1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at AFIP ARCHIVES 801 From the Archives of the AFIP Pediatric Liver Masses: Radiologic-Pathologic Correlation Part 1. Benign Tumors 1 CME FEATURE See accompanying test at /education /rg_cme.html LEARNING OBJECTIVES FOR TEST 6 After reading this article and taking the test, the reader will be able to: Describe an ageappropriate differential diagnosis for a liver mass in a child. List the clinical, pathologic, and imaging features of common benign liver tumors in children. Discuss how to distinguish benign liver tumors from other hepatic tumors on the basis of clinical and imaging data. TEACHING POINTS See last page Ellen M. Chung, COL, MC, USA Regino Cube, CPT, MC, USA Rachel B. Lewis, LCDR, MC, USN Richard M. Conran, COL, MC, USA Benign hepatic tumors in children include lesions that are unique to the pediatric age group and others that are more common in adults. Infantile hemangioendothelioma, or infantile hepatic hemangioma, is a benign vascular tumor that may cause serious clinical complications. It is composed of vascular channels lined by endothelial cells. At imaging, large feeding arteries and draining veins and early, intense, peripheral nodular enhancement with centripetal filling on delayed images are characteristic features. Mesenchymal hamartoma of the liver occurs in young children and is characterized pathologically by mesenchymal proliferation with fluid-containing cysts of varying size and number. The mesenchymal component or cystic component may predominate; this predominance determines the imaging appearance of the tumor. Benign epithelial tumors that are common in adults may infrequently occur in childhood. These include focal nodular hyperplasia (FNH), hepatocellular adenoma, and nodular regenerative hyperplasia. All are composed of hyperplastic hepatocytes similar to surrounding liver parenchyma and may be difficult to discern at imaging. Preferential hepatic arterial phase enhancement helps distinguish FNH and hepatic adenoma from uninvolved liver. Hepatic adenoma often has intracellular fat and a propensity for intratumoral hemorrhage, neither of which are seen in FNH. Unlike adenoma, FNH often contains enough Kupffer cells to show uptake at sulfur colloid scintigraphy. Nodular regenerative hyperplasia is often associated with portal hypertension, which may be evident at imaging. Knowledge of how the pathologic features of these tumors affect their imaging appearances helps radiologists offer an appropriate differential diagnosis and management plan. radiographics.rsna.org Abbreviations: AFP = α-fetoprotein, CHF = congestive heart failure, FNH = focal nodular hyperplasia, GLUT1 = glucose transporter protein 1, H-E = hematoxylin-eosin, NRH = nodular regenerative hyperplasia, UES = undifferentiated (embryonal) sarcoma RadioGraphics 2010; 30: Published online /rg Content Codes: 1 From the Department of Radiology and Radiological Sciences (E.M.C.) and Department of Pathology (R.M.C.), Edward F. Hebert School of Medicine, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd, Bethesda, MD 20814; Department of Radiologic Pathology, Armed Forces Institute of Pathology, Washington, DC (E.M.C., R.B.L.); Department of Radiology, Madigan Army Medical Center, Tacoma, Wash (R.C.); and Department of Radiology, National Naval Medical Center, Bethesda, Md (R.B.L.). Received September 15, 2009; revision requested December 8 and received January 15, 2010; accepted January 19. For this CME activity, the authors, editors, and reviewers have no relevant relationships to disclose. Address correspondence to E.M.C. ( The opinions or assertions contained herein are the private views of the authors and are not to be construed as official nor as reflecting the views of the Departments of the Army, Navy, or Defense.
2 802 May-June 2010 radiographics.rsna.org Introduction Although primary hepatic neoplasms represent only a small percentage of solid tumors that occur in children, the finding of focal hepatic lesions in a child is not an uncommon event in a busy radiology practice. The most common neoplasm involving the liver in children, as in adults, is metastatic disease. Most primary liver tumors in children are malignant, but one-third are benign; benign lesions may be of mesenchymal or epithelial origin. In a series of 716 hepatic tumors in patients under the age of 21 years from the Armed Forces Institute of Pathology (1), the most common benign tumors were, in decreasing order of frequency, infantile hemangioendothelioma, focal nodular hyperplasia (FNH), mesenchymal hamartoma, nodular regenerative hyperplasia (NRH), and hepatocellular adenoma. In this article, we focus on benign liver tumors in children. The clinical, pathologic, and imaging features of these tumors are reviewed and correlated. Infantile Hemangioendothelioma Infantile hemangioendothelioma, or infantile hepatic hemangioma, is a vascular neoplasm and the most common benign hepatic tumor of infancy. About one-half of cases occur as solitary masses and one-half are multifocal. The biologic behavior is benign, but serious clinical complications may develop. Nomenclature Our understanding of vascular lesions in infants is markedly hampered by widely varied terminology. The term infantile hemangioendothelioma is generally preferred in the pathology literature to differentiate this neoplasm of infancy from the common benign liver lesion of young adult women widely known as hemangioma (1 3). Others assert that the term hemangioendothelioma leads to confusion with epithelioid hemangioendothelioma, a distinct tumor of adults with borderline malignant potential (4,5). The terms capillary hemangioma, which is often applied to the lesion in infants, and cavernous hemangioma, which is often applied to the lesion in adults, are less favored because both capillary- and cavernous-sized vascular spaces are encountered in infantile hemangioendothelioma (3,6). The name adopted by the International Society for the Study of Vascular Anomalies and based on the classification of Mulliken and Glowacki (7) is infantile hepatic hemangioma. This term emphasizes the similarity of the hepatic lesion to the most common neoplasm of infancy, which, when it occurs in the skin and other organs, is known as infantile hemangioma (4,8,9). Epidemiology and Clinical Features Nearly 90% of infantile hemangioendotheliomas are diagnosed in the first 6 months of life, and one-third are diagnosed within the first month (3,10). They are rarely discovered after 1 year of age, and biopsy is indicated for older patients to exclude malignant tumors (8,9,11). There is a slight female predominance but no racial predilection. There is an increased prevalence in patients with hemihypertrophy and Beckwith- Wiedemann syndrome (2). Most infantile hemangioendotheliomas manifest as an asymptomatic abdominal mass, but life-threatening complications may occur (3). Hemangiomas involving other sites, such as the skin, trachea, thorax, adrenal gland, and dura mater, have been reported to occur in up to 68% of patients with multifocal liver tumors, but larger series suggest that the prevalence is lower (10% 15%) (3). Patients with multiple liver lesions should be evaluated with chest radiography and brain imaging to exclude additional lesions (11). Serious complications include high-output congestive heart failure (CHF) due to associated large arteriovenous shunts and the Kasabach- Merritt syndrome of coagulopathy due to intratumoral platelet sequestration. CHF may accompany both solitary and multifocal lesions and is associated with a poorer prognosis. In addition, severe hypothyroidism may be caused by high levels of type 3 iodothyronine deiodinase activity produced by the tumor; the hypothyroidism may lead to cardiac dysfunction and mental retardation (5,12). Rarely, patients may present acutely with hemoperitoneum due to tumor rupture (3). Laboratory tests frequently show anemia and occasionally show hyperbilirubinemia. Serum α-fetoprotein (AFP) levels are rarely elevated above the normal reference range for age (adult levels are not reached until age 6 months). If elevated, the serum AFP level is much lower than is typical with hepatoblastoma (1,3,13). Classification of Vascular Lesions of the Liver Vascular anomalies in children are now understood to represent a range of pathologic entities that can be divided, according to the classification of Mulliken and Glowacki (7), into two broad categories: high-flow and low-flow lesions. High-flow lesions include arteriovenous malformations and the true vasoproliferative neoplasm, infantile hemangioma. Low-flow lesions include vascular malformations composed of venous, lymphatic, and capillary components. It is likely that the vascular lesions occurring in the liver in children also represent a heterogeneous group of malformations and neoplasms, giving rise to the confusion in the nomenclature.
3 RG Volume 30 Number 3 Chung et al 803 Three Clinical Categories of Hepatic Vascular Malformations* Type of Malformation Clinical Presentation GLUT1 Reactivity Multifocal Focal Diffuse Patients are usually asymptomatic, but some have CHF; manifests in first few months of life Patients are usually symptomatic and may have CHF; manifests in perinatal period Manifests with mass effect; patients may develop abdominal compartment syndrome or severe hypothyroidism; no CHF GLUT1 positive GLUT1 negative Not yet established Pathologic Features Small with no central necrosis Large with central necrosis, hemorrhage, or fibrosis Liver enlarged and replaced by masses Outcome Proliferation followed by involution Involute by age months Complicated clinical course Source. Reference 5. *As proposed by two large North American referral centers for vascular anomalies. The malformations differ in clinical presentation, pathologic appearance, and prognosis. Common cutaneous infantile hemangiomas are now pathologically differentiated from other vascular lesions on the basis of positive immunoreactivity to erythrocyte-type glucose transporter protein 1 (GLUT1) in the former (14,15). Similarly, in a study of 19 pediatric vascular lesions of the liver in the pathology literature, Mo et al (9) were able to distinguish two groups of lesions on the basis of their immunoreactivity to GLUT1. Group 1 consisted of tumors that showed positive immunostaining for GLUT1. The tumors were usually multifocal without necrosis or large vessels, and most underwent involution. The authors called these tumors hepatic infantile hemangiomas and believed that these represented the hepatic counterpart of infantile (or juvenile) cutaneous hemangiomas (9). Group 2 consisted of GLUT1-negative lesions (9), which were usually solitary with central necrosis and large peripheral vessels. These did not regress or respond to medical therapy. The authors designated these GLUT1-negative lesions as hepatic vascular malformations with capillary proliferation (9). Other authors have described additional GLUT1-negative vascular hepatic lesions that do involute (16); thus, GLUT1-negative lesions represent a heterogeneous group of anomalies. Clinical investigators from two large North American referral centers for vascular anomalies divide hepatic vascular lesions into three categories with distinctive clinical presentations, features, and outcomes (5,8) (Table). The first category consists of multifocal lesions. These stain positive for GLUT1, do not have central necrosis, and may or may not have associated arteriovenous shunts or cutaneous hemangiomas. They exhibit a natural history of proliferation followed by involution, similar to the natural history of common cutaneous infantile hemangiomas. Many patients are asymptomatic, but some are symptomatic with CHF due to arteriovenous shunting. These are the same as the group 1 lesions of Mo et al (9) and represent typical infantile hepatic hemangiomas or hemangioendotheliomas. The second category is made up of focal lesions, which do not stain for GLUT1 and often contain central areas of hemorrhage, necrosis, or thrombosis. These lesions variably demonstrate arteriovenous shunts, are usually symptomatic, and are often diagnosed at birth or at antenatal ultrasonography (US). They are rarely associated with cutaneous hemangiomas. The authors consider these the hepatic counterpart of the cutaneous rapidly involuting congenital hemangioma, which is also GLUT1 negative and completely involutes by age months (5,8). The third category is diffuse disease with the liver largely replaced by growing tumors, which cause massive hepatomegaly and secondary respiratory distress, inferior vena cava compression, and abdominal compartment syndrome. These patients frequently also have severe hypothyroidism. Although arteriovenous shunts may be present, these patients do not have highoutput CHF (5,8). Pathologic Features Solitary tumor size varies from 0.5 to 14 cm in maximum dimension. Multifocal lesions are usually around 1 cm in diameter (Fig 1). On cut sections, the mass varies from red-brown and spongy to tan-white and firm. Central areas of hemorrhage, necrosis, thrombosis, or fibrosis and gritty calcifications are frequent in large solitary tumors (Fig 2) (2,3).
4 804 May-June 2010 radiographics.rsna.org Figure 1. Multifocal infantile hemangioendothelioma in a 6-month-old girl. (a) Intraoperative photograph obtained in another patient shows multiple small, purplish masses bulging out from the surface of the liver. (Reprinted, with permission, from reference 1.) (b) Transverse US image shows several small, well-demarcated, homogeneous hypoechoic lesions (arrowheads) in the liver. (c) Color Doppler image shows peripheral flow around some of the lesions. (d) Computed tomographic (CT) image obtained without intravenous contrast material shows that the lesions (arrowheads) are hypoattenuating relative to the liver. (e) Contrast material enhanced CT image shows that the nodules enhance intensely and uniformly (arrowheads). (f) Coronal fatsaturated T2-weighted magnetic resonance (MR) image shows numerous well-defined hyperintense nodules in the liver. Arrow = gallbladder. (g) Coronal T1-weighted MR image shows that the nodules (arrowheads) are hypointense relative to the liver. (h) Coronal gadolinium-enhanced fat-saturated T1-weighted MR image shows uniform enhancement of the nodules (arrowheads).
5 RG Volume 30 Number 3 Chung et al 805 Figure 2. Hepatic vascular lesion (GLUT1 immunoreactivity unknown) in a 12-week-old boy. (a) Photograph of the cut specimen shows a tan mass with a cystic space (*) and large blood vessel (arrowhead). (b) Photomicrograph (original magnification, 100; hematoxylin-eosin [H-E] stain) shows interconnecting vascular spaces (*) lined by endothelial cells and surrounded by fibrous stroma (S). (c) Longitudinal US image shows a markedly enlarged right hepatic vein (arrowhead). (d) Longitudinal US image shows a large celiac axis (arrowhead) and tapering of the aorta distal to its origin. (e) On a duplex US image, the spectral waveform of the artery supplying the mass shows little variation in flow between systole and diastole. (f ) Nonenhanced CT image shows tiny calcifications (arrowheads) in the tumor, which has mixed attenuation and replaces the right hepatic lobe. (g) Arterial phase CT image shows an enlarged hepatic artery (arrowhead) and intense, nodular, peripheral enhancement of the mass (arrows). (h) Equilibrium phase CT image shows peripheral fill-in of contrast enhancement but persistent low attenuation in the tumor center.
6 806 May-June 2010 radiographics.rsna.org Figure 3. Congenital hepatic vascular lesion (GLUT1 immunoreactivity unknown) in a 12-day-old girl who was premature (born at 31 weeks gestation). (a) Plain radiograph of the chest and abdomen shows an enlarged cardiac silhouette, paucity of bowel gas with lateral deviation of the stomach, and body wall edema. (b) Axial T2-weighted MR image shows a predominantly hyperintense mass (arrow) with a central hypointense area and adjacent flow voids (arrowhead), which represent enlarged hepatic veins. (c) Axial nonenhanced T1-weighted spoiled gradientecho MR image shows that the mass (T) is hypointense relative to the liver. (d) Arterial phase gadolinium-enhanced T1-weighted MR image shows intense, peripheral, papillary enhancement (arrowheads) of the mass. (e) Delayed phase gadolinium-enhanced T1- weighted MR image shows centripetal enhancement of the mass with a persistent hypointense area (arrowhead). At histologic examination, the tumor is composed of thin vascular channels lined by a single layer of plump endothelial cells within a scanty fibrous stroma (Fig 2). The vascular channels vary in size from small (capillary) to large (cavernous), as described by Dehner and Ishak (17) as a type 1 infantile hemangioendothelioma. The type 2 lesion of Dehner and Ishak (17) is now believed to represent an angiosarcoma (3). Areas of involutional or regressive change are frequently seen, including cavernous vas- cular spaces lined by a single layer of flattened endothelial cells, usually in the center of the tumor. Thrombosis in these spaces may lead to infarction, fibrosis, and dystrophic calcification. As involution continues, cellularity is replaced by loose fibrofatty stroma (3,17,18).
7 RG Volume 30 Number 3 Chung et al 807 Figure 4. Congenital hepatic vascular malformation (GLUT1 negative) in a 3-month-old girl. (a) Prenatal MR image shows a large hyperintense mass (straight arrow) in the left hepatic lobe (the fetus is in cephalic presentation) with a large adjacent flow void (arrowhead). Curved arrow = right kidney. (b) Transverse US image shows a well-demarcated heterogeneous mass (arrowheads) in the left hepatic lobe. (c) Transverse color Doppler image shows flow within and adjacent to the tumor. (d) Coronal gadolinium-enhanced MR angiogram shows many large vessels, including a very large draining vein (*). Imaging Features The imaging features of infantile hemangioendotheliomas depend on whether the lesions are focal, multifocal, or diffuse and reflect their vascular nature (8,18). Multifocal lesions are small and uniform in appearance (5,8). Large focal lesions often demonstrate findings related to central hemorrhage, necrosis, fibrosis, and calcification (5,8,18). In diffuse disease, the liver is massively enlarged and replaced by multiple large masses, causing mass effect on adjacent organs and compression of the inferior vena cava (5,8). Typically, evidence of high flow is apparent, as manifest by enlargement of the hepatic arteries and veins and possibly tapering of the abdominal aorta below the origin of the celiac axis (Fig 2) (8,18). Owing to the risk of bleeding, biopsy of these masses is avoided, and the diagnosis is made on the basis of typical imaging findings and the demonstration of involution at follow-up. Plain radiographs of the abdomen often show hepatomegaly or an abdominal mass (Fig 3). Fine calcifications are seen in about 16% of cases (18). In infants with CHF, chest radiography demonstrates cardiomegaly and pulmonary edema (Fig 3). At prenatal US, polyhydramnios and a hypoechoic liver mass may be detected. Findings of fetal hydrops, including anasarca, ascites, pleural effusion, and cardiomegaly, should be sought because these have prognostic import (18). At postnatal US, infantile hemangioendotheliomas appear as well-demarcated masses that are generally hypoechoic or of mixed echogenicity relative to adjacent liver (Figs 1, 4) (18). The typical
8 808 May-June 2010 radiographics.rsna.org Figure 5. Diffuse form of hemangioendothelioma in a 10-week-old girl with severe hypothyroidism. (a, b) Transverse (a) and longitudinal (b) US images show numerous large masses (* in a) replacing the liver and compressing the inferior vena cava (arrow in a). AO in a = aorta. (c) Longitudinal color Doppler image shows a direct portal vein to hepatic vein shunt. (d) Contrast-enhanced CT image, obtained in the early portal venous phase, shows peripheral corrugated enhancement of the masses (arrowheads) and compression of the inferior vena cava (arrow). (e) Delayed phase CT image shows centripetal enhancement of the masses. hyperechoic appearance of adult hemangioma is uncommon in infantile hemangioendothelioma (8,18). Tiny echogenic foci with posterior acoustic shadowing representing calcifications are seen in up to 36% of cases (8,18). Small multifocal lesions are homogeneous, whereas the echotexture is more often heterogeneous in large focal lesions with central hemorrhage, necrosis, or fibrosis (8,18). Diffuse disease may appear as an enlarged liver without discrete masses, or the liver may be replaced by large predominantly hypoechoic masses (Fig 5) (8). Color and spectral Doppler analysis demonstrates a variety of flow patterns: arteries with waveforms with little systolic-diastolic variation, a finding indicative of arteriovenous shunting; arterial and venous waveforms with high-frequency shifts; and arteries and veins with low-frequency signals (Fig 2) (6). The hepatic arteries and veins generally appear enlarged, and large feeding and draining vessels are seen surrounding and within the tumors (Figs 1, 4). Direct arteriovenous or portovenous shunts may be visualized (Fig 5) (8). Some anechoic areas may show venous flow (6,18). Follow-up of treated or observed lesions
9 RG Volume 30 Number 3 Chung et al 809 demonstrates a decrease in flow velocity in the feeding arteries and resolution of arteriovenous shunts, with a decrease in the size of the masses (5,6). Sonographic and Doppler features are suggestive of hemangioendothelioma but not diagnostic. The main role of US is in detection and localization of lesions and in follow-up (6,8). Findings at dynamic contrast-enhanced CT are often diagnostic. Precontrast images show well-defined masses that are hypoattenuating to the adjacent uninvolved liver (Figs 1, 2) (8,18,19). Speckled calcifications are noted in up to 50% of cases, usually in the large focal tumors (Fig 2) (8,18,19). The enhancement pattern of infantile hemangioendothelioma is similar to that of adult hemangioma. On arterial phase images, there is generally intense peripheral nodular or corrugated enhancement. On portal venous and delayed phase images, there is progressive centripetal fill-in of the enhancement of the tumor (Figs 2, 5). Small multifocal tumors enhance intensely and uniformly, whereas large focal tumors with central hemorrhage, necrosis, or fibrosis enhance centripetally and may never completely enhance in the center, in contradistinction to the typical adult hemangioma (Figs 1, 2) (8,18,19). Patients with diffuse disease demonstrate near total replacement of the liver by innumerable lesions with centripetal enhancement (Fig 5) (5,8). MR imaging is the preferred modality for evaluating infantile hemangioendothelioma, as characteristic findings at T2-weighted and gradient-echo imaging as well as dynamic gadoliniumenhanced imaging allow confident diagnosis (8,11,20). On precontrast T1-weighted images, infantile hemangioendotheliomas are generally hypointense to surrounding normal parenchyma, although occasionally hyperintense foci reflecting hemorrhage may be encountered (Figs 1, 3) (18). On T2-weighted images, infantile hemangioendotheliomas are markedly hyperintense owing to their vascular nature, similar to adult hemangiomas (Figs 1, 3) (5,8,18). Small multifocal lesions are almost always homogeneous in signal intensity, whereas larger focal lesions may demonstrate heterogeneous signal intensity due to central thrombosis, necrosis, or fibrosis (Figs 1, 3) (8). Flow voids are commonly seen in or adjacent to some of the lesions (Figs 3, 4) (8). At dynamic gadolinium-enhanced imaging, the pattern of enhancement is intense peripheral nodular enhancement with centripetal fill-in, similar to that seen at dynamic contrast-enhanced CT (Fig 3) (5,8,21). Central varices, if present, also enhance (8,11). Angiography was the mainstay of diagnosis in the past but has been largely supplanted by dynamic contrast-enhanced MR imaging and CT. Angiography is now reserved for patients with intractable complications from arteriovenous shunts in whom use of embolotherapy is contemplated (11,18). Arteriography frequently shows dilated tortuous feeding arteries including the hepatic arteries and adjacent systemic arteries. Early draining veins due to arteriovenous shunts are seen (11,18). Focal lesions may have large venous varices with anomalous draining veins (Fig 4) (8,11). Infantile hemangioendotheliomas have been studied with both technetium 99m ( 99m Tc) labeled sulfur colloid and 99m Tc-tagged red blood cells. Blood flow images show early uptake with both studies, in contrast to findings in adult hemangioma, which does not show early increased flow. Delayed sulfur colloid images show a photopenic defect at the site of the tumor, whereas delayed images from tagged red blood cell studies reveal increased radiotracer accumulation, although a central photopenic defect may be encountered in large tumors with hemorrhage, necrosis, or fibrosis (18,22). Differential Diagnosis The principal diagnostic considerations are solitary and multifocal hepatic tumors that occur in the same age group. Hepatoblastoma rarely occurs in the newborn but can be seen in young infants (3). This tumor is distinguished by a heterogeneous rather than intense centripetal enhancement pattern and markedly elevated levels of AFP in 90% of patients (3,18). AFP level is rarely elevated in infantile hemangioendothelioma (13). Mesenchymal hamartoma of the liver, like infantile hemangioendothelioma, may also be found in the perinatal period. This benign tumor differs in imaging appearance from infantile hemangioendothelioma in that it usually appears as a multicystic, multilocular mass with enhancement of only the septa and solid portions. Less commonly, mesenchymal hamartoma may be predominantly solid, but it differs from infantile hemangioendothelioma in that it is hypovascular at dynamic contrast-enhanced imaging (18). Metastatic neuroblastoma can mimic the appearance of multifocal infantile hemangioendothelioma, but neuroblastoma is associated with elevated levels of urinary catecholamines. At CT,
10 810 May-June 2010 radiographics.rsna.org Figure 6. Mesenchymal hamartoma in a 16-month-old girl. (a) Photograph of the resected specimen shows a partly cystic (arrowheads) and partly solid (T) tumor. * = normal liver. (b) Photomicrograph (original magnification, 100; H-E stain) shows compressed, branching ductules (arrowheads) surrounded by loose mesenchyme. * = normal liver. (c) Photomicrograph (original magnification, 40; H-E stain) shows fibrils of collagen within loose mesenchyme; these separate to form early cysts (*). (d) Transverse US image shows cystic (arrowheads) and solid (T) portions of the tumor and adjacent normal liver (*). (e) Longitudinal color Doppler image shows no flow to the cystic component, which contains low-level echoes (arrowhead). Minimal flow is seen in the solid component (arrows). (f) Coronal CT image obtained with intravenous and oral contrast material shows the mixed cystic (arrowheads) and solid (T) tumor replacing the left hepatic lobe. * = normal liver. neuroblastoma metastases in the liver generally enhance less instead of more than the adjacent liver (18). Further, imaging findings of additional sites of metastases or the primary tumor in the adrenal gland, retroperitoneum, or posterior mediastinum suggest the proper diagnosis. Angiosarcoma should also be considered, as there are reports of angiosarcomas arising in preexisting hemangioendotheliomas (3,8,23). Presentation after age 1 year or lack of response
11 RG Volume 30 Number 3 Chung et al 811 to treatment should prompt further evaluation with biopsy. Atypical imaging features, such as heterogeneous signal intensity in multifocal lesions on T2-weighted images, lack of flow voids, and central or only mild peripheral enhancement, should also lead one to consider biopsy (8). Treatment and Prognosis Most infantile hemangioendotheliomas are asymptomatic and spontaneously involute, but a minority cause serious complications. Overall survival is about 90% in series with selection bias for complicated cases, so the actual survival rate is likely higher (3,8,18). Most deaths are secondary to CHF (18). Both GLUT1-positive infantile hemangioendotheliomas and GLUT1-negative focal lesions may exhibit arteriovenous shunting and cause CHF. Kassarjian et al (8) found that diffuse disease with massive replacement of the liver by tumors is associated with hypothyroidism, respiratory distress, abdominal compartment syndrome, and a complicated clinical course (5). A diagnosis and treatment algorithm proposed by authors from two North American vascular anomalies centers provides a rational approach to infantile hemangioendotheliomas based on the imaging appearance of the lesions and the presence or absence of complications (5). Patients with focal or multifocal disease and symptoms related to tumor size or arteriovenous shunting are initially treated with corticosteroids followed by interferon-α-2a or vincristine, if necessary. Cardiac failure is managed with diuretics and digoxin. Patients with shunts who fail medical therapy benefit from embolotherapy. Those with diffuse disease replacing most of the liver benefit from medical therapy, including treatment of associated hypothyroidism, but may require transplantation. These patients do not have CHF and do not benefit from embolotherapy (5). Mesenchymal Hamartoma Mesenchymal hamartoma of the liver is the second most common benign liver mass in children after infantile hemangioendothelioma (1,3,24). The gross appearance, which ranges from predominantly cystic to predominantly solid, determines the imaging features. The vast majority of mesenchymal hamartomas contain cysts. Epidemiology and Clinical Features Mesenchymal hamartoma is most commonly discovered in children younger than 2 years of age, with nearly all lesions (95%) discovered by age 5 years (3,24). There is a slight male predominance (3:2), with no known racial predilection (3,24). The most common presentation is painless abdominal distention. The abdominal enlargement is usually gradual, although distention can develop fairly rapidly due to fluid accumulation within the cysts (3,24,25). Mesenchymal hamartoma has been diagnosed prenatally and has been associated with hydrops (25 27). There is no specific laboratory marker for mesenchymal hamartoma. Serum AFP levels are typically normal, although mild elevation above the age-adjusted reference range occasionally occurs; this elevation presumably originates from the peripheral hepatocyte component of the lesion (28 32). Pathologic Features The gross pathologic appearance of mesenchymal hamartoma is typically a large, well-marginated, solitary mass measuring up to 30 cm (24). Most lesions (85%) contain cysts of varying sizes, ranging from a few millimeters to more than 15 cm (Fig 6) (1). In the series of 30 cases described by Stocker and Ishak (24), 83% of tumors contained gross cysts. Those without cysts tend to be found in younger patients (24). The cystic areas of the mass contain a clear amber fluid or gelatinous material. The mass arises in the right lobe in 75% of cases and may be pedunculated with a thin or thick pedicle (1,3,24). The appearance of the mass ranges from predominantly cystic to predominantly stromal (mesenchymal). At histologic analysis, mesenchymal hamartoma is characterized by mesenchymal proliferation containing variably sized cysts, bile ducts, and hepatocyte cords. The mesenchymal component consists of stellate cells in a loose mucopolysaccharide-rich matrix surrounding interspersed vessels and bile ducts (Fig 6). Loose areas of mesenchyme may contain fibrils of collagen that separate to form the cystic spaces. The cysts typically have no discrete endothelial lining and are delimited only by slightly more dense mesenchymal tissue (3,24). In addition to the stromal element, interspersed bile ducts and hepatocytes are seen. The single or branching bile ducts appear to constitute an active proliferating component, whereas the hepatocytes, which are compressed into thin strips at the periphery of the mass, likely represent an inactive component (Fig 6) (1). Cytologic sampling limited to the peripheral hepatocyte component may lead to an erroneous diagnosis of hepatoblastoma (32). Hemorrhage and necrosis are infrequently seen and are features that suggest a malignant tumor (3).
12 812 May-June 2010 radiographics.rsna.org Figure 7. Mesenchymal hamartoma of the liver in a 2-year-old boy. * = normal liver. (a) Transverse US image shows a well-defined cystic mass with multiple septa in the liver. (b) Axial T2- weighted MR image shows the markedly hyperintense mass containing thin septa (arrows). (c) Coronal nonenhanced T1-weighted MR image shows that the mass (arrows) is homogeneously hypointense relative to the liver. (d) Coronal contrast-enhanced T1-weighted MR image obtained at the same level shows that enhancement is limited to the septa (arrows). Pathogenesis Mesenchymal hamartoma is characterized by uncoordinated proliferation of primitive mesenchyme in the periportal tracts (3,24). Mesenchymal hamartoma has generally been considered to represent a congenital lesion, which has been attributed to a multiplicity of factors including developmental anomaly of the ductal plate, bile duct obstruction, hepatic lobe ischemia or degeneration, and lymphatic duct obstruction (1,3). The finding of expanded portal areas in satellite lesions at the periphery suggests that the mass proliferates by extending along the portal tracts, causing compression of adjacent parenchyma. Fluid accumulation and cyst formation then develop in the resulting areas of atrophy and degeneration (3,24). More recently, a few reports of cytogenetic analysis and flow cytometry studies of mesenchymal hamartomas have demonstrated balanced translocations at 19q13.4 and aneuploidy, findings that suggest that the lesion may in fact represent a true neoplasm (3,26,31,33,34). Although mesenchymal hamartoma is generally regarded as a benign lesion with no malignant potential, whereas undifferentiated (embryonal) sarcoma (UES) is an aggressive malignant tumor, there are several common histopathologic, immunohistochemical, and cytogenetic features of mes-
13 RG Volume 30 Number 3 Chung et al 813 enchymal hamartoma and UES that suggest a relationship between the two (1,3). Furthermore, recent reports in the literature identify recurring chromosomal abnormalities for cytogenetically characterized mesenchymal hamartomas involving alterations of 19q with a breakpoint at band 13.4, suggesting that alteration in this location may serve as a genetic marker for mesenchymal hamartoma (33 35). Alterations at the same locus have also been described in UES (26,35). In addition, several reports in the literature describe cases of UES arising in a background of mesenchymal hamartoma (1,3,26,35,36). These raise the question of whether the UES arose within a preexisting mesenchymal hamartoma or simply represents a malignant entity with areas resembling the histologic appearance of mesenchymal hamartoma (1,3). Imaging Features At imaging evaluation, the appearance of mesenchymal hamartoma depends on its gross pathologic appearance, which constitutes a spectrum from a predominantly cystic mass with thin or thick septa to a predominantly solid (stromal or mesenchymal) mass containing a few small cysts. Cystic portions are avascular, and stromal portions are relatively hypovascular (37). At sonography, the cystic portions of the mass are anechoic or nearly anechoic with thin or thick echogenic septa. The solid portions appear echogenic. Portions with very small cysts may appear completely solid at US (Figs 6, 7). Low-level echoes may be seen within the fluid, presumably reflecting gelatinous contents (Fig 6) (38). Color Doppler imaging shows relatively little blood flow, which is limited to solid portions and septa (Fig 6). Intraoperative US may also be used to guide resection and define vascular anatomy (31). At CT, mesenchymal hamartoma appears as a complex cystic mass. The cystic components show water attenuation, whereas the stromal components are hypoattenuating to surrounding liver. After administration of iodinated intravenous contrast material, enhancement of the septa and solid (stromal) elements is observed (Fig 6) (21,37,39). Hemorrhage is not typical in mesenchymal hamartoma (39). At MR imaging, the appearance of mesenchymal hamartoma depends on the cystic versus stromal (mesenchymal) composition of the mass, as well as the protein content of the fluid in the cysts (21,39,40). Solid portions may appear hypointense to adjacent liver on both T1- and T2-weighted images owing to fibrosis (21,37,41). The cystic portions are generally close to water signal intensity on T2-weighted images and demonstrate variable signal intensity on T1-weighted images, depending on the protein content of the cyst fluid (Fig 7) (21,40,41). After intravenous administration of gadolinium contrast material, enhancement is mild and limited to the septa and stromal components (Fig 7) (21). Differential Diagnosis Several diagnostic considerations remain for a hepatic mass in a young child. Hepatoblastoma is a malignant tumor that occurs in the same age group; it is generally distinguished from mesenchymal hamartoma by marked elevation of the serum AFP level and the solid appearance of and finding of calcification in hepatoblastoma; however, occasionally, the AFP may be low in hepatoblastoma or mildly elevated in mesenchymal hamartoma, and mesenchymal hamartoma may appear predominantly solid (stromal), leading to diagnostic difficulty. Even biopsy results may be misleading, as mesenchymal hamartoma may histopathologically resemble hepatoblastoma if sampling is limited to the peripheral hepatocyte-rich component of the lesion (30,32,42). In such instances, the uncertainty is resolved only at surgery. The focal form of infantile hemangioendothelioma with myxoid change of the stroma can also resemble mesenchymal hamartoma and occurs in the same age group (3). One-half of hemangioendotheliomas show calcification at CT, whereas mesenchymal hamartoma does not contain calcifications. In addition, the markedly vascular nature of infantile hemangioendothelioma, with enlarged vessels and peripheral nodular enhancement with centripetal fill-in, distinguishes this tumor from the hypovascular mesenchymal hamartoma. Rarely, initial peripheral enhancement with progressive filling has been described in mesenchymal hamartoma; however, the peripheral enhancement is slower and much less intense than that seen in vascular tumors (28). UES shares many imaging and pathologic features with mesenchymal hamartoma but is seen in an older age group (6 10 years of age). At pathologic analysis, UES is distinguished by the frequent finding of hemorrhage and necrosis and by frankly malignant stroma.
14 814 May-June 2010 radiographics.rsna.org Figure 8. FNH in a 6-year-old girl. (a) Photograph of the sectioned gross specimen shows a nodular mass with a stellate scar (arrowhead). Note the adjacent vessel (arrow). * = normal liver. (b) Photomicrograph (original magnification, 40; H-E stain) shows the vascular central scar (arrow) with radiating septa (arrowheads) that separate the hyperplastic hepatocytes into nodules. (c) Transverse US image shows the well-circumscribed, homogeneous, slightly hypoechoic mass (arrows) in the liver. (d) Color Doppler image shows flow in vessels radiating outward from the central scar. (e) On a duplex US image, the Doppler spectrum of the intratumoral vessels shows an arterial waveform. (f) Arterial phase coronal CT image shows the tumor (arrow) enhancing more than the adjacent liver and lack of enhancement of the central scar (arrowhead). (g) Coronal CT image obtained posterior to f shows intensely enhancing vessels (arrow) adjacent to the tumor.
15 RG Volume 30 Number 3 Chung et al 815 For predominantly cystic mesenchymal hamartomas, differential diagnostic considerations include simple cyst, hydatid disease, and abscess if the mass is intrahepatic and choledochal cyst, enteric duplication cyst, and mesenteric lymphangioma if the mass is pedunculated. Simple cysts can be distinguished from mesenchymal hamartoma by the lack of any internal enhancement (43). Hydatid disease and abscess may be suggested by a history of travel or of fever or immunocompromise. Choledochal cyst is located in the porta hepatis and can be shown with nuclear scintigraphy to communicate with the biliary tree. Enteric duplication cysts demonstrate gut signature in their walls and peristalsis at US. The mesenteric origin of lymphangioma may be demonstrated with multiplanar imaging, although intrahepatic lymphangiomas rarely occur. Treatment and Prognosis The natural history of mesenchymal hamartoma is to enlarge during the first several months of life and then stabilize or continue to grow. Spontaneous partial regression has been reported (1,26,44). The definitive treatment, if possible, is complete surgical excision with hepatic lobectomy or nonanatomic resection (3,31). Partial resection and drainage with marsupialization have been used for unresectable lesions, although disease recurrence may follow (1,3). Orthotopic liver transplantation has also been reported (1), but the benign nature of the mass and reports of spontaneous regression support a conservative surgical approach in lesions that involve vital structures (44). Observation of mesenchymal hamartoma is discouraged due to the potential for rapid growth, as well as the rare reports of malignant transformation to UES (26,35,36). The long-term survival rate is high (90%), even with incomplete resection (1,24). Focal Nodular Hyperplasia FNH is most often seen in adult women but uncommonly occurs in young children and adolescents. FNH is a benign epithelial liver tumor arising from a polyclonal proliferation of hepatocytes, Kupffer cells, vascular structures, and biliary ductules. The lesion demonstrates a complex architecture, with well-differentiated hepatocytes forming nodules subdivided by fibrous septa, which coalesce to form a characteristic central vascular stellate scar (45). Pathogenesis Although the exact pathogenesis of the lesion remains uncertain, it is generally accepted that FNH is the result of a vascular abnormality and most likely represents a hyperplastic response to a preexisting vascular malformation within the central scar (45,46). Some authors have suggested that the mass arises from a focal injury or circulatory disturbance within the hepatic parenchyma leading to vascular thrombosis, subsequent recanalization, and reperfusion with resultant hepatocyte proliferation (45). Several studies in children show an increased prevalence of FNH many years after antineoplastic and radiation therapy for solid malignancies, suggesting that chemotherapy-induced vascular injury, including veno-occlusive disease, leads to development of FNH (47). Oral contraceptive use and pregnancy, once considered risk factors for the development of FNH, are no longer considered etiologic factors (45). Epidemiology and Clinical Features FNH represents 2% of all primary hepatic tumors in children from birth to age 20 years (1). In the pediatric population, the lesion is typically diagnosed between the ages of 2 and 5 years (48). Although generally regarded as the result of a congenital vascular malformation, FNH has not been reported in a newborn or stillborn, to our knowledge. A marked female predominance of the lesion is reported (45). As a benign mass with nonaggressive features, FNH is most commonly an incidental finding at imaging, in surgical specimens, or at autopsy. Symptoms of a mass lesion are described in 20% of cases (45). Abdominal pain is another common symptom. Tumor rupture and hemorrhage are rare (45). AFP levels are not elevated (45). Pathologic Features At gross inspection, FNH appears as a solitary mass or, less commonly, multiple lesions that may bulge from the surface of the liver. The mass is well-circumscribed, lobulated, and unencapsulated, although it may be surrounded by a rim of fibrous tissue of variable thickness. Most arise in the right lobe (1,40,45). A central fibrous scar can be seen macroscopically within the light red brown-tan mass in most cases (Figs 8, 9) (4,7). Foci of hemorrhage, necrosis, or infarction are rare, in contradistinction to the findings of hepatocellular adenoma (45).
16 816 May-June 2010 radiographics.rsna.org Figure 9. FNH in a 14-year-old girl. (a) Photograph of the resected specimen shows a nodular mass with a central stellate scar (arrowhead) and an adjacent large vessel (arrow). * = normal liver. (b) Axial T2-weighted MR image shows that the mass (curved arrow) is homogeneously isointense except for the hyperintense central scar (arrowhead) and a large flow void (straight arrow) at the periphery. (c) Nonenhanced axial T1-weighted MR image shows that the mass (curved arrows) is minimally hyperintense relative to adjacent liver and that the central scar (arrowhead) is hypointense. Straight arrow = adjacent artery. (d) Arterial phase axial T1-weighted MR image shows that the mass (arrow) uniformly enhances more than the liver. The central scar does not enhance (arrowhead). (e) Delayed phase axial MR image shows that the mass (arrow) is isointense relative to the liver; there is some enhancement of the central scar (arrowhead). (f) Coronal image from hepatobiliary scintigraphy shows focal increased activity in the mass (arrow) compared with that in the adjacent liver. * = biliary tree. At histologic examination, the lesion parenchyma consists predominantly of hyperplastic hepatocytes. Normal acinar architecture, portal tracts, and interlobular bile ducts are absent (Fig 8). The hyperplastic hepatocytes are similar to normal hepatocytes but may be larger and paler. In addition to the hepatocyte proliferation, there is proliferation of biliary epithelium, which forms
17 RG Volume 30 Number 3 Chung et al 817 ductules but no bile ducts, so that there is no connection to the biliary tree. Kupffer cells are typically present (45). The vascular central stellate scar is also characteristic of FNH. Composed predominantly of large arteries and smaller venous structures in a myxomatous stroma, the vascular component is present throughout the septa that radiate from the central scar (Fig 8) (45). Imaging Features The appearance of FNH at imaging reflects its pathologic features. Because the mass is composed predominantly of hepatocytes, it appears similar to normal liver, and the lesion may be inapparent except for mass effect on adjacent structures. The presence of the central scar may aid identification of the mass on nonenhanced scans (49). The vascular supply from the hepatic artery causes early contrast enhancement relative to the adjacent parenchyma. The scar often demonstrates delayed enhancement as contrast material diffuses into the myxomatous stroma (21). Atypical imaging features are fairly common, and multiple imaging studies may be required to obtain a specific diagnosis. At US, FNH appears as a homogeneous, wellcircumscribed mass that may be iso-, hypo-, or hyperechoic (Fig 8) (50). The central scar appears hyperechoic relative to the remainder of the mass (48,50). Calcification is rare. Color and power Doppler evaluation of the mass reveals increased blood flow in the central scar extending to the periphery in a spoke-wheel pattern (Fig 8) (21,51,52). Spectral analysis of intratumoral flow reveals arterial waveforms, a finding that distinguishes FNH from hepatocellular adenoma, in which intratumoral flow is venous (51). At unenhanced CT, FNH is typically well circumscribed and iso- to slightly hypoattenuating to uninvolved liver, and the scar is hypoattenuating (49,50,52 54). FNH typically demonstrates early, uniform enhancement after intravenous administration of iodinated contrast material. The mass enhances more than the adjacent liver in the arterial and early portal venous phases and becomes isoattenuating to the liver in the late portal venous and delayed phases (49,50,53,54). Enlarged feeding arteries may be apparent on arterial phase images (Fig 8) (49,53). The stellate scar is typically hypoattenuating on early contrast-enhanced images and demonstrates enhancement on delayed images (Fig 8) (49). An enhancing artery may be seen within the hypoattenuating scar on arterial phase images (49,53). Atypical features may be observed including lack of the central scar, rapid washout of contrast material in the portal venous phase, lack of enhancement of the central scar on delayed images, early draining veins, and partial peripheral rim-like enhancement on delayed images (49,53). At MR imaging, FNH typically appears homogeneous and iso- to slightly hypointense to the liver on T1-weighted images and iso- to slightly hyperintense on T2-weighted images (Fig 9) (50,55,56). The scar is usually hypointense to uninvolved liver on T1-weighted images and hyperintense on T2-weighted images owing to edema within the myxomatous tissue of the scar (Fig 9) (50,55,56). Dynamic imaging after intravenous administration of gadolinium contrast material shows uniform enhancement of the mass, which is hyperintense to the liver on arterial phase images and isointense to slightly hyperintense on portal venous phase images (Fig 9) (21,52,55). In general, delayed images demonstrate enhancement of the central scar (Fig 9) (56). In surgical series, which have a selection bias for cases with difficult imaging diagnoses, up to one-half of lesions display an atypical appearance at MR imaging (56). Atypical features include lack of a scar, a scar that is hypointense on T2-weighted images, a T1-hypointense enhancing pseudocapsule due to compression of surrounding parenchyma with mild fibrosis, and a strongly hyperintense lesion on T2-weighted images or diffusely hyperintense lesion on T1-weighted images (56). FNH demonstrates a characteristic appearance at scintigraphy that correlates with its histologic features. 99m Tc sulfur colloid imaging typically exhibits normal uptake in 60% 75% of lesions owing to the presence of Kupffer cells (Fig 10) (48,57). The abundance of Kupffer cells is variable in FNH, and the remainder of the lesions show either increased or, less commonly, decreased radiotracer accumulation relative to normal liver parenchyma. Normal or increased uptake of colloid by the mass distinguishes FNH from hepatic adenoma and malignant tumors (50,52). For smaller lesions, SPECT is particularly useful in localizing the region of radiopharmaceutical uptake. At cholescintigraphy, increased uptake with delayed excretion is shown in 90% of cases, presumably due to uptake by functional hepatocytes within the lesion and abnormal excretion by the biliary ductules, which do not communicate with the biliary tree (Fig 9) (57).
18 818 May-June 2010 radiographics.rsna.org Figure 10. FNH in a 15-year-old girl. (a) Arterial phase coronal T1-weighted MR image shows a homogeneously enhancing mass with hypointense eccentric scars (arrowhead). (b) Coronal single-photonemission computed tomographic (SPECT) image from a sulfur colloid study shows slightly increased uptake in the mass (arrow) relative to the adjacent liver. Differential Diagnosis Differential diagnostic considerations for FNH include other solid tumors that occur in children. The typical homogeneous, nearly isoattenuating appearance distinguishes FNH from the malignant tumors hepatoblastoma and hepatocellular carcinoma, which are more likely to appear heterogeneous due to hemorrhage, necrosis, and calcification. In addition, both are associated with elevated levels of serum AFP, which is absent in FNH. On the other hand, atypical features of FNH overlap with imaging findings in malignant tumors. In such cases, biopsy may be necessary. Fibrolamellar carcinoma may also occur in adolescents and demonstrate a central scar. Unlike the vascular myxomatous scar of FNH, the scar of fibrolamellar carcinoma is collagenous and consequently is hypointense, rather than hyperintense, on T2-weighted images and does not enhance on delayed images. Hepatocellular adenoma may also occur in adolescents, especially girls taking oral contraceptives. FNH may be differentiated from hepatic adenoma on the basis of imaging features, as described in the Hepatocellular Adenoma section. Treatment and Prognosis FNH has no known malignant potential, grows very slowly, rarely causes complications such as hemorrhage or rupture, and may be managed conservatively in asymptomatic patients (48). Symptomatic patients should undergo surgical resection, if possible, or, alternatively, ablative therapy or embolization (48). Hepatocellular Adenoma Hepatocellular adenoma, or hepatic adenoma, is a rare benign hepatic neoplasm that is etiologically associated with the use of steroids, especially oral contraceptives. Imaging findings reflect its histologic composition of sheets of hepatocytes containing intracellular fat and glycogen and its propensity for intratumoral hemorrhage. Clinical Features Most cases of hepatocellular adenoma occur in women in their reproductive years with a mean age of 30 years. Pediatric patients mainly consist of girls over 10 years old, most of whom have a history of oral contraceptive use (24,58). Androgenic steroid therapy is also associated with an increased prevalence of hepatic adenoma and accounts for the occurrence of these neoplasms in pediatric patients with Fanconi anemia (59). Hepatocellular adenomas have been reported in association with several diseases, particularly glycogen storage disease types I and III, and also galactosemia and familial diabetes mellitus. There is also an association with congenital and acquired abnormalities of the hepatic vasculature, such as portal vein absence or occlusion, and other hypervascular hepatic neoplasms, including adult hemangioma and FNH (60,61). The main clinical concern is intratumoral hemorrhage, which occurs in approximately 10% of patients, or, in rare instances, rupture with intraperitoneal hemorrhage and hypovolemic shock (60). More commonly, patients are asymptomatic or present with an abdominal mass. Chronic and acute abdominal pain are other reported symptoms. Results of liver function tests are usually normal with no elevation of AFP level.
19 RG Volume 30 Number 3 Chung et al 819 Figure 11. Multiple hepatocellular adenomas in a gravida 1, para 1 16-year-old girl. (a) Photograph of the sectioned explanted liver shows multiple well-demarcated, yellow-tan masses. (b) In-phase axial T1-weighted gradient-echo MR image shows a heterogeneous, predominantly hypointense mass (arrowheads) with a small hyperintense focus consistent with hemorrhage. In addition, there is also an isointense mass (arrow). (c) Out-of-phase axial MR image shows a decrease in the signal intensity of both masses (arrowheads, arrow), a finding indicative of intralesion fat. (d) Nonenhanced axial T1-weighted spoiled gradient-echo MR image shows the well-defined masses (T). One is slightly hypointense relative to the liver; the other is isointense. (e) Arterial phase axial T1-weighted MR image shows that both masses (T) enhance slightly more than the liver. An additional smaller lesion is visible (arrow). (f) Portal venous phase MR image shows that the masses (T) are isointense to slightly hypointense relative to the liver. Straight arrow = additional smaller lesion, curved arrow = adjacent enlarged vein. Pathologic Features At macroscopic examination, approximately 70% 80% of hepatocellular adenomas are solitary. They are more often multiple in the setting of anabolic androgen therapy or glycogen storage disease (45). Liver adenomatosis has been defined as a separate entity consisting of over 10 adenomas per patient without underlying glycogen storage disease or steroid use (Fig 11) (62,63).
20 820 May-June 2010 radiographics.rsna.org Figure 12. Hepatocellular adenoma in a 19-year-old woman. (a) Photograph of the sectioned gross specimen shows a heterogeneous mass with a pseudocapsule (arrowhead) and intratumoral hemorrhage (arrow). (b) Photomicrograph (original magnification, 400; H-E stain) of a specimen from an 8-week-old patient shows hepatocytes arranged in sheets without normal acinar architecture. Some cells contain clear lipid vacuoles. (c) Axial contrast-enhanced CT image shows the heterogeneous mass with its pseudocapsule (arrowheads). The mass has a layered appearance with the dependent portion being relatively hyperattenuating, a finding that corresponds to the hemorrhage seen in a. (d) Axial nonenhanced T1-weighted MR image shows the mass in the left lobe (arrowheads) and the dependent area of high signal intensity representing hemorrhage (arrow). (e) Axial T2-weighted MR image shows that the mass is heterogeneous, with the area of hemorrhage being markedly hypointense (arrow). Hepatocellular adenomas are spherical or ovoid well-circumscribed masses (45). Most are 1 15 cm in diameter and yellow to tan-brown (Fig 11). Heterogeneity is frequent due to areas of necrosis, hemorrhage, myxoid stroma, or calcification (Fig 12) (61). They are usually unencapsulated, although a pseudocapsule of compressed adjacent hepatic parenchyma may be present. At histologic examination, hepatocellular adenomas are composed of benign-appearing hepatocytes in sheets or cords rather than the normal acinar pattern (Fig 12). The cells usually contain increased amounts of fat and glycogen compared with the hepatocytes in the surrounding normal liver, except in the glycogenoses, in which the opposite is true (45). Kupffer cells are present, although they demonstrate reduced numbers and function compared with those in normal liver, so that little uptake is seen after 99m Tc sulfur colloid administration (61). Bile ducts are absent. Large peri-
21 RG Volume 30 Number 3 Chung et al 821 Figure 13. Hepatocellular adenoma in a 21-year-old woman. * = normal liver. (a) Photograph of the gross specimen shows hemorrhage (arrowheads) within the mass. (b) Nonenhanced CT image shows the heterogeneous mass replacing the right hepatic lobe. The hyperattenuating focus (arrowhead) is indicative of acute hemorrhage. tumoral arteries feed the sinusoids; in combination with poor connective tissue support, this feature is thought to predispose these neoplasms to hemorrhage. Imaging Features The appearance of hepatocellular adenoma varies depending on its pathologic composition. Those without hemorrhage are homogeneous and similar in appearance to adjacent normal liver. The presence of intratumoral hemorrhage or intracellular fat produces distinguishing imaging features. The US appearance of hepatocellular adenomas depends both on the composition of the lesion and that of the surrounding liver. Lesions with a high lipid content or hemorrhage may be hyperechoic to the normal liver; however, in the background of diffuse fatty infiltration or glycogen storage disease, adenomas may be hypoechoic compared with the remainder of the liver (64). Color Doppler evaluation may demonstrate central vessels with a triphasic pattern or a continuous flat venous waveform with no central arterial flow (65), in contrast to FNH, which has predominant central arterial flow. Peripheral peritumoral arterial and venous waveforms may be seen. At CT, hepatocellular adenomas are typically sharply marginated, with a pseudocapsule seen in 25% 30% (Fig 12) (61,66). On unenhanced images, most lesions are hypoattenuating compared with normal liver, although areas of hyperattenuation are seen with recent hemorrhage in approximately 15% 43% (Fig 13) (61,66 68). They may be heterogeneous with areas of lipid or fat seen at CT in 7% 10% and calcification in 5% 15% (61,64,66). Smaller lesions, less than 4 cm, are typically homogeneously enhancing, whereas larger lesions heterogeneously enhance because of necrosis, fat, hemorrhage, and calcification (Fig 12). Hepatocellular adenomas demonstrate preferentially hepatic arterial enhancement after administration of iodinated contrast material, with most being hyperattenuating compared with the normal liver in the arterial phase and isoattenuating in the portal venous and delayed phases. At MR imaging, most hepatocellular adenomas are predominantly hyperintense to the normal liver on T1-weighted and T2-weighted images (35% 77% and 47% 74%, respectively) (61,69 71). T1 hyperintensity from intracellular glycogen or lipid demonstrates signal dropout on opposed-phase or fat-suppressed images in 36% 77% of cases (Fig 11) (61). However, this finding is not specific for adenoma, as 40% of hepatocellular carcinomas also histologically contain fat. T1 hyperintensity can also be due to hemorrhage in 52% 93% of cases (Fig 12) (61). T2 hyperintense areas may represent hemorrhage or areas of peliosis-like changes at pathologic analysis (60,69). A peripheral pseudocapsule may be seen that is hypointense on T1-weighted images, is variable on T2-weighted images, and may enhance (Fig 12). According to a study of 51 adenomas by Arrive et al (69), 88% of hepatic adenomas demonstrated one of the following findings: tumor heterogeneity, a peripheral rim, or hyperintense T1 signal. As with CT, hepatic adenomas usually demonstrate early arterial enhancement on MR images after intravenous administration of gadolinium contrast material, becoming isointense to the liver on portal venous and delayed phase images (Fig 11). Nuclear medicine studies show nonspecific findings. A focal photopenic defect is seen on 99m Tc sulfur colloid scans. At hepatobiliary scintigraphy, because of the lack of bile ducts, hepatocellular adenomas demonstrate increased uptake or retention of the radiotracer (72).
22 822 May-June 2010 radiographics.rsna.org Figure 14. NRH. (a) Photograph of the sectioned resected specimen from a 10-year-old girl shows replacement of part of the liver by a cluster of yellow-brown nodules. * = normal liver. (b) Photomicrograph (original magnification, 40; H-E stain) shows coalescing relatively pale nodules surrounded by darker intervening parenchyma. (c) US image obtained in a 21-year-old man shows a well-circumscribed, homogeneous, hypoechoic hepatic mass (arrow). (d) On a contrast-enhanced CT image, the mass (arrow) diffusely enhances more than adjacent liver. (e) Axial T1-weighted MR image shows that the mass (arrow) is ill defined and slightly hypointense relative to the liver with a slightly hyperintense partial rim. (f) Axial T2-weighted MR image shows the ill-defined hyperintense mass (arrow). Differential Diagnosis Other liver lesions that are hyperattenuating in the arterial phase of contrast-enhanced studies include FNH, hepatocellular carcinoma, and fibrolamellar carcinoma. FNH frequently has a stellate scar and is homogeneous, whereas hepatic adenoma does not have a scar and may be quite heterogeneous in appearance due to intratumoral hemorrhage or fat. Also, FNH lacks the intrale-
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