreated biliary atresia is extremely poor, with death from liver failure usually occurring within two years. However, hepato-por-to-enteroanastomy can restore bile flow in many cases if surgery is performed sufficiently quickly after diagnosis. Additional predictors of a poor outcome are caucasian race, the severity of the in-trahepatic biliary cholangiopathy, the presence of cirrhosis on initial biopsy, and absence of ducts at the level of the liver hilus. The outcome correlates directly with the size of the bile duct remnants identified in the porta hepatis at surgery. Bile duct profiles of more than 150 mm and lined with columnar epithelium have been associated with a good surgical result [11,24].

Agenesis of the Gallbladder

Failure of development of the caudal foregut diver-ticulum or failure of vacuolization after the solid phase of embryonic development results in agenesis of the gallbladder. In about two thirds of patients with gallbladder agenesis it is possible to ob serve other congenital anomalies, such as congenital heart lesions, polysplenia, imperforate anus, absence of one or more bones, and rectovaginal fistula [66].

Patients may be asymptomatic or present with right upper abdominal pain, jaundice, and vomiting. The preoperative diagnosis of gallbladder agenesis is difficult. Whereas imaging techniques such as US and CT may suggest the diagnosis, confirmation of gallbladder agenesis is usually an intraoperative finding, when its absence is discovered at cholangiography.

MR cholangiography can be considered an alternative non-invasive imaging method. The possibility of visualizing the biliary tree by means of 3D-reconstructions and to assess the absence of the gallbladder permits information to be acquired that is similar to that available by intraoperative cholangiography.

Duplication of the Gallbladder

Gallbladder duplication occurs when there is excessive budding of the caudal diverticulum. It is caused by incomplete revacuolization of the primitive gallbladder resulting in a persistent longitudinal septum that divides the gallbladder lengthwise. Gallbladder duplication may also occur due to the occurrence of separate cystic buds. Cholecystitis with cholelithiasis is a relatively frequent occurrence in these patients. The duplicated cystic ducts frequently enter the common bile duct separately, or alternatively, unite to form a common cystic duct. Less frequently they drain independently into the hepatic ducts.

US is not specific for the demonstration of this anomaly since entities such as choledochal cyst, bilobed gallbladder, and gallbladder diverticulum may mimic gallbladder duplication. MRC reliably demonstrates the presence of two gallbladders as hyperintense sacs, and can depict the type of drainage into the common bile duct [53].

Anomalies of Gallbladder Shape

Phrygian cap is the most common abnormality of gallbladder shape. The term "Phrygian cap" derives from a resemblance to folded hats worn in the ancient country of Phrygia. It is characterized by a fold or septum of the gallbladder between the body and fundus (Fig. 18). Although clinically unimportant, it may be mistaken on radiological examination for a stone or a pathological septum.

Multiseptate gallbladder is characterized by the presence of multiple internal septa of various sizes

Phrygian Cap Gallbladder
Fig. 18. Phrygian cap gallbladder. On US a hyperechoic septum (arrow/) in the gallbladder is easily visible. This corresponds to a fold or septum of the gallbladder between the body and fundus

which divide the gallbladder lumen into several chambers. Although these chambers communicate with one another by means of one or more orifices, these septations may lead to stasis of bile and gallstone formation. On US, multiple, communicating, hyperechoic septations and locules can be seen bridging the gallbladder lumen with a honeycomb pattern [56].

MRC is not routinely performed for evaluation of this type of anomaly although it is able to demonstrate morphologic abnormalities and the internal septa.

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  • Keijo Valo
    What does triangular cord sign biliary atresia represents?
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