The Spleen

Chapter 95

The Spleen

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.


Plain radiographs of the abdomen may reveal the spleen in the left upper quadrant, displacing the stomach medially and the colon inferiorly. The spleen may be obscured when large amounts of gas or stool are present in the gastrointestinal tract.

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.

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.

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

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).

Angiography is rarely used for intrasplenic disease; CT angiography and MR angiography offer excellent visualization of the spleen and its vessels.

Accessory Spleens

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.

Wandering Spleen

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).

Splenogonadal Syndrome

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).

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

Splenorenal Fusion

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

Abnormal Visceroatrial Situs

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.16,1820

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

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.


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.

Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on The Spleen

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