(Radiographics. 1999;19:1465-1485.)
© RSNA, 1999
A Pattern-oriented Approach to Splenic Imaging in Infants and Children1
Anne Paterson, MRCP, FRCR ,
Donald P. Frush, MD ,
Lane F. Donnelly, MD ,
Joseph N. Foss, MD ,
Sara M. O'Hara, MD and
George S. Bisset, III, MD
1 From the Department of Radiology, Division of Pediatric Radiology, Duke University Medical Center, Durham, NC 27710. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received February 16, 1999; revision requested March 16 and received April 1; accepted April 1. Address reprint requests to D.P.F.
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Abstract
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The spleen in infants and children is commonly involved in a variety of pathologic processes. Some of these processes cause isolated splenic disease, whereas others involve the spleen as part of a systemic illness. To facilitate differential diagnosis of splenic abnormalities, a pattern-oriented approach to the imaging evaluation of the pediatric spleen was developed. With this approach, splenic anomalies are categorized as anomalies of splenic shape (clefts, notches, lobules), location (eg, wandering spleen), number (polysplenia, asplenia), or size (splenomegaly, splenic atrophy); solitary lesions (eg, cysts, lymphangiomas, hemangiomas, hamartomas); multiple focal lesions (eg, trauma, infection and inflammation, neoplasms, storage disorders); and diffuse disease without focal lesions (eg, infarction, heavy metal deposition, hemangioendotheliomas, peliosis). A variety of imaging modalities can be used in splenic assessment, including computed tomography, magnetic resonance imaging, ultrasound, and technetium-99m scintigraphy. The imaging appearance of the pediatric spleen depends on the patient's age and the modality used; however, familiarity with the spectrum of radiologic patterns of splenic involvement will facilitate correct diagnosis and prompt treatment.
Index Terms: Children, gastrointestinal system, 775.**2 • Infants, gastrointestinal system, 775.**2 • Spleen, abnormalities, 775.134, 775.1653 • Spleen, CT, 775.12112 • Spleen, MR, 775.12141 • Spleen, radionuclide studies, 775.12171 • Spleen, size, 775.372 • Spleen, US, 775.1298
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INTRODUCTION
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The spleen in infants and children is commonly involved in a wide variety of pathologic conditions. Splenic disorders may be isolated or may be due to multiorgan or systemic disease. The spleen can be evaluated with a number of imaging modalities including ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging. In this article, we discuss and illustrate normal variations in the imaging appearance of the spleen in pediatric patients and demonstrate the common radiologic patterns of splenic involvement in a variety of disease processes.
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NORMAL SPLEEN
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Embryologic and Histologic Features
The spleen arises from mesenchymal cells between the layers of the dorsal mesogastrium during the fifth gestational week. The mesenchymal cells of the splenic primordium differentiate to form the capsule, connective tissue framework, and splenic parenchyma. The characteristic lobulated configuration of the fetal spleen is recognizable by the third gestational month as the aggregations of mesenchymal tissue fuse (1).
At histologic analysis, the spleen is composed of red and white pulp. The red pulp is made up of numerous vascular sinuses. Between these sinuses lie the lymphoid follicles and the cells of the reticuloendothelial system, which together constitute the white pulp (2). The ratio of white to red pulp increases with patient age and progressive antigenic stimulation (3). This unique anatomy of the spleen leads to normal variations in appearance that can be appreciated at CT and MR imaging.
Helical CT
The helical CT appearance of the spleen largely depends on the timing of intravenous bolus administration of contrast material. In up to 72% of pediatric patients, the spleen may demonstrate heterogeneous enhancement during the first minute after initiation of intravenous administration of contrast material because of the different rates of flow through the cords of the red and white pulp (4–7). This heterogeneity is itself variable in appearance; patterns include arciform (alternating bands of high and low attenuation) (Fig 1), focal (Fig 2), and diffuse heterogeneity. The frequency of these artifacts increases with increased injection rate and patient age as well as absence of splenomegaly (4). Familiarity with these enhancement characteristics minimizes the chance that artifacts will be mistaken for disease. In more than 95% of pediatric CT examinations, splenic heterogeneity is resolved within 70 seconds of the initiation of contrast material injection (4). Consequently, low-attenuation lesions that are seen after this time should raise suspicion for a disease process. Helical CT scans obtained during the portal venous phase usually demonstrate homogeneous attenuation throughout the spleen.
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Figure 1. Arciform splenic enhancement artifact in a 10-year-old girl with undifferentiated sarcoma. Contrast material-enhanced CT scan shows alternating bands of high and low attenuation. The artifact occurs during the early phase of contrast enhancement—in this case, only 20 seconds after the initiation of contrast material injection.
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Figure 2. Focal artifact in a 10-year-old boy with a history of lymphoproliferative disorder who had undergone liver transplantation. Contrast-enhanced CT scan shows focal low-attenuation artifact mimicking a splenic mass (arrow).
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MR Imaging
The normal MR imaging appearance of the spleen varies with patient age. Splenic signal intensity is directly related to the ratio of white to red pulp (2). In adults and older children, the spleen is bright on T2-weighted images. In the neonate, however, before maturation of the lymphoid system and proliferation of white pulp, the spleen is hypointense relative to the liver on both T1- and T2-weighted spin-echo images (Fig 3). The spleen does not assume its normal high-signal-intensity adult appearance on T2-weighted images until the white pulp has matured at approximately 8 months of age (Fig 4) (2). Red pulp, which predominates in the infant, probably contributes to the low signal intensity of the spleen on T2-weighted images because it consists of sinusoids of nonthrombotic blood. During the latter part of infancy, the white pulp probably contributes to high signal intensity on T2-weighted images because of the higher water content of the lymphoid tissue. The normal low signal intensity of the spleen seen during the first months of life should not be confused with pathologic conditions such as hemochromatosis (2,8).
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Figure 3. Normal spleen in a 4-day-old male infant. T2-weighted (repetition time msec/echo time msec = 1,800/80) MR image demonstrates hypointensity of the spleen (arrow) relative to the liver. The nonthrombotic blood in the splenic sinusoids contributes to this finding, which should not be confused with a pathologic condition such as hemochromatosis.
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Figure 4. Normal spleen in a 5-year-old child. T2-weighted (1,800/80) MR image demonstrates hyperintensity of the spleen (arrow) relative to the liver. The high water content of the lymphoid tissue of the white pulp contributes to this finding.
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Ultrasonography
At US, the spleen has a homogeneous echotexture and differentiation between red and white pulp is not possible. The presence of focal heterogeneity in echotexture should raise suspicion for a pathologic condition.
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ANOMALIES OF SPLENIC SHAPE, LOCATION, NUMBER, OR SIZE
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Splenic clefts, notches, and lobules may persist into adult life as variations in normal shape. In addition, the spleen may be found in a variety of locations (Fig 5). Congenital diaphragmatic eventrations or hernias can lead to an intrathoracic location (9), or a deep lateral peritoneal recess can leave the spleen lying posterior to the left kidney (10).
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Figure 5a. Abnormal splenic location in an infant girl with cyanotic congenital heart disease. The spleen could not be visualized at US. (a) On an anterior technetium-99m sulfur colloid scintigram, only the liver is clearly identified; the radiotracer is normally taken up by both the liver and spleen. (b) Anterior Tc-99m denatured red cell scintigram clearly depicts only the spleen (arrow), which lies beneath the right lobe of the liver.
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Figure 5b. Abnormal splenic location in an infant girl with cyanotic congenital heart disease. The spleen could not be visualized at US. (a) On an anterior technetium-99m sulfur colloid scintigram, only the liver is clearly identified; the radiotracer is normally taken up by both the liver and spleen. (b) Anterior Tc-99m denatured red cell scintigram clearly depicts only the spleen (arrow), which lies beneath the right lobe of the liver.
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Failure of the individual clumps of mesenchymal cells to fuse properly results in accessory spleens, which are found in up to 30% of autopsies (11). These spleens vary from a few millimeters to several centimeters in size. Accessory spleens range from one to six in number and are usually found near the splenic hilum, along the course of the splenic vessels, or within the layers of the omentum (10,11). Accessory spleens can occur anywhere in the abdomen, and, owing to the close relationship between the developing spleen, mesonephros, and left gonadal anlage, they may even be found attached to the left ovary or within the scrotum. The latter condition is referred to as splenogonadal fusion and is important primarily because failure to recognize it can lead to unnecessary orchiectomy. However, splenogonadal fusion can be diagnosed preoperatively with US or Tc-99m sulfur colloid scintigraphy (12). An accessory or ectopic spleen has imaging characteristics identical to those of normal splenic tissue and may be identified at US, CT, or Tc-99m sulfur colloid scintigraphy. Any accessory splenic tissue is capable of hypertrophy. When splenectomy is performed for hypersplenism, hypertrophy of an accessory spleen may cause recurrent disease (Fig 6) (9–11).
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Figure 6. Hypertrophic accessory spleen in a young girl with hereditary spherocytosis who had undergone splenectomy 30 days earlier. The surgeon had removed all visible splenic tissue. A mass was palpated in the left upper quadrant at follow-up. Contrast-enhanced CT scan shows regeneration of the accessory spleen (arrow).
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If the ligamentous attachments of the spleen are lax or absent, the spleen is free to "wander" from its normal location in the left upper quadrant of the abdomen (Fig 7). Wandering spleen has been described with increasing frequency in patients with deficient musculature of the anterior abdominal wall, such as that which occurs in prune-belly syndrome (13). Children with a wandering spleen may present with an unexplained abdominal mass or acute abdominal symptoms secondary to torsion about an elongated pedicle. Radiography may demonstrate absence of the normal splenic outline in the left upper quadrant and an associated soft-tissue mass in the center of the abdomen or pelvis. Cross-sectional imaging with US or CT helps confirm the absence of the spleen in its expected location and the presence of a homogeneous soft-tissue mass more inferiorly within the abdomen or pelvis. The hilum of the wandering spleen is often located anteriorly. Torsion about the pedicle leads to splenic ischemia or even infarction. In splenic torsion, Doppler US demonstrates no flow within the spleen itself and a low diastolic velocity with an elevated resistive index in the proximal splenic artery (14). CT demonstrates heterogeneous enhancement with lower attenuation (15). Another useful CT finding that has been described is the characteristic whorled appearance of the twisted splenic pedicle that is created by alternating bands of high-attenuation vessels and adjacent low-attenuation fat (3,16).
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Figure 7a. Wandering spleen without evidence of torsion in a 7-year-old girl. (a) Contrast-enhanced CT scan reveals an anterior mass at the level of the cecal pole (solid arrows) with vessels entering posteromedially (open arrow). (b) Anterior Tc-99m sulfur colloid scintigram shows the mass to be an abnormally located spleen (arrow). The liver also demonstrates radiotracer uptake (top).
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Figure 7b. Wandering spleen without evidence of torsion in a 7-year-old girl. (a) Contrast-enhanced CT scan reveals an anterior mass at the level of the cecal pole (solid arrows) with vessels entering posteromedially (open arrow). (b) Anterior Tc-99m sulfur colloid scintigram shows the mass to be an abnormally located spleen (arrow). The liver also demonstrates radiotracer uptake (top).
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Splenosis occurs when traumatized splenic tissue is scattered about the abdominal cavity, where it attaches to the adjacent peritoneal surface. The significance of this disease process is threefold. First, such nodules may provide some protection against infection if the pediatric patient has undergone splenectomy (17). Second, the nodules may mimic mass lesions such as metastases or lymphoma at subsequent imaging (18). Third, if a hematologic problem such as idiopathic thrombocytopenic purpura develops later in the patient, the splenic nodules may be responsible for disease recurrence after splenectomy (9). As with accessory and ectopic spleens, a variety of imaging modalities can be used to detect splenosis. Scintigraphy with Tc-99m sulfur colloid or with denatured red cells are reported to be the most sensitive techniques (17,19).
Abnormalities in splenic size, number, and location can also accompany congenital heart disease. Either polysplenia or asplenia may be seen with abdominal situs ambiguous. Polysplenia is more common in females. In polysplenia, numerous small splenic masses can be seen predominantly in the right upper quadrant at US, CT, MR imaging, or Tc-99m sulfur colloid scintigraphy (Figs 8 –10). Additional features of polysplenia syndrome include interruption of the infrahepatic portion of the inferior vena cava with azygous continuation and a tendency for bilateral distribution of left-sided viscera. Associated cardiac disease is usually amenable to surgery and commonly takes the form of acyanotic left-to-right shunts such as septal defects (20). Malrotation of the bowel and absence of the gallbladder have also been reported.
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Figure 8. Heterotaxia syndrome in a 2-year-old girl. Axial T1-weighted (600/11) MR image shows polysplenia (solid arrows) with azygous continuation of the inferior vena cava (open arrow). The intrahepatic portion of the inferior vena cava is absent. The accessory spleens are isointense relative to the adjacent spleen.
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Figure 9. Heterotaxia syndrome in a 5-month-old infant with congenital heart disease. Axial T1-weighted (600/20) MR image shows polysplenia (arrows). The accessory spleens are all isointense relative to normal splenic tissue.
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Figure 10. Heterotaxia syndrome in a male neonate with biliary atresia. Axial T1-weighted (600/10) MR image shows the liver and midline polysplenia (solid arrow) with a right-sided stomach (open arrow). A preduodenal portal vein (not shown) was also present.
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Asplenia has a greater prevalence in males. Documentation of the absence of the spleen is more difficult than confirmation of its presence. At microscopic analysis, the peripheral blood will contain Heinz or Howell-Jolly bodies. Bakir et al (19) described the use of Tc-99m–labeled denatured red cells in this setting to separate the overlying liver from the spleen on blood pool images. In asplenia, the inferior vena cava and abdominal aorta lie on the same side of the spine and there is bilateral right-sided distribution of the viscera. Unlike polysplenia, asplenia tends to be associated with complex cyanotic heart disease (20). Midgut malrotation, microgastria, and gallbladder duplication have all been described in association with asplenia.
Absence of splenic uptake of radiotracer can also occur with functional asplenia in sickle cell disease, secondary to radiation therapy and chemotherapy, secondary to tumor invasion of the spleen, with splenic anoxia, or after bone marrow transplantation (9). The term functional asplenia refers to a marked decrease in splenic phagocytic function despite the presence in the body of splenic tissue. Congenital splenic hypoplasia is rare. Radiotracer uptake is decreased or absent, depending on the absolute amount of splenic tissue present (21).
At birth, the spleen can weigh as little as 15 g and is less than 6.0 cm in length. During childhood, there is a roughly logarithmic increase in splenic length with increasing age (22). Most pediatric radiology textbooks include graphs of organ length versus the patient's age (23). Splenomegaly may be an isolated sign at presentation or can occur with a constellation of other problems (Fig 11). The main causes of splenomegaly are listed in Table 1.
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Figure 11. Splenomegaly in a 15-year-old boy with cystic fibrosis, cirrhosis, and portal hypertension. Contrast-enhanced CT scan obtained at the level of the superior mesenteric artery shows a portosystemic shunt (arrow).
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One of the most common noninfectious causes of splenomegaly in children is portal hypertension. With the increase in resistance to portal venous blood flow, both hepatopetal (portal-to-portal) and hepatofugal (portosystemic) collateral vessels develop. If the main portal vein itself is thrombotic, collateral vessels develop at the porta hepatis. This is known as cavernous transformation of the portal vein, or cavernoma (Fig 12). Patients often present with significant gastrointestinal bleeding. Most cases of portal vein thrombosis in children are idiopathic.
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Figure 12a. Cavernous transformation of the portal vein in a 16-year-old girl with idiopathic portal hypertension who presented with hypersplenism. Coronal T1-weighted (500/10) (a) and axial gradient-echo (33/12, 30° flip angle) (b) MR images show massive splenomegaly. Multiple low-signal-intensity lesions are seen within the spleen in b. These lesions are due to susceptibility artifact from hemosiderin-laden siderotic nodules, which developed secondary to repeated hemorrhage.
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Figure 12b. Cavernous transformation of the portal vein in a 16-year-old girl with idiopathic portal hypertension who presented with hypersplenism. Coronal T1-weighted (500/10) (a) and axial gradient-echo (33/12, 30° flip angle) (b) MR images show massive splenomegaly. Multiple low-signal-intensity lesions are seen within the spleen in b. These lesions are due to susceptibility artifact from hemosiderin-laden siderotic nodules, which developed secondary to repeated hemorrhage.
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Intrahepatic causes of portal hypertension include cirrhosis and chronic liver disease. In such cases, US, CT, MR imaging, and Tc-99m sulfur colloid scintigraphy demonstrate the enlarged spleen and the shrunken, irregularly marginated liver; scintigraphy will also show decreased hepatic uptake of radiotracer. In severe cases of cirrhosis, a shift in colloid distribution occurs, with the majority of radiotracer being taken up by the spleen (Fig 13).
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Figure 13. Shift in colloid distribution in an adolescent girl with portal hypertension secondary to hepatic veno-occlusive disease who had undergone bone marrow transplantation. Posterior Tc-99m sulfur colloid scintigram shows radiotracer uptake predominantly in the spleen (arrowhead) but also in the liver (open arrow) and faintly in the bone marrow (solid arrow). These findings resolved completely after successful anticoagulation therapy.
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One emergent cause of splenomegaly is acute splenic sequestration (Fig 14). This condition occurs predominantly in young children with sickle cell disease before functional asplenia develops. The triggering event is unknown. At clinical examination, patients demonstrate massive splenic enlargement and a rapid drop in hemoglobin and platelet counts as the spleen traps large volumes of blood. Hypovolemic shock can set in rapidly. The diagnosis of splenic sequestration is usually based on clinical findings, including a history of sickle cell disease, left upper quadrant pain, splenomegaly, and thrombocytopenia. At US, the spleen will appear enlarged and heterogeneous with areas of decreased echogenicity. Doppler US shows the main splenic vessels to be patent (3,24). CT demonstrates peripheral areas of decreased attenuation with areas of increased attenuation secondary to acute hemorrhage. Areas of increased signal intensity on both T1- and T2-weighted MR images represent subacute hemorrhage (3,24).
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Figure 14. Splenomegaly secondary to acute sequestration crisis in a 20-month-old girl with sickle cell anemia. An enlarged spleen was palpated at physical examination. Abdominal radiograph shows a large, soft-tissue structure in the left upper quadrant.
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Extramedullary hematopoiesis is associated with hemolytic anemias and infiltrative bone marrow disorders in children. The spleen is one of the major sites of hematopoiesis in the fetus until around 28 weeks gestation, but it retains the capacity to produce blood cells until well into adult life (1). At CT, the spleen may be diffusely enlarged, or focal masses of hematopoietic tissue that are isoattenuating relative to normal splenic tissue may be seen after intravenous administration of contrast material (11).
Splenomegaly can also develop in infants who undergo extracorporeal membrane oxygenation. The mechanism is thought to be related to the red cell damage that occurs, with the spleen removing these damaged cells (25).
Splenic atrophy is less common than splenic enlargement (Table 1). Congenital splenic atrophy is associated with recurrent bacterial infections (21).
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PATTERNS OF INVOLVEMENT IN PARENCHYMAL DISEASE
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Solitary Lesions
Cysts.—Splenic cysts are classified as either true cysts (ie, having an epithelial cell lining) or pseudocysts (ie, lacking an epithelial cell lining) (Table 2). True cysts include congenital or epidermoid cysts and parasitic cysts secondary to ecchinococcal infection. Pseudocysts tend to follow trauma or infarction. Reliable differentiation between true cysts and pseudocysts is usually not possible at imaging (26). Complications of splenic cysts include infection and cystic rupture (26).
Epidermoid cysts account for 10% of all benign, nonparasitic splenic cysts worldwide (27). At US, epidermoid cysts manifest as well-defined, thin-walled anechoic lesions that do not change over time (Fig 15). Wall calcification has been reported in 10% of cases (27). Septations and cyst wall trabeculation may also be present. Intracystic fluid may have increased echogenicity due to cholesterol crystals, inflammatory debris, or hemorrhage (26). At CT, epidermoid cysts manifest as rounded, well-demarcated nonenhancing lesions with near water attenuation (Fig 16). Trabeculations and calcifications may be more clearly depicted at CT. MR imaging also demonstrates a rounded, homogeneous lesion. An uncomplicated epidermoid cyst will have a signal intensity similar to that of water. If there is hemorrhage into the cyst, the signal intensity reflects the chemical state of the hemoglobin present. Increased signal intensity on both T1- and T2-weighted MR images has been reported with subacute hemorrhage in epidermoid cysts (28).
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Figure 15. Splenic epidermoid cyst in a 5-year-old boy. Transverse US scan through the spleen shows an anechoic lesion with internal septations (arrow). The cyst was discovered incidentally.
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Figure 16. Epidermoid cyst in a 7-year-old boy. Contrast-enhanced CT scan demonstrates a splenic epidermoid cyst (arrow). The lesion was initially discovered at US for urinary tract infection. The diagnosis was confirmed at histopathologic analysis.
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Echinococcal infections involve the spleen in approximately 2% of cases (29) and occur secondary to systemic dissemination or intraperitoneal spread of a ruptured liver cyst. Infection in humans is usually caused by E granulosa. The most common radiographic findings are splenomegaly or a soft-tissue mass in the left upper quadrant. Linear calcification may also be seen at radiography (29). Well-defined cystic masses are seen at US. These cysts are usually solitary, but there may be smaller, subjacent daughter cysts. Hydatid sand and infolded membranes may produce the US appearance of a solid lesion (29). When present, calcification is easier to visualize at CT. The cyst contents are predominantly of water attenuation with higher-attenuation areas representing internal debris (29,30). No enhancement occurs with intravenous administration of contrast material (29).
Lymphangiomas.—Lymphangiomas are vascular lesions that may be single or multiple. When they are multiple, these lesions may form part of a generalized angiomatosis (30–32). At histopathologic analysis, lymphangiomas are made up of multiple endothelium-lined vascular channels filled with lymph (30). Capillary, cavernous, and cystic lymphangiomas have been identified, depending on the size of the channels (31,33). Radiography may demonstrate splenomegaly with calcification in the dilated lymphatic vessels (33). US, CT, and MR imaging typically demonstrate septate, subcapsular cystic lesions. At US, the lesions are hypoechoic and may contain debris (32). Curvilinear calcification can be seen at CT (33,34), and the lesions do not enhance with use of contrast material. The cyst contents have increased signal intensity on T2-weighted MR images (28,32) and may also have high signal intensity on T1-weighted images owing to the proteinaceous nature of the fluid or to internal hemorrhage (30,35). The fibrous septa appear as linear areas of decreased signal intensity on both T1- and T2-weighted images. The lesions do not take up radiotracer on Tc-99m sulfur colloid scintigrams, and a pathognomonic "Swiss cheese" appearance has been described at angiography (32,33).
Hemangiomas.—Hemangiomas are the most common primary neoplasm of the spleen and are composed of endothelium-lined vascular channels filled with red blood cells (11,31,35,11,31,35, 36). The lesions are divided into capillary and cavernous types, depending on the size of the channels. They may appear cystic, solid, or a combination of the two at imaging (30,31, 35, 30, 31, 35, 37). Like lymphangiomas, hemangiomas may be multiple and form part of a generalized angiomatosis such as Klippel-Trénaunay-Weber syndrome (11,30,31,36,37). Hemangiomas have also been reported in association with Beckwith-Wiedemann syndrome (38) and Turner syndrome (39). The lesions are usually asymptomatic but can cause portal hypertension (36), splenic rupture (11,31), or Kasabach-Merritt syndrome (11,36,37). The latter can occur with large hemangiomas anywhere in the body secondary to platelet trapping, consumptive coagulopathy, or anemia.
The US appearance of hemangiomas is nonspecific. Lesions may be well-marginated and predominantly hyperechoic with occasional calcifications (37,40) or cysts (30,37), depending on the size of the vascular channels. Doppler US may demonstrate flow within the mass (30,37). Findings at unenhanced CT reflect histopathologic findings. Lesions may be either cystic or solid (11,30,31,37). Solid areas may
be hypo- or isoattenuating relative to normal splenic tissue. With dynamic contrast-enhanced technique, lesions typically enhance from the periphery inward as do liver hemangiomas (11,30, 11, 30, 31, 37). The predominantly cystic lesions are avascular, and only the solid components enhance (31). Calcification may demonstrate a linear or mottled appearance (11,30,31, 11, 30, 31, 37). MR imaging findings are also similar to those in liver hemangiomas (Fig 17). The lesions are hypo- or isointense on T1-weighted images and hyperintense on T2-weighted images relative to normal splenic tissue (30,35–37). Lesions may appear heterogeneous on T2-weighted images if there are mixed cystic and solid components (37). If hemorrhage into the lesion has occurred and imaging is performed subacutely, increased signal intensity will be seen on T1-weighted images (30). Low signal intensity may be seen with hemosiderin deposition with all sequences (37). Hemangiomas do not show radiotracer uptake on Tc-99m sulfur colloid scintigrams (37).
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Figure 17. Hemangiomatosis in a 1-month-old boy. Axial fat-saturated T2-weighted fast spin-echo (4,000/102) MR image shows multiple areas of increased signal intensity within an enlarged and distorted liver and small foci of increased signal intensity within the spleen (arrows).
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Hamartomas.—Hamartomas are nonneoplastic lesions composed of a mixture of normal splenic components. They are typically single and may be associated with hamartomas elsewhere as in tuberous sclerosis (36). Most lesions contain both white and red pulp (36). The majority of patients are asymptomatic. At CT, hamartomas have an attenuation similar to that of normal splenic tissue and in some cases are seen only if the splenic contour is abnormal (11,36). Other investigators have reported considerable heterogeneity of the lesions with some calcification (31). Hamartomas are isointense relative to normal splenic tissue on T1-weighted MR images (35) and heterogeneously hyperintense on T2-weighted images (35,36). Hamartomas can demonstrate prolonged, heterogeneous enhancement after intravenous administration of contrast material (36).
Multiple Focal Abnormalities
Trauma.—The spleen is one of the most frequently injured intraperitoneal organs in both children and adults (3,11,41). In recent years, the majority of splenic injuries have been managed nonsurgically owing to the risk of sepsis in the postsplenectomy patient. The fact that children have a relatively thicker splenic capsule than adults probably accounts for the more successful nonsurgical management of splenic trauma in children (3).
There are varying degrees of splenic injury, which includes lacerations, fractures, rupture, and intrasplenic and subcapsular hematomas. Contrast-enhanced CT is extremely sensitive in the evaluation of splenic injury. Several grading systems are used to classify the extent of traumatic anatomic organ disruption at CT. One of the more commonly used grading systems was devised by the Organ Injury Scaling Committee of the American Association for the Surgery of Trauma (42). However, the grade of splenic injury at CT does not directly influence clinical management (42–44). The need for surgical intervention is assessed with clinical criteria such as recalcitrant hypotension due to hemorrhage. The finding at contrast-enhanced CT that is most often considered to require surgical intervention is active extravasation of intravenously administered contrast material from the region of splenic injury (43,44). This association exists even for those patients with lacerations and hematomas that do not involve the hilar vessels because delayed hemorrhage can occur (44).
A splenic laceration is seen at CT as an irregular, low-attenuation defect traversing the splenic parenchyma and capsule. If the cleft extends through two capsular surfaces, it is called a fracture (Fig 18). Lacerations are associated with free intraperitoneal fluid. If there is active arterial bleeding from the injury at the time of scanning, a focus of high attenuation that is iso- or hyperintense relative to the major arteries will be identified (Fig 19) (7,44). At contrast-enhanced CT, an intrasplenic hematoma manifests as a well-defined lesion with decreased attenuation relative to normal splenic tissue. A subcapsular hematoma also has low attenuation but is lentiform and flattens the spleen subjacent to the capsule.
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Figure 18a. Splenic trauma in a 3-year-old boy. (a) Contrast-enhanced CT scan shows a ruptured spleen with free intraperitoneal fluid. The patient also had an associated liver laceration (not shown). (b) Contrast-enhanced CT scan obtained 6 weeks later after conservative management shows a posttraumatic cyst (arrow).
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Figure 18b. Splenic trauma in a 3-year-old boy. (a) Contrast-enhanced CT scan shows a ruptured spleen with free intraperitoneal fluid. The patient also had an associated liver laceration (not shown). (b) Contrast-enhanced CT scan obtained 6 weeks later after conservative management shows a posttraumatic cyst (arrow).
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Figure 19. Splenic trauma in an adolescent girl who was involved in a motor vehicle accident. CT scan shows active extravasation of intravenously administered contrast material (arrows). This finding is considered to require surgical intervention.
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Delayed rupture of the spleen is defined as hemorrhage occurring more than 48 hours after trauma in a patient who was previously in stable condition and demonstrated normal findings at CT. An underlying subcapsular hematoma is thought to be responsible (3). Spontaneous rupture of the spleen is also known to occur in association with underlying disease, resulting in splenomegaly (Table 1) (Fig 20) (3), hemangioma (11,31,36), epidermoid cyst (27), peliosis (45), and previous splenic infarction (3).
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Figure 20. Spontaneous splenic rupture in a 15-year-old boy with splenomegaly who had undergone bone marrow transplantation for leukemia. US showed nonspecific heterogeneity of the splenic echotexture. On a contrast-enhanced CT scan, the splenic fragments are readily appreciated (arrows).
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Infection and Inflammation.—The rarity of primary splenic abscesses is probably related to splenic phagocytic immune functions (3). A splenic abscess may be bacterial, fungal, or granulomatous (Fig 21). In infants and children, splenic abscesses occur most frequently in immunocompromised patients. Abscesses may be single or multiple. With fungal infections in an immunocompromised patient, abscesses are typically multiple.
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Figure 21a. Calcified granulomas due to congenital cytomegalovirus infection in a 2-day-old girl. (a) Abdominal radiograph shows calcifications within the liver (open arrow) and spleen (solid arrow). (b) Unenhanced CT scan (bone window) shows the extent of the calcifications more clearly (arrowhead).
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Figure 21b. Calcified granulomas due to congenital cytomegalovirus infection in a 2-day-old girl. (a) Abdominal radiograph shows calcifications within the liver (open arrow) and spleen (solid arrow). (b) Unenhanced CT scan (bone window) shows the extent of the calcifications more clearly (arrowhead).
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Pyogenic abscesses can be secondary to underlying sepsis or spread by hematogenous seeding. Amebic dysentery, otitis media, mastoiditis, peritonsillar abscess, cutaneous infection, pneumonia, empyema, appendicitis, osteomyelitis, and intravenous drug abuse are all risk factors (9). Patients with hemoglobinopathies are also at risk for splenic abscess formation secondary to infarction and necrosis as well as functional asplenia (3,9).
Pyogenic abscesses manifest as ill-defined, hypoechoic lesions at US. Debris and internal septations may be present. In rare cases, gas bubbles may be seen. If present, intralesional gas is pathognomonic for pyogenic infection. At CT, pyogenic abscesses typically manifest as single, irregularly marginated lesions with low attenuation. Rim enhancement can be seen on contrast-enhanced scans (Fig 22) (3,11,30).
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Figure 22. Pyogenic splenic abscess in a 2-year-old girl with aplastic anemia. Contrast-enhanced CT scan shows a well-defined, low-attenuation lesion in the tip of the spleen (arrow). The abscess was drained, and culture was positive for E coli and mixed gram-positive organisms. (Courtesy of B. Spector, MD, University of North Carolina Memorial Hospital, Chapel Hill, NC.)
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Fungal abscesses are small lesions, typically only a few millimeters in diameter (3). The most common infecting organisms are Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans (30). M tuberculosis, M avium intracellulare, and P carinii infection can have similar appearances (7,35). Fungal abscesses have a variable appearance at US (Fig 23). Typically, they manifest as rounded, hypoechoic lesions with a central area of increased echogenicity, creating a "target" or "bull's-eye" appearance. These findings correspond to fibrotic tissue surrounding a central inflammatory core at histopathologic analysis. The "wheel-in-a-wheel" appearance is seen when the central hyperechoic portion becomes necrotic and hypoechoic (3,30). Hepatosplenomegaly is usually associated with fungal abscesses. CT typically demonstrates multiple small, low-attenuation lesions. The lesions may be missed unless intravenously administered contrast material is used (11).
Cat-scratch fever is caused by the gram-negative bacillus Bartonella henselae (46). It occurs in children and adolescents with a history of scratches or bites from a cat or dog. In the majority of patients, the clinical course is mild and the symptoms remit after weeks or months. However, some children have systemic manifestations that can involve the reticuloendothelial system. Splenomegaly and microabscesses can develop. The latter can heal to form calcified granulomas. These lesions can be detected with both US and CT (Fig 24) (47,48).
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Figure 24. Cat-scratch fever in a 6-year-old boy who presented with a fever of unknown origin. Contrast-enhanced CT scan shows multiple low-attenuation lesions within a normal-size spleen. These lesions can be occult without the use of intravenously administered contrast material.
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Because of the close anatomic relationship of the pancreatic tail to the splenic hilum, inflammatory pancreatic processes may extend to involve the spleen. Although it is rare, pancreatitis can lead to intrasplenic pseudocyst formation, abscess, hemorrhage, infarction, splenic rupture, venous thrombosis, and pseudoaneurysm formation. These complications are said to occur in 1%–5% of patients with severe pancreatitis, although most reported occurrences have involved adult patients (49).
Neoplasms.—The majority of splenic malignancies are due to leukemia (Fig 25) or lymphoma. Both Hodgkin and non-Hodgkin lymphoma can involve the spleen. Lymphomatous involvement of the spleen may manifest as either focal lesions or diffuse disease. Primary lymphoma arising within the spleen can invade the capsule and extend beyond the spleen. Diffuse involvement usually manifests as splenomegaly with no discernible alterations in splenic echotexture (9,30). This finding corresponds to infiltrative disease or tiny miliary deposits of lymphomatous tissue seen at pathologic analysis. The majority of focal lesions seen at US are hypoechoic and lack acoustic enhancement (40,50). At CT, lesions typically have low attenuation. CT is also useful in assessing lymphadenopathy at the splenic hilum and along the supporting ligaments. Multiple inhomogeneous lesions of varying size may be seen at contrast-enhanced CT (Figs 26, 27) (11,30). These lesions represent larger deposits of lymphomatous tissue (11,30,50).
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Figure 25. Leukemic involvement of the spleen in a 13-year-old girl with sickle cell disease. Transverse US scan through the splenic hilum shows multiple hypoechoic nodules (arrows). The spleen was not enlarged, and there was no evidence of recurrent disease elsewhere within the abdomen.
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Figure 26. Multifocal splenic lymphoma in a 17-year-old girl with Hodgkin disease. Contrast-enhanced CT scan obtained just inferior to the level of the splenic hilum shows multiple low-attenuation nodules of varying size within an enlarged spleen. Moderate hepatomegaly and intraabdominal lymphadenopathy (not shown) were also found.
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Figure 27. Multifocal masses from lymphoproliferative disease in a male infant who had undergone liver transplantation. Contrast-enhanced CT scan shows multifocal low-attenuation masses in the spleen (arrows).
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Langerhans cell histiocytosis is characterized by a proliferation of bone marrow–derived histiocytes and predominantly involves the skin, bone, bone marrow, reticuloendothelial system, and lungs. It may cause splenic enlargement or (less often) multiple hypoechoic nodules within the spleen that do not necessarily disappear after therapy (51,52).
Storage Disorders.—Gaucher disease is a lysosomal storage disorder caused by lack of the enzyme glucocerebrosidase. Glucocerebroside accumulates in the cells of the reticuloendothelial system. Several clinical subtypes have been described, but hepatosplenomegaly is seen in all cases. At US, patients with Gaucher disease may have multiple hyper- or hypoechoic splenic nodules that correspond to clusters of Gaucher cells seen at histopathologic analysis (53). Foci of extramedullary hematopoiesis may also be present (53). On MR images, T1 signal intensity tends to be lower for Gaucher disease than for normal spleen owing to the accumulation of glucocerebroside. However, no significant change in splenic T2 signal intensity is present (54). Nodular clusters of Gaucher cells usually appear isointense on T1-weighted images and hypointense on T2-weighted images (55). Splenic infarction (Fig 28) and fibrosis may also demonstrate a multifocal pattern.
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Figure 28a. Gaucher disease in an adolescent girl. Axial T1-weighted (600/12) (a) and T2-weighted fast spin-echo (4,000/104) (b) MR images obtained at routine follow-up show massive splenomegaly with areas of low signal intensity (arrows). These findings are consistent with fibrosis after splenic infarction, which is typical with Gaucher disease. The liver also appears somewhat enlarged.
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Figure 28b. Gaucher disease in an adolescent girl. Axial T1-weighted (600/12) (a) and T2-weighted fast spin-echo (4,000/104) (b) MR images obtained at routine follow-up show massive splenomegaly with areas of low signal intensity (arrows). These findings are consistent with fibrosis after splenic infarction, which is typical with Gaucher disease. The liver also appears somewhat enlarged.
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Miscellaneous Conditions.—Sarcoidosis is a multisystem granulomatous disease of unknown origin. Abdominal involvement is uncommon during the first decade of life but may be seen in adolescents (56). Findings in this patient population include lymphadenopathy and hepatosplenomegaly (56). Low-attenuation splenic nodules up to several centimeters in diameter have been seen at CT in adults with sarcoidosis (57). To our knowledge, such nodules have not been reported in children (56).
Diffuse Disease without Focal Lesions
Certain disease processes may involve the entire spleen, producing subtle changes in appearance such as an alteration in splenic echotexture (Fig 29), mottled enhancement at contrast-enhanced CT, or diffuse signal intensity changes at MR imaging. These disease processes include infection, tumor infiltration, infarction, heavy metal deposition, and vascular disorders. The imaging findings need not be accompanied by splenomegaly.
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Figure 29. Disseminated mycobacterial infection in an 11-year-old boy. Transverse US scan through the upper pole of the spleen shows heterogeneity of the splenic echotexture. No focal lesion is seen. There was no associated splenomegaly.
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Infarction.—Branches of the splenic artery are noncommunicating end arteries, and their occlusion leads to splenic infarction. In children, infarction usually occurs in the setting of sickle cell hemoglobinopathies and hematologic malignancies (3). Other recognized causes of infarction include cardiac emboli, torsion, collagen vascular disease, portal hypertension, and infiltrative disorders such as Gaucher disease (3,30,55). Complications of infarcts include acute febrile illness, abscess formation, splenic pseudocyst formation, splenic rupture, and hemorrhage (3). Splenic infarcts have a variable appearance at US. Initially, they appear as ill-defined, hypoechoic lesions. At histopathologic analysis, these findings are secondary to inflammation, edema, and necrosis. With organization and fibrosis, the lesions become increasingly well-defined and echogenic (30). The CT appearance of infarcts depends on the time elapsed since the insult. In the hyperacute phase, the spleen demonstrates a mottled echotexture secondary to hemorrhagic infarction with intravenous administration of contrast material. Over time, the lesions become better defined. Classically, they are peripheral and wedge-shaped, but they may have an irregular margin (Fig 30) (3,11). With time, the anomalies may resolve completely, leaving only a cortical defect or a focus of calcification (3,11). In rare cases, the entire spleen may undergo infarction, leaving only a rim of enhancing capsule (Figs 31–33) (41).
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Figure 30. Splenic infarction secondary to severe fungal infection in an immunocompromised 4-year-old boy. Contrast-enhanced CT scan shows several large, wedge-shaped areas of nonenhancing splenic tissue. The liver and kidneys are enlarged.
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Figure 31a. Wandering spleen with infarction in a 3-year-old boy. (a) Transverse US scan shows the spleen in the right lower quadrant (arrow). There are no discernible abnormalities in echotexture. (b) Anterior Tc-99m sulfur colloid scintigram shows the liver in its normal location in the right upper quadrant (arrow). There is no evidence of splenic uptake of radiotracer. These findings helped confirm the clinical suspicion for splenic infarction secondary to torsion about the elongated vascular pedicle.
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Figure 31b. Wandering spleen with infarction in a 3-year-old boy. (a) Transverse US scan shows the spleen in the right lower quadrant (arrow). There are no discernible abnormalities in echotexture. (b) Anterior Tc-99m sulfur colloid scintigram shows the liver in its normal location in the right upper quadrant (arrow). There is no evidence of splenic uptake of radiotracer. These findings helped confirm the clinical suspicion for splenic infarction secondary to torsion about the elongated vascular pedicle.
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Figure 32. Splenic infarction secondary to idiopathic pancreatitis and splenic vein thrombosis in an adolescent girl. Contrast-enhanced CT scan obtained at the level of the pancreatic tail shows a nonenhancing spleen. The pancreatic tail is inflamed, and there is subjacent stranding in the peripancreatic and splenic fat (arrow).
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Figure 33. Splenic infarction in a 7-year-old boy with sickle cell disease. Contrast-enhanced CT scan shows a predominantly low-attenuation enlarged spleen with capsular enhancement (arrow). This finding is due to a separate arterial supply to the splenic capsule.
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Patients with sickle cell disease are prone to splenic infarction. Areas of increased echogenicity in the spleen have been reported in patients with sickle cell disease, and it is postulated that these represent areas of previous infarction (58). Conversely, areas of decreased echogenicity in an otherwise echogenic spleen may well represent preserved functioning islands of splenic tissue (59). These lesions take up Tc-99m sulfur colloid, which suggests that they represent normal splenic tissue. Both radiography and CT can depict dense splenic calcification. The spleen has decreased signal intensity on both T1- and T2-weighted MR images (Fig 34). This finding is thought to be secondary to a combination of hemosiderin deposition, fibrosis, and splenic calcification (59,60).
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Abstract
INTRODUCTION
