DOI: 10.1148/rg.244045006
RadioGraphics 2004;24:1137-1163
From the Archives of the AFIP
Primary Vascular Neoplasms of the Spleen: Radiologic-Pathologic Correlation1
Robert M. Abbott, MD,
Angela D. Levy, LTC, MC, USA,
Nadine S. Aguilera, MD,
Luis Gorospe, MD and
William M. Thompson, MD
1 The opinions and assertions contained herein are the private views of the authors and are not to be construed as official nor as reflecting the views of the Departments of the Army or Defense.
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Abstract
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Primary vascular neoplasms of the spleen constitute the majority of nonhematolymphoid splenic tumors. The benign primary vascular tumors include hemangioma, hamartoma, and lymphangioma, whereas those of variable or uncertain biologic behavior include littoral cell angioma, hemangioendothelioma, and hemangiopericytoma. The primary malignant vascular neoplasm of the spleen is angiosarcoma. Peliosis is a rare lesion of unknown cause that is usually found incidentally in asymptomatic patients but may be associated with hematologic or metastatic disease. Although these vascular neoplasms of the spleen are uncommon, their importance lies in that they must be differentiated from the more common neoplastic disorders of the spleen, such as lymphoma and metastasis. The most common echogenic solid or complex cystic mass in an asymptomatic patient is splenic hemangioma. However, the imaging appearance of splenic hemangiomas may be complex, and differentiation of these lesions from malignant disease may not be possible. The diagnosis of splenic hamartoma may be suggested when findings of increased blood flow on color Doppler images are seen in association with a homogeneous solid echogenic mass. A large subcapsular solitary cystic abnormality discovered incidentally in a child in association with internal septations and tiny mural nodules favors the diagnosis of lymphangioma. Any invasion of the surrounding splenic parenchyma by a splenic lesion should indicate a more aggressive or malignant process. Evaluation of a focal splenic abnormality identified on sonograms should be followed up with computed tomography or magnetic resonance imaging with and without contrast material enhancement. Splenectomy may be required for definitive evaluation of a splenic mass with atypical features.
Index Terms: Angioma, 775.3194 • Hamartoma, 775.314 • Hemangiopericytoma, 775.3193 • Hemangioendothelioma, 775.3199 • Lymphangioma, 775.3194 • Sarcoma, 775.322 • Spleen, neoplasms, 775.314, 775.3193, 775.3194, 775.3199, 775.322
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Identify the pathologic features of primary vascular neoplasms of the spleen.
- Describe the radiologic features of primary vascular neoplasms of the spleen.
- Discuss the differential diagnosis of primary nonhematolymphoid tumors of the spleen.
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Introduction
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Primary splenic tumors are uncommon and are classified as lymphoid tumors, nonhematolymphoid tumors, and tumorlike lesions. Vascular neoplasms are the most common primary nonhematolymphoid tumors and arise from the vascular elements that compose splenic red pulp. In contrast, splenic white pulp is composed of lymphatic tissue and gives rise to lymphoid neoplasms.
Clinically, there is a wide range of presenting signs and symptoms that may be encountered in patients with primary vascular neoplasms of the spleen. These patients are frequently asymptomatic, and the neoplasms are discovered incidentally during an imaging evaluation conducted for other reasons. On the other hand, the clinical presentation may be dramatic because these tumors may cause spontaneous splenic rupture and massive hemoperitoneum.
The biologic behavior of primary vascular splenic neoplasms ranges from benign to malignant. Hemangioma is the most common benign primary neoplasm of the spleen. Other less common benign vascular neoplasms include hamartoma, lymphangioma, and littoral cell angioma. Although rare, angiosarcoma is the most common malignant primary vascular neoplasm of the spleen. Hemangioendothelioma is considered by some authors to represent an intermediate entity between hemangioma and angiosarcoma. Hemangiopericytoma is most often encountered as a soft-tissue primary tumor, but occasionally it originates in the spleen. Hemangiopericytoma is often characterized as having variable biologic behavior, but it is regarded as a tumor that may have very high malignant potential. Finally, peliosis is rare nonneoplastic tumorlike disorder that is included in the discussion of primary vascular neoplasms because its imaging and pathologic appearances mimic those of neoplasms.
This article summarizes the current literature and our experience with primary vascular neoplasms of the spleen. Knowledge of the clinical, pathologic, and radiologic spectrum of these neoplasms is important because of the wide spectrum of clinical and radiologic manifestations. Herein, we review the clinical, pathologic, and radiologic features of these entities, with emphasis on those characteristics that may allow a more specific diagnosis.
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Normal Spleen
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The spleen is an intraperitoneal organ that is normally located in the left upper quadrant of the abdomen and supported by the gastrosplenic and splenorenal ligaments. The normal adult spleen weighs approximately 150 g (1). A thin, connective tissue capsule invests the spleen. A branching network of trabeculae extends from the inner capsular surface and subdivides the spleen into communicating compartments (Figs 1, 2). The capsule is penetrated at the hilus by blood vessels, lymphatics, and nerves. Branches of arteries, veins, nerves, and lymphatics travel through the spleen in the trabecular network (2).
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Figure 1. Normal spleen. Drawing depicts normal splenic architecture. A branching network of trabeculae (black arrows) extends from the inner aspect of the capsule (arrowheads). Primary and secondary lymphoid follicles of the white pulp (white arrow) are scattered throughout communicating compartments of red pulp.
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Figure 2. Normal spleen. Photomicrograph (original magnification, x10; hematoxylin-eosin [H-E] stain) shows a trabecular branch (arrow) arising from the capsule (*) and extending into normal splenic red pulp.
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The spleen contains two distinct tissues: red pulp and white pulp (Fig 3). There is a large volume of erythrocytes within the red pulp owing to the four types of vascular structures within the pulp. The red pulp is composed of slender and nonanastomosing arterial vessels, thin-walled venous vessels called splenic sinuses, plates of cells called splenic cords that lie between sinusoids, and red pulp veins that drain the sinusoids (Fig 3) (1).
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Figure 3a. Normal splenic red pulp. (a) Photomicrograph (original magnification, x20; H-E stain) shows normal red pulp (*) and T cells in the periarteriolar lymphoid sheath (arrows). (b) Photomicrograph (original magnification, x40; H-E stain) shows splenic sinuses (S) lined by tapered endothelial cells. The splenic cords (C) may contain erythrocytes, macrophages, and lymphoid cells.
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Figure 3b. Normal splenic red pulp. (a) Photomicrograph (original magnification, x20; H-E stain) shows normal red pulp (*) and T cells in the periarteriolar lymphoid sheath (arrows). (b) Photomicrograph (original magnification, x40; H-E stain) shows splenic sinuses (S) lined by tapered endothelial cells. The splenic cords (C) may contain erythrocytes, macrophages, and lymphoid cells.
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The white pulp is composed of lymphatic tissue. The organization of lymphoid cells within the white pulp is similar to that found in the cortex of a lymph node. T cells are usually found in the periarteriolar sheath (Fig 3a), and B cells are found in primary and secondary follicles (Fig 4). Lymphoid follicles (malpighian corpuscles) have a central artery that is surrounded by a germinal center, mantle zone, and marginal zone (Fig 4). The marginal zone is the transition between the white and red pulp.
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Figure 4. Normal splenic white pulp. Photomicrograph (original magnification, x40; H-E stain) shows a secondary follicle from splenic white pulp. The germinal center (*) is surrounded by B lymphocytes in the mantle zone (mz) and marginal zone (mrz).
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On cross-sectional images, the normal spleen is typically located in the left upper quadrant, although its position and orientation may vary considerably from person to person. On sonograms, the spleen has homogeneous mid- to low-level echotexture (Fig 5). On computed tomographic (CT) scans, the normal spleen enhances in a mottled pattern during the arterial (peak aortic enhancement) and early portal venous phases of intravenous contrast material enhancement. The mottled enhancement pattern is caused by variable flow rates through the cords and sinuses of the splenic red pulp (3). The splenic parenchyma becomes homogeneous in the middle to late portal venous phases of contrast enhancement. The equilibrium phase of contrast enhancement typically shows washout of contrast material (Fig 6).
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Figure 6a. Contrast-enhanced CT images of the normal spleen show a mottled pattern of enhancement in the early portal venous phase (a), homogeneous enhancement during the portal venous phase (b), and washout of contrast material during the equilibrium phase of contrast enhancement (c).
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Figure 6b. Contrast-enhanced CT images of the normal spleen show a mottled pattern of enhancement in the early portal venous phase (a), homogeneous enhancement during the portal venous phase (b), and washout of contrast material during the equilibrium phase of contrast enhancement (c).
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Figure 6c. Contrast-enhanced CT images of the normal spleen show a mottled pattern of enhancement in the early portal venous phase (a), homogeneous enhancement during the portal venous phase (b), and washout of contrast material during the equilibrium phase of contrast enhancement (c).
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The normal splenic parenchyma has low signal intensity on T1-weighted magnetic resonance (MR) images and high signal intensity on T2-weighted MR images. MR images obtained after dynamic administration of a gadolinium contrast agent may show a homogeneous or mottled pattern of enhancement during the arterial phase (4). The mottled pattern is similar to that observed on arterial phase contrast-enhanced CT scans and is secondary to variable flow rates through the cords and sinuses of the red pulp (Fig 7).
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Figure 7a. MR imaging appearance of the normal spleen. (a) Gadolinium-enhanced fast spoiled gradient-echo image obtained during the arterial phase shows a mottled pattern of enhancement throughout the spleen. (b) Gadolinium-enhanced T1-weighted image obtained during the portal venous phase shows uniform high signal intensity throughout the spleen. (c) Fast spin-echo T2-weighted image shows high signal intensity throughout the spleen.
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Figure 7b. MR imaging appearance of the normal spleen. (a) Gadolinium-enhanced fast spoiled gradient-echo image obtained during the arterial phase shows a mottled pattern of enhancement throughout the spleen. (b) Gadolinium-enhanced T1-weighted image obtained during the portal venous phase shows uniform high signal intensity throughout the spleen. (c) Fast spin-echo T2-weighted image shows high signal intensity throughout the spleen.
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Figure 7c. MR imaging appearance of the normal spleen. (a) Gadolinium-enhanced fast spoiled gradient-echo image obtained during the arterial phase shows a mottled pattern of enhancement throughout the spleen. (b) Gadolinium-enhanced T1-weighted image obtained during the portal venous phase shows uniform high signal intensity throughout the spleen. (c) Fast spin-echo T2-weighted image shows high signal intensity throughout the spleen.
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Hemangioma
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Clinical Features
Hemangioma, although rare, is the most common benign primary neoplasm of the spleen. Its prevalence at autopsy ranges from 0.3% to 14%, and hemangiomas are found most often in adults from mid-30s to mid-50s years of age (5–7). Some studies indicate that hemangioma occurs with equal frequency among men and women, but others indicate that there is a slight predominance among men (8). Most hemangiomas are small lesions that are found incidentally and patients usually have no symptoms. The natural course of hemangiomas is slow growth, and symptoms or complications, when present, occur late. Hemangiomas can become large and manifest as a palpable nontender mass in the left upper quadrant. Generalized splenomegaly may be present, but results of laboratory evaluation are often normal.
Splenic hemangiomas may occur as part of generalized angiomatosis as seen in Klippel-Trénaunay syndrome. Complications include rupture, hypersplenism, and malignant degenera-tion (7,9). Spontaneous rupture has been reported as the most common complication, occurring in 25% of patients (9). Kasabach-Merritt syndrome (anemia, thrombocytopenia, and coagulopathy) has been reported in patients with large hemangiomas (10). Splenectomy is curative for patients with symptoms.
Pathologic Features
Splenic hemangiomas are thought to be congenital in origin, arising from sinusoidal epithelium. Histopathologic evaluation reveals a nonencapsulated proliferation of vascular channels of variable size, ranging from capillary to cavernous, which are lined with a single layer of endothelium filledwith red blood cells (Fig 8) (11). These blood-filled spaces are separated by thin fibrous septa or splenic pulp tissue. Splenic hemangiomas are most frequently cavernous and may be single or multiple (12). In diffuse angiomatosis, neoplastic vascular channels may replace the whole spleen. Gross examination will reveal solitary or multiple blue-red spongy nodules in the spleen (Fig 9). Size is variable, but most lesions are less than 2 cm in diameter. These lesions may be intrasplenic or protruding and can be solid or cystic. Smaller hemangiomas, both capillary and cavernous, tend to be solid, whereas larger cavernous lesions can develop thrombosis, infarction, fibrosis, and pseudocystic degeneration caused by necrosis.
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Figure 8a. Splenic hemangioma. (a) Photomicrograph (original magnification, x4; H-E stain) shows a solitary, nonencapsulated splenic hemangioma (arrows) that is well demarcated from the adjacent normal spleen. The hemangioma is composed of multiple blood-filled spaces. (b) Photomicrograph (original magnification, x40; H-E stain) shows the blood-filled spaces of the hemangioma (H) lined by flat endothelial cells (arrows).
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Figure 8b. Splenic hemangioma. (a) Photomicrograph (original magnification, x4; H-E stain) shows a solitary, nonencapsulated splenic hemangioma (arrows) that is well demarcated from the adjacent normal spleen. The hemangioma is composed of multiple blood-filled spaces. (b) Photomicrograph (original magnification, x40; H-E stain) shows the blood-filled spaces of the hemangioma (H) lined by flat endothelial cells (arrows).
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Figure 9a. Splenic hemangiomatosis in a 9-year-old boy with Klippel-Trénaunay syndrome and worsening left upper quadrant pain. (a) Longitudinal sonogram of the spleen shows splenomegaly and multiple echogenic masses (arrows). (b) Axial T1-weighted MR image shows multiple subtle hypointense masses (arrow) throughout the spleen. (c) Axial T2-weighted MR image shows several high-signal-intensity masses (arrow). (d) Photograph of the cut surface of the resected spleen shows multiple spongy masses (arrow). Central fibrosis (arrowhead) is present in several of the hemangiomas.
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Figure 9b. Splenic hemangiomatosis in a 9-year-old boy with Klippel-Trénaunay syndrome and worsening left upper quadrant pain. (a) Longitudinal sonogram of the spleen shows splenomegaly and multiple echogenic masses (arrows). (b) Axial T1-weighted MR image shows multiple subtle hypointense masses (arrow) throughout the spleen. (c) Axial T2-weighted MR image shows several high-signal-intensity masses (arrow). (d) Photograph of the cut surface of the resected spleen shows multiple spongy masses (arrow). Central fibrosis (arrowhead) is present in several of the hemangiomas.
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Figure 9c. Splenic hemangiomatosis in a 9-year-old boy with Klippel-Trénaunay syndrome and worsening left upper quadrant pain. (a) Longitudinal sonogram of the spleen shows splenomegaly and multiple echogenic masses (arrows). (b) Axial T1-weighted MR image shows multiple subtle hypointense masses (arrow) throughout the spleen. (c) Axial T2-weighted MR image shows several high-signal-intensity masses (arrow). (d) Photograph of the cut surface of the resected spleen shows multiple spongy masses (arrow). Central fibrosis (arrowhead) is present in several of the hemangiomas.
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Figure 9d. Splenic hemangiomatosis in a 9-year-old boy with Klippel-Trénaunay syndrome and worsening left upper quadrant pain. (a) Longitudinal sonogram of the spleen shows splenomegaly and multiple echogenic masses (arrows). (b) Axial T1-weighted MR image shows multiple subtle hypointense masses (arrow) throughout the spleen. (c) Axial T2-weighted MR image shows several high-signal-intensity masses (arrow). (d) Photograph of the cut surface of the resected spleen shows multiple spongy masses (arrow). Central fibrosis (arrowhead) is present in several of the hemangiomas.
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Solid hemangiomas are firm and darker in color than normal splenic red pulp. Completely solid hemangiomas may contain both vascular channels and areas of fibrosis, but they do not have cystic spaces. Fibrotic changes, which appear light-gray to white, result in a relative decrease in the overall proportion of the remaining blood-filled vascular channels. Cystic hemangiomas are composed of cystic spaces of various sizes that are filled with serous or hemorrhagic fluid due to necrosis. Calcium deposits may be present in firm fibrotic areas of the mass or in the surrounding intratumoral cystic spaces (5).
Radiologic Features
The radiologic appearance of hemangioma ranges from solid to cystic, depending on gross morphology, but predominantly a hemangioma appears as a solid mass with cystic spaces (5,13). On radiographs, the lesion may manifest as a mass in the left upper quadrant or as splenomegaly. Calcification, when present, appears as multiple small punctate calcifications or peripheral curvilinear calcifications.
On sonograms, a hemangioma may manifest as a well-defined intrasplenic or pedunculated echogenic solid or complex cystic mass (Fig 9). Echogenic calcifications with acoustic shadowing may be present (Fig 10).
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Figure 10a. Splenic hemangioma in a 61-year-old woman who complained of nausea, vomiting, and epigastric pain. (a) Longitudinal sonogram of the spleen shows a well-defined hypoechoic mass containing a central, shadowing echogenic focus (arrow). (b) Contrast-enhanced CT scan obtained during the late portal venous phase shows a nearly isoattenuating mass in the splenic hilus with a central calcification (arrow). (c) Photograph of the cut surface of the resected spleen shows a heterogeneous mass with fibrous septa and a focus of central fibrosis (arrow).
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Figure 10b. Splenic hemangioma in a 61-year-old woman who complained of nausea, vomiting, and epigastric pain. (a) Longitudinal sonogram of the spleen shows a well-defined hypoechoic mass containing a central, shadowing echogenic focus (arrow). (b) Contrast-enhanced CT scan obtained during the late portal venous phase shows a nearly isoattenuating mass in the splenic hilus with a central calcification (arrow). (c) Photograph of the cut surface of the resected spleen shows a heterogeneous mass with fibrous septa and a focus of central fibrosis (arrow).
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Figure 10c. Splenic hemangioma in a 61-year-old woman who complained of nausea, vomiting, and epigastric pain. (a) Longitudinal sonogram of the spleen shows a well-defined hypoechoic mass containing a central, shadowing echogenic focus (arrow). (b) Contrast-enhanced CT scan obtained during the late portal venous phase shows a nearly isoattenuating mass in the splenic hilus with a central calcification (arrow). (c) Photograph of the cut surface of the resected spleen shows a heterogeneous mass with fibrous septa and a focus of central fibrosis (arrow).
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On unenhanced CT scans, capillary hemangiomas appear as hypoattenuating or isoattenuating, well-marginated masses. Homogeneous and marked contrast enhancement occurs during intravenous administration of contrast material (Fig 11). Cavernous hemangiomas have a combination of solid and cystic components. The solid component appears isoattenuating or hypoattenuating relative to normal spleen, with enhancement of only the solid tissue (Fig 12). Ferrozzi et al (14) have described late- or delayed-phase contrast enhancement of cavernous hemangiomas as discrete mottled areas of heterogeneous attenuation rather than centripetal enhancement as seen in the liver. This finding likely reflects the fact that the cystic spaces, often central in location, do not contain blood-filled vascular channels. Curvilinear or eggshell calcification is most often seen in cystic hemangiomas. Mottled central calcification is more common in solid lesions, whereas coarse calcification may be found in areas of necrosis or long-standing thrombosis (Fig 10b) (5,14).
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Figure 11a. Multiple splenic hemangiomas in a 74-year-old asymptomatic man with a history of prostate cancer. (a) Contrast-enhanced CT scan obtained during the early portal venous phase shows multiple, densely enhancing splenic masses (arrows). (b) On a CT scan obtained during the equilibrium phase of enhancement, the hemangiomas (arrows) are isoattenuating compared with the adjacent normal spleen.
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Figure 11b. Multiple splenic hemangiomas in a 74-year-old asymptomatic man with a history of prostate cancer. (a) Contrast-enhanced CT scan obtained during the early portal venous phase shows multiple, densely enhancing splenic masses (arrows). (b) On a CT scan obtained during the equilibrium phase of enhancement, the hemangiomas (arrows) are isoattenuating compared with the adjacent normal spleen.
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Figure 12a. Cavernous hemangioma in a 29-year-old man with left upper quadrant pain and a palpable mass. (a) Contrast-enhanced CT scan shows a well-defined intrasplenic mass with peripheral enhancement surrounding areas of nonenhancement (*). (b) Photograph of the cut surface of the resected spleen shows a well-demarcated cavernous hemangioma with central fibrosis (*) that corresponds to the areas of CT nonenhancement.
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Figure 12b. Cavernous hemangioma in a 29-year-old man with left upper quadrant pain and a palpable mass. (a) Contrast-enhanced CT scan shows a well-defined intrasplenic mass with peripheral enhancement surrounding areas of nonenhancement (*). (b) Photograph of the cut surface of the resected spleen shows a well-demarcated cavernous hemangioma with central fibrosis (*) that corresponds to the areas of CT nonenhancement.
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The MR imaging appearance of splenic hemangiomas has been described as being similar to that of hepatic hemangiomas (8,15). Splenic hemangiomas are hypo- to isointense, compared with normal spleen, on T1-weighted images and hyperintense on T2-weighted images (Fig 9). Dynamic MR imaging after administration of gadopentetate dimeglumine has shown that splenic hemangiomas have three patterns of enhancement: (a) immediate homogeneous enhancement that persists, (b) early peripheral enhancement with uniform delayed enhancement, and (c) peripheral enhancement with centripetal progression but persistent enhancement of a central fibrous scar (16). Others have described central persistent low signal intensity on contrast-enhanced T1-weighted images in those lesions with a central scar (8). However, larger hemangiomas may have a variable MR imaging appearance because of complicating features such as hemorrhage, infarction, and thrombosis (Fig 13). As a result, differentiation of a splenic hemangioma from malignant disease may not be possible solely on the basis of MR imaging findings.
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Figure 13a. Splenic hemangioma in a 69-year-old woman who complained of left upper quadrant pain. (a) Axial T1-weighted MR image shows a large hypointense mass completely replacing the spleen. The mass contains several foci of high signal intensity (arrow) that may represent hemorrhage. (b) Coronal T2-weighted MR image shows that the mass is medium in signal intensity with linear areas of low signal intensity and a focus of high-signal-intensity hemorrhage (arrow).
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Figure 13b. Splenic hemangioma in a 69-year-old woman who complained of left upper quadrant pain. (a) Axial T1-weighted MR image shows a large hypointense mass completely replacing the spleen. The mass contains several foci of high signal intensity (arrow) that may represent hemorrhage. (b) Coronal T2-weighted MR image shows that the mass is medium in signal intensity with linear areas of low signal intensity and a focus of high-signal-intensity hemorrhage (arrow).
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Ramani et al (8) reported that both splenic hemangiomas and hepatic hemangiomas demonstrate peripheral enhancement with centripetal progression. However, splenic hemangiomas do not have well-defined peripheral nodules that coalesce over time. This characteristic is thought to reflect the differences in vascular supply to the background organ rather than inherent differences between splenic and hepatic hemangiomas (8). This hypothesis suggests that enhancing peripheral nodules (seen in hepatic hemangiomas on both contrast-enhanced CT and MR images) may be less conspicuous in splenic hemangiomas during the arterial phase because splenic enhancement obscures them. In addition, hemangiomas in the spleen may be less conspicuous compared with those in the liver because of the longer T2 values of the splenic parenchyma on T2-weighted images.
The contrast enhancement patterns of splenic hemangiomas as seen on CT and MR images and described by Ferrozzi et al (14) and Ramani et al (8), respectively, appear to differ with regard to progressive centripetal enhancement. In the Ramani et al series, 19 of 22 lesions demonstrated a progressive centripetal pattern of enhancement with dynamic contrast enhancement techniques. In addition, two small splenic hemangiomas in their series demonstrated early uniform enhancement that persisted on delayed T1-weighted images. These findings correlate with the pattern of enhancement of capillary splenic hemangiomas on CT scans as reported by Ferrozzi et al. (Note that Ramani et al did not classify the majority of the lesions into capillary or cavernous splenic hemangiomas, unlike Ferrozzi et al, who did.) To our knowledge, there is no additional evidence to support the finding that the contrast enhancement patterns of splenic hemangiomas would differ significantly between current CT and MR imaging techniques. Moreover, a consistent finding on both CT and MR contrast-enhanced images is that larger splenic hemangiomas appear to lack well-defined enhancing peripheral nodules.
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Hamartoma
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Clinical Features
Hamartomas, which are also known as splenomas, splenadenomas, or nodular hyperplasia of the spleen, are rare benign lesions first described by Rokitansky in 1861 (17). Approximately 120 cases of splenic hamartoma have been reported in the English-language literature. Review of autopsy series has shown that the incidence of splenic hamartoma ranges from 0.024% to 0.13% (18). Hamartomas may occur at any age with equal gender predilection. Most patients have no symptoms, and the discovery of a splenic hamartoma is an incidental finding. Larger lesions may manifest with a palpable mass, splenomegaly, or rupture. Thrombocytopenia and anemia may occur from sequestration of hematopoietic cells. Signs and symptoms usually associated with larger lesions are more common in female patients (19).
Hamartomas of the spleen have been associated with hamartomas elsewhere in the body and have been reported in cases of tuberous sclerosis and Wiskott-Aldrich–like syndrome (17,20–22). The association of splenic hamartoma with tuberous sclerosis lends support to the hamartomatous nature of the latter condition. In addition, an association of splenic hamartoma with malignancy has been suggested. In a study by Lam et al, three of six splenic hamartomas were associated with neoplastic diseases (18,23).
Pathologic Features
Splenic hamartoma is a malformation composed of an anomalous mixture of normal splenic red pulp elements. The hamartoma is thought to be congenital in origin, reflecting a focal developmental disturbance in the spleen. Some consider a splenic hamartoma to be a neoplasm (a form of hemangioma or lymphangioma) or possibly a posttraumatic lesion (17,24). Still others believe that splenic hamartoma might arise from an acquired proliferative process, a theory that supports the association of hamartoma with malignancy (23).
Hamartomas are usually well-circumscribed, solid, bulging nodular lesions that tend to compress the adjacent parenchyma. They are most often solitary but may manifest as multiple nodules. Their gross appearance is typically dark red to grayish-white, and lesions up to 19 cm in size have been reported (18). Despite their well-defined appearance at gross examination, hamartomas do not appear well defined at microscopic analysis. Their expansile growth compresses the surrounding red pulp, which can be demonstrated with a reticulum stain. They lack fibrous trabeculae, but focal sclerosis as well as minute calcifications may be present (1). At histopathologic examination, they contain a mixture of unorganized vascular channels lined by endothelial cells and surrounded by fibrotic cords of predominant splenic red pulp with or without (lymphoid) white pulp (Fig 14) (17). No organized lymphoid follicles (malpighian corpuscles) are present. Additional findings include plasmacytosis; extramedullary hematopoiesis; and increased numbers of macrophages, eosinophils, and mast cells (17,25).
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Figure 14a. Splenic hamartoma. (a) Photomicrograph (original magnification, x10; H-E stain) shows disorganized sinuses and splenic red pulp elements (*) compared with the organized sinuses in the normal spleen (upper portion of the image). (b) Photomicrograph (original magnification, x40; H-E stain) shows an irregular, disorganized splenic sinus containing a megakaryocyte and nucleated red cells. (c) Photomicrograph (original magnification, x40; CD8 stain) shows CD8 positivity of the sinus lining cells (brown staining).
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Figure 14b. Splenic hamartoma. (a) Photomicrograph (original magnification, x10; H-E stain) shows disorganized sinuses and splenic red pulp elements (*) compared with the organized sinuses in the normal spleen (upper portion of the image). (b) Photomicrograph (original magnification, x40; H-E stain) shows an irregular, disorganized splenic sinus containing a megakaryocyte and nucleated red cells. (c) Photomicrograph (original magnification, x40; CD8 stain) shows CD8 positivity of the sinus lining cells (brown staining).
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Figure 14c. Splenic hamartoma. (a) Photomicrograph (original magnification, x10; H-E stain) shows disorganized sinuses and splenic red pulp elements (*) compared with the organized sinuses in the normal spleen (upper portion of the image). (b) Photomicrograph (original magnification, x40; H-E stain) shows an irregular, disorganized splenic sinus containing a megakaryocyte and nucleated red cells. (c) Photomicrograph (original magnification, x40; CD8 stain) shows CD8 positivity of the sinus lining cells (brown staining).
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Pathologic differentiation of hamartoma from hemangioma may be difficult. It has been suggested that hamartomas are sclerosed angiomas (6). When immunohistochemical techniques are used, the endothelial cells of splenic hamartoma are CD8 positive (Fig 14c), whereas those of hemangioma are not (26). Hamartomas contain sinus and pulp cordlike elements, whereas hemangiomas encompass well-organized lymphoid tissue. When sclerosis is a predominant feature, a diagnosis of a sclerosed hemangioma rather than hamartoma is suggested (1). In patients with Hodgkin lymphoma, the presence of a hamartoma may be confused with lymphomatous involvement of the spleen (17). However, the absence of Reed-Sternberg cells and the compression (rather than invasion) of the surrounding parenchyma allow differentiation of splenic hamartoma from lymphoma.
Radiologic Features
The radiologic features of splenic hamartoma have been previously described (14,16,27–32). Sonography appears to be more sensitive than CT (30). On sonograms, splenic hamartomas are typically solid homogeneous masses, but some may be heterogeneous with cystic changes or, in rare cases, some contain coarse calcification secondary to ischemia or hemorrhage (33,34). Most hamartomas are hyperechoic relative to the adjacent normal splenic parenchyma. On color Doppler images, these lesions often demonstrate increased blood flow (Fig 15) (27). On angiograms, a splenic hamartoma appears as a hypervascular mass consisting of tumor vessels with aneurysmal dilatation, arteriovenous shunts, vascular lakes, and tumor blush resembling a typical malignant vascular pattern (35). The typical hypervascularity seen with both color Doppler imaging and angiography is thought to reflect the hypervascularity of the red pulp within the hamartoma. However, a single case of an avascular hamartoma with associated marked calcification has been described (36).
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Figure 15a. Splenic hamartoma in an asymptomatic 4-year-old girl who was being evaluated for a urinary tract infection. (a) Transverse sonogram of the spleen shows a rounded, well-defined mixed echotexture mass. (b) Color Doppler sonogram shows hypervascularity within the mass.
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Figure 15b. Splenic hamartoma in an asymptomatic 4-year-old girl who was being evaluated for a urinary tract infection. (a) Transverse sonogram of the spleen shows a rounded, well-defined mixed echotexture mass. (b) Color Doppler sonogram shows hypervascularity within the mass.
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On CT scans, hamartomas often appear nearly isoattenuating relative to normal spleen before and after intravenous administration of contrast material and, therefore, can be difficult to detect; however, they can also appear heterogeneous with contrast enhancement (Fig 16). A contour abnormality may be the only finding present (30,33, 34,37).
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Figure 16a. Incidentally discovered splenic hamartoma in a 67-year-old man. (a) Longitudinal sonogram of the spleen shows a mass with poorly defined margins (white arrow) that bulges the splenic hilum (black arrow). (b) Contrast-enhanced CT scan shows heterogeneous enhancement of the mass (arrows).
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Figure 16b. Incidentally discovered splenic hamartoma in a 67-year-old man. (a) Longitudinal sonogram of the spleen shows a mass with poorly defined margins (white arrow) that bulges the splenic hilum (black arrow). (b) Contrast-enhanced CT scan shows heterogeneous enhancement of the mass (arrows).
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Ramani et al (8) have shown that splenic hamartomas are isointense relative to normal splenic parenchyma on T1-weighted MR images, heterogeneously hyperintense on T2-weighted MR images, and heterogeneously diffusely enhanced on T1-weighted MR images obtained immediately after gadolinium injection (Fig 17). On delayed MR images, hamartomas were shown to have a more uniform homogeneous pattern of enhancement (8). When visible at CT and MR imaging, hamartomas are well-defined masses with smooth borders and no infiltration of the surrounding splenic parenchyma.
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Figure 17a. Splenic hamartoma in a 67-year-old man with transient upper abdominal pain. (a-c) MR images show the mass to be isointense with T1-weighted pulse sequences (a), slightly hyperintense relative to the normal splenic parenchyma with T2-weighted pulse sequences (b), and homogeneously enhancing after intravenous gadolinium administration (c). (d) Photograph of the cut surface of the resected surgical specimen shows a smoothly marginated, predominantly homogeneous mass.
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Figure 17b. Splenic hamartoma in a 67-year-old man with transient upper abdominal pain. (a-c) MR images show the mass to be isointense with T1-weighted pulse sequences (a), slightly hyperintense relative to the normal splenic parenchyma with T2-weighted pulse sequences (b), and homogeneously enhancing after intravenous gadolinium administration (c). (d) Photograph of the cut surface of the resected surgical specimen shows a smoothly marginated, predominantly homogeneous mass.
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Figure 17c. Splenic hamartoma in a 67-year-old man with transient upper abdominal pain. (a-c) MR images show the mass to be isointense with T1-weighted pulse sequences (a), slightly hyperintense relative to the normal splenic parenchyma with T2-weighted pulse sequences (b), and homogeneously enhancing after intravenous gadolinium administration (c). (d) Photograph of the cut surface of the resected surgical specimen shows a smoothly marginated, predominantly homogeneous mass.
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Figure 17d. Splenic hamartoma in a 67-year-old man with transient upper abdominal pain. (a-c) MR images show the mass to be isointense with T1-weighted pulse sequences (a), slightly hyperintense relative to the normal splenic parenchyma with T2-weighted pulse sequences (b), and homogeneously enhancing after intravenous gadolinium administration (c). (d) Photograph of the cut surface of the resected surgical specimen shows a smoothly marginated, predominantly homogeneous mass.
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The importance of imaging splenic hamartomas lies in the need to differentiate them from malignant lesions of the spleen such as lymphoma and metastasis. Hamartoma should be included in the differential diagnosis of a focal splenic mass that demonstrates substantial increased blood flow at color Doppler imaging. Although the radiologic features seen with splenic hamartoma may be suggestive of the diagnosis, a definitive preoperative diagnosis can rarely be made on the basis of imaging findings alone.
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Lymphangioma
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Clinical Features
Splenic lymphangioma is a relatively rare benign tumor with clinical manifestations that range from an asymptomatic incidental finding to a large multicentric, symptomatic mass requiring surgical intervention. Most splenic lymphangiomas occur in children, with adult cases being reported less frequently. Splenic lymphangiomas usually initially grow without causing significant clinical effects; when the lesions cause symptoms, they are related to compression of adjacent structures. There is a close relationship between the occurrence of symptoms and splenic size (38). Abdominal symptoms related to the size of the spleen include left upper quadrant pain, nausea, and abdominal distention. The complications associated with more extensive or larger lymphangiomas of the spleen include bleeding, consumptive coagulopathy, hypersplenism, and portal hypertension (39,40).
Lymphangiomatosis is a syndrome in which multiple organs are involved. Frequent anatomic sites of involvement include the mediastinum, retroperitoneum, axilla, and neck. Case reports in which cystic hygroma of the neck was a synchronous or metachronous finding have been described (41–43). In children with lymphangiomatosis, Wadsworth et al (44) reported simultaneous involvement in the liver, pericardium, mediastinum, lung, and bone. These findings suggest a possible relationship between the occurrence of multiorgan involvement and patient age. In a young patient with splenic lymphangioma, the diagnostic evaluation should be extended to include extrasplenic organs (44).
Treatment of incidental or small lesions typically does not require surgery. However, symptomatic larger lesions have generally been treated with splenectomy or partial splenectomy. Although percutaneous aspiration techniques are safe, they appear to have little value in long-term control of splenic lymphangiomas (45).
Pathologic Features
The pathologic appearance of splenic lymphangioma covers a broad spectrum, which includes solitary nodules, multiple nodules, and diffuse lymphangiomatosis. Lymphangiomas of the spleen are usually microcystic or solid and may show central scarring (42,46). On the basis of size and location of the vascular channels, lymphangiomas can be divided into three types: capillary, cavernous, and cystic (41). Unlike the random localization seen with hemangiomas, lymphangioma often involves the capsule and trabeculae of the spleen, where lymphatics are normally concentrated (1).
Of the solitary focal lesions, the subcapsular lymphangioma is most common. Similar-appearing satellite lesions may surround a larger lesion. A solitary focal lymphangioma may also be intraparenchymal. With larger multifocal lesions, the tumors are separated by distinct residual splenic tissue and they cause the spleen to be nodular and enlarged.
Lymphangioma may also manifest as a large solitary cyst or may be part of diffuse lymphangiomatosis involving the spleen. With lymphangiomatosis, the spleen may be diffusely replaced by expanding lymphangiomas that leave little remaining splenic parenchyma (47,48). Conversely, the spleen may not be extensively involved in lymphangiomatosis, but vasoformative malformations or tumors may be found in other organs. The liver is the most frequent secondary organ involved (43).
As seen at histologic analysis, capillary, cavernous, and cystic lymphangioma each consists of a single layer of flattened endothelium-lined spaces, which are filled with eosinophilic proteinaceous material instead of blood as seen in hemangiomas (Fig 18). When the histologic characteristics are not clear, the endothelial origin of the cyst may be established with immunohistochemical techniques that demonstrate reactivity for factor VIII, a finding that confirms the diagnosis of lymphangioma (49). At gross examination, these cysts have thick fibrous walls with an internal morphology characterized by fibrous trabeculae. Hyalinization and calcification of the fibrous connective tissue may be present (50).
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Figure 18. Photomicrograph (original magnification, x40; H-E stain) of a splenic lymphangioma shows thin-walled cystic spaces filled with proteinaceous fluid (*). Attenuated endothelial cells (arrow) line the cysts.
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Both splenic lymphangioma and hemangioma are vasoformative tumors and they are closely related, but splenic lymphangioma is less common. There is no firm consensus as to the exact origin of splenic lymphangioma, which may represent a hamartomatous rather than a neoplastic lesion (1,51). Others have proposed a unified concept of lymphangioma and cystic hygroma as being a congenital developmental defect (52). There have been very few reports of a splenic lymphangioma developing into malignant lymphangiosarcoma (
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Abstract
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