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Pediatric liver magnetic resonance imaging
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Pediatric liver magnetic resonance imaging Marilyn J. Siegel, MD Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, St. Louis, MO 63110, USA
Imaging is a standard part of the evaluation of pediatric liver disease. Advances in MRI have improved the detection, characterization, and staging of hepatic lesions. Clinical information, however, is still important in selecting the best imaging study and in correctly interpreting the examination. This article addresses the clinical and imaging features of the common hepatic and biliary lesions in children. In addition, the techniques for performing hepatic MRI are reviewed. Clinical indications The common clinical applications for MRI studies of the liver in children include (1) determination of the extent and character of a hepatic mass, (2) determination of the presence or absence of parenchymal disease in patients with abnormal liver function tests or indeterminate CT examinations, (3) evaluation of the liver anatomy before transplantation and postoperative complications, and (4) evaluation of causes of neonatal jaundice. Technical factors Coils MRI examinations should be performed with the smallest coil that fits tightly around the body part being studied [1,2]. A head coil often is adequate in infants and small children, whereas a phased-array coil should be used in larger children and adolescents. Phased-array coils are surface coils that are placed around the abdomen, allowing the receiver coils to be in close proximity to the generated signal. This optimizes the signalto-noise ratio, which allows the use of thinner E-mail address: [email protected] (M.J. Siegel).
slices and enables higher resolution images compared with the standard body coil. Pulse sequences and scan planes At our institution, we routinely perform T1- and T2-weighted spin-echo sequences, unenhanced T1weighted gradient-echo sequences, and enhanced T1-weighted gradient-echo sequences. All images are acquired in the axial plane. The use of transaxial images for all pulse sequences, both enhanced and unenhanced, allows the character and extent of a lesion to be easily compared. The T1-weighted spin-echo image is also acquired in the coronal plane to further delineate anatomic relations. Spin-echo images Precontrast T1- and T2-weighted images are useful to improve confidence in lesion detection and characterization of blood and fat. The T1weighted images (short repetition time [TR], short echo time [TE]) provide excellent anatomic detail and superb contrast differentiation between fat and soft tissues. The T2-weighted spin-echo sequences (long TR, long TE) improve the contrast differentiation between normal and abnormal soft tissues. They require a relatively longer imaging time, however, and thus are subject to motion-related artifacts. Therefore, the T2weighted images are obtained using fast spin-echo sequences. These are significantly faster than the conventional T2-weighted sequences, but they are still equivalent to conventional spin-echo images for lesion detection and characterization [3–5]. There is a difference in image contrast, however. Fat has a higher signal intensity on the fastimaging sequences than it does on the conventional T2-weighted sequences. The T2-weighted images are usually obtained with fat-suppression techniques to improve the contrast-to-noise ratio.
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Unenhanced gradient-echo sequences Gradient-echo sequences (short TR, short TE, small flip angle) result in a high signal in flowing blood; hence, they are useful to assess the patency of hepatic vascular structures. They also can reduce imaging time. This affords the ability to perform dynamic imaging after the administration of gadolinium-chelate agents. Contrast-enhanced images Gadolinium-chelate compounds remain the contrast agent of choice to evaluate focal liver lesions [6,7]. Liver-specific contrast agents are available, including hepatocyte-specific and reticuloendothelial agents, but their role in liver imaging in children is still unclear. Gadolinium chelates are extracellular contrast agents. They rapidly equilibrate between intravascular and extravascular spaces, requiring dynamic imaging to maximize the differential enhancement of normal and abnormal parenchyma. Ideally, dynamic imaging should be performed by means of a breath-hold technique. Nevertheless, useful information can still be obtained in sedated children or younger children who are unable to suspend respiration. Sequential images are obtained through the liver during the arterial phase (20–30 seconds after injection), during the portal venous phase (60–80 seconds after injection), and at equilibrium (3 minutes after injection). Delayed images can be obtained if needed for further lesion characterization. The contrast material is given as a bolus injection followed by a saline flush, with the patient positioned inside the magnet. Optional imaging sequences Optional imaging techniques include spatial presaturation and chemical shift imaging. Spatial presaturation helps to characterize the direction of blood flow. This technique uses saturation bands cephalad and caudad to the imaging volume to saturate the spin in blood flowing into the slice volume, thus eliminating intravascular signal. With spatial presaturation, flowing blood appears black. Chemical shift imaging is helpful to detect intracellular fat. This technique exploits differences in relaxation times of fat and water. Gradient-echo images are obtained in-phase (TE ¼ 4.2 milliseconds, flip angle ¼ 70°, 1.5 T) and out-of-phase (also called opposed phase) (TE ¼ 2.1, flip angle ¼ 70°, 1.5 T). Fatty infiltration has an increased signal intensity on in-phase images and decreased signal intensity on out-ofphase images.
Other technical factors MRI scans are usually obtained with 4- to 8-mm interval sections and slice thickness and with 128 to 192 phase-encoding steps. The interval and thickness vary with patient size. Spatial resolution can be improved with the use of 256 phaseencoding steps, but this approach prolongs imaging time. Normal liver The signal intensity of normal hepatic parenchyma is slightly greater than that of muscle on both T1- and T2-weighted images. The normal liver enhances after the administration of gadolinium-chelate agents. The vascular anatomy of the liver, which defines the lobes and segments of the liver, is easily shown on MRI. Traditionally, the liver is divided into right and left lobes by the middle hepatic vein superiorly and by the gallbladder fossa inferiorly. The right lobe is divided into anterior and posterior segments by the right hepatic vein. The left lobe is divided into medial and lateral segments by the left hepatic vein superiorly and by the fissure for the ligamentum teres inferiorly. This traditional classification makes no distinction between the superior and inferior divisions of each major segment. In the classification system of Couinaud, the hepatic segments are divided not only by three vertical planes along the hepatic veins but by a transverse plane defined by the portal venous supply [8]. Eight segments are defined by this system. Each segment has separate afferent and efferent vessels and biliary channels. This classification is widely used because it divides the liver into segments that are surgically resectable [9,10]. Suspected liver mass Primary hepatic neoplasms constitute between 0.5% and 2.0% of pediatric tumors and are the third most common abdominal malignancy in childhood after Wilms tumor and neuroblastoma [11]. The common presentation of benign and malignant liver masses is a palpable mass on physical examination. Malignant neoplasms are usually hepatoblastomas or hepatocellular carcinoma; less often, they include lymphoproliferative disorder, lymphoma, metastatic disease, undifferentiated (embryonal) sarcoma, and primary endodermal sinus tumor
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[11,12]. Benign lesions are usually hemangioendothelioma; less commonly, they include mesenchymal hamartoma, cavernous hemangioma, focal nodular hyperplasia, and hepatic adenoma [13–16]. Clinical information plays an important role in narrowing the differential diagnosis in cases where the imaging findings are nonspecific. Patient age, clinical signs and symptoms, and a-fetoprotein levels, are critical discriminators in the evaluation of hepatic tumors. Age is an important factor, because the incidence of various neoplasms varies in specific age groups. Hemangioendothelioma is the most common mass in the first 6 months of life. Hepatoblastoma, mesenchymal hamartoma, and metastatic disease from neuroblastoma or Wilms tumor is usually present in the first 3 years of life. Hepatocellular carcinoma, undifferentiated (embryonal) metastases from lymphoma, focal nodular hyperplasia, and hepatic adenoma usually occur in older children and adolescents. The clinical presentation also can suggest a specific diagnosis. Congestive heart failure in a neonate with a liver mass suggests a diagnosis of hemangioendothelioma, whereas a history of immunosuppression in a transplant patient suggests lymphoproliferative disorder or fungal abscesses [17]. Laboratory findings, particularly serum a-fetoprotein levels, can be important in making a diagnosis. Certain liver tumors, such as hepatoblastoma and hepatocellular carcinoma, are associated with elevated serum a-fetoprotein levels [11]. Imaging strategies Although the presence of an abdominal mass is often evident on physical examination, the organ of origin is often uncertain. The role of imaging is to determine the organ of origin as well as the character and extent of the lesion. The evaluation of pediatric hepatic masses relies on the use of cross-sectional imaging examinations, such as ultrasonography (US), CT, and MRI [17–19]. US is readily available, fast, and relatively inexpensive. It can usually reveal the location, extent, and solid or cystic nature of a mass and assess vascular invasion. Because of these advantages, US usually is considered the screening technique of choice for evaluation of a pediatric abdominal mass. If the sonogram is normal, further radiographic evaluation generally is not required. If US cannot yield adequate information, or if it suggests a mass, further evaluation with either CT or MRI is needed [13–17,20,21]. The selection
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of one of these two examinations is usually based on personal expertise and availability of the equipment. CT scanning is generally used more often than MRI because it is more widely available and can provide excellent anatomic detail. If CT cannot assess the extent of tumor or depict vascular structures, which is important information in assessing resectability, MRI is performed. Because it has excellent soft tissue contrast, MRI can play an important role in determining the extent of hepatic neoplasms. Primary malignant neoplasms The major role of imaging is to define the extent of the lesion and its relation to lobar and segmental anatomy and vascular structures for preoperative planning and to monitor the response of the tumor to chemotherapy or radiation [10,15]. Most hepatic malignancies can be cured only with complete resection of the primary tumor or liver transplantation [11,22]. Four types of liver resection are performed: right lobectomy, left lobectomy; left lateral segmentectomy, and trisegmentectomy (right lobe and medial segment of the left lobe) [9]. Complete excision is possible in 50% to 60% of cases of hepatoblastoma and in about one third of cases of hepatocellular carcinomas in children [11,14]. Chemotherapy has been used as an adjuvant in tumors that are completely excised as well as in those tumors that are initially nonresectable. If the tumor decreases in size and meets the anatomic criteria for resection, the patient undergoes surgery. If the tumor is still unresectable, liver transplantation is considered [23]. Hepatoblastoma and hepatocellular carcinoma Hepatoblastoma Hepatoblastoma is the most common primary liver tumor of childhood. The tumor usually affects infants and young children. The median age at diagnosis is 1 year. Conditions associated with an increased risk of hepatoblastoma include Beckwith-Wiedemann syndrome, hemihypertrophy, fetal alcohol syndrome, familial polyposis coli, and Gardner’s syndrome [14,17,21]. Hepatoblastoma most often presents as an asymptomatic mass. Other features include abdominal pain, anorexia, weight loss, jaundice, and precocious puberty (related to the secretion of chorionic gonadotropins). Some degree of osteopenia is present in all patients, and severe osteopenia is present in 20% to 30% of patients.
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Serum a-fetoprotein levels are elevated in 80% to 90% of patients with hepatoblastomas [11,14]. Pathologically, hepatoblastoma contains small primitive epithelial cells resembling fetal liver and occasionally mesenchymal elements. The tumor is usually unifocal, and the right lobe of the liver is most often affected. Multifocal disease or diffuse infiltration can occur, however. The tumor has no association with cirrhosis. Metastatic disease occurs in approximately 10% to 20% of patients [14]. Metastases are chiefly to the lungs and porta hepatis and less commonly to the brain and skeleton. The overall 2-year survival rate for patients with hepatoblastoma is approximately 65% [14]. Hepatocellular carcinoma Hepatocellular carcinoma is the second most common pediatric liver malignancy after hepatoblastoma. In the pediatric population, patients with hepatocellular carcinoma have a median age of 12 years, with a range of 5 to 15 years, and the disease is relatively rare in patients younger than 5 years of age [11,14]. Preexisting liver disease, such as hepatitis B infection, type I glycogen storage disease, tyrosinemia, familial cholestatic cirrhosis, hemochromatosis, or a1-antitrypsin deficiency, is present in approximately one half of cases [21,22,24]. Abdominal distention and a right upper quadrant mass are the most common presenting features of hepatocellular carcinoma in children. Serum a-fetoprotein levels are elevated in up to 50% of cases [11]. Pathologically, hepatocellular carcinoma consists of large, pleomorphic, multinucleated cells with variable degrees of differentiation [11]. The tumor is often locally invasive or multifocal at the time of diagnosis such that resection is possible in fewer than 30% of patients. The 2-year survival rate is less than 30% [22]. MRI appearance Hepatoblastoma and hepatocellular carcinoma have similar imaging features. Both tumors are usually solitary masses, but they may be multifocal or, less commonly, diffusely infiltrating. The right lobe is involved twice as often as the left lobe. Both hepatoblastomas and hepatomas have a tendency to invade vascular structures, the portal vein more commonly than the hepatic vein. Portal venous invasion or compression results in obstruction of blood flow to the involved segment. Malignant hepatic lesions are usually predominantly hypointense relative to normal liver on T1weighted images and hyperintense on T2-weighted
images (Figs. 1–3). Other appearances are not uncommon, especially in hepatocellular carcinoma, and include either isointensity or hyperintensity on T1- and T2-weighted sequences, hypointensity on T1-weighted images and isointensity on T2-weighted images, and isointensity on T1-weighted images and hyperintensity on T2-weighted images [25]. After gadolinium administration, hepatoblastoma and hepatocellular carcinoma show immediate diffuse homogeneous or heterogeneous enhancement followed by rapid washout. The degree of enhancement is related to the extent of arterial hypervascularity. Internal heterogeneity is common as a result of areas of hemorrhage, fat, or necrosis and is seen better on T2-weighted images than on T1weighted images [21,26,27]. Hemorrhage can appear hypo- or hyperintense on T1-weighted pulse sequences; depending on the age of the blood; it usually is hyperintense on T2-weighted images. Necrosis is hypointense on T1-weighted images and hyperintense on T2-weighted images. Steatosis appears hyperintense on conventional T1- and T2-weighted spin-echo images and hypointense on fat-suppressed images. Vascular invasion causes a focus of increased signal within a normally echo-free vessel on spin-echo sequences and a low intensity area on gradient-echo imaging. Biliary ductal dilatation is rare but may be seen when there is ductal compression by the tumor. Other hepatic malignancies Fibrolamellar hepatocellular carcinoma Fibrolamellar hepatocellular carcinoma is a rare histologic subtype of hepatocellular carcinoma with distinctive clinical and pathologic features [28–30]. It occurs predominantly in adolescents and young adults without underlying hepatic disease. Histologically, the tumor contains eosinophilic-laden hepatocytes that are separated into cords by multilamellated fibrous bands. Some tumors have a central scar. Hepatomegaly and abdominal pain are common presenting features. Fibrolamellar hepatocellular carcinoma is less aggressive than the typical variety of hepatocellular carcinoma, and patients have a more favorable prognosis [11,29]. Serum a-fetoprotein levels are usually normal. Fibrolamellar carcinoma is commonly solitary and well marginated. On MRI, it is heterogeneous, predominantly hypointense on T1-weighted images, and hyperintense on T2-weighted images (Fig. 4). Less often, it appears isointense on both T1- and T2-weighted images [27,29,31]. On
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dynamic gadolinium-enhanced images, the tumor shows immediate diffuse heterogeneous enhancement [31]. The central scar is hypointense on T1and T2-weighted images and does not enhance on delayed images after contrast administration. The
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signal intensity of the central scar can be helpful in differentiating fibrolamellar carcinoma from focal nodular hyperplasia. The scar in focal nodular hyperplasia is hyperintense on T2-weighted images and shows delayed enhancement (see below).
Fig. 1. Hepatoblastoma in a 3-year-old boy. (A) T1-weighted axial MRI (repetition time [TR] ¼ 525 milliseconds, echo time [TE] ¼ 10 milliseconds) shows a slightly hypointense mass involving both lobes of the liver. The right portal vein (arrows) is splayed and displaced posteriorly. (B) On T2-weighted MRI (TR ¼ 2415 milliseconds, TE ¼ 90 milliseconds), the signal intensity of the mass increases relative to normal parenchyma and approximates that of subcutaneous fat. (C) Fat-suppressed gradient-echo MRI (TR ¼ 155 milliseconds, TE ¼ 4 milliseconds, flip angle ¼ 70°) during the arterial phase (0 minutes after injection of gadolinium) shows a heterogenously enhancing mass. (D) On a delayed MRI scan during the portal venous phase (5 minutes after injection), the tumor has become slightly hypointense to normal parenchyma. In this patient, the tumor margins and relation of the tumor to the hepatic vasculature were seen better on MRI than on CT. This patient received chemotherapy and then underwent a trisegmentectomy.
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Fig. 1 (continued )
Undifferentiated (embryonal) sarcoma Undifferentiated embryonal sarcoma (also known as malignant mesenchymoma or hepatic mesenchymal sarcoma) is a rare malignancy that primarily affects older children and adolescents. More than 50% of cases are diagnosed in patients between 6 and 10 years of age, and 90% occur by 15 years of age [14,21,32,33]. Clinical findings include fever, a painful mass, and normal levels of a-fetoprotein. Grossly, the tumor is a large mass, ranging from 7 to 20 cm in diameter. It contains cystic spaces as well as cellular areas. Histologically, undifferentiated embryonal sarcoma contains un-
differentiated sarcomatous tissue in a myxoid matrix [27]. The prognosis is poor, with a median survival time of approximately 1 year [33]. On T1-weighted MR sequences, the cystic parts of the tumor are predominantly hypointense relative to normal liver. Focal areas of increased signal intensity representing hemorrhage may be seen. On T2-weighted images, embryonal sarcoma is predominantly hyperintense. The septa are hypointense on both pulse sequences. On gradient-echo images, the solid areas enhance and the cystic spaces appear hypointense (Fig. 5). Metastases are to the lungs and bone.
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Fig. 2. Multifocal hepatoblastoma. T1-weighted (450/10) image. Numerous intermediate signal intensity masses replace both lobes of the liver.
Hepatic metastases The malignant tumors of childhood that most frequently metastasize to the liver are Wilms tumor, neuroblastoma, rhabdomyosarcoma, and lymphoma. Neuroblastoma may affect the liver in either stage IV or stage IV-S disease. Stage IV disease is characterized by the presence of a retroperitoneal mass and distant metastases to the skeleton, liver, or nodes. Stage IV-S neuroblastoma occurs in patients under 1 year of age, who have small ipsilateral tumors (not crossing the midline)
and metastases to the liver, skin, and bone marrow but not to cortical bone. Clinically, patients with hepatic metastases present with hepatomegaly, jaundice, abdominal pain or a mass, or abnormal hepatic function test results. Hepatic metastases are typically multiple and well circumscribed. They usually are hypointense on T1-weighted MRI and hyperintense on T2weighted MRI, and they may be homogeneous or heterogeneous (Figs. 6 and 7). Other findings include mass effect with displacement of vessels and vessel invasion or amputation.
Fig. 3. Hepatocellular carcinoma in a 14-year-old girl. (A) T1-weighted (450/10) image shows a large hypointense tumor (T) in the right hepatic lobe and a small satellite lesion (open arrows) in the lateral segment of the left lobe. (B) On the T2weighted (3150/120) image, both lesions increase in signal intensity.
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Fig. 4. Fibrolamellar hepatocellular carcinoma. (A) T1-weighted (300/10) image shows a hypointense mass (arrows) in the left hepatic lobe. (B) The mass (arrow) becomes slightly hyperintense to adjacent liver on the T2-weighted (3150/120) image. The lesion has caused biliary ductal dilatation. The dilated bile ducts appear as hypointense channels on T1weighted images and as hyperintense channels on T2-weighted images.
Most metastatic lesions are hypovascular on the arterial and portal venous phases of enhancement, although they may show peripheral (ring) enhancement during the hepatic arterial phase. Hypervascular tumors are rare in children. These include sarcomas, renal cell carcinoma, pancreatic islet cell tumors, and thyroid tumors. Hypervascular metastases appear as hyperintense masses during the hepatic arterial phase
and become isointense during the redistribution phase. Diffuse replacement of the liver by metastatic disease is usually secondary to stage IV-S neuroblastoma. MRI shows widespread heterogeneity. The differential diagnostic considerations for this appearance include hepatic fibrosis, cirrhosis, fatty infiltration, and diffuse infiltrating hepatoblastoma or hepatocellular carcinoma.
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Fig. 5. Embryonal sarcoma. (A) T1-weighted (350/11) image shows a hypointense mass (curved arrows) replacing most of the right hepatic lobe. (B) After administration of gadolinium-chelate agents, the solid components in the tumor enhance. The cystic areas remain hypointense (ie, black). (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
Benign neoplasms Angiomatous lesions Hemangioendothelioma Hemangioendothelioma is the most common benign hepatic tumor of childhood [16,21,34,35]. Most affected patients are young infants less than 6 months old who present with congestive heart failure as a result of high-output overcirculation. Occasionally, these patients present with asymptomatic hepatomegaly, thrombocytopenia in association with a consumptive coagulopathy (Kasabach-Merritt syndrome), or massive hemoperitoneum as a result of tumor rupture.
Histologically, hemangioendothelioma is a vascular tumor arising from the supporting tissue (mesenchyme) of the liver. Two types of infantile hemangioma have been described. Type I is composed of a network of vascular channels lined by plump endothelial cells that are supported by reticular fibers. Type II contains larger and more irregular branching spaces lined by immature pleomorphic cells. This form has some malignant potential, and transformation into angiosarcoma has been described, but this is a rare complication [36–38]. Areas of fibrosis, calcification, hemorrhage, and cystic degeneration are common in larger lesions. Hemangiomas may be solitary or multifocal masses.
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Fig. 6. Hepatic metastases from rhabdomyosarcoma. T2-weighted (4000/120) image shows multiple hyperintense hepatic masses.
Cavernous hemangioma Cavernous hemangioma is the most common benign tumor of the liver in adults. Although it can occur in children, it is a rare lesion. It is usually asymptomatic and detected as an incidental finding on sonography, CT, or MRI.
Microscopically, cavernous hemangiomas are composed of multiple blood-filled spaces that are lined by a single layer of flat endothelial cells supported by fibrous septa. On cut sections, hemangiomas are often heterogeneous with areas of fibrosis, hemorrhage, necrosis, or cystic change.
Fig. 7. Metastatic lymphoma. T2-weighted (2700/90) image shows a solitary metastasis in the right hepatic lobe that is mildly hyperintense to surrounding tissue.
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Malignant potential is absent. Most are solitary and found in the periphery of the posterior segment of the right lobe.
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steroids, and interferon. If these methods fail, chemotherapy, irradiation, or embolic or surgical treatment may be required for treatment [43–45]. Mesenchymal hamartoma
MRI appearance Hemangioendothelioma and cavernous hemangioma tend to be well-circumscribed lesions. Characteristically, they are hypointense compared with normal liver on T1-weighted images and markedly hyperintense on T2-weighted images (Fig. 8). Signal intensity is often heterogeneous because of the presence of hemorrhage, necrosis, and fibrosis [21,27,34,39]. Internal heterogeneity is especially common in larger lesions. Dynamic imaging with gadolinium-chelate agents may show three patterns of enhancement depending on the size of the lesion [40,41]: complete early enhancement (usually small lesions), peripheral nodular enhancement progressing centripetally to complete central enhancement (Fig. 9), and peripheral nodular enhancement with a persistent central hypointense area. A secondary finding in neonates with multiple hemangioendotheliomas is a small infrahepatic aorta distal to the level of the celiac artery. This is related to shunting of blood into the tumor via the celiac artery. Because hemangioendotheliomas have a natural history of regression and involution within 12 to 18 months [42], the initial treatment is medical management, including digitalis, diuretics,
Mesenchymal hamartoma is a benign hepatic tumor that arises from the mesenchyme of the portal tract [21,27,46,47]. On gross pathologic sections, it is a well-circumscribed mass that is usually large (range: 5–20 cm) and commonly located in the right lobe of the liver. On cut sections, it is composed of multiple cystic spaces ranging from a few millimeters to 15 cm in diameter [47]. These spaces contain watery or gelatinous material and are separated by fibrous stroma containing mesenchyme, abnormal bile ducts, and hepatocytes. Most affected children are under 3 years of age, and the tumor is slightly more common in boys than in girls. Affected patients usually present with an asymptomatic abdominal mass or abdominal distention. Ascites as a result of cyst rupture or congestive heart failure caused by arteriovenous shunting is an uncommon presenting sign [48]. Treatment is surgical resection. Malignant transformation to mesenchymal hamartoma has been reported but is rare [49]. On MRI, mesenchymal hamartoma appears as a well-circumscribed multilocular mass containing fluid-filled locules intermixed with thin septa (Fig. 10) [14,21,27,46]. The cystic locules have low signal intensity on T1-weighted sequences and high signal intensity on T2-weighted sequences. The signal intensity on the T1-weighted images may increase if the tumor contains large amounts of protein or debris, however [27]. The stromal components may enhance after the administration of gadolinium-chelate agents. Epithelial lesions
Fig. 8. Multiple hemangioendotheliomas in a newborn girl. T2-weighted spin-echo image shows multiple lesions that are markedly hyperintense to the normal liver parenchyma. (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
Focal nodular hyperplasia Focal nodular hyperplasia and hepatic adenomas are uncommon lesions in childhood, accounting for less than 5% of hepatic tumors. Focal nodular hyperplasia is slightly more common than hepatic adenomas. It is a tumor-like condition that is thought to be a result of hyperplasia of normal hepatocytes caused by a vascular malformation [50]. Grossly, focal nodular hyperplasia is a well-circumscribed and usually solitary mass that is often in a subcapsular location or pedunculated. Histologically, it is composed of normal hepatocytes, bile ducts, blood vessels, and Kupffer cells, and it often contains a central fibrous scar. Internal
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hemorrhage and necrosis are usually absent, because the growth of the lesion remains proportional to its blood supply. There is no strong association with preexisting abnormalities. The lesion is most often an incidental finding on imaging examinations. Patients with large lesions may present with hepatomegaly or right upper quadrant discomfort, however. Because focal nodular hyperplasia comprises normal hepatocytes with an abnormal architecture, the signal characteristics of the lesion are often similar to those of normal liver. Focal nod-
ular hyperplasia is iso- or hypointense on T1weighted images and iso- or slightly hyperintense to normal hepatic parenchyma on T2-weighted images [46,50,51]. Similarly, the central scar is hypointense on T1-weighted images and hyperintense on T2-weighted images. Small calcifications have been reported, although they are rare, occurring in less than 5% of tumors [52]. On contrast-enhanced dynamic MRI, focal nodular hyperplasia becomes hyperintense during the arterial and early portal venous phases and isointense to normal parenchyma during the equilibrium phase and on
Fig. 9. Cavernous hemangioma. (A) Precontrast gradient-echo (200/6.1/70°) image shows a hypointense lesion in the right lobe posteriorly. (B) Early contrast-enhanced gradient-echo image shows peripheral enhancement in the lesion. (C) An image 2 minutes later shows nearly complete enhancement of the mass.
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Fig. 9 (continued )
delayed images (Fig. 11). The central scar may become hyperintense on late images. This appearance is in contrast to the low signal intensity of the central scar in fibrolamellar hepatocellular carcinoma.
Hepatic adenomas Hepatic adenoma in childhood has been associated with type I glycogen storage disease (von Gierke’s disease), Fanconi’s anemia, and galactosemia. Histologically, it is composed of cords of
Fig. 10. Mesenchymal hamartoma. T2-weighted (3500/85) image shows a well-circumscribed hyperintense mass in the dome of the liver. Several septations can be noted. (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
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Fig. 11. Focal nodular hyperplasia. (A) A precontrast gradient-echo image shows a slightly hypointense mass (arrowheads) in the right hepatic lobe. (B) On the fat-saturated turbo T2-weighted image, the lesion (arrowheads) is isointense to adjacent parenchyma and contains a small hypointense scar (arrow). (C) Postcontrast gradient-echo image. The lesion (arrowheads) is mildly hyperintense to adjacent parenchyma on an early image acquired after the administration of gadolinium-chelate agent. The central scar is hypointense. (D) Postcontrast gradient-echo image. The lesion (arrowheads) becomes isointense during the redistribution (portal venous) phase of contrast enhancement.
normal hepatocytes. The hepatocytes contain fat and glycogen, which contribute to the imaging characteristics. Bile ducts and portal tracts are absent. Patients may be asymptomatic or may present with hepatomegaly or mild right upper quadrant pain. Rarely, hepatic adenoma causes acute abdominal pain secondary to tumor infarction, hemorrhage, or rupture. Hepatic adenomas are heterogeneous lesions. They usually contain hyperintense areas on T1weighted images as a result of the presence of hemorrhage, glycogen, or fat and hypointense areas resulting from necrosis [46,53]. On T2-
weighted images, they are usually hyper- or isointense to normal parenchyma [53]. On contrast-enhanced images, most adenomas become hyperintense in the arterial phase and isointense to adjacent parenchyma on delayed images. Hepatic cysts Hepatic cysts are rare in children. Congenital cysts arise from intrahepatic biliary ducts that fail to involute. Acquired cysts are the result of inflammation, trauma, or parasitic disease. Hepatic cysts may be multiple or solitary. Multiple cysts
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are usually seen in association with autosomal dominant polycystic disease. Most cysts are detected incidentally on imaging studies, although large ones may present as an abdominal mass or hepatomegaly. The classic features of a cyst on any imaging examination are a unilocular, round, or oval mass with thin and well-circumscribed walls [18,19]. Simple cysts are hypointense on T1-weighted images and markedly hyperintense on T2-weighted images (Fig. 12). Cysts do not enhance on contrast-enhanced dynamic MRI studies. Other cystic masses, including metastases, echinococcal cyst, biloma, chronic hematoma, and abscess, may have signal intensities identical to those of simple hepatic cysts. Atypical features, such as a thick wall, internal septations, mural nodules, or a high T1-weighted signal intensity, should suggest a lesion other than a simple cyst.
Artifacts in tumor imaging Focal hepatic lesions may be simulated by hypointense veins on spin-echo images (because of the flow void phenomenon), aortic pulsation artifacts, respiratory-related ghosting artifacts,
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cardiac pulsations, and fatty infiltration. Artifacts from respiratory motion, poor tissue contrast as a result of inadequate T1 or T2 weighting, and susceptibility artifacts may obscure hepatic lesions. Diffuse parenchymal disease Steatosis Hepatic steatosis is the result of excessive accumulation of triglycerides within hepatocytes. There are two morphologic types of hepatic steatosis: microvacuolar and macrovacuolar [54]. In microvacuolar steatosis, tiny fat droplets or vacuoles fill the cell without displacing the nucleus. It is seen in association with Reye’s syndrome and massive tetracycline therapy. Patients are acutely ill and present with a painful liver, vomiting, jaundice, and coma. Microvacuolar steatosis is rarely reversible. In the macrovacuolar type of steatosis, large droplets of fat fill the hepatocyte without expanding it and push the nucleus against the cell wall. Macrovacuolar steatosis is usually clinically silent, but it may be associated with hepatomegaly or right upper quadrant pain. It is associated with nutritional abnormalities (eg, kwashiorkor, obesity, intestinal bypass), metabolic diseases, drug
Fig. 12. Hepatic cyst. T2-weighted spin-echo (4000/160) image shows a small, well-defined, hyperintense lesion (arrow) in the right hepatic lobe. The lesion did not enhance after administration of gadolinium-chelate agents, distinguishing it from a vascular lesion.
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or corticosteroid use, and viral infections. Macrovacuolar steatosis is reversible if the underlying abnormality can be corrected. Steatosis may be diffuse or focal. Conventional spin-echo sequences can be relatively insensitive for detecting diffuse fatty infiltration, especially if there is only mild or moderate fat deposition. Focal fatty infiltration can be easy to detect, appearing as an area of high signal intensity on T1-weighted spin-echo images, but it is not usually visible on conventional T2-weighted images. Fat-suppression techniques and opposedphase gradient-echo imaging are more sensitive techniques for detecting fat deposition. On opposed-phase images, areas of fatty replacement show relative signal loss and thus appear hypointense (Fig. 13). Focal steatosis has several other features that can be helpful in differentiating it from mass lesions. It often has a segmental or wedge-shaped configuration, and it characteristically produces no mass effect or bulging of the hepatic margin. Vessels often can be seen traversing the areas of focal fatty metamorphosis, and they maintain a normal branching pattern. Moreover, focal fatty replacement often occurs in typical locations, usually anterior to the portal vein or adjacent to the fissure for the ligamentum teres.
The signal alteration is usually diffuse, but it can be focal on rare occasions.
Liver transplantation MRI can be useful for evaluating hepatic vasculature and calculating liver volume before transplantation. The presence of abnormalities that can alter the surgical approach, including a thrombosed portal vein or anatomic variants, such as interruption of the inferior vena cava, preduodenal portal vein, and anomalous hepatic arterial supply, can be easily seen by MRI [56].
Iron overload Hemochromatosis refers to increased deposition of iron within the parenchymal cells of the liver and other organs (including the pancreas, kidneys, bowel, and heart) with resultant organ damage. It can be further categorized as primary or secondary [55]. Primary hemochromatosis is an inherited disorder caused by an inborn error of metabolism, which leads to increased absorption of ingested iron. Secondary hemochromatosis is usually found in patients who receive multiple blood transfusions for chronic anemia. Other causes include excessive iron ingestion, congenital transferring deficiency, and cirrhosis. Secondary hemochromatosis is more common than primary hemochromatosis in the pediatric population. MRI is sensitive for detecting clinically significant iron overload in the liver. The characteristic finding of excess iron deposition is a low hepatic signal intensity. The reduction in signal intensity is a result of the paramagnetic effect of the ferric ions, which causes shortening of the T1 and T2 relaxation protons. The T2 shortening is seen best on T2-weighted or gradient-echo images (Fig. 14).
Fig. 13. Focal hepatic steatosis. (A) T1-weighted (725/ 15) image shows homogeneous liver parenchyma. (B) Opposed-phase T1-weighted gradient-echo image (176/ 7.0/70°). The right lobe anteriorly (arrows) is hypointense as a result of focal fatty replacement.
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Fig. 14. Hemochromatosis. Gradient-echo (155/4.0/70°) image shows a diffusely hypointense liver as a result of iron deposition. The patient had received multiple blood transfusions for sickle cell anemia.
After transplantation, MRI is useful for evaluating suspected complications, including infarction, vascular thrombosis or stenosis, hepatic artery pseudoaneurysm, and biliary obstruction.
axial planes using a two-dimensional multislice acquisition mode. Source images are postprocessed using a maximum-intensity projection algorithm to produce reconstructed three-dimensional models. Biliary atresia and neonatal hepatitis
Neonatal jaundice The three most common causes of jaundice in neonates are biliary atresia, neonatal hepatitis, and choledochal cyst [57]. US is the preliminary imaging procedure used to detect intrahepatic ductal dilatation associated with obstruction as well as cystic diseases. This can be supplemented by radionuclide studies using hepatobiliary imaging agents [58–60]. MR cholangiography has proven to be a useful noninvasive alternative to endoscopic retrograde pancreatography to delineate the anatomy of the biliary system when the results of sonography or CT are indeterminate or additional information is needed for surgical planning [61–66]. This technique is performed with two-dimensional, fat-suppressed, turbo T2-weighted, spin-echo sequences. Images are acquired by means of a breath-hold technique in cooperative children. In neonates, in whom non-breath-hold techniques are required, the signal acquisitions can be increased to increase the signal-to-noise ratio and to compensate for motion. Images are obtained in the coronal and
Distinguishing between neonatal hepatitis and biliary atresia is important, because neonatal hepatitis is managed medically, whereas biliary atresia requires early surgical intervention to prevent biliary cirrhosis [57,67]. MR cholangiopancreatography can help to differentiate between these two conditions [61,63]. Extrahepatic ducts are usually visualized in neonates with hepatitis, whereas they are usually absent in neonates with biliary atresia. Choledochal cyst A choledochal cyst is a congenital cystic or fusiform dilatation of the common bile duct. It is usually diagnosed in infancy or childhood, but the condition can be recognized first in adolescents or adults. The classic clinical presentation includes jaundice, abdominal pain, and mass, although this triad occurs in only 20% to 50% of patients [59]. Choledochal cysts can be classified into five types. A type 1 cyst (80–90% of cases) is characterized by
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Fig. 15. Choledochal cyst in a 2-year-old boy with jaundice. Axial (A) and coronal (B) fat-suppressed turbo T2-weighted (3157/189/90°) images demonstrate a high signal intensity cyst (C) in the porta hepatis separate from the gallbladder (g). (Courtesy of Peter Strouse MD, Ann Arbor, MI.)
dilatation of the common bile duct. A type 2 cyst is a true diverticulum arising from the common duct. A type 3 cyst is a choledochocele involving only the intraduodenal portion of the duct. A type
4 cyst is characterized by multiple extrahepatic cysts, and the intrahepatic ducts may or may not be dilated. A type 5 cyst, or Caroli’s disease, is characterized by multiple intrahepatic cysts [68].
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Choledochal cysts in neonates and young infants may coexist with biliary atresia [69]. The cause of choledochal cysts is unknown, but it is postulated that an anomalous pancreaticobiliary junction is the initiating factor. This anomaly results in chronic reflux of pancreatic enzymes into the biliary tree, which leads to inflammation, dilatation, and scarring. The dilated common and intrahepatic bile ducts as well an anomalous pancreaticobiliary junction can be easily shown by MR cholangiography (Fig. 15) [64].
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Pediatric liver magnetic resonance imaging Marilyn J. Siegel, MD Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, St. Louis, MO 63110, USA
Imaging is a standard part of the evaluation of pediatric liver disease. Advances in MRI have improved the detection, characterization, and staging of hepatic lesions. Clinical information, however, is still important in selecting the best imaging study and in correctly interpreting the examination. This article addresses the clinical and imaging features of the common hepatic and biliary lesions in children. In addition, the techniques for performing hepatic MRI are reviewed. Clinical indications The common clinical applications for MRI studies of the liver in children include (1) determination of the extent and character of a hepatic mass, (2) determination of the presence or absence of parenchymal disease in patients with abnormal liver function tests or indeterminate CT examinations, (3) evaluation of the liver anatomy before transplantation and postoperative complications, and (4) evaluation of causes of neonatal jaundice. Technical factors Coils MRI examinations should be performed with the smallest coil that fits tightly around the body part being studied [1,2]. A head coil often is adequate in infants and small children, whereas a phased-array coil should be used in larger children and adolescents. Phased-array coils are surface coils that are placed around the abdomen, allowing the receiver coils to be in close proximity to the generated signal. This optimizes the signalto-noise ratio, which allows the use of thinner E-mail address: [email protected] (M.J. Siegel).
slices and enables higher resolution images compared with the standard body coil. Pulse sequences and scan planes At our institution, we routinely perform T1- and T2-weighted spin-echo sequences, unenhanced T1weighted gradient-echo sequences, and enhanced T1-weighted gradient-echo sequences. All images are acquired in the axial plane. The use of transaxial images for all pulse sequences, both enhanced and unenhanced, allows the character and extent of a lesion to be easily compared. The T1-weighted spin-echo image is also acquired in the coronal plane to further delineate anatomic relations. Spin-echo images Precontrast T1- and T2-weighted images are useful to improve confidence in lesion detection and characterization of blood and fat. The T1weighted images (short repetition time [TR], short echo time [TE]) provide excellent anatomic detail and superb contrast differentiation between fat and soft tissues. The T2-weighted spin-echo sequences (long TR, long TE) improve the contrast differentiation between normal and abnormal soft tissues. They require a relatively longer imaging time, however, and thus are subject to motion-related artifacts. Therefore, the T2weighted images are obtained using fast spin-echo sequences. These are significantly faster than the conventional T2-weighted sequences, but they are still equivalent to conventional spin-echo images for lesion detection and characterization [3–5]. There is a difference in image contrast, however. Fat has a higher signal intensity on the fastimaging sequences than it does on the conventional T2-weighted sequences. The T2-weighted images are usually obtained with fat-suppression techniques to improve the contrast-to-noise ratio.
1064-9689/02/$ - see front matter Ó 2002, Elsevier Science (USA). All rights reserved. PII: S 1 0 6 4 - 9 6 8 9 ( 0 1 ) 0 0 0 0 6 - X
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Unenhanced gradient-echo sequences Gradient-echo sequences (short TR, short TE, small flip angle) result in a high signal in flowing blood; hence, they are useful to assess the patency of hepatic vascular structures. They also can reduce imaging time. This affords the ability to perform dynamic imaging after the administration of gadolinium-chelate agents. Contrast-enhanced images Gadolinium-chelate compounds remain the contrast agent of choice to evaluate focal liver lesions [6,7]. Liver-specific contrast agents are available, including hepatocyte-specific and reticuloendothelial agents, but their role in liver imaging in children is still unclear. Gadolinium chelates are extracellular contrast agents. They rapidly equilibrate between intravascular and extravascular spaces, requiring dynamic imaging to maximize the differential enhancement of normal and abnormal parenchyma. Ideally, dynamic imaging should be performed by means of a breath-hold technique. Nevertheless, useful information can still be obtained in sedated children or younger children who are unable to suspend respiration. Sequential images are obtained through the liver during the arterial phase (20–30 seconds after injection), during the portal venous phase (60–80 seconds after injection), and at equilibrium (3 minutes after injection). Delayed images can be obtained if needed for further lesion characterization. The contrast material is given as a bolus injection followed by a saline flush, with the patient positioned inside the magnet. Optional imaging sequences Optional imaging techniques include spatial presaturation and chemical shift imaging. Spatial presaturation helps to characterize the direction of blood flow. This technique uses saturation bands cephalad and caudad to the imaging volume to saturate the spin in blood flowing into the slice volume, thus eliminating intravascular signal. With spatial presaturation, flowing blood appears black. Chemical shift imaging is helpful to detect intracellular fat. This technique exploits differences in relaxation times of fat and water. Gradient-echo images are obtained in-phase (TE ¼ 4.2 milliseconds, flip angle ¼ 70°, 1.5 T) and out-of-phase (also called opposed phase) (TE ¼ 2.1, flip angle ¼ 70°, 1.5 T). Fatty infiltration has an increased signal intensity on in-phase images and decreased signal intensity on out-ofphase images.
Other technical factors MRI scans are usually obtained with 4- to 8-mm interval sections and slice thickness and with 128 to 192 phase-encoding steps. The interval and thickness vary with patient size. Spatial resolution can be improved with the use of 256 phaseencoding steps, but this approach prolongs imaging time. Normal liver The signal intensity of normal hepatic parenchyma is slightly greater than that of muscle on both T1- and T2-weighted images. The normal liver enhances after the administration of gadolinium-chelate agents. The vascular anatomy of the liver, which defines the lobes and segments of the liver, is easily shown on MRI. Traditionally, the liver is divided into right and left lobes by the middle hepatic vein superiorly and by the gallbladder fossa inferiorly. The right lobe is divided into anterior and posterior segments by the right hepatic vein. The left lobe is divided into medial and lateral segments by the left hepatic vein superiorly and by the fissure for the ligamentum teres inferiorly. This traditional classification makes no distinction between the superior and inferior divisions of each major segment. In the classification system of Couinaud, the hepatic segments are divided not only by three vertical planes along the hepatic veins but by a transverse plane defined by the portal venous supply [8]. Eight segments are defined by this system. Each segment has separate afferent and efferent vessels and biliary channels. This classification is widely used because it divides the liver into segments that are surgically resectable [9,10]. Suspected liver mass Primary hepatic neoplasms constitute between 0.5% and 2.0% of pediatric tumors and are the third most common abdominal malignancy in childhood after Wilms tumor and neuroblastoma [11]. The common presentation of benign and malignant liver masses is a palpable mass on physical examination. Malignant neoplasms are usually hepatoblastomas or hepatocellular carcinoma; less often, they include lymphoproliferative disorder, lymphoma, metastatic disease, undifferentiated (embryonal) sarcoma, and primary endodermal sinus tumor
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[11,12]. Benign lesions are usually hemangioendothelioma; less commonly, they include mesenchymal hamartoma, cavernous hemangioma, focal nodular hyperplasia, and hepatic adenoma [13–16]. Clinical information plays an important role in narrowing the differential diagnosis in cases where the imaging findings are nonspecific. Patient age, clinical signs and symptoms, and a-fetoprotein levels, are critical discriminators in the evaluation of hepatic tumors. Age is an important factor, because the incidence of various neoplasms varies in specific age groups. Hemangioendothelioma is the most common mass in the first 6 months of life. Hepatoblastoma, mesenchymal hamartoma, and metastatic disease from neuroblastoma or Wilms tumor is usually present in the first 3 years of life. Hepatocellular carcinoma, undifferentiated (embryonal) metastases from lymphoma, focal nodular hyperplasia, and hepatic adenoma usually occur in older children and adolescents. The clinical presentation also can suggest a specific diagnosis. Congestive heart failure in a neonate with a liver mass suggests a diagnosis of hemangioendothelioma, whereas a history of immunosuppression in a transplant patient suggests lymphoproliferative disorder or fungal abscesses [17]. Laboratory findings, particularly serum a-fetoprotein levels, can be important in making a diagnosis. Certain liver tumors, such as hepatoblastoma and hepatocellular carcinoma, are associated with elevated serum a-fetoprotein levels [11]. Imaging strategies Although the presence of an abdominal mass is often evident on physical examination, the organ of origin is often uncertain. The role of imaging is to determine the organ of origin as well as the character and extent of the lesion. The evaluation of pediatric hepatic masses relies on the use of cross-sectional imaging examinations, such as ultrasonography (US), CT, and MRI [17–19]. US is readily available, fast, and relatively inexpensive. It can usually reveal the location, extent, and solid or cystic nature of a mass and assess vascular invasion. Because of these advantages, US usually is considered the screening technique of choice for evaluation of a pediatric abdominal mass. If the sonogram is normal, further radiographic evaluation generally is not required. If US cannot yield adequate information, or if it suggests a mass, further evaluation with either CT or MRI is needed [13–17,20,21]. The selection
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of one of these two examinations is usually based on personal expertise and availability of the equipment. CT scanning is generally used more often than MRI because it is more widely available and can provide excellent anatomic detail. If CT cannot assess the extent of tumor or depict vascular structures, which is important information in assessing resectability, MRI is performed. Because it has excellent soft tissue contrast, MRI can play an important role in determining the extent of hepatic neoplasms. Primary malignant neoplasms The major role of imaging is to define the extent of the lesion and its relation to lobar and segmental anatomy and vascular structures for preoperative planning and to monitor the response of the tumor to chemotherapy or radiation [10,15]. Most hepatic malignancies can be cured only with complete resection of the primary tumor or liver transplantation [11,22]. Four types of liver resection are performed: right lobectomy, left lobectomy; left lateral segmentectomy, and trisegmentectomy (right lobe and medial segment of the left lobe) [9]. Complete excision is possible in 50% to 60% of cases of hepatoblastoma and in about one third of cases of hepatocellular carcinomas in children [11,14]. Chemotherapy has been used as an adjuvant in tumors that are completely excised as well as in those tumors that are initially nonresectable. If the tumor decreases in size and meets the anatomic criteria for resection, the patient undergoes surgery. If the tumor is still unresectable, liver transplantation is considered [23]. Hepatoblastoma and hepatocellular carcinoma Hepatoblastoma Hepatoblastoma is the most common primary liver tumor of childhood. The tumor usually affects infants and young children. The median age at diagnosis is 1 year. Conditions associated with an increased risk of hepatoblastoma include Beckwith-Wiedemann syndrome, hemihypertrophy, fetal alcohol syndrome, familial polyposis coli, and Gardner’s syndrome [14,17,21]. Hepatoblastoma most often presents as an asymptomatic mass. Other features include abdominal pain, anorexia, weight loss, jaundice, and precocious puberty (related to the secretion of chorionic gonadotropins). Some degree of osteopenia is present in all patients, and severe osteopenia is present in 20% to 30% of patients.
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Serum a-fetoprotein levels are elevated in 80% to 90% of patients with hepatoblastomas [11,14]. Pathologically, hepatoblastoma contains small primitive epithelial cells resembling fetal liver and occasionally mesenchymal elements. The tumor is usually unifocal, and the right lobe of the liver is most often affected. Multifocal disease or diffuse infiltration can occur, however. The tumor has no association with cirrhosis. Metastatic disease occurs in approximately 10% to 20% of patients [14]. Metastases are chiefly to the lungs and porta hepatis and less commonly to the brain and skeleton. The overall 2-year survival rate for patients with hepatoblastoma is approximately 65% [14]. Hepatocellular carcinoma Hepatocellular carcinoma is the second most common pediatric liver malignancy after hepatoblastoma. In the pediatric population, patients with hepatocellular carcinoma have a median age of 12 years, with a range of 5 to 15 years, and the disease is relatively rare in patients younger than 5 years of age [11,14]. Preexisting liver disease, such as hepatitis B infection, type I glycogen storage disease, tyrosinemia, familial cholestatic cirrhosis, hemochromatosis, or a1-antitrypsin deficiency, is present in approximately one half of cases [21,22,24]. Abdominal distention and a right upper quadrant mass are the most common presenting features of hepatocellular carcinoma in children. Serum a-fetoprotein levels are elevated in up to 50% of cases [11]. Pathologically, hepatocellular carcinoma consists of large, pleomorphic, multinucleated cells with variable degrees of differentiation [11]. The tumor is often locally invasive or multifocal at the time of diagnosis such that resection is possible in fewer than 30% of patients. The 2-year survival rate is less than 30% [22]. MRI appearance Hepatoblastoma and hepatocellular carcinoma have similar imaging features. Both tumors are usually solitary masses, but they may be multifocal or, less commonly, diffusely infiltrating. The right lobe is involved twice as often as the left lobe. Both hepatoblastomas and hepatomas have a tendency to invade vascular structures, the portal vein more commonly than the hepatic vein. Portal venous invasion or compression results in obstruction of blood flow to the involved segment. Malignant hepatic lesions are usually predominantly hypointense relative to normal liver on T1weighted images and hyperintense on T2-weighted
images (Figs. 1–3). Other appearances are not uncommon, especially in hepatocellular carcinoma, and include either isointensity or hyperintensity on T1- and T2-weighted sequences, hypointensity on T1-weighted images and isointensity on T2-weighted images, and isointensity on T1-weighted images and hyperintensity on T2-weighted images [25]. After gadolinium administration, hepatoblastoma and hepatocellular carcinoma show immediate diffuse homogeneous or heterogeneous enhancement followed by rapid washout. The degree of enhancement is related to the extent of arterial hypervascularity. Internal heterogeneity is common as a result of areas of hemorrhage, fat, or necrosis and is seen better on T2-weighted images than on T1weighted images [21,26,27]. Hemorrhage can appear hypo- or hyperintense on T1-weighted pulse sequences; depending on the age of the blood; it usually is hyperintense on T2-weighted images. Necrosis is hypointense on T1-weighted images and hyperintense on T2-weighted images. Steatosis appears hyperintense on conventional T1- and T2-weighted spin-echo images and hypointense on fat-suppressed images. Vascular invasion causes a focus of increased signal within a normally echo-free vessel on spin-echo sequences and a low intensity area on gradient-echo imaging. Biliary ductal dilatation is rare but may be seen when there is ductal compression by the tumor. Other hepatic malignancies Fibrolamellar hepatocellular carcinoma Fibrolamellar hepatocellular carcinoma is a rare histologic subtype of hepatocellular carcinoma with distinctive clinical and pathologic features [28–30]. It occurs predominantly in adolescents and young adults without underlying hepatic disease. Histologically, the tumor contains eosinophilic-laden hepatocytes that are separated into cords by multilamellated fibrous bands. Some tumors have a central scar. Hepatomegaly and abdominal pain are common presenting features. Fibrolamellar hepatocellular carcinoma is less aggressive than the typical variety of hepatocellular carcinoma, and patients have a more favorable prognosis [11,29]. Serum a-fetoprotein levels are usually normal. Fibrolamellar carcinoma is commonly solitary and well marginated. On MRI, it is heterogeneous, predominantly hypointense on T1-weighted images, and hyperintense on T2-weighted images (Fig. 4). Less often, it appears isointense on both T1- and T2-weighted images [27,29,31]. On
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dynamic gadolinium-enhanced images, the tumor shows immediate diffuse heterogeneous enhancement [31]. The central scar is hypointense on T1and T2-weighted images and does not enhance on delayed images after contrast administration. The
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signal intensity of the central scar can be helpful in differentiating fibrolamellar carcinoma from focal nodular hyperplasia. The scar in focal nodular hyperplasia is hyperintense on T2-weighted images and shows delayed enhancement (see below).
Fig. 1. Hepatoblastoma in a 3-year-old boy. (A) T1-weighted axial MRI (repetition time [TR] ¼ 525 milliseconds, echo time [TE] ¼ 10 milliseconds) shows a slightly hypointense mass involving both lobes of the liver. The right portal vein (arrows) is splayed and displaced posteriorly. (B) On T2-weighted MRI (TR ¼ 2415 milliseconds, TE ¼ 90 milliseconds), the signal intensity of the mass increases relative to normal parenchyma and approximates that of subcutaneous fat. (C) Fat-suppressed gradient-echo MRI (TR ¼ 155 milliseconds, TE ¼ 4 milliseconds, flip angle ¼ 70°) during the arterial phase (0 minutes after injection of gadolinium) shows a heterogenously enhancing mass. (D) On a delayed MRI scan during the portal venous phase (5 minutes after injection), the tumor has become slightly hypointense to normal parenchyma. In this patient, the tumor margins and relation of the tumor to the hepatic vasculature were seen better on MRI than on CT. This patient received chemotherapy and then underwent a trisegmentectomy.
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Fig. 1 (continued )
Undifferentiated (embryonal) sarcoma Undifferentiated embryonal sarcoma (also known as malignant mesenchymoma or hepatic mesenchymal sarcoma) is a rare malignancy that primarily affects older children and adolescents. More than 50% of cases are diagnosed in patients between 6 and 10 years of age, and 90% occur by 15 years of age [14,21,32,33]. Clinical findings include fever, a painful mass, and normal levels of a-fetoprotein. Grossly, the tumor is a large mass, ranging from 7 to 20 cm in diameter. It contains cystic spaces as well as cellular areas. Histologically, undifferentiated embryonal sarcoma contains un-
differentiated sarcomatous tissue in a myxoid matrix [27]. The prognosis is poor, with a median survival time of approximately 1 year [33]. On T1-weighted MR sequences, the cystic parts of the tumor are predominantly hypointense relative to normal liver. Focal areas of increased signal intensity representing hemorrhage may be seen. On T2-weighted images, embryonal sarcoma is predominantly hyperintense. The septa are hypointense on both pulse sequences. On gradient-echo images, the solid areas enhance and the cystic spaces appear hypointense (Fig. 5). Metastases are to the lungs and bone.
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Fig. 2. Multifocal hepatoblastoma. T1-weighted (450/10) image. Numerous intermediate signal intensity masses replace both lobes of the liver.
Hepatic metastases The malignant tumors of childhood that most frequently metastasize to the liver are Wilms tumor, neuroblastoma, rhabdomyosarcoma, and lymphoma. Neuroblastoma may affect the liver in either stage IV or stage IV-S disease. Stage IV disease is characterized by the presence of a retroperitoneal mass and distant metastases to the skeleton, liver, or nodes. Stage IV-S neuroblastoma occurs in patients under 1 year of age, who have small ipsilateral tumors (not crossing the midline)
and metastases to the liver, skin, and bone marrow but not to cortical bone. Clinically, patients with hepatic metastases present with hepatomegaly, jaundice, abdominal pain or a mass, or abnormal hepatic function test results. Hepatic metastases are typically multiple and well circumscribed. They usually are hypointense on T1-weighted MRI and hyperintense on T2weighted MRI, and they may be homogeneous or heterogeneous (Figs. 6 and 7). Other findings include mass effect with displacement of vessels and vessel invasion or amputation.
Fig. 3. Hepatocellular carcinoma in a 14-year-old girl. (A) T1-weighted (450/10) image shows a large hypointense tumor (T) in the right hepatic lobe and a small satellite lesion (open arrows) in the lateral segment of the left lobe. (B) On the T2weighted (3150/120) image, both lesions increase in signal intensity.
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Fig. 4. Fibrolamellar hepatocellular carcinoma. (A) T1-weighted (300/10) image shows a hypointense mass (arrows) in the left hepatic lobe. (B) The mass (arrow) becomes slightly hyperintense to adjacent liver on the T2-weighted (3150/120) image. The lesion has caused biliary ductal dilatation. The dilated bile ducts appear as hypointense channels on T1weighted images and as hyperintense channels on T2-weighted images.
Most metastatic lesions are hypovascular on the arterial and portal venous phases of enhancement, although they may show peripheral (ring) enhancement during the hepatic arterial phase. Hypervascular tumors are rare in children. These include sarcomas, renal cell carcinoma, pancreatic islet cell tumors, and thyroid tumors. Hypervascular metastases appear as hyperintense masses during the hepatic arterial phase
and become isointense during the redistribution phase. Diffuse replacement of the liver by metastatic disease is usually secondary to stage IV-S neuroblastoma. MRI shows widespread heterogeneity. The differential diagnostic considerations for this appearance include hepatic fibrosis, cirrhosis, fatty infiltration, and diffuse infiltrating hepatoblastoma or hepatocellular carcinoma.
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Fig. 5. Embryonal sarcoma. (A) T1-weighted (350/11) image shows a hypointense mass (curved arrows) replacing most of the right hepatic lobe. (B) After administration of gadolinium-chelate agents, the solid components in the tumor enhance. The cystic areas remain hypointense (ie, black). (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
Benign neoplasms Angiomatous lesions Hemangioendothelioma Hemangioendothelioma is the most common benign hepatic tumor of childhood [16,21,34,35]. Most affected patients are young infants less than 6 months old who present with congestive heart failure as a result of high-output overcirculation. Occasionally, these patients present with asymptomatic hepatomegaly, thrombocytopenia in association with a consumptive coagulopathy (Kasabach-Merritt syndrome), or massive hemoperitoneum as a result of tumor rupture.
Histologically, hemangioendothelioma is a vascular tumor arising from the supporting tissue (mesenchyme) of the liver. Two types of infantile hemangioma have been described. Type I is composed of a network of vascular channels lined by plump endothelial cells that are supported by reticular fibers. Type II contains larger and more irregular branching spaces lined by immature pleomorphic cells. This form has some malignant potential, and transformation into angiosarcoma has been described, but this is a rare complication [36–38]. Areas of fibrosis, calcification, hemorrhage, and cystic degeneration are common in larger lesions. Hemangiomas may be solitary or multifocal masses.
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Fig. 6. Hepatic metastases from rhabdomyosarcoma. T2-weighted (4000/120) image shows multiple hyperintense hepatic masses.
Cavernous hemangioma Cavernous hemangioma is the most common benign tumor of the liver in adults. Although it can occur in children, it is a rare lesion. It is usually asymptomatic and detected as an incidental finding on sonography, CT, or MRI.
Microscopically, cavernous hemangiomas are composed of multiple blood-filled spaces that are lined by a single layer of flat endothelial cells supported by fibrous septa. On cut sections, hemangiomas are often heterogeneous with areas of fibrosis, hemorrhage, necrosis, or cystic change.
Fig. 7. Metastatic lymphoma. T2-weighted (2700/90) image shows a solitary metastasis in the right hepatic lobe that is mildly hyperintense to surrounding tissue.
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Malignant potential is absent. Most are solitary and found in the periphery of the posterior segment of the right lobe.
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steroids, and interferon. If these methods fail, chemotherapy, irradiation, or embolic or surgical treatment may be required for treatment [43–45]. Mesenchymal hamartoma
MRI appearance Hemangioendothelioma and cavernous hemangioma tend to be well-circumscribed lesions. Characteristically, they are hypointense compared with normal liver on T1-weighted images and markedly hyperintense on T2-weighted images (Fig. 8). Signal intensity is often heterogeneous because of the presence of hemorrhage, necrosis, and fibrosis [21,27,34,39]. Internal heterogeneity is especially common in larger lesions. Dynamic imaging with gadolinium-chelate agents may show three patterns of enhancement depending on the size of the lesion [40,41]: complete early enhancement (usually small lesions), peripheral nodular enhancement progressing centripetally to complete central enhancement (Fig. 9), and peripheral nodular enhancement with a persistent central hypointense area. A secondary finding in neonates with multiple hemangioendotheliomas is a small infrahepatic aorta distal to the level of the celiac artery. This is related to shunting of blood into the tumor via the celiac artery. Because hemangioendotheliomas have a natural history of regression and involution within 12 to 18 months [42], the initial treatment is medical management, including digitalis, diuretics,
Mesenchymal hamartoma is a benign hepatic tumor that arises from the mesenchyme of the portal tract [21,27,46,47]. On gross pathologic sections, it is a well-circumscribed mass that is usually large (range: 5–20 cm) and commonly located in the right lobe of the liver. On cut sections, it is composed of multiple cystic spaces ranging from a few millimeters to 15 cm in diameter [47]. These spaces contain watery or gelatinous material and are separated by fibrous stroma containing mesenchyme, abnormal bile ducts, and hepatocytes. Most affected children are under 3 years of age, and the tumor is slightly more common in boys than in girls. Affected patients usually present with an asymptomatic abdominal mass or abdominal distention. Ascites as a result of cyst rupture or congestive heart failure caused by arteriovenous shunting is an uncommon presenting sign [48]. Treatment is surgical resection. Malignant transformation to mesenchymal hamartoma has been reported but is rare [49]. On MRI, mesenchymal hamartoma appears as a well-circumscribed multilocular mass containing fluid-filled locules intermixed with thin septa (Fig. 10) [14,21,27,46]. The cystic locules have low signal intensity on T1-weighted sequences and high signal intensity on T2-weighted sequences. The signal intensity on the T1-weighted images may increase if the tumor contains large amounts of protein or debris, however [27]. The stromal components may enhance after the administration of gadolinium-chelate agents. Epithelial lesions
Fig. 8. Multiple hemangioendotheliomas in a newborn girl. T2-weighted spin-echo image shows multiple lesions that are markedly hyperintense to the normal liver parenchyma. (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
Focal nodular hyperplasia Focal nodular hyperplasia and hepatic adenomas are uncommon lesions in childhood, accounting for less than 5% of hepatic tumors. Focal nodular hyperplasia is slightly more common than hepatic adenomas. It is a tumor-like condition that is thought to be a result of hyperplasia of normal hepatocytes caused by a vascular malformation [50]. Grossly, focal nodular hyperplasia is a well-circumscribed and usually solitary mass that is often in a subcapsular location or pedunculated. Histologically, it is composed of normal hepatocytes, bile ducts, blood vessels, and Kupffer cells, and it often contains a central fibrous scar. Internal
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hemorrhage and necrosis are usually absent, because the growth of the lesion remains proportional to its blood supply. There is no strong association with preexisting abnormalities. The lesion is most often an incidental finding on imaging examinations. Patients with large lesions may present with hepatomegaly or right upper quadrant discomfort, however. Because focal nodular hyperplasia comprises normal hepatocytes with an abnormal architecture, the signal characteristics of the lesion are often similar to those of normal liver. Focal nod-
ular hyperplasia is iso- or hypointense on T1weighted images and iso- or slightly hyperintense to normal hepatic parenchyma on T2-weighted images [46,50,51]. Similarly, the central scar is hypointense on T1-weighted images and hyperintense on T2-weighted images. Small calcifications have been reported, although they are rare, occurring in less than 5% of tumors [52]. On contrast-enhanced dynamic MRI, focal nodular hyperplasia becomes hyperintense during the arterial and early portal venous phases and isointense to normal parenchyma during the equilibrium phase and on
Fig. 9. Cavernous hemangioma. (A) Precontrast gradient-echo (200/6.1/70°) image shows a hypointense lesion in the right lobe posteriorly. (B) Early contrast-enhanced gradient-echo image shows peripheral enhancement in the lesion. (C) An image 2 minutes later shows nearly complete enhancement of the mass.
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Fig. 9 (continued )
delayed images (Fig. 11). The central scar may become hyperintense on late images. This appearance is in contrast to the low signal intensity of the central scar in fibrolamellar hepatocellular carcinoma.
Hepatic adenomas Hepatic adenoma in childhood has been associated with type I glycogen storage disease (von Gierke’s disease), Fanconi’s anemia, and galactosemia. Histologically, it is composed of cords of
Fig. 10. Mesenchymal hamartoma. T2-weighted (3500/85) image shows a well-circumscribed hyperintense mass in the dome of the liver. Several septations can be noted. (Courtesy of Lane Donnelly MD, Cincinnati, OH.)
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Fig. 11. Focal nodular hyperplasia. (A) A precontrast gradient-echo image shows a slightly hypointense mass (arrowheads) in the right hepatic lobe. (B) On the fat-saturated turbo T2-weighted image, the lesion (arrowheads) is isointense to adjacent parenchyma and contains a small hypointense scar (arrow). (C) Postcontrast gradient-echo image. The lesion (arrowheads) is mildly hyperintense to adjacent parenchyma on an early image acquired after the administration of gadolinium-chelate agent. The central scar is hypointense. (D) Postcontrast gradient-echo image. The lesion (arrowheads) becomes isointense during the redistribution (portal venous) phase of contrast enhancement.
normal hepatocytes. The hepatocytes contain fat and glycogen, which contribute to the imaging characteristics. Bile ducts and portal tracts are absent. Patients may be asymptomatic or may present with hepatomegaly or mild right upper quadrant pain. Rarely, hepatic adenoma causes acute abdominal pain secondary to tumor infarction, hemorrhage, or rupture. Hepatic adenomas are heterogeneous lesions. They usually contain hyperintense areas on T1weighted images as a result of the presence of hemorrhage, glycogen, or fat and hypointense areas resulting from necrosis [46,53]. On T2-
weighted images, they are usually hyper- or isointense to normal parenchyma [53]. On contrast-enhanced images, most adenomas become hyperintense in the arterial phase and isointense to adjacent parenchyma on delayed images. Hepatic cysts Hepatic cysts are rare in children. Congenital cysts arise from intrahepatic biliary ducts that fail to involute. Acquired cysts are the result of inflammation, trauma, or parasitic disease. Hepatic cysts may be multiple or solitary. Multiple cysts
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are usually seen in association with autosomal dominant polycystic disease. Most cysts are detected incidentally on imaging studies, although large ones may present as an abdominal mass or hepatomegaly. The classic features of a cyst on any imaging examination are a unilocular, round, or oval mass with thin and well-circumscribed walls [18,19]. Simple cysts are hypointense on T1-weighted images and markedly hyperintense on T2-weighted images (Fig. 12). Cysts do not enhance on contrast-enhanced dynamic MRI studies. Other cystic masses, including metastases, echinococcal cyst, biloma, chronic hematoma, and abscess, may have signal intensities identical to those of simple hepatic cysts. Atypical features, such as a thick wall, internal septations, mural nodules, or a high T1-weighted signal intensity, should suggest a lesion other than a simple cyst.
Artifacts in tumor imaging Focal hepatic lesions may be simulated by hypointense veins on spin-echo images (because of the flow void phenomenon), aortic pulsation artifacts, respiratory-related ghosting artifacts,
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cardiac pulsations, and fatty infiltration. Artifacts from respiratory motion, poor tissue contrast as a result of inadequate T1 or T2 weighting, and susceptibility artifacts may obscure hepatic lesions. Diffuse parenchymal disease Steatosis Hepatic steatosis is the result of excessive accumulation of triglycerides within hepatocytes. There are two morphologic types of hepatic steatosis: microvacuolar and macrovacuolar [54]. In microvacuolar steatosis, tiny fat droplets or vacuoles fill the cell without displacing the nucleus. It is seen in association with Reye’s syndrome and massive tetracycline therapy. Patients are acutely ill and present with a painful liver, vomiting, jaundice, and coma. Microvacuolar steatosis is rarely reversible. In the macrovacuolar type of steatosis, large droplets of fat fill the hepatocyte without expanding it and push the nucleus against the cell wall. Macrovacuolar steatosis is usually clinically silent, but it may be associated with hepatomegaly or right upper quadrant pain. It is associated with nutritional abnormalities (eg, kwashiorkor, obesity, intestinal bypass), metabolic diseases, drug
Fig. 12. Hepatic cyst. T2-weighted spin-echo (4000/160) image shows a small, well-defined, hyperintense lesion (arrow) in the right hepatic lobe. The lesion did not enhance after administration of gadolinium-chelate agents, distinguishing it from a vascular lesion.
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or corticosteroid use, and viral infections. Macrovacuolar steatosis is reversible if the underlying abnormality can be corrected. Steatosis may be diffuse or focal. Conventional spin-echo sequences can be relatively insensitive for detecting diffuse fatty infiltration, especially if there is only mild or moderate fat deposition. Focal fatty infiltration can be easy to detect, appearing as an area of high signal intensity on T1-weighted spin-echo images, but it is not usually visible on conventional T2-weighted images. Fat-suppression techniques and opposedphase gradient-echo imaging are more sensitive techniques for detecting fat deposition. On opposed-phase images, areas of fatty replacement show relative signal loss and thus appear hypointense (Fig. 13). Focal steatosis has several other features that can be helpful in differentiating it from mass lesions. It often has a segmental or wedge-shaped configuration, and it characteristically produces no mass effect or bulging of the hepatic margin. Vessels often can be seen traversing the areas of focal fatty metamorphosis, and they maintain a normal branching pattern. Moreover, focal fatty replacement often occurs in typical locations, usually anterior to the portal vein or adjacent to the fissure for the ligamentum teres.
The signal alteration is usually diffuse, but it can be focal on rare occasions.
Liver transplantation MRI can be useful for evaluating hepatic vasculature and calculating liver volume before transplantation. The presence of abnormalities that can alter the surgical approach, including a thrombosed portal vein or anatomic variants, such as interruption of the inferior vena cava, preduodenal portal vein, and anomalous hepatic arterial supply, can be easily seen by MRI [56].
Iron overload Hemochromatosis refers to increased deposition of iron within the parenchymal cells of the liver and other organs (including the pancreas, kidneys, bowel, and heart) with resultant organ damage. It can be further categorized as primary or secondary [55]. Primary hemochromatosis is an inherited disorder caused by an inborn error of metabolism, which leads to increased absorption of ingested iron. Secondary hemochromatosis is usually found in patients who receive multiple blood transfusions for chronic anemia. Other causes include excessive iron ingestion, congenital transferring deficiency, and cirrhosis. Secondary hemochromatosis is more common than primary hemochromatosis in the pediatric population. MRI is sensitive for detecting clinically significant iron overload in the liver. The characteristic finding of excess iron deposition is a low hepatic signal intensity. The reduction in signal intensity is a result of the paramagnetic effect of the ferric ions, which causes shortening of the T1 and T2 relaxation protons. The T2 shortening is seen best on T2-weighted or gradient-echo images (Fig. 14).
Fig. 13. Focal hepatic steatosis. (A) T1-weighted (725/ 15) image shows homogeneous liver parenchyma. (B) Opposed-phase T1-weighted gradient-echo image (176/ 7.0/70°). The right lobe anteriorly (arrows) is hypointense as a result of focal fatty replacement.
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Fig. 14. Hemochromatosis. Gradient-echo (155/4.0/70°) image shows a diffusely hypointense liver as a result of iron deposition. The patient had received multiple blood transfusions for sickle cell anemia.
After transplantation, MRI is useful for evaluating suspected complications, including infarction, vascular thrombosis or stenosis, hepatic artery pseudoaneurysm, and biliary obstruction.
axial planes using a two-dimensional multislice acquisition mode. Source images are postprocessed using a maximum-intensity projection algorithm to produce reconstructed three-dimensional models. Biliary atresia and neonatal hepatitis
Neonatal jaundice The three most common causes of jaundice in neonates are biliary atresia, neonatal hepatitis, and choledochal cyst [57]. US is the preliminary imaging procedure used to detect intrahepatic ductal dilatation associated with obstruction as well as cystic diseases. This can be supplemented by radionuclide studies using hepatobiliary imaging agents [58–60]. MR cholangiography has proven to be a useful noninvasive alternative to endoscopic retrograde pancreatography to delineate the anatomy of the biliary system when the results of sonography or CT are indeterminate or additional information is needed for surgical planning [61–66]. This technique is performed with two-dimensional, fat-suppressed, turbo T2-weighted, spin-echo sequences. Images are acquired by means of a breath-hold technique in cooperative children. In neonates, in whom non-breath-hold techniques are required, the signal acquisitions can be increased to increase the signal-to-noise ratio and to compensate for motion. Images are obtained in the coronal and
Distinguishing between neonatal hepatitis and biliary atresia is important, because neonatal hepatitis is managed medically, whereas biliary atresia requires early surgical intervention to prevent biliary cirrhosis [57,67]. MR cholangiopancreatography can help to differentiate between these two conditions [61,63]. Extrahepatic ducts are usually visualized in neonates with hepatitis, whereas they are usually absent in neonates with biliary atresia. Choledochal cyst A choledochal cyst is a congenital cystic or fusiform dilatation of the common bile duct. It is usually diagnosed in infancy or childhood, but the condition can be recognized first in adolescents or adults. The classic clinical presentation includes jaundice, abdominal pain, and mass, although this triad occurs in only 20% to 50% of patients [59]. Choledochal cysts can be classified into five types. A type 1 cyst (80–90% of cases) is characterized by
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Fig. 15. Choledochal cyst in a 2-year-old boy with jaundice. Axial (A) and coronal (B) fat-suppressed turbo T2-weighted (3157/189/90°) images demonstrate a high signal intensity cyst (C) in the porta hepatis separate from the gallbladder (g). (Courtesy of Peter Strouse MD, Ann Arbor, MI.)
dilatation of the common bile duct. A type 2 cyst is a true diverticulum arising from the common duct. A type 3 cyst is a choledochocele involving only the intraduodenal portion of the duct. A type
4 cyst is characterized by multiple extrahepatic cysts, and the intrahepatic ducts may or may not be dilated. A type 5 cyst, or Caroli’s disease, is characterized by multiple intrahepatic cysts [68].
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Choledochal cysts in neonates and young infants may coexist with biliary atresia [69]. The cause of choledochal cysts is unknown, but it is postulated that an anomalous pancreaticobiliary junction is the initiating factor. This anomaly results in chronic reflux of pancreatic enzymes into the biliary tree, which leads to inflammation, dilatation, and scarring. The dilated common and intrahepatic bile ducts as well an anomalous pancreaticobiliary junction can be easily shown by MR cholangiography (Fig. 15) [64].
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