Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

disease are prone to developing hepatocellular adenomas, with an occasional one progressing to hepatocellular carcinoma; one recommendation is that serum a-fetoprotein levels and yearly US be obtained in these patients.

Some of these patients undergo a portocaval shunt. Liver transplantation is an option in some with type Ia disease. In teenagers, transplantation restores normal metabolic balance, provides a growth spurt, and improves overall quality of life; liver transplantation does not, however, prevent focal glomerulosclerosis that is part of type Ia disease.

Type IV disease usually progresses rapidly, with death before 4 years of age, although a mild variant is seen in adults as a myopathy. Some of these infants undergo liver transplantation.

Computed tomography findings in patients with glycogen storage disease vary depending on activity. Glycogen deposition leads to a hyperdense liver, although associated steatosis often modifies the appearance. Once cirrhosis and hepatosplenomegaly develop, US reveals a hyperechoic liver.

13C MR spectroscopy using a whole-body MR is a noninvasive test for determining liver glycogen content.

Tyrosinemia

Tyrosinemia leads to progressive hepatocyte damage and regeneration, with surviving children developing dysplastic nodules and subsequent hepatocellular carcinoma. Imaging cannot reliably differentiate between regenerating nodules and neoplasms and, as a result, liver transplantation is recommended early in the course of this condition.

a1-Antitrypsin Deficiency

a1-Antitrypsin is a glycoprotein found in body fluids, serving mostly an inhibitory function. Some newborns manifest with cholestasis, which gradually clears. Some children with a homozygous deficiency develop chronic liver disease, which gradually progresses to liver failure and death, often by adolescence. Some adult cirrhotics have a1-antitrypsin deficiency, but the relationship is unclear. Some of these patients mimic hemochromatosis patients.

a1-ntitrypsin levels become normal after liver transplantation.

Wilson’s Disease

Wilson’s disease is an autosomal-recessive disorder of copper metabolism affecting approximately 5 persons per million. The primary defect is in the liver and results in copper accumulation within liver parenchyma and other structures.

A brief digression into copper metabolism is in order. Copper is found in two forms in the human body: Cu+ and Cu2+. Cu+ is diamagnetic and normal amounts do not affect MR signals. Cu2+ is paramagnetic and decreases both T1 and T2 signals. Most normal liver copper is bound to metallothionein and is Cu+ and thus not paramagnetic, but evidence suggests that some oxidation to Cu2+ takes place, although the precise mechanisms in normal liver and tumors are poorly understood. Copper in hepatocellular carcinomas also appears to be bound to metallothionein. Distribution of copper does not correlate with intensity on T1-weighted images,

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and the paramagnetic effect of divalent copper accumulation is insufficient to affect results.

Clinically, Wilson’s disease is defined by several stages. First, asymptomatic copper accumulates within the liver, the liver enlarges, and steatosis develops. Next, copper is redistributed throughout the body and hepatocellular necrosis, fibrosis, and hemolysis ensue. Progression to cirrhosis leads to liver atrophy, while accumulation of copper in body tissues results in neurologic damage, at times irreversible.

Initially, either hepatic or neurologic findings tend to predominate. Fulminant hepatic failure, even in a child, is an occasional initial presentation. Copper levels in serum, urine, and liver tissue suggest the diagnosis. The ceruloplasmin level is low.

If detected sufficiently early, the use of chelating agents prevents copper overload and achieves homeostasis. When diagnosed later in its course, chelating agents may slow progression. When fulminant or advanced and the patient does not respond to conventional therapy, orthotopic liver transplantation is an option, realizing that liver transplantation only partially corrects the metabolic defect by converting a homozygous disease into a heterozygote condition.

In most Wilson’s disease patients imaging studies are noncontributory. Some children with Wilson’s disease and cirrhosis have marked hepatosplenomegaly and imaging evidence of portal hypertension. Although liver CT attenuation is mildly increased in many adults, sufficient overlap with normal livers makes this finding of limited use.

Imaging in one patient with Wilson’s disease revealed multiple, small, enhancing nodules during the early arterial phase (10); biopsy identified dysplastic nodules.

Not all elevated hepatic copper levels in children represent Wilson’s disease. An Indian childhood cirrhosis associated with excess copper ingestion exists. Excess copper ingestion in an occasional non-Indian child leads to cirrhosis, liver failure, and increased liver copper levels.

Gaucher’s Disease

Gaucher’s disease, an autosomal-recessive condition, is discussed in more detail in Chapter 15.

Hepatomegaly is common in patients with type 1 Gaucher’s disease, at times progressing to massive hepatic fibrosis and portal hypertension. Focal intrahepatic tumors develop in some; these are hypointense on T1and hyperintense on T2-weighted MR images.

Technetium-99m–red blood cell SPECT imaging in a patient with Gaucher’s disease revealed an appearance similar to that seen with a hemangioma, believed to be secondary to focal intrahepatic extramedullary hematopoiesis (11).

Niemann-Pick Disease

Niemann-Pick disease is a metabolic disorder that progresses to cirrhosis. Some of these children develop a hepatocellular carcinoma.

Sickle Cell Disease

Although uncommon, intrahepatic cholestasis does occur in sickle cell disease. These patients develop hepatomegaly, hyperbilirubinemia, coagulopathy, and, on rare occasion, acute liver failure. Exchange transfusion appears to be effective therapy.

These patients do not have excess iron absorption, and MR does not reveal excess liver iron. After blood transfusions, however, iron in organs containing reticuloendothelial cells results in low T2 signal intensity.

Polycystic Diseases

Autosomal Dominant

Although renal involvement in patients with adult polycystic disease leads to progressive loss of renal tissue, this does not hold true in the liver; liver function tends to remain normal in most individuals until late in the disease. In distinction to autosomal-recessive congenital hepatic fibrosis, little fibrosis is evident in this entity. Of note is that in some patients adult polycystic disease mostly spares the kidneys and primarily involves the liver. In this patient population the differential diagnosis also includes rare cystic neuroendocrine or gynecologic metastases.

Dilated small bile ducts surrounded by fibrous stroma, called von Meyenburg complexes, are common in patients with adult

polycystic disease. A majority of patients with sufficient polycystic renal involvement requiring transplantation also have hepatic cysts, and in an occasional postrenal transplant patient symptomatic liver cystic disease is the primarily cause of death.

Clinical findings consist of abdominal pain, ascites, or leg edema.

Marked hepatomegaly develops, with CT showing multiple homogeneous, hypodense, variable-size cysts scattered throughout the liver (Fig. 7.4). The remaining parenchyma is compressed by these cysts, which in some patients replace most of the liver parenchyma. No wall or cyst enhancement is evident postcontrast.

As expected, these cysts are hypointense on T1and homogeneously hyperintense on T2weighted MR images. They do not enhance postcontrast. Intracyst hemorrhage varies their appearance even to the point of suggesting a neoplasm. An occasional patient presents with an elevated a-fetoprotein level, suggesting a hepatocellular carcinoma.

These cysts can become infected. Indium 111 leukocyte scintigraphy aids in localizing such an infected cyst.

Some of these patients develop sufficient symptoms to require surgical intervention. Either cyst fenestration or partial hepatic resection is a viable option. Aspirated fluid cytology and cyst wall biopsy to exclude a neoplasm

ADVANCED IMAGING OF THE ABDOMEN

appear reasonable prior to fenestration and fluid spread into the peritoneal cavity. Ascites is a postoperative complication of cyst fenestration. Hepatomegaly occasionally recurs.

Congenital Hepatic Fibrosis (Caroli’s Disease)

The current definition of Caroli’s disease is somewhat muddled. Some authors limit this term to the rare communicating biliary saccular ectasia as originally describe by Caroli (12); whereas others apply it to a broader spectrum of congenital hepatic fibrosis. Some employ Caroli’s disease as a descriptive term and then associate it either with congenital hepatic fibrosis or infantile polycystic kidney disease. Still others use the term Caroli’s disease to describe the rarer isolated biliary ectasia and Caroli’s syndrome if both ectasia and hepatic fibrosis are evident.

Embryologically, intrahepatic bile ducts develop from liver progenitor cells adjacent to portal vein mesenchyme and form ductal plates, which eventually evolve into bile ducts. Lack of or disordered ductal plate remodeling leads to a number of congenital intrahepatic bile duct disorders, including congenital hepatic fibrosis. The latter represents a cholangiopathy with surrounding fibrosis. Kidney involvement is variable in these patients and ranges from renal tubular ectasia to various forms of polycystic disease, most often autosomal recessive and

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only rarely autosomal dominant. An interesting association is Caroli’s disease and occasional acute pancreatitis.

Histologically, bile ductules become ectatic but still maintain their communication with bile ducts. As an isolated finding, ectasia is found only in a minority; over time, progressive fibrosis ensues and accounts for the typical appearance of extensive periportal fibrosis and biliary dilation.

Two manifestations predominate: (1) Those patients developing extensive fibrosis early in life tend not to have prominent intrahepatic bile duct dilation. (2) Dilation is more common in those individuals who are asymptomatic until adulthood, when signs and symptoms of chronic bile stasis develop. In some of the latter patients dilated ducts predominate in one lobe. Also, in some patients Caroli’s disease is associated with extrahepatic bile duct dilation, and in an occasional patient an extrahepatic choledochal cyst is the initial presentation. Calculi tend to develop either in intrahepatic cysts, in bile ducts, or both.

With severe involvement death occurs during the neonatal period from renal causes, before liver damage is evident. Some develop hepatomegaly early in life, others remain asymptomatic, and still others progress to fibrosis, liver failure, and portal hypertension; varices and hematemesis is their initial presentation. Bile stasis and infection lead to acute cholangitis, at times at an early age. Intrahepatic calculi develop in some, but the involved ducts are not obstructed. Hepatic function tends to be preserved until relatively late. Generally most of the liver is involved, although occasionally cysts are limited to one lobe; some patients have a preponderance of left lobe disease.

These patients are at increased risk of a developing hepatocellular carcinomas or cholangiocarcinomas. A not uncommon progression consists of calculi formation, pyogenic cholangitis, intrahepatic abscesses, and eventual cholangiocarcinoma.

In adults, Caroli’s disease can be suspected with most imaging (Fig. 7.5). Findings include hepatomegaly, parenchymal fibrosis, numerous cysts scattered throughout the liver, or multiple cyst-like dilated bile ducts. It is necessary to show that the cysts communicate with bile ducts to distinguish this condition from autosomaldominant polycystic disease and multiple

intrahepatic abscesses. Although some intrahepatic abscesses do communicate with bile ducts, differentiation of abscesses from dilated bile ducts is generally straightforward with cholangiography.

Ultrasonography reveals extensive collaterals and a prominent periportal hyperechoic pattern, a finding also seen in other conditions. Liver parenchymal texture tends toward a heterogeneous appearance containing multiple high echoes.

With progressive fibrosis adults tend to develop portal hypertension, generally attributable to intrahepatic compression of portal vein branches by fibrosis. Doppler US findings vary depending on underlying hemodynamics. Intrinsically, the portal vein is patent, although some patients have portal vein thrombosis and cavernous transformation.

Magnetic resonance cholangiography also detects cystic intrahepatic biliary dilation.

Technetium-99m-IDA scintigraphy reveals bile stasis in cystic structures. Scintigraphy confirms that these cysts communicate with the bile ducts.

Regardless of how it is performed, cholangiography confirms the diagnosis by identifying numerous segmental dilated intrahepatic bile ducts, either saccular or fusiform in appearance.

Hereditary Hemorrhagic

Telangiectasia (Osler-Weber-Rendu

Disease)

Hereditary hemorrhagic telangiectasia, or

Osler-Weber-Rendu disease, is an autosomaldominant disorder manifesting primarily by epistaxis, yet numerous vascular malformations consisting of telangiectasias, arteriovenous fistulas, and aneurysms in the liver, spleen, and other organs often have more serious ramifications. An association of hereditary hemorrhagic telangiectasia and familial juvenile polyposis has been described in several families. Liver arteriovenous malformations are associated with fibrosis and progression to cirrhosis. High output cardiac failure, liver failure, and orthotopic liver transplantation are not uncommon. Why fibrosis and atrophy of some segments and enlargement of others develop is unknown although focal ischemia appears to play a role.

Telangiectasia defines a collection of dilated small vessels. Dilated, tangled vascular communications are common and range from small to large confluent vascular masses. Arteriovenous communications are either to a hepatic or portal vein. Extensive arteriohepatic venous shunting leads to hepatomegaly and congestive heart failure or abdominal angina. Arterioportal shunting, on the other hand, tends to progress to portal hypertension.

In a setting of extensive vascular malformation, the hepatic artery blood flow increases and the artery and its branches dilate and become

tortuous. Arterial phase and portal venous phase CT detects arteriovenous shunting, and reveals enlarged feeding vessels and tangled vessels within a malformation.

Doppler US can screen relatives of patients with hereditary hemorrhagic telangiectasia to detect intrahepatic arteriovenous shunts. Dilated vessels tend to mimic bile ducts with gray-scale US, but color Doppler US waveforms should confirm extensive shunting and suggest the diagnosis. Doppler US shows a marked increase in hepatic artery mean velocity. Enlarged hepatic veins are common. In most

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patients portal venous blood velocity is unchanged compared to normals, except with an arterioportal or even portovenous shunt.

Contrast-enhanced MRI also identified shunting and simultaneous enhancement of both hepatic arteries and veins.

Angiography readily identifies multiple intrahepatic vascular malformations. The hepatic arteries have been successfully embolized in stages in symptomatic patients with hereditary hemorrhagic telangiectasia; this is not an innocuous procedure, however, and deaths from hepatic infarction and necrosis have been reported (13).

Trauma

Management Issues

Previously in a number of institutions peritoneal lavage was an initial diagnostic study performed in patients with suspected blunt abdominal trauma, and, if positive, the patient underwent laparotomy. It was difficult to evaluate outcomes of various liver injuries because investigators used their own nomenclature for liver injury. To overcome some of these problems, a liver injury classification scale was devised by the American Association for the Surgery of Trauma (Table 7.2).

Currently peritoneal lavage has been abandoned in favor of CT and a more conservative approach than used previously. Emergency CT has evolved as the first diagnostic procedure performed in trauma patients. It has led to more nonsurgical management of liver trauma, especially in hemodynamically stable patients. Even those with a moderate-to-large hemoperitoneum have been managed nonoperatively as long as the patient is hemodynamically stable. Thus some patients with grade III liver injuries are managed nonoperatively. Most blunt hepatic trauma in children is also managed conservatively without surgery; in general, the severity of injury as detected by CT does not correlate with a need for surgery.

Severe liver trauma (such as type V on the liver injury scale in Table 7.2) has a very poor prognosis. A majority of patients with grade V injuries are unstable and require laparotomy. The initial surgical concern is control of hemorrhage. One approach is percutaneous intraaortic balloon occlusion using a femoral route, followed by surgical vascular exclusion of the liver.

One complication of liver trauma is a subsequent abscess. Risk of developing an abscess is higher in patients undergoing surgery than in those managed nonoperatively. Presumably infection develops from infected bile or is spread hematogenously, with a hematoma or