Spleen

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). Splenic tissue can also be imaged with technetium 99m (99mTc) labeled sulfur colloid, which is rapidly sequestered by the mononuclear phagocytic system (including in the liver and bone marrow). The vascularity of the red pulp creates a variable enhancement pattern, particularly in the arterial phase, and should not be mistaken for splenic disease. Any difficulty is usually resolved by imaging during the portal venous phase (PVP) when the spleen is homogeneously enhanced (Fig. 7-2).

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Figure 7-1 Plain abdominal radiograph in a 37-year-old woman with leukemic splenic infilration and splenomegaly (arrows).
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Figure 7-2 Axial arterial and PVP CT in a 36-year-old woman demonstrating marked irregular arterial enhancment (A) becoming uniform during the PVP (B).
Being highly vascular, the spleen is susceptible to many blood-borne pathogens, particularly metastatic and infectious disease, either as discrete lesions or as diffuse infiltration of the whole organ with or without splenomegaly. Differentiation between benign and malignant splenic lesions, either single or multiple, may ultimately require positron emission tomography (PET) or preferably PET/CT or even percutaneous biopsy, a relatively safe procedure when performed by experienced interventionalists.

Splenic Disorders

Congenital Disorders

Accessory Spleen

Typically the spleen is a single organ, but it is not uncommon for smaller amounts of splenic tissue (splenule or accessory spleen) to surround the main body, particularly close to the pancreatic tail. Usually these are single, but sometimes a few are present. Splenules are characteristically rounded, smooth-walled masses, most often 1 to 2 cm (but can be larger), that are located in the proximity of the spleen (usually the splenic hilum). They typically demonstrate a similar density to the spleen, whether on contrast-enhanced or noncontrast imaging (Fig. 7-3), which usually differentiates them from lymphadenopathy or peritoneal and omental masses.
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Figure 7-3 Axial contrast-enhanced CT in a 45-year-old woman with a splenule (accessory splenic tissue) (arrow).

Asplenia and Polysplenia Syndromes

Asplenia and polysplenia syndromes belong to a spectrum of heterotaxic syndromes referring to abnormal positioning of the internal organs. Situs solitus refers to the normal position, and situs inversus to the mirror image. When the position of the organs is between the two (or ambiguous), it is referred to as situs ambiguus. There are two primary classifications of situs ambiguus, which depend on the cardiac atrial morphology. If both atria have right-sided morphologies, it is known as right isomerism or asplenic syndrome (the spleen is absent). Conversely, if both atria have left atrial morphologies, this is known as left isomerism or polysplenism (multiple small splenic masses). However, the features and positioning of the abdominal organs in situs ambiguus are inconsistent, and precise definition of the type is often difficult.
Right isomerism (asplenia) usually presents in infancy with numerous other congenital anomalies, such as imperforate anus, Hirschsprung disease, and annular pancreas. It is often fatal. Left isomerism (polysplenia) can be fatal, but not usually as early as right isomerism. Patients with left isomerism are prone to biliary obstruction, esophageal and duodenal atresia, and biliary atresia, as well as other anomalies.
On CT, right isomerism is identified with asplenia, a centrally located liver, the aorta and inferior vena cava on the same side (usually the right), both lungs trilobed, and bilateral morphological right atria. Left isomerism is characterized by multiple splenic nodules, intrahepatic inferior vena cava interruption with azygous or hemiazygous continuation of the inferior vena cava, bilobed lungs, and bilateral left-sided atria (Fig. 7-4).
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Figure 7-4 Axial noncontrast CT in a 26-year-old man with polysplenia (large arrow). The liver is predominantly on the left (small arrows) with splenic tissue on the right.

Wandering Spleen

The so-called wandering spleen is caused by an abnormal congenital development of the lienorenal ligament, resulting in a long splenic vascular pedicle that allows the spleen the “freedom to wander” within the peritoneum. Given that it is on a long pedicle, its position within the abdomen or pelvis can vary from one scan to another (Fig. 7-5). For similar reasons, it is susceptible to torsion.
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Figure 7-5 Coronal contrastenhanced CT in a 57-year-old woman with splenomegaly caused by polycythemia rubra vera and a “wandering” spleen in the left lower quadrant (arrow).

Splenosis and Residual Splenic Tissue

Splenosis is usually secondary to blunt splenic trauma, in which either the whole or parts of the shattered spleen distribute splenic tissue throughout the abdomen and pelvis. The chest may be involved if the diaphragm is breached, and sometimes other organs are affected if they also underwent traumatic laceration. Similarly, splenic remnants can remain after splenectomy (Fig. 7-6). These nodules, which are often multiple, must be differentiated from other abdominal masses, although their smooth-walled, homogeneous, and rounded appearance and their enhancement characteristics, similar to those of the spleen, should be a clue to the diagnosis. The diagnosis may ultimately require 99mTc-labeled red blood cells or sulfur colloid tests to confirm the splenic nature of the mass, whether in the abdomen (Fig. 7-6) or in the mediastinum (Fig. 7-7).
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Figure 7-6 Axial contrastenhanced CT (A) in a 47-year-old woman with prior splenectomy and now a 3-cm left upper quadrant mass (arrow), proved to be splenic tissue on 99mTc sulfur colloid scan (B; arrowhead). There is also normal hepatic uptake.
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Figure 7-7 Axial contrastenhanced CT (A) in the same patient as in Figure 7-6 with a 2-cm pleural-based left upper lobe mass (arrows) demonstrating splenic activity at 99mTc sulfur colloid imaging (B).

Splenomegaly

Splenomegaly is defined as splenic enlargement and should not be confused with hypersplenism (see later in the chapter), which is caused by splenic functional abnormalities in distinction to simple splenic enlargement. There are numerous disparate causes of an enlarged spleen (Box 7-1), usually defined on US as >13 cm in long axis or >500 cm3 volume, although these measurements are relative given the size and morphology of the individual.
 
Box 7-1   Causes of Splenomegaly
Vascular Congestion

Portal hypertension
Sickle cell disease
Hereditary spherocytosis
Thalassemia
Right heart failure
Malignancy

Lymphoma
Leukemia
Metastases
Myelofibrosis
Multiple myeloma
Hematological

Polycythemia rubra vera
Trauma (hemorrhage)
Infectious

Infectious mononucleosis
Leptospirosis
Brucellosis
Malaria
Leishmaniasis
Acute tuberculosis and histoplasmosis
Typhoid
Fungal infection
Schistosomiasis
HIV-related
Multiple splenic infected emboli (endocarditis)
Storage

Gaucher disease
Niemann-Pick disease
Mucopolysaccharidosis
Langerhans cell histiocytoses
Amyloidosis
Autoimmune

Rheumatoid arthritis (Felty syndrome)
Sjögren syndrome
Systemic lupus erythematosus
Idiopathic thrombocytopenia purpura
Autoimmune hemolytic anemia

Congenital Splenomegaly

Hematological Abnormalities

Hematological genetic abnormalities usually result in splenomegaly because the continuously produced defective red blood cells are sequestered in a steadily increasing spleen. These include thalassemia, early sickle cell disease (in the later stages, the spleen infarcts and becomes small), hereditary spherocystosis, and elliptocytosis.

Depositional Metabolic Disease

Gaucher disease is the most common lysosomal storage disease caused by a genetic defect (autosomal recessive) in the enzyme glucosylceramidase, resulting in glucosylceramide accumulation, predominantly in tissues abundant in mononuclear leukocytes (macrophages), namely the spleen, lungs, kidneys, liver, brain, and bone marrow. There are types I, II, and III, and patients with types I and III usually survive into adulthood. These may present with hepatosplenomegaly (Fig. 7-8) as the unmetabolized lipids steadily accumulate within the spleen, or they may be deposited as complex focal masses known as gaucheromas.
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Figure 7-8 Axial T2-weighted MRI in a 46-year-old man with Gaucher disease and multiple splenic gaucheromas (arrows).
Niemann-Pick disease is a lysosomal storage disorder in which sphingomyelin accumulates (owing to lack of sphingomyelinase) in the liver, spleen, brain, lungs, and bone marrow.
Mucopolysaccharidoses are a group of lysosomal storage disorders caused by deficiency of lysosomal enzyme activity (the subclassification is dependent on the missing enzyme) with accumulation of glycosaminoglycans, which are deposited in the peripheral nervous cysts, eyes, liver, and spleen.
Langerhans cell histiocytoses (LCH) are a group of disorders with excessive deposition of Langerhans histiocytic cells. The systemic manifestations involve multiple organs and include splenomegaly. Subtypes (now all referred to as LCH) were known as histiocytosis X, eosinophilic granuloma, Hand-Schüller-Christian disease, and Letterer-Siwe disease.

Vascular Congestion

The most common cause of splenomegaly is portal hypertension as a result of liver cirrhosis, although any cause of portal hypertension can lead to splenomegaly, including right-sided heart failure, hepatic fibrosis, Budd-Chiari syndrome, portal or splenic vascular thrombosis, and occlusion. The findings are readily appreciated with CT, particularly when signs of liver cirrhosis are obvious. Splenic venous enlargement and tortuosity are caused by the chronically raised venous pressure, and collaterals commonly form, particularly around the splenic hilum (Fig. 7-9). At MRI, multiple small T1 and T2 hypointense lesions, known at Gamna-Gandy bodies, can be observed, which represent areas of hemosiderosis, probably from prior microhemorrhages induced by the vascular congestive process (Fig. 7-10).
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Figure 7-9 Axial (A) and coronal (B) contrastenhanced CT in a 57-year-old man with cirrhosis, ascites (arrowhead), splenic varices (arrows), and splenomegaly.
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Figure 7-10 Axial T1-weighted fat-saturated postcontrast MRI in a 44-year-old man with cirrhosis and multiple hypointense foci in the spleen (arrows) caused by Gamna-Gandy bodies.

Lymphoma

Lymphoma is the most common malignant tumor of the spleen and frequently a site of both Hodgkin (30%) and non-Hodgkin disease (30%). Secondary or metastatic involvement from lymphoma elsewhere is more common than isolated primary splenic lymphoma. For staging purposes, splenomegaly is considered nodal in Hodgkin disease and extranodal in non-Hodgkin disease (see “Lymphoma Staging,”Chapter 4).
At imaging, the disease may be a solitary mass (Fig. 7-11), a few or multiple small (Fig. 7-12) or larger (Fig. 7-13) masses, or diffuse splenic involvement (Fig. 7-14). These are mostly hypodense on contrast-enhanced CT, but larger lesions can demonstrate some necrotic or cystic areas. There is usually evidence of extrasplenic lymphoma, particularly mesenteric or retroperitoneal adenopathy (Fig. 7-15). The splenic CT findings are relatively nonspecific, since other infectious or infiltrative disease (Box 7-1) can give similar appearances.
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Figure 7-11 Axial contrast-enhanced CT in a 66-year-old woman with almost complete splenic replacement by a primary lymphomatous mass (arrows). There is an incidental hemangioma in the liver (small arrow).
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Figure 7-12 Axial contrastenhanced CT in a 75-year-old woman with multiple tiny splenic lesions (arrows) caused by small lymphocytic lymphoma.
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Figure 7-13 Axial contrastenhanced CT in a 51-year-old woman with multiple hypodense splenic lesions (arrows) caused by B-cell lymphoma.
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Figure 7-14 Axial noncontrast CT in a 37-year-old man with splenomegaly (arrows) caused by diffuse infiltration with Epstein-Barr virus舐induced lymphoma. There is associated ascites.
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Figure 7-15 Axial (A) and coronal (B) contrast-enhanced CT in a 66-year-old woman demonstrating homogeneous splenomegaly (short arrows) caused by non-Hodgkin lymphoma. There is diffuse intraabdominal adenopathy (arrows).

Leukemia

Most leukemias involve the spleen, although this is less common with acute lymphoblastic leukemia. The disease typically affects the spleen uniformly as an infiltrative process of malignant leukemic cells. Splenomegaly can reach massive sizes, particularly with chronic leukemias (especially chronic myelocytic leukemia) (Fig. 7-16). At imaging, the spleen appears uniformly and homogeneously enlarged. With massive splenomegaly the spleen may demonstrate some heterogeneous regions because of either tumor deposits or areas of splenic infarction (wedge shaped or rounded), since some anatomy of the speen is arterially compromised owing to its massive size (Fig. 7-16).
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Figure 7-16 Sagittal US (A), axial (B), and coronal (C) contrast-enhanced CT in a 76-year-old woman with splenomegaly resulting from chronic lymphocytic leukemia. On US the spleen measures 21 cm in length. CT demonstrates small associated peripheral splenic infarctions (arrows).

Myeloproliferative Disease

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Figure 7-17 Plain frontal abdominal radiograph (A) in a 77-year-old woman with myelofibrosis and massive splenomegaly (arrows). Axial (B) and coronal (C) contrast-enhanced CT demonstrates splenomegaly and several small hypodense splenic tumors (small arrow). There is associated ascites.
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Figure 7-18 Axial contrast-enhanced CT in a 58-year-old man with polycythemia rubra vera with splenomegaly and ill-defined splenic hypodensities (arrows) caused by extramedullary hematopoiesis.

Splenic Metastases

Hematogenous metastases are common because of the rich splenic vascular supply and are observed in numerous malignancies, but particularly melanoma, breast cancer, and lung cancer. There is often a history of malignant disease, which helps to differentiate single or multiple splenic lesions from other neoplastic, infectious, or infiltrative causes. Should metastatic disease cause splenomegaly, it is usually because of mass effect from single or, more often, multiple lesions rather than homogeneous enlargement (Fig. 7-19).
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Figure 7-19 Axial (A) and coronal (B) contrast-enhanced CT in a 74-year-old man with lung cancer demonstrating splenomegaly and numerous hypodense splenic metastases.

Infectious Splenomegaly

Parasites

Many infectious diseases cause splenomegaly (and often hepatosplenomegaly), particularly parasitic diseases that sometimes cause massive enlargement (especially leishmaniasis, schistosomiasis, and malaria). Splenomegaly can be secondary to the sequestration of parasitic agents or, as in malaria, an immunoglobulin M (IgM) response from repeated infections with splenic lymphocytic infiltration, also known as tropical splenomegaly syndrome (Fig. 7-20).
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Figure 7-20 Axial (A) and coronal (B) contrast-enhanced CT in a 28-year-old woman with splenomegaly resulting from chronic malarial infection. By CT, the splenomegaly cannot be differentiated from many other causes of splenomegaly.

Viral Splenic Infection

Similar to other infective agents, viral splenic infection is usually associated with hepatomegaly (see Chapter 6). It can be part of a generalized acute viral hepatitis (hepatitis A through E, human immunodeficiency virus [HIV]) or infectious mononucleosis, but can also be seen in cytomegalovirus and rubella infection. Infectious mononucleosis is secondary to infection with the Epstein-Barr virus (a herpes virus), and there is characteristic preferential splenic enlargement, which is at particular risk of spontaneous rupture, especially following contact sport injuries (Fig. 7-21).
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Figure 7-21 Coronal (A) and axial (B) contrast-enhanced CT in a 24-year-old woman with infectious mononucleosis and splenomegaly, splenic rupture (large arrow), and intraabdominal hemorrhage (small arrows).

Bacterial Splenic Infection

A number of bacterial infections can cause diffuse splenomegaly, particularly brucellosis, leptospirosis, and typhoid fever. Mycobacterium tuberculosis and histoplasmosis often cause diffuse hepatosplenomegaly in the acute phase and are usually associated with concomitant multiple, hypodense lesions (Fig. 7-22). Repeated embolic assault, particularly from bacterial endocarditis, can cause splenomegaly, including splenic abscess (Fig. 7-23).
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Figure 7-22 Axial (A) and coronal (B) contrast-enhanced CT in a 53-year-old man with tuberculosis and mild splenomegaly and multiple hypodense tuberculous splenic lesions.
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Figure 7-23 Axial contrast-enhanced CT in a 66-year-old man with splenomegaly and a 10-cm splenic abscess with air/fluid level (arrow) caused by gas-forming organisms.

Depositional Disease

Amyloidosis (see Chapter 4)
Splenomegaly is usually secondary to primary systemic amyloidosis (AL-type) with accumulation of monoclonal immunoglobulin light chains within the spleen and multiple other organs.

Hypersplenism

Hypersplenism is a pancytopenia (erythrocytes, platelets, and granulocytes) to a variable degree caused by an enlarged spleen that is responsible for their premature destruction. Hypersplenism results from splenomegaly from almost any cause (Box 7-2), but not all cases of splenomegaly cause hypersplenism. Hypersplenism may or may not be associated with increased bone marrow activity as a counter to the pancytopenia.

Autoimmune Disease

Many autoimmune conditions can cause splenomegaly (Box 7-1).

Autoimmune Hemolytic Anemia

As its name suggests, autoimmune hemolytic anemia is an autoimmune reaction to red blood cells. The primary disease is idiopathic, whereas secondary disease can be caused by a number of lymphoproliferative or autoimmune disorders (systemic lupus erythematosus, ulcerative colitis, rheumatoid arthritis, and scleroderma). The damaged red blood cells are sequestered in the spleen, leading to splenomegaly.

Idiopathic Thrombocytopenic Purpura

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder in which antibody production against platelets leads to thrombocytopenia and hypersplenism as the defective platelets are sequestered in the spleen. The disease may be asymptomatic but often causes purpura or bleeding diathesis.

Systemic Lupus Erythematosus

Systemic lupus erythematosus is a systemic autoimmune disease with repeated episodes of vasculitis and inflammatory disease. In the acute phase, this can result in hepatosplenomegaly, although it more commonly causes glomerulonephritis, dermatological rashes, arthritis, and neuropsychiatric disorders.

Granulomatosis with Polyangiitis (Wegener Granulomatosis)

A multisystemic vasculitis, usually requiring lifelong immunosuppressive therapy, Wegener granulomatosis (granulomatosis with polyangiitis) can cause repeated splenic infarctions leading ultimately to a “shrunken” spleen (Fig. 7-24).
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Figure 7-24 Axial contrast-enhanced CT in a 41-year-old man with Wegener granulomatosis and a shrunken heterogeneous spleen (arrow) as a result of multiple infarctions.

Felty Syndrome

Splenomegaly is part of Felty syndrome with associated neutropenia (secondary to splenic sequestration from granulocytic abnormalities) and rheumatoid arthritis. The spleen can be markedly enlarged. Anemia and thrombocytopenia often accompany this syndrome.

Sjögren Syndrome

Sjögren syndrome is a systemic autoimmune disease that predominantly affects the exocrine glands (parotid and salivary glands). However, it is often associated with other autoimmune connective tissue disorders, and splenomegaly may result (Fig. 7-25).
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Figure 7-25 Axial (A) and coronal (B) contrast-enhanced CT in a 28-year-old woman with Sjögren syndrome and spelnomegaly (arrows).

Small or Shrunken Spleen (Box 7-2)

Congenital (Fanconi Syndrome)

A small spleen as a congenital condition is very uncommon but has been described in Fanconi syndrome, a disease of the proximal renal tubules with loss of bicarbonate renal tubular acidosis and phosphate and rickets formation. Causes of Fanconi syndrome include cystinosis and Wilson disease, among others.
 
Box 7-2   Causes of Small Spleen
Congenital (Fanconi syndrome)
Sickle cell anemia
Essential thrombocytopenia
Irradiation
Thorotrast
Wegener granulomatosis

Sickle Cell Disease

Although the spleen is commonly enlarged in the more acute phases of sickle cell disease, the repetitive splenic infarctions ultimately lead to a small, often fibrotic spleen that is effectively nonfunctioning, such that it is frequently termed an autosplenectomy (Fig. 7-26). The small residual mass may calcify (Fig. 7-27).
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Figure 7-26 Axial contrast-enhanced CT in a 39-year-old woman with sickle cell disease and a small spleen (arrow) resulting from repeated thrombotic episodes.
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