Chapter 95 The spleen is maintained in its normal position by ligaments formed by peritoneal folds. The two major ligaments are the gastrosplenic ligament and the splenorenal ligament (Fig. 95-1). Other ligaments that help support the spleen are the phrenicosplenic, splenocolic, pancreaticosplenic, phrenocolic, and pancreaticocolic ligaments. The spleen is the largest of the body’s lymphatic structures and the second largest organ of the reticuloendothelial system. A combination of red pulp (75%) and white pulp (25%) constitute the splenic parenchyma,1 which is surrounded by a relatively tough capsule. The red pulp is composed of the splenic cords and vascular sinuses and contains a large number of erythrocytes, whereas the white pulp is composed largely of lymphocytes and macrophages. The unique anatomy of the spleen is closely linked to its function and lends itself to some normal variations seen on computed tomography (CT) and magnetic resonance imaging (MRI). The primary function of the embryonic spleen is erythropoiesis, which is maximal in the middle of the second trimester and subsequently diminishes. The spleen is later responsible for filtering red blood cells that are aged or lack contractility, as well as antigen-coated cells, bacteria, and foreign particles. The spleen also acts as a platelet reservoir, releasing platelets in response to epinephrine or consuming platelets in case of splenomegaly.1 These functional aspects of the pediatric spleen can be evaluated scintigraphically. The spleen is easily identified on abdominal ultrasonography. It has a homogeneous sonographic texture, is slightly more echogenic than are the kidneys, and is isoechoic to slightly hyperechoic to the liver. The splenic hilar vessels usually are well visualized (Fig. 95-2), but intrasplenic vessels typically require color Doppler imaging for identification. Figure 95-2 Normal spleen. On CT, the normal spleen has a higher attenuation than the liver. Transient heterogeneous splenic enhancement patterns often are encountered during the first minute of contrast-enhanced CT, particularly with the rapid bolus technique (e-Fig. 95-3). This normal phenomenon is thought to be a result of variations in blood flow through the red and white pulp of the spleen; it is more pronounced with contrast injection rates of 1 mL/sec or greater and in children older than 1 year. Common patterns of heterogeneity have been described as: (1) archiform, consisting of ring-like or zebra-stripe bands of alternating density; (2) focal areas of low density; and (3) diffuse, mottled areas of inhomogeneity.2 More uniform enhancement is seen approximately 70 seconds after initiation of the contrast injection. e-Figure 95-3 Contrast bolus artifact on computed tomography (CT). On MRI, the spleen signal intensity varies with age (Table 95-1; Fig. 95-4). In the neonate, the spleen is T1 and T2 isointense to hypointense with respect to the liver. The T2 hypointensity is because of immaturity of the white pulp. After age 8 months, the spleen is T2 hyperintense relative to the liver because of white pulp maturation, and it maintains this appearance through adulthood.3 Table 95-1 Magnetic Resonance Signal Intensity of Spleen Relative to Liver by Age Figure 95-4 Change in spleen T2 signal with age. Scintigraphic splenic imaging with technetium-99m (99mTc)–labeled sulfur colloid, which is removed from the blood by the reticuloendothelial system, is useful for the identification of splenic ectopia, as well as several entities discussed later in this chapter. It is not useful in cases of heterotaxy because splenic and hepatic tissue cannot be distinguished when neither location nor shape is an identifying criterion. Similarly, selective spleen scans can be misleading when the spleen is absent (e-Fig. 95-5). e-Figure 95-5 Asplenia. Overview: The most common congenital anomaly of the spleen is the presence of one or more accessory spleens, or splenuli. These accessory spleens are present in 20% to 35% of postmortem examinations of the normal population4 and usually are found incidentally at autopsy or on imaging studies. They number six or fewer and are located most commonly in the splenic hilum, in association with the splenic vessels, or in the gastrosplenic ligament. However, accessory spleens can be found virtually anywhere in the abdomen. They rarely exceed 2 cm in diameter and can be confused with splenic hilar or parapancreatic lymph nodes. Etiology: Normally, the spleen forms from the coalescence of multiple small splenic masses. Accessory spleens therefore are not uncommon. Clinical Presentation: The presentation is incidental, when accessory spleens are found during imaging for unrelated reasons. Imaging: Accessory spleens can be identified on ultrasound, CT, or MRI, but when in question, the definitive imaging study is a 99mTc sulfur colloid liver-spleen scan. Overview: A wandering spleen is a congenital anomaly that results from maldevelopment of the splenic suspensory ligaments, including the gastrosplenic, splenorenal, and phrenicocolic ligaments. Acquired cases also have been described and may be a consequence of splenomegaly, traumatic injury, or ligamentous laxity. Etiology: Normally, during embryonic life, the residuum of the dorsal mesogastrium fuses with the posterior peritoneum, helping to support the spleen in its normal position. When this fusion does not take place, the dorsal mesogastrium may persist as a long mesentery, allowing the spleen to migrate, yielding the so-called “wandering spleen.” The most common location for the ectopic spleen is the left lower quadrant. Clinical Presentation: The clinical presentation is variable; patients may be asymptomatic or present with a mobile mass on physical examination. More typically the presentation is an acute abdomen because of torsion of the vascular pedicle, with subsequent ischemia, impaired venous return, acute enlargement, and painful capsular tension.5 Imaging: The abnormal position and orientation of the spleen can be identified by ultrasound, CT, or radionuclide imaging. It is important to pay close attention to the abnormal orientation and location of the spleen. Typically, no splenic tissue can be identified in the left upper quadrant, although a small accessory spleen may remain in the normal anatomic location. If the spleen undergoes torsion, a “whorled” appearance of the splenic artery in the splenic pedicle has been described as a characteristic CT sign of torsion6 (Fig. 95-6, A and B). The twisted spleen has little uptake on radionuclide scintigraphy7 and no contrast enhancement on CT (Fig 95-6, C and D). Color Doppler sonography shows lack of flow in the splenic hilar vessels (Fig. 95-6, E) and also may demonstrate the whorled appearance at the splenic hilum. Because of the defective ligamentous support, gastric volvulus has been associated with a wandering spleen8 (Fig. 95-6, F). Figure 95-6 A wandering spleen in a 14-year-old girl with Niemann-Pick disease and the acute onset of abdominal pain. Overview: Splenogonadal syndrome is a rare anomaly in which a portion of the spleen is conjoined with left gonadal tissue. Although this congenital anomaly is uncommon, identifying it is important because 30% to 50% of cases result in unnecessary orchiectomy because of concern that a extratesticular neoplasm may be present.10 Etiology: Splenogonadal fusion results when a portion of the splenic anlage fuses with primitive left gonadal tissue between the fifth and eighth weeks of gestation. Despite the fused splenic tissue, a normal spleen is present in the left upper quadrant. The splenogonadal fusion shows a splenic cord continuous with the ectopic, fused splenic tissue in approximately 55% of cases; it is discontinuous in approximately 45% of cases.10 Splenogonadal fusion has been reported in association with transverse testicular ectopia.11 Clinical Presentation: Splenogonadal fusion is much more common in males, with a male to female ratio of 16 : 1. The condition may be asymptomatic and discovered incidentally or at autopsy. It may be associated with left cryptorchidism, inguinal hernia, or testicular torsion, particularly when it is continuous. Multiple other anomalies may be present, particularly in the continuous type. In females, fusion of splenic tissue with the left ovary or mesovarium occurs; this connection does not result in ovarian ectopia. Imaging: Sonography can reliably demonstrate the extratesticular location of a palpable scrotal mass in these cases. The mass is typically oval or round and of similar echotexture to the adjacent normal testis, but often it has a slightly different size or configuration (e-Fig. 95-7, A). Color Doppler sonography shows abundant vascularity in the splenic tissue (e-Fig. 95-7, B). Radionuclide imaging with 99mTc sulfur colloid adds specificity to the diagnosis by revealing radiopharmaceutical uptake in the ectopic splenic tissue either in the left hemiscrotum or in the left inguinal canal when associated with cryptorchidism. A linear pattern extending from the left upper quadrant of the abdomen to the pelvis or scrotum may be detected in the continuous type (e-Fig. 95-7, C). e-Figure 95-7 Splenogonadal fusion in a boy with a painless left scrotal mass. Although it is not the imaging modality of choice, contrast-enhanced CT may reveal a rounded, enhancing, well-circumscribed soft tissue mass in the left hemiscrotum or left hemipelvis that may or may not continue cephalad toward the spleen.12 MRI is useful to obtain further detail.11 Overview: Splenorenal fusion is a rare developmental anomaly in which congenital fusion of splenic and renal tissue is present. Fusion usually involves the left kidney and rarely the right kidney.13,14 Unlike posttraumatic splenosis, patients with congenital splenorenal fusion demonstrate an intact spleen with a separate blood supply. Recognition of this anomaly is important to prevent an unnecessary nephrectomy for a presumed malignancy. Etiology: One theory to explain the origin of this anomaly is that fusion of the mesogastrium and left posterior peritoneum brings the splenic anlage and the left mesonephric ridge in close proximity during the eighth week of gestation, allowing the two organs to fuse as they migrate toward the pelvis.15 Alternatively, it is postulated that splenic cells could migrate caudally to reach the metanephros and retroperitoneum, where there is no barrier to crossing the midline; this theory would explain reported right-sided fusion anomalies.13 Splenorenal fusion also may be acquired from posttraumatic or postsplenectomy splenosis, where splenic tissue implants on the kidney and regrowth occurs.14,15 Clinical Presentation: The condition may present incidentally on imaging, or it may cause symptoms as a result of the effect of the mass or hypersplenism, manifesting as anemia and thrombocytopenia. Imaging: Conventional imaging with ultrasound, CT, or MR typically will not reliably distinguish this entity from a renal or retroperitoneal malignancy. When suspected, the diagnosis can be made reliably with 99mTc sulfur colloid imaging, or, in the case of hypersplenism, with 99mTc-labeled, heat-damaged red blood cell imaging. Overview: Abnormal visceroatrial situs is a spectrum of abnormalities related to isomerisms of the atrial appendages, which typically involve abnormalities of the spleen. The normal visceroatrial anatomy is known as “situs solitus,” which means “usual position.” “Situs inversus” refers to mirror-image visceroatrial anatomy. Patients with situs inversus frequently are asymptomatic, although they have a slightly higher incidence of congenital heart disease than do patients with situs solitus. “Situs ambiguous,” also called “visceroatrial heterotaxia,” refers to deranged visceroatrial asymmetry. Patients with this abnormality are divided into two major groups: those with a tendency toward right-sided symmetry and those with a tendency toward left-sided symmetry. Therefore each patient, within broad categories, has a unique constellation of anatomic findings that must be evaluated and described individually.16,17 Recognition of the spectrum of situs anomalies and the altered anatomy is important because of the increased risk in these children for anomalies such as congenital heart disease, malrotation with potential for development of midgut volvulus, and immunodeficiency in patients with asplenia.16,18–20 Etiology: Although the external human features are largely symmetric, asymmetry is characteristic of viscerovascular anatomy. In patients with heterotaxy, although it is not yet not fully understood, derangement of embryonic left-right recognition at the molecular level is present, which relates to abnormalities in ciliary movement, planar cell polarity, asymmetric gene cascades, and genes that generate a barrier for specific gene products to cross the embryonic midline. Underlying causative mechanisms include teratogenic exposures and genetic factors.21–27 Clinical Presentation: Patients with right-sided atrial isomerism typically have asplenia, which is associated with immune deficiency and overwhelming sepsis, particularly as a result of Streptococcus pneumoniae.28 The ambiguous atrium resembles the right atrium, and severe congenital cardiac lesions typically are present, usually with diminished pulmonary blood flow and often with associated total anomalous pulmonary venous return with or without obstruction. Patients thus will present with cyanosis and/or pulmonary edema.16,17 Despite modern palliative procedures, mortality remains high, with 5-year survival reported at 20%, regardless of whether the diagnosis is made before or after birth.27,29 Intestinal malrotation is common. Patients with left-sided atrial isomerism typically have multiple splenules, known as polysplenia. Congenital heart disease often is present, although some patients with polysplenia are asymptomatic, and the diagnosis may be made incidentally.30 In a study of a large series of people with left atrial isomerism, approximately 14% of patients had a normal heart and presented with extracardiac abnormalities. This condition is associated with biliary atresia in as many as 10% of patients.31 Intestinal malrotation is common. Imaging: In patients with situs ambiguus, plain radiographs may denote abnormal situs, with discordance of heart, stomach, and liver position. On chest radiographs, patients with right-sided atrial isomerism may demonstrate bilateral right lungs with identification of the minor fissure and eparterial bronchi. Patients with left-sided isomerism, on the other hand, may demonstrate bilateral left-sided hila with hyparterial bronchi. However, hilar anatomy often is not clear because of overlying thymus. The plain film appearance may be indistinguishable from normal and falsely suggest situs solitus in some patients.32 Ultrasound, CT, and MRI confirm absence of the spleen in the vast majority of patients with right-atrial isomerism and may identify other anomalies such as horseshoe adrenals fused in the midline (e-Fig. 95-8).33,34 Subdiaphragmatic total anomalous venous connections are easily identified, because the anomalous vessel courses anterior to the esophagus into the abdomen.16 The inferior vena cava (IVC) is nearly invariably present and may lie to the right or left of the aorta, crossing the midline anterior to the aorta to enter the atrium, if necessary.16,32 e-Figure 95-8 Horseshoe adrenal in asplenia. In patients with left-sided atrial isomerism, because splenic tissue develops in the dorsal mesogastrium,25 ultrasound, CT, and MRI will identify the splenules dorsal to the stomach along the greater curvature, whether the stomach lies on the left or the right.16 The appearance of the splenules is variable and ranges from a conglomerate of multiple splenules to a sometimes septated, largely single splenic mass (Fig. 95-9 and e-Fig. 95-10). Interruption of the intrahepatic IVC is seen at least 50% of patients, with either right- or left-sided azygous continuation.16 When the IVC is present, it may lie to the right or left of the aorta. A preduodenal portal vein may be seen. In patients presenting with biliary atresia, it is important to evaluate the continuity of the IVC and the course of the portal vein, because these vascular derangements are important in patients who are later referred for liver transplantation. Figure 95-9 Polysplenia. e-Figure 95-10 Polysplenia. Treatment: Treatment is individualized on the basis of the associated anomalies. Patients with asplenia are at risk for sepsis and need to be treated for immunodeficiency. Patients with congenital heart disease or gastrointestinal anomalies of midgut malrotation and biliary atresia typically require surgical correction. Overview: Splenomegaly refers to enlargement of the spleen, usually as a result of excessive destruction of abnormal blood cells, excessive antigenic stimulation, storage or infiltrative disorders, or portal venous congestion. Hypersplenism, in contrast, refers to the syndrome of sequestration by the enlarged spleen of blood cell lines, particularly platelets. Etiology: The spleen may become enlarged in several inherited conditions (Box 95-1). The hemolytic anemias frequently cause splenomegaly, with hereditary spherocytosis, hereditary elliptocytosis, and thalassemia being the most common. Sickle cell anemia initially leads to splenomegaly, followed by splenic atrophy as a result of multiple infarcts; the pathophysiology is sequestration of impaired red blood cells by the spleen, leading to splenomegaly, anemia, and thrombocytopenia.
The Spleen
Imaging
A, A normal spleen in a 15-year-old girl. A transverse ultrasound image shows normal homogeneous parenchymal echotexture and hilar vessels. B, A normal spleen in a 3-month-old infant with ascites.
An arcuate or “archiform” contrast enhancement pattern is seen in the spleen, with ringlike or zebra-stripe bands of alternating density. A CT scan with rapid bolus technique was performed to evaluate the hepatic hemangioma.
Age
T1
T2
Neonate
Isointense/hypointense
Isointense/hypointense
Postneonate infant
Hypointense
Minimally hyperintense
>8 mo
Hypointense
Hyperintense
>1 yr
Hypointense
Hyperintense
A, An axial T2-weighted fat-suppressed image of the upper abdomen in a 2-month-old child shows that the spleen is nearly isointense to liver. B, An axial T2-weighted fat-suppressed image of the upper abdomen in a 4-year-old child shows hyperintensity of the spleen compared with the liver.
A damaged red blood cell scan in an infant with asplenia shows midline liver with extension into the left upper quadrant, which could be construed erroneously as representing the spleen. (Courtesy Marta Hernanz-Schulman, MD, Nashville, TN.)
Accessory Spleens
Wandering Spleen
A, A contrast-enhanced computed tomography (CT) image of the abdomen shows a “whorled” appearance of the splenic vessels and pancreatic tail at the expected location of the splenic hilum. The spleen shows low attenuation without contrast enhancement as a result of absent perfusion. B, A close-up view of “whorled” hilar vessels and the pancreatic tail from A. C, Below the level of A, the caudal location of the splenic mass is shown. D, Coronal reformatting underscores the displacement and abnormal orientation of the spleen and again shows lack of contrast enhancement. E, A color Doppler ultrasound image shows no vascular flow into the spleen. Also note the abnormal echotexture of the spleen. SAG SPL, Sagittal spleen. F, One year after undergoing a splenectomy, the child presented with hypotension and abdominal distention. Coronal reconstruction of abdominal CT scan performed with oral contrast reveals reversal of the usual relationship of the gastric fundus and gastric outlet, consistent with gastric volvulus. Note the gastric pneumatosis. (Courtesy Jeanne G. Hill, MD, MUSC.)
Splenogonadal Syndrome
A, A longitudinal ultrasound image of the left hemiscrotum reveals round-shaped splenic tissue cephalad to the testicle, similar in echotexture and fused to the more oval-shaped testis below. B, A color Doppler image shows increased vascularity of the splenic tissue compared with that of the testicle. C, A technetium-99m sulfur colloid liver-spleen scan shows radiopharmaceutical uptake in the spleen in the left upper quadrant and in the left hemiscrotum; note continuous radiopharmaceutical uptake within the persistent cord of tissue connecting the spleen with the left testis. (Courtesy A. Schlesinger, MD, Houston, TX.)
Splenorenal Fusion
Abnormal Visceroatrial Situs
Initial ultrasound evaluation of 1-day-old infant with congenital heart disease and asplenia. A, A transverse image through the upper abdomen shows the adrenals fused across the midline anterior to the aorta (A), which is located just to the right of the midline. Gas from the left-sided stomach (S) obscures a portion of the left adrenal gland. Note the right-sided inferior vena cava (IVC) anterior to the right adrenal gland (arrow). B, At a slightly lower level, adrenal fusion is again seen. The adrenal on the right is seen between the upper pole of the right kidney (RK) and the IVC (arrow), anterior to the aorta (A). Note the extension of the liver into the left upper quadrant around the stomach (S). (Courtesy Marta Hernanz-Schulman, MD, Nashville, TN.)
A, Multiple splenules are present in the left upper quadrant, behind the stomach. Note the midline liver. The inferior vena cava (IVC) is intact, located to the right of the aorta. Note the midline liver, centrally located portal vein (arrow), which was noted to be preduodenal on lower sections. B, A 2-month-old infant with complex congenital heart disease and single ventricle anatomy. Note two splenules (arrows) in the left upper quadrant behind the stomach, and the left-sided azygous continuation of the interrupted IVC. The left azygous vein drained into the left-sided superior vena cava. (A, Courtesy Marta Hernanz-Schulman, MD, Nashville, TN.)
Multiple splenules in the right upper quadrant of a 2-year-old with left-sided atrial isomerism and polysplenia are identified on a transverse sonogram of the abdomen. (Courtesy Marta Hernanz-Schulman, MD, Nashville, TN.)
Splenomegaly
