Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

reveals hypodense tumors that enhance postcontrast.

Pneumocystis carinii infection has led to acute hepatic failure due to P. carinii obstructing the hepatic sinuses and capillaries. Calcifications develop in lymph nodes, spleen, liver, and kidneys.

Liver function tests are abnormal but no specific imaging findings are seen with liver toxoplasmosis.

Immunocompromised children tend to develop multiple small liver abscesses, often fungal in origin, rather than a large drainable abscess.

Although disseminated tuberculosis is not uncommon in HIV patients, hepatic tuberculous abscesses are rare. Focal liver involvement is unusual and only an occasional AIDS patient develops liver tuberculomas.

Malignancy

An occasional hepatocellular carcinoma develops in an HIV-infected patient with no evidence of chronic liver disease or viral infection. Primary liver lymphomas also are found in HIV patients. Discrete tumors, rather than diffuse infiltration, predominate. A biopsy should be diagnostic.

Kaposi’s sarcomas tend to infiltrate the portal triads.

Rare hepatic leiomyomas and leiomyosarcomas have developed in children with AIDS.

Postoperative Changes

Liver Transplantation

Pretransplant

Clinical

Children

The most common indication for orthotopic liver transplantations among 198 children was biliary atresia (42%), followed by a1-antitrypsin deficiency (8%), Alagille’s syndrome (8%), and fulminant hepatic failure (7%) (158); over half of these children were under 5 years of age. Other indications for a liver transplant in children include cryptogenic cirrhosis, and an occasional child has cystic fibrosis and resultant biliary cirrhosis. A severe organ shortage exists

ADVANCED IMAGING OF THE ABDOMEN

for children. In part, this shortage has been alleviated by using reduction hepatectomy to produce more manageable-sized liver allografts; only the left lobe or even a segment of the lobe is transplanted.

Similar to transplantation of an entire liver, infants with reduced transplants (left lateral segment or split-liver transplant grafts) also undergo a Roux-en-Y choledochojejunostomy. The vascular and biliary anatomy is different from that seen with whole liver transplantation if only a partial liver transplant is performed.

At times TIPS stabilizes an adult or child with liver failure and life-threatening variceal bleeding sufficiently to permit liver transplantation later.

In one center the 1-year actuarial survival rate in children was 80% (increasing to 88% over the last 5 study years) and for those surviving more than 1 year, the 3-, 5-, and 10-year actuarial survival rates were 95%, 93%, and 93%, respectively (158).

Adults

The most common indications for orthotopic liver transplantation in adults are cirrhosis, sclerosing cholangitis, and fulminant hepatic failure. End-stage hepatitis B cirrhosis patients were considered to be poor candidates for transplantation due to a high recurrence rate, but more recent medical therapy has led to a more favorable response. Hepatitis C virus infection recurs in most patients posttransplant and appears to be relatively benign, but the longterm sequelae are not known. In select patients transplantation is a viable option for early primary liver cancer. Prevalence of hepatocellular carcinoma is greater in a transplant recipient undergoing transplantation for cirrhosis than in the general population, with some of these cancers not detected by pretransplant imaging. Performing both CT arterioportography and DSA pretransplant achieves a sensitivity of about 85% in detecting hepatocellular carcinomas in cirrhotic livers but these tests have a relatively high false positive rate (159). Although pretransplant knowledge of an incidental neoplasm is of obvious importance, one may argue that due to the generally small size of most of these tumors the patient would still be eligible for transplantation.

Patients with primary sclerosing cholangitis who have developed a cholangiocarcinoma do

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poorly after liver transplantation; the current trend is to perform liver transplantation earlier in the course of primary sclerosing cholangitis.

Spontaneous bacterial peritonitis, a complication of cirrhosis, is not a contraindication to liver transplantation provided adequate therapy for peritonitis is administered prior to transplantation.

The role of TIPS prior to transplantation is discussed in Chapter 17. The malposition of TIPS stents, however, alters and prolongs liver transplantation by interfering with crossclamping at usual vascular sites.

Living donor transplantation involves right lobectomy or segmentectomy or left lobectomy or segmentectomy. Regeneration is a rapid process, with a transplant doubling in size within three or so weeks. Postoperative complications do occur in liver donors. Complications occur more often in right lobe than left lobe donors (160); many of these complications are amenable to interventional management, such as percutaneous drainage, bile duct dilation, arterial embolization or stent placement and resolve.

Imaging

Preoperative recipient assessment is designed to detect any anatomic variance such as portal vein patency and its major branches, and the caliber, location, and patency of the hepatic artery, hepatic veins, and inferior vena cava. Probably the most useful single imaging modality for preoperative evaluation of a potential liver transplant candidate is contrast-enhanced CT, especially multislice. This study calculates liver volume, evaluates adjacent structures, and defines underlying vascular anatomy.

Multidetector multiphase CT provide comprehensive parenchymal, vascular, and volumetric evaluation of potential living adult donors for right lobe liver transplantation. Agreement is found in donors between virtual CT right lobe volumes and graft weights obtained at surgery.

Arterial phase and portal venous phase CT with 3D volume rendering techniques can define major vessel origins, portal vein thromboses and cavernous transformation, collateral vessels, and detect unsuspected liver tumors. Such vascular information appears similar to or even superior to that obtained with DSA.

At times resection of only the left lobe or left lateral segment is performed in living donors for related transplantation, and any anatomic venous variation needs to be determined. Often US is sufficient for this task. It can identify whether the hepatic veins form a common trunk or drain separately into the inferior vena cava.

Preoperative right lobe living donor evaluation is also feasible with comprehensive abdominal T1and T2-weighted MRI, MR cholangiography, and MR angiography; Preoperative MR evaluation in right hepatic lobe donors provides right lobe volume data similar to surgically obtained volumes, outlines intrahepatic bile duct anatomy in more patients than intraoperative cholangiography, and depicts portal veins more completely than DSA (161). Preoperative MRI findings can exclude donors, although a right hepatectomy was aborted at laparotomy in several patients because of intraoperative cholangiography findings at variance to preoperative imaging (162). A specific role for MRI is yet to be established in living donors. Of interest is a study of iodipamide enhanced multidetector CT cholangiography, showing significantly better donor biliary tract visualization than with conventional MR or mangafodipir enhanced excretory MR cholangiography (163).

Technetium-99m-GSA, binding to asialoglycoprotein liver receptors, is useful in evaluating hepatic functional reserve both prior to and after transplantation.

Is selective angiography necessary in children with end-stage liver disease who present for orthotopic liver transplantation? Such selective study does provide detailed portal vein and hepatic artery anatomy but at some risk to these children.

Intraoperative

In addition to preand posttransplantation evaluation, intraoperative vascular US appears useful if vascular compromise is suspected. Intraoperative US aids in establishing a liver transection line for an extended lateral segmentectomy by identifying the left medial vein.

A typical liver transplantation requires five anastomoses: four vascular ones involving the hepatic artery, portal vein, and supraand infrahepatic inferior vena cava, and an end-to-end biliary anastomosis. A T-tube stent was often

left in place across the biliary anastomosis, although a number of surgeons have abandoned T-tube drainage to prevent bile leakage from the site. With the latter, biliary complications must be approached via ERCP. If a biliary anastomosis is not feasible, a choledochojejunostomy is created. A cholecystectomy is performed.

Posttransplant

The consequences of prolonged immunosuppressive therapy are still not completely understood.

Imaging

Computed tomography detection of focal subcapsular hepatic necrosis at some point in time is common after liver transplantation. In general, this finding is of little clinical prognostic significance, although it is associated with acute rejection.

A suprahepatic circumcaval calcification is occasionally detected by CT after transplantation. It is probably of little consequence.

Although IV Levovist in liver transplant patients results in significantly better color Doppler US arterial signals, little or no improvement is evident for the main portal vein and hepatic vein.

Magnetic resonance imaging defines hepatic venous anatomy and determines the liver volume and portal venous blood flow.

Complications

Rejection

Rejection is usually first detected roughly a week after transplantation. No specific imaging finding suggests liver rejection. During acute rejection the liver becomes edematous and intrahepatic bile ducts are compressed, resulting in incomplete filling during cholangiography (Fig. 7.51). Chronic rejection manifests by multiple bile duct strictures and a gradual and progressive reduction in number of interlobular bile ducts. In a setting of suspected rejection, imaging is used primarily to exclude biliary, vascular and other causes that clinically mimic rejection.

In some patients CT and MRI show a perivascular collar around central portal vein branches, probably secondary to impaired lymphatic drainage and resultant lymph edema.

Figure 7.51. Presumed rejection of second liver in patient with autoimmune hepatitis. Numerous narrowed and dilated biliary segments are scattered throughout the liver. Ischemia can have a similar appearance. (Courtesy of David Waldman, M.D., University of Rochester.)

Doppler US changes in vessel diameter and blood flow data do not correlate consistently with acute rejection or with liver biopsy findings.

Biliary Complications

Posttransplant biliary complications encountered during the acute period consist of leakage and obstruction. Bile duct necrosis is uncommon. Strictures or stones develop on a more chronic basis.

Cholangiography, via an inserted catheter, endoscopic approach,or percutaneously,studies the suspected biliary complications (Fig. 7.52). Magnetic resonance cholangiopancreatography is evolving into a viable alternative by identifying first-order intrahepatic and extrahepatic bile ducts in over 90% of recipients. Enhancement with mangafodipir trisodium outperform conventional MR cholangiography in detecting and excluding biliary abnormalities (164).

In children, a diagnostic cholangiogram can be obtained in over 90% of attempted percutaneous transhepatic cholangiograms and a drainage catheter successfully inserted in most (165); of note is that a diagnostic cholan-

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Figure 7.52. Appearance of a choledochocholedochostomy after liver transplantation. Two cystic duct stumps are evident, with a choledochal tube inserted into the proximal (transplant) one.

giogram was obtained in 92% even when intrahepatic bile ducts were not dilated.

Acute: The most common early biliary complication is biliary leakage, usually at an anastomosis. Some leaks manifest only after T-tube removal. A less common cause of bile leak is liver biopsy. Most bilomas are amenable to nonsurgical therapy, but one must ensure that a fluid collection does indeed represent bile rather than a vascular aneurysm; the latter is excluded with Doppler US.

The bile ducts receive their entire blood supply from the hepatic artery and are rather sensitive to ischemia. Thus the risk of biliary complications increases considerably with hepatic artery stenosis. Ischemic complications include leaks, strictures, and adjacent abscesses, with the most common complication being a nonanastomotic biliary stricture. In patients with complete interruption of arterial blood flow, about half also have a biliary complication.

Acute obstruction also occurs due to mechanical T-tube malposition or bile duct kinking. Partial donor cystic duct remnant obstruction and distention due to retained mucus or sludge (mucocele) occasionally compresses the adja-

cent hepatic duct. Ultrasonography reveals a cystic duct mucocele as an anechoic ovoid structure adjacent to bile duct. Such cystic duct mucoceles develop in a small minority of transplanted livers.

Acute biliary complications are usually evaluated by cholangiography. The role of US is controversial. In general, an abnormal US finding is predictive of biliary obstruction with a high specificity, but normal US findings do not exclude a biliary stricture or bile leakage.

Chronic: A biliary stricture is the most common long-term complication after liver transplantation. Stenoses occur most often in the recipient common bile duct, followed by the donor liver common bile duct and anastomotic site. Nonanastomotic strictures presumably are secondary to ischemia. Stones develop proximal to some stenoses.

Magnetic resonance cholangiopancreatography is a viable option in detecting late biliary complications. More invasive biliary procedures are then reserved either if MRCP does not define underlying anatomy or if interventional procedures are contemplated.

Biliary strictures are readily dilated using interventional radiology techniques. Although a success rate up to 90% can be achieved in dilating these strictures, they tend to recur. The success rate of dilating restenoses is generally lower than for an initial stenosis, and stents should be considered in this setting. Although some stents do obstruct by sludge and debris, their patency can be maintained by various interventional maneuvers.

Intrabiliary defects consist of sludge, stones, and necrotic debris.

Surprisingly, cholangitis is not common. Pancreatitis is rare.

Vascular Complications

Arteriography is the accepted gold standard in evaluating vascular complications, although both CT and US detect some complications. Multislice 3D CT angiography with volume rendering, in particular, is a promising approach in these patients. Currently, however, for suspected vascular complication Doppler US is more common than CT or MR. For therapeutic interventions an angiographic approach is necessary.

Magnetic resonance angiography is assuming a greater role in evaluating vascular anasto-