AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Absent or defective splenic function is associated with a high risk of fulminant bacterial infections, especially with encapsulated bacteria. Asplenia and splenic hypoplasia are terms used to indicate complete or partial lack of splenic function. Loss of splenic function usually occurs as a result of surgical removal or autosplenectomy, ie, infarction in patients with hemoglobinopathies. Congenital splenic anomalies are usually accompanied by abnormalities in other organ systems, especially cardiac abnormalities, but they may occur in isolation. Polysplenia, ie, bilateral left-sidedness, is also frequently associated with congenital cardiac anomalies.

Patients with polysplenia have multiple spleens, and their splenic function is usually normal. Isolated asplenia or hyposplenia is often diagnosed only after the patient has had a serious, fulminant, and often fatal infection. These conditions are extremely difficult to diagnose in the absence of other indicators. Morphologic anomalies of peripheral blood erythrocytes, such as Howell-Jolly (HJ) bodies, may be the only evidence of the presence of a nonfunctional spleen (see Workup).

Pathophysiology

The embryologic control of splenogenesis resides in the homeobox gene HOXD11. In humans, the spleen is the site for early hematopoietic development, particularly the development of erythrocytes during the first 4 months of gestation.

After birth, the spleen has several important functions such as the provision of primary immunologic defensive responses. The spleen has an active role in phagocytosis and in the production of immunoglobulin M (IgM) antibodies and complement. It also plays a significant role in the functional maturation of antibodies. The spleen is a significant reservoir for T lymphocytes. The percentages of total T cells (CD3) and T helper cells (CD4) and the lymphoproliferative responses to mitogens (concanavalin A, phytohemagglutinin, pokeweed mitogen) may decrease in patients with asplenia. However, these T-cell changes reflect the loss of the spleen as a reservoir rather than a direct T-cell abnormality.

The impaired clearance of opsonized particles, decreased IgM levels, and poor antibody production (especially in response to polysaccharide antigens) contribute to the increased susceptibility of these patients to serious and often fatal infections. Apart from this filtering and immunologic function, the spleen acts as an important scavenger. For example, the spleen participates in the destruction of all 3 blood elements: erythrocytes, white cells, and platelets. It also plays an important role in the selective removal of abnormal cells (spherocytes, poikilocytes) and intracellular inclusions (Heinz bodies, HJ bodies). These functions are known as culling and pitting, respectively, and are the basis of the hematologic abnormalities observed in patients with absent splenic function.

The white pulp of the spleen contains germinal centers with B lymphocytes, plasma cells, and macrophages. The red pulp, composing the largest part of the spleen, consists of endothelial cords of Billroth and sinusoids. In the red pulp, erythrocytes are processed, and inclusions such as HJ bodies, Heinz bodies, and autophagic vacuoles are removed.

Because the spleen is important in antibody synthesis and has a critical role in clearing bacteria from the bloodstream, a patient with asplenia is at significant risk for life-threatening infections and fulminant sepsis, especially in their first 2 years of life. In infants younger than 6 months, gram-negative enteric organisms such as Klebsiella species and Escherichia coli are the most common pathogens. After age 6 months, Streptococcus pneumoniae and Haemophilus influenzae type b may cause fulminant sepsis; Neisseria meningitidis is less common. Malaria, babesiosis, and certain viral infections may also be more severe in individuals with asplenia. The younger the patient at the time of splenic function loss, the higher his or her risk for serious infection.

Asplenia is most often found in association with other anomalies. The most common of these anomalies is the Ivemark syndrome, which is also referred to as asplenia syndrome. Visceral heterotaxy is present with bilateral right-sidedness. The right-sided organs are duplicated, and organs that are normally present on the left side are absent.

Infants with Ivemark syndrome usually present during the neonatal period with cyanosis and respiratory distress resulting from complex cardiac anomalies. Transposition of the great arteries with pulmonary stenosis (72%) or atresia (88%) and total anomalous venous drainage (72%) are common. Accompanying malformations may involve the gastrointestinal system secondary to aberrant mesenteric attachments and renal anomalies. The liver tends to be symmetrical and transverse, and the stomach may be in the midline and hypoplastic. This condition is more common in males than in females, and most patients (79%) die in their first year of life because of cardiovascular complications. A clue to the underlying problems may be obtained by carefully examining radiographs, which may reveal abnormal placement of the cardiac apex, stomach bubble, and liver.

Other associated conditions include Pearson syndrome (pancreatic insufficiency, sideroblastic anemia), which is a mitochondrial disorder associated with splenic atrophy. Asplenia is also present in Stormorken syndrome (thrombocytopenia and miosis). Occasionally, asplenia may be present in Smith-Fineman-Myers syndrome (mental retardation, short stature, cryptorchidism) and ATR-X syndrome (a-thalassemia and mental retardation). Asplenia may be associated with caudal deficiency or cystic disease of the liver, kidney, and pancreas. It has also been reported in association with Fanconi aplastic anemia.

Functional asplenia is associated with conditions such as sickle cell disease, hemoglobin SC disease, and sickle cell hemoglobin (Hb S) b-thalassemia. Most children with these hemoglobinopathies are functionally hyposplenic in the first year of life and anatomically asplenic (due to autoinfarction) by the second decade of life. The infection risks in these individuals parallel those of patients with asplenia. Patients who undergo splenectomy because of thalassemia or Hodgkin disease have a higher risk of overwhelming infection than those patients with functional hyposplenia secondary to sickle cell disease. Additional conditions associated with splenic hypofunction include neonatal age, rheumatologic diseases (systemic lupus erythematous [SLE], rheumatoid arthritis), inflammatory bowel disease, graft versus host disease, and nephrotic syndrome. Patients may also have traumatic injuries to the spleen and require surgical splenectomy.

Congenital anomalies of the spleen may be isolated, but most cases of asplenia or polysplenia result from interference in the establishment of normal right-left symmetry during embryogenesis (laterality sequences). Asplenia may be viewed as bilateral right-sidedness, of which Ivemark syndrome is an example. Asplenia is associated with dextrocardia in approximately one third of the cases. Congenital cardiac anomalies are more frequent and often more severe in asplenia than in polysplenia. Polysplenia may be regarded as bilateral left-sidedness, and it may be associated with left atrial isomerism.

Vascular disturbances, including failure of the splenic artery to reach the developing spleen, may be a possible explanation for isolated asplenia. Familial situs abnormalities may be related to chromosome band Xq24-q27.1. Splenic hypoplasia is a poorly defined and infrequently recognized condition. It is usually not associated with other anomalies and may be familial.

Asplenia or polysplenia may be associated with significant abnormalities of the cardiovascular system, with occasional involvement of the pulmonary, gastrointestinal, and genitourinary systems. The cardiac abnormalities are generally complex and include endocardial cushion defects, pulmonary atresia or stenosis, transposition of the great vessels, total anomalous pulmonary venous return, and a double-outlet right ventricle. Similar cardiac defects may be present in both polysplenia and asplenia. However, cyanotic heart diseases, including severe atrioventricular canal defects, tend to be more common in asplenia, whereas acyanotic defects, which usually occur with increased pulmonary blood flow, are more common in polysplenia.

In polysplenia, the stomach may be on the right side, and multiple spleens are found along the greater curvature. Absence of the hepatic portion of the inferior vena cava with an azygous venous connection is characteristic. Data regarding splenic competency in polysplenia are scarce. Reports vary from suboptimal function to normal function. Accessory spleens should be distinguished from polysplenia. In polysplenia, a normal spleen with multisystem involvement is absent. Accessory spleens are usually located in the hilus of the normal spleen or in the tail of the pancreas. The accessory splenules are typically small and clinically insignificant, but they may become hypertrophied in certain situations.

Frequency

United States

The exact incidence of these conditions is not known. Asplenia or polysplenia is present in approximately 3% of neonates with structural heart disease and in 30% of patients who die from cardiac malposition. Isolated asplenia or hyposplenia is probably an underdiagnosed condition that is most often recognized at autopsy.

Mortality/Morbidity

• Compared with mortality rates in healthy children, the rate in children with a splenectomy caused by trauma is increased 50-fold, and the rate in patients with sickle cell disease is increased 350-fold.
• Neonates with asplenia have high morbidity and mortality rates usually caused by related cardiovascular insufficiency.
• Infants who survive past the age of 1 month have a higher risk of dying from sepsis than from associated cardiac disease. Therefore, the early identification of asplenia in infants with congenital heart disease is of paramount importance.

Sex

• The male-to-female predominance in asplenia syndrome (ie, Ivemark syndrome) is 2:1.
• Polysplenia syndrome is more predominant in females, whereas asplenia is more common in males.

Age

The risk of bacteremia is higher in younger children compared with older children.

CLINICAL

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History

All patients with congenital or acquired asplenia or splenic dysfunctional are at significant risk of fulminant bacteremia, especially from encapsulated bacteria. S pneumoniae is the most common pathogen implicated in bacteremia in these patients. Other encapsulated organisms include H influenzae type b, N meningitidis, E coli, Staphylococcus aureus, and other streptococci. Gram-negative bacilli including Salmonella species, Klebsiella species, and Pseudomonas aeruginosa are less common causes of bacteremia in patients with asplenia. These patients are also at risk for malaria and babesiosis.

• Worldwide, most patients with asplenia or hyposplenia have an underlying hemoglobinopathy such as sickle cell disease.
• • Isolated asplenia and polysplenia are commonly associated with significant abnormalities involving other organ systems.
  • An awareness of these associations and syndromes may help in screening the patient for splenic dysfunction.
• The most important clinical indication for the evaluation of splenic function is the presence of complex congenital heart disease. Patients should be evaluated for splenic dysfunction if any of the following are present:
• • Recurrent infection or sepsis, especially with encapsulated organisms
  • Family history of asplenia or polysplenia
  • Cyanotic congenital heart disease or complex cardiac malformations
  • Evidence of visceral heterotaxy or other associated malformations
  • Bilateral trilobed or bilobed lungs on chest radiographs
• In contrast, the presentation of patients with isolated congenital absence or hypoplasia of the spleen may be less dramatic.
• • Children with these conditions may present to the primary caretaker with fever or overwhelming sepsis, or they may even be moribund.
  • Associated cardiovascular, pulmonary, gastrointestinal, or genitourinary abnormalities may not be present to alert the physician to their underlying immunocompromised state.
• Features such as thrombocytosis, HJ bodies in red cells, and recurrent episodes of invasive infections with encapsulated organisms may be helpful in identifying individuals with isolated absence or hypoplasia of the spleen. The absence of these features, however, does not exclude splenic malfunction, although it may make the diagnosis more difficult.

Physical

• At clinical examination, the spleen is usually not palpable, except in individuals with thin abdominal musculature.
• In visceral heterotaxy, a right-sided liver may be mistaken for splenic enlargement.
• The physical findings depend on the associated anomalies.

Causes

• Asplenia and polysplenia may be sporadic or familial.
• Because congenital asplenia has been documented in multiple members of the same family and because it is a component of several well-defined syndromes, genetic factors may play an important role in its pathogenesis.
• However, no specific genetic defect has been identified.
• Both asplenia and polysplenia have been described in the same family; this finding suggests that these defects may define a spectrum of related conditions.
• Surgical splenectomy may occur after significant splenic trauma or other clinical disorders, such as idiopathic thrombocytic purpura.

DIFFERENTIALS

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Other Problems to be Considered

Immune deficiency
Aberrant (wandering) spleen

WORKUP

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Lab Studies

• Often the first clues to functional asplenia in an asymptomatic patient are abnormalities in the peripheral blood smear.
• • The initial evaluation should begin with a review to identify HJ bodies (see Image 1).
  • The nuclear remnants are small, round, densely stained inclusions in red blood cells. They can be seen as a normal variant in the newborn period and are occasionally seen in leukemia, steatorrhea, and a variety of anemias (megaloblastic anemia, dyserythropoietic anemia, thalassemia).
  • The presence of HJ bodies in the peripheral smear of an individual older than 7 days should suggest splenic dysfunction.
  • Other red cell abnormalities include an increased presence of target cells, Heinz bodies, Pappenheimer bodies (small basophilic inclusions that contain nonheme iron), reticulocytes, and spherocytes.
  • In addition, thrombocytosis and leukocytosis are observed because of decreased destruction.
• Another helpful means of screening the splenic function is by determining the pit count or counting the number of pocked erythrocytes.
• • Normally, less than 2% of red cells have these pocks. A pocked erythrocyte count of more than 3.5% suggests functional hyposplenia, and a count of more than 12% is indicative of asplenia.
  • This technique involves the use of special equipment (Nomarski optics) that is not always readily accessible.
• An assessment of the argyrophilic granules in the peripheral smear may be a helpful and easy method to detect splenic dysfunction, but the procedure needs further evaluation.

Imaging Studies

• Various imaging modalities may be helpful in defining splenic anomalies.
• Certain associated anomalies, especially cardiac and visceral changes, often lead to further evaluation of the spleen.
• Abdominal ultrasonography can be performed to document the presence of the spleen and its size, and newer ultrasound techniques with color Doppler sonography have shown promise in assessing splenic function. A small spleen with absent parenchymal vascularization on color Doppler sonography has been associated with functional asplenia, but this should be confirmed with further imaging before declaring a patient functionally asplenic.
• The absence of the spleen is best confirmed with a technetium-99m radionuclide scan. This agent is taken up by the reticuloendothelial cells and enables better assessment of splenic function.
• Absence of the intrahepatic segment of the inferior vena cava should trigger careful evaluation of abdominal masses, which could represent splenules. These masses can be confused with multiple metastatic lesions in patients, especially adults, in whom asplenia or polysplenia is undiagnosed.
• An MRI or CT scan of the abdomen may also show absence or hypoplasia of the spleen. These studies have no place in the routine workup of isolated asplenia or hyposplenia but they may be useful if they are obtained for other accompanying indications, such as visceral heterotaxy. Newer MRI techniques have expanded the role of MRI in the detection and characterization of splenic diseases.
• Computerized models are available to determine the splenic volume, but this approach is mainly used to judge the increased size (eg, tumors, infiltrations) of organs. With more experience, computerized models may provide important information about conditions that decrease the size and volume of the spleen.
• If the spleen is not visualized with radiographic imaging and if no hematologic data support the diagnosis of asplenia, the extremely rare condition of wandering spleen may be considered. In this condition, a functional spleen is present, but because of its long pedicle, it may be in an abnormal location, such as the pelvis.

Histologic Findings

A hypoplastic spleen may exhibit a hyperemic red pulp with underdevelopment of the white pulp and a paucity of lymphoid follicles. When hyposplenia is secondary to an underlying hemoglobinopathy such as sickle cell disease, specific histologic features may be observed because of infarction (see History).

TREATMENT

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Medical Care

Once the diagnosis of anatomic or functional asplenia is confirmed, aggressive management is the key to decreasing the morbidity and mortality associated with this condition.

Any episode of fever or signs of infection should be treated promptly and aggressively.

Medical care involves 4 key components: antibiotic prophylaxis, appropriate immunization, aggressive management of suspected infection, and parent education.

• Antibiotic prophylaxis
• • Antibiotic prophylaxis should be initiated immediately upon the diagnosis of asplenia because these patients are at significant risk of pneumococcal infections. For children younger than 2 years, oral penicillin V may be given twice a day. Amoxicillin has also been recommended as an appropriate prophylactic antibiotic. Erythromycin is an alternate choice in patients who are allergic to penicillin.
  • In general, antimicrobial prophylaxis should be considered for all children with asplenia or splenic dysfunction until age 5 years and for at least 1 year after surgical splenectomy. Some experts recommend continuing prophylaxis into adulthood, particularly for high-risk patients. The need for prophylaxis for children who have splenectomy after trauma has not been agreed upon.
• Immunization
  • All patients should receive all standard childhood and adolescent immunizations at the recommended age. Most importantly, vaccinations against encapsulated organisms, including pneumococcal conjugate and/or polysaccharide, H influenzae type b conjugate, and meningococcal conjugate and/or polysaccharide vaccines, should be administered on the standard schedule.
  • Approximately 80% of the pediatric pneumococcal bacteremias in the United States are caused by the 7 serotypes covered in the vaccine: 4, 6B, 9V, 14, 18C, 19F, and 23F. The conjugated vaccine has been effective in dramatically reducing the occurrence of invasive pneumococcal disease. In children younger than 2 years, the incidence of all invasive pneumococcal infections has decreased by 80% after conjugated vaccine was recommended in the routine childhood immunization schedule. Infections caused by vaccine and vaccine-related serotypes have decreased by 90% in older children and adults.
  • The immunization schedule for pneumococcal conjugate vaccine (PCV7) consists of a primary series of 4 doses (0.5 mL each) at age 2, 4, 6, and 12-15 months. Catch-up immunization schedules are published regarding appropriate dosing schedules for children aged 5 years or younger. Administration of a single dose of PCV7 to children of any age is not contraindicated, especially for patients with asplenia or splenic dysfunction who are at high risk for invasive pneumococcal disease.
  • The pneumococcal polysaccharide vaccine against 23 serotypes (PPV23) should be given after age 24 months for supplemental protection. PCV7 should be administered first, with administration of PPV23 at least 8 weeks after the last dose of PCV7. A booster dose 3-5 years after the first dose of PPV23 is appropriate.
  • Patients should also receive quadrivalent meningococcal vaccine. Two licensed meningococcal vaccines are available in the United States against serotypes A, C, Y, and W-135. Meningococcal conjugate vaccine (MCV4) was licensed in 2005 for people aged 11-55 years. Meningococcal polysaccharide vaccine (MPSV4) is licensed for children aged 2 years and older. Immunization with MPSV4 is recommended for children aged 2-10 years and older who have functional or anatomic asplenia. MCV4 should be used if the patient is aged 11 years or older. Because of its ability to induce a T-cell response, MCV4 is expected to confer immunity for approximately 10 years, as opposed to about 4 years of immunity from MPSV4. Immunization with MCV4 should be considered in adolescents aged 3-5 years after receiving MPSV4. Revaccination schedules with MCV4 are ongoing.
  • The recommended vaccination schedule for H influenzae type b is a primary series of 3 doses given at age 2, 4, and 6 months or 2 doses given at age 2 and 4 months, depending on the particular conjugate vaccine product administered. A booster dose at age 12 months is recommended for all vaccine products. Children who are undergoing scheduled splenectomy after completion of their primary series and booster dose, may benefit from an additional dose of conjugate vaccine at least 7-10 days before surgery. Catch-up immunization schedules regarding H influenzae type b vaccine are published.
  • Yearly influenza vaccine is also recommended to minimize the likelihood of secondary bacterial infections.
• Management of suspected infection
  • The risk of serious bacterial infection is ever present in these patients. Many patients have trivial symptoms yet rapidly develop fulminant sepsis and death within hours.
  • All patients with impaired splenic function with suspected infection must be urgently and promptly evaluated. Obtain blood; urine; and, if indicated, cerebrospinal fluid (CSF) cultures. Initiate broad-spectrum intravenous antibiotics effective against S pneumoniae, H influenzae type b, and N meningitidis. Second- or third-generation cephalosporins may be the initial choices. If multiple-drug resistance is a concern, vancomycin should be added to the regimen. In addition, many patients require supportive care with intravenous fluids, volume expanders, and pressor support.
  • Because of the potential rapid progression of a serious bacterial infection, some experts recommend that asplenic patients have access to "stand-by" antibiotics, which can be initiated at the first sign of infection (fever, chills, or malaise). That the initiation of "stand-by" antibiotics is not a substitute for seeking immediate medical attention at the onset of an illness cannot be overemphasized.
  • Patients with asplenia are at an increased risk of sepsis, shock, and meningitis secondary to Capnocytophaga canimorsus resulting from dog, cat, or rodent bites. The diagnosis may be made by means of Gram staining of the buffy coat, blood, and CSF cultures. Early treatment with penicillin is the therapy of choice, but cephalosporins, clindamycin, and erythromycin may also be used.
• Parent education
• • The most important component in the treatment of these patients is parent education. Risks must be explained to all caretakers because they are an integral part of the management team. Seeking medical advice at the first sign of illness is crucial.
  • Ongoing education must become a part of each physician-parent encounter so that the parents remain vigilant, which allows potentially serious infections to be identified early and managed aggressively. The child should wear a Medic Alert bracelet. Written instructions should be given to the parents in a form that they can keep with them. For example, they can be given a wallet-sized card with the child's diagnosis and concise guidelines for early treatment and intervention.

Surgical Care

• Elective splenectomy for conditions such as hemolytic anemia are strongly discouraged before the age of 5 years and should be delayed as long as possible.
• Options to splenectomy should be considered when appropriate. These include partial splenectomy or embolization, conservative management of splenic trauma, and autotransplantation.
• To the author's knowledge, no data support the routine use of prophylactic antibiotics in the perioperative period.
• When surgical splenectomy is imminent, administration of pneumococcal, H influenzae type b, and meningococcal vaccines at least 2 weeks before splenectomy, if possible, is appropriate. If the immunizations are not received prior to surgery, some recommend immunization 14-21 days postsurgery because of enhanced immune response, compared with immediately postsurgery.
• Surgical splenectomy in patients with immunodeficiency should be avoided because of increased risk of invasive bacterial infections.

Activity

• No restrictions on activities are usually advised.
• Infections with H influenzae type b and pneumococcal and meningococcal bacteria are known to be increased among immunologically competent children and adults in daycare centers, college dormitories, military barracks, and other crowded facilities. Therefore, the risks of these situations should be explained to patients and their families.

MEDICATION

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The aim of medical therapy is to prevent invasive disease secondary to polysaccharide-encapsulated organisms, especially pneumococci. Penicillin and amoxicillin are currently the drugs of choice.

Drug Category: Antibiotics, prophylactic

These agents are used to prevent invasive bacterial disease. Antibiotic prophylaxis is given to patients before they undergo procedures that may cause bacteremia.

Drug Category: Vaccines

Active immunization increases resistance to infection. Vaccines consist of microorganisms or cellular components that act as antigens. The administration of the vaccine stimulates the production of antibodies with specific protective properties.

Given the increased problem of penicillin resistance in S pneumoniae, prevention by using PCV7 in children or by using PPV23 in children and adults is mandatory. Similarly, immunizations with the conjugated H influenzae type b vaccine and the meningococcal conjugated or polysaccharide vaccine are essential.

FOLLOW-UP

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Further Inpatient Care

• The most difficult and crucial aspect of asplenia is establishing the diagnosis.
• • Although this task is relatively simple in patients with accompanying anomalies, especially complex cyanotic cardiac problems, and in those with a family history of the condition, the patient with isolated asplenia or hyposplenia may not be easily identified.
  • The diagnosis is often made at autopsy.
• Patients require regular monitoring with an established provider.
• All immunizations, including routine childhood vaccinations and additional immunizations, are recommended (see Medical Care).
• • These vaccinations should be administered at the earliest opportunity.
  • Close observation and monitoring is mandatory, especially in the first few years of childhood, to educate the family and to ensure compliance with antibiotic prophylaxis.

Prognosis

• With early diagnosis and aggressive treatment, the long-term prognosis of a child with isolated congenital asplenia is good.
• • The risk of overwhelming sepsis, although it does not end, significantly decreases in individuals older than 5 years.
  • The primary care physician plays an integral role in the identification and long-term treatment of patients with asplenia.
• Congenital asplenia, polysplenia, and hypoplasia may be underdiagnosed. An increased awareness of their existence may be crucial and life saving in immunocompromised individuals with these conditions.

Patient Education

• See Medical Care.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Unfortunately, isolated asplenia or hyposplenia is often diagnosed at autopsy.
• A high index of suspicion and increased awareness are important for the diagnosis.

MULTIMEDIA

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Media file 1:  Peripheral blood smear shows Howell-Jolly (HJ) bodies in RBCs.
	View Full Size Image
Media type:  Photo

REFERENCES

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Article Last Updated: Aug 2, 2006