DOI: 10.1148/rg.233025073
(Radiographics. 2003;23:719-729.)
© RSNA, 2003
Inflammatory Pseudotumor1
Lakshmana Das Narla, MD,
Beverley Newman, MD,
Stephanie S. Spottswood, MD,
Shireesha Narla, MD and
Rajasekhar Kolli, MD
1 From the Department of Radiology, Medical College of Virginia VCU Health System, Main Hospital 3rd Fl, 1250 E Marshall St, Richmond, VA 23298 (L.D.N., S.S.S.); Department of Radiology, Children’s Hospital of Pittsburgh, Pa (B.N.); Department of Primary Care Physicians, McGuire Veterans Hospital of Richmond, Va (S.N.); and Department of Surgery, Long Island Jewish Hospital, New Hyde Park, NY (R.K.). Presented as an education exhibit at the 2001 RSNA scientific assembly. Received April 1, 2002; revision requested May 13 and received December 10; accepted December 12. Address correspondence to L.D.N. (e-mail: ldnarla@hsc.vcu.edu).
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Abstract
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Inflammatory pseudotumor is a quasineoplastic lesion that most commonly involves the lung and the orbit, but it has been reported to occur in nearly every site in the body. The pathogenesis, natural history, clinical presentation, imaging findings, and treatment options for inflammatory pseudotumor in the lung, heart, gastrointestinal tract, adrenal gland, iliopsoas muscle, orbit, and central nervous system are discussed. Because inflammatory pseudotumors mimic malignant tumors both clinically and radiologically, the radiologist should be familiar with this entity and help avoid unnecessary radical surgery when possible.
© RSNA, 2003
Index Terms: Abdomen, neoplasms, 70.3197 • Heart, neoplasms, 50.319 • Lung neoplasms, 60.3181 • Orbit, neoplasms, 22.365
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Describe the spectrum of clinical and radiologic features of inflammatory pseudotumors.
- Identify the various treatment options for inflammatory pseudotumors.
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Introduction
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Inflammatory pseudotumor was first observed in the lung and described by Brunn in 1939 and was so named by Umiker et al in 1954 because of its propensity to clinically and radiologically mimic a malignant process (1). Since that time, inflammatory pseudotumor has been described in the literature by many different names (Table 1), a fact that suggests the complexity and variable histologic characteristics and behavior of this entity.
Inflammatory pseudotumor is a quasineoplastic lesion consisting of inflammatory cells and myofibroblastic spindle cells (2,3). Inflammatory pseudotumor most commonly involves the lung and the orbit, but it has been reported to occur in nearly every site in the body, from the central nervous system to the gastrointestinal tract (Table 2).
Understanding the pathophysiologic characteristics and natural history of inflammatory pseudotumor and considering this entity in the differential diagnosis of soft-tissue tumors may prevent unnecessary radical surgery. The aim of this article is to review the pathogenesis of inflammatory pseudotumor, describe the various anatomic locations where inflammatory pseudotumors occur, and briefly discuss the differential diagnoses. Medical and surgical treatment options are also reviewed.
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Pathogenesis
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The causes of inflammatory pseudotumor are unknown. Some authors believe this tumor is a low-grade fibrosarcoma with inflammatory (lymphomatous) cells. The propensity of inflammatory pseudotumors to be locally aggressive, to frequently be multifocal, and to progress occasionally to a true malignant tumor supports this idea (3–7). Immunohistochemical studies of T- and B-cell subpopulations may be helpful in distinguishing inflammatory pseudotumor from lymphoma. Inflammatory pseudotumors usually contain both T cells and B cells, whereas in lymphoma, a (clonal) B- or T-cell population predominates. Furthermore, the heterogeneity of the inflammatory cell population in inflammatory pseudotumor tends to exclude lymphoma.
In some cases, inflammatory pseudotumor is thought to result from inflammation following minor trauma or surgery or to be associated with other malignancy (8,9). An immune-autoimmune mechanism has also been implicated. In one case, inflammatory pseudotumor was associated with vasculitis and inferior vena caval thrombosis, with anti-C3 and antifibrinogen deposits found in the vessel wall (10).
There appears to be a subset of inflammatory pseudotumors that occur secondary to infection. Organisms found in association with inflammatory pseudotumor include mycobacteria associated with spindle cell tumor; Epstein-Barr virus found in splenic and nodal pseudotumors; actinomycetes and nocardiae found in hepatic and pulmonary pseudotumors, respectively; and mycoplasma in pulmonary pseudotumors (5). There have been case reports of inflammatory pseudotumor associated with infections caused by other organisms, including Mycobacterium avium–intracellulare complex, Corynebacterium equi, Escherichia coli, Klebsiella, Bacillus sphaericus, Pseudomonas, Helicobacter pylori, and Coxiella burnetti (3,5,8,11,12). It has been suggested that histiocytic cells predominate in inflammatory pseudotumors associated with infection, whereas myofibroblastic cells characterize the lesions more likely to be considered true neoplasms (5).
Many of the features of inflammatory pseudotumor can be related to the production of inflammatory mediators such as cytokines and particularly interleukin-1 (13). Interleukin-1, which is produced mainly by monocytes, by macrophages, and to a lesser extent by other cells, has a wide range of local and systemic effects. Locally, it stimulates the proliferation of fibroblasts, the extravasation of neutrophils, and the activation and increase of procoagulant activity of the vascular endothelium. Systemically, it induces production of acute-phase reactants by hepatocytes, proteolysis, and neurologic disturbances.
Clinically, patients with inflammatory pseudotumor tend to have varying degrees of fever, growth impairment, iron deficiency anemia, thrombocytosis, and hypergammaglobulinemia (9,14).
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Pulmonary Inflammatory Pseudotumor
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Inflammatory pseudotumor is the most common primary lung mass seen in children, constituting approximately 50% of benign intrapulmonary tumors seen in pediatric patients (3,4). These tumors have no sex predilection, and their peak prevalence is in the second decade of life. Cough, fever, dyspnea, and hemoptysis are the usual presenting symptoms (3,15). Although many children are asymptomatic, approximately 20% have an antecedent pulmonary insult, usually infection (3,16).
On the basis of the predominant histopathologic features, the lesions can be divided into three histologic types: (a) organizing pneumonia pattern, characterized by airways filled with plump fibroblasts and foamy histiocytes and parenchyma replaced with a mixture of histiocytes, mononuclear cells, and fibroblasts; (b) fibrous histiocytic pattern, which is the most common, and is characterized by spindle-shaped myofibroblasts arranged in whorls; and (c) lymphohistiocytic pattern, which is the least common (4,16), and is characterized by a mixture of lymphocytes and plasma cells with only minimal fibrous connective tissue.
Because myofibroblasts and histiocytes usually predominate, the terms inflammatory myofibroblastic tumor or inflammatory myofibrohistiocytic proliferation have been proposed as being more descriptive names for inflammatory pseudotumors arising in the lung as well as in extrapulmonary sites (Table 1) (4,17).
On radiographs, pulmonary inflammatory pseudotumor typically appears as a solitary, peripheral, sharply circumscribed, lobulated mass with an anatomic bias for the lower lobes (4,16). On computed tomographic (CT) scans, inflammatory pseudotumors have a variable and nonspecific appearance, but most commonly they appear with heterogeneous attenuation and enhancement. On T1-weighted magnetic resonance (MR) images, these tumors have intermediate signal intensity; they have high signal intensity on T2-weighted images (4). Calcification within the lesion occurs more frequently in children than in adults (4,16) (Fig 1). The calcification pattern ranges from an amorphous, mixed, or fine fleck-like pattern to heavy mineralization (3). Cavitation and lymphadenopathy are rare. Atelectasis and pleural effusion may occur (4).
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Figure 1a. Pulmonary pseudotumor in a 9-year-old boy with a 1-year history of fever and cough. (a) Frontal chest radiograph reveals a rounded area of soft-tissue opacity in the right upper lobe. No associated pleural effusion or bony abnormalities were noted. (b) Axial unenhanced CT scan demonstrates a well-circumscribed mass with focal calcification in the right upper lobe. No mediastinal lymphadenopathy was noted. Findings from surgical excision and histologic analysis confirmed the diagnosis of inflammatory pseudotumor.
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Figure 1b. Pulmonary pseudotumor in a 9-year-old boy with a 1-year history of fever and cough. (a) Frontal chest radiograph reveals a rounded area of soft-tissue opacity in the right upper lobe. No associated pleural effusion or bony abnormalities were noted. (b) Axial unenhanced CT scan demonstrates a well-circumscribed mass with focal calcification in the right upper lobe. No mediastinal lymphadenopathy was noted. Findings from surgical excision and histologic analysis confirmed the diagnosis of inflammatory pseudotumor.
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Multiple lesions are seen in 5% of cases, with endobronchial masses constituting 10% of cases (16) (Fig 2). Inflammatory pseudotumor has also been observed in the pulmonary artery (4).
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Figure 2a. Endobronchial inflammatory pseudotumor in a 7-year-old boy with a prolonged history of cough and fever. (a) Chest radiograph shows complete opacification of the left lung with ipsilateral cardiomediastinal shift, findings suggestive of atelectasis. (b) Axial contrast material-enhanced CT scan reveals a patent right main stem bronchus, an obstructed left main stem bronchus with left mediastinal shift, and atelectasis of the left lung. The left main stem bronchus lesion was resected and pathologically diagnosed as inflammatory pseudotumor. (c) Postoperative frontal chest radiograph shows reexpansion of the left lung.
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Figure 2b. Endobronchial inflammatory pseudotumor in a 7-year-old boy with a prolonged history of cough and fever. (a) Chest radiograph shows complete opacification of the left lung with ipsilateral cardiomediastinal shift, findings suggestive of atelectasis. (b) Axial contrast material-enhanced CT scan reveals a patent right main stem bronchus, an obstructed left main stem bronchus with left mediastinal shift, and atelectasis of the left lung. The left main stem bronchus lesion was resected and pathologically diagnosed as inflammatory pseudotumor. (c) Postoperative frontal chest radiograph shows reexpansion of the left lung.
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Figure 2c. Endobronchial inflammatory pseudotumor in a 7-year-old boy with a prolonged history of cough and fever. (a) Chest radiograph shows complete opacification of the left lung with ipsilateral cardiomediastinal shift, findings suggestive of atelectasis. (b) Axial contrast material-enhanced CT scan reveals a patent right main stem bronchus, an obstructed left main stem bronchus with left mediastinal shift, and atelectasis of the left lung. The left main stem bronchus lesion was resected and pathologically diagnosed as inflammatory pseudotumor. (c) Postoperative frontal chest radiograph shows reexpansion of the left lung.
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Classification of pulmonary inflammatory pseudotumors based on histologic pattern does not correlate with any specific radiologic features. Delay in diagnosis and treatment may result in encroachment on hilar and mediastinal structures (3) (Fig 3). The radiologic differential diagnosis for inflammatory pseudotumor occurring as a solitary pulmonary nodule includes primary or secondary neoplasm, hamartoma, chondroma, hemangioma, granuloma, and pulmonary sequestration. Inflammatory pseudotumor may resemble pulmonary intralobar sequestration in that its blood supply is derived from the systemic arteries (4,16).
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Figure 3a. Pulmonary pseudotumor in a 10-year-old girl who developed left-sided anterior chest pain after minor trauma. (a) Initial chest radiograph shows a 3-cm rounded opaque area in the left mid lung with a small pleural effusion. The patient was treated with antibiotics. Ten months later, she developed pleuritic chest pain, night sweats, and decreased exercise tolerance. (b) Repeat chest radiograph shows marked increase in the size of the mass and volume loss of the left lung. (c) Contrast-enhanced CT scan of the chest reveals a mildly enhancing, large left-sided mass surrounding the left bronchus and extending into the left chest wall. Analysis of the specimen obtained at CT-guided fine-needle aspiration confirmed a diagnosis of inflammatory pseudotumor. (d) Low-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) shows inflammatory cells and myofibroblasts. Because the mass was deemed unresectable, the patient was given prednisone (20 mg three times a day). The patient’s symptoms improved, and the dose of steroids was reduced to 5 mg every other night over the next 18 months and finally stopped. (e) Repeat chest CT scan, obtained with intravenous contrast material, shows resolution of the mass with some residual scarring.
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Figure 3b. Pulmonary pseudotumor in a 10-year-old girl who developed left-sided anterior chest pain after minor trauma. (a) Initial chest radiograph shows a 3-cm rounded opaque area in the left mid lung with a small pleural effusion. The patient was treated with antibiotics. Ten months later, she developed pleuritic chest pain, night sweats, and decreased exercise tolerance. (b) Repeat chest radiograph shows marked increase in the size of the mass and volume loss of the left lung. (c) Contrast-enhanced CT scan of the chest reveals a mildly enhancing, large left-sided mass surrounding the left bronchus and extending into the left chest wall. Analysis of the specimen obtained at CT-guided fine-needle aspiration confirmed a diagnosis of inflammatory pseudotumor. (d) Low-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) shows inflammatory cells and myofibroblasts. Because the mass was deemed unresectable, the patient was given prednisone (20 mg three times a day). The patient’s symptoms improved, and the dose of steroids was reduced to 5 mg every other night over the next 18 months and finally stopped. (e) Repeat chest CT scan, obtained with intravenous contrast material, shows resolution of the mass with some residual scarring.
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Figure 3c. Pulmonary pseudotumor in a 10-year-old girl who developed left-sided anterior chest pain after minor trauma. (a) Initial chest radiograph shows a 3-cm rounded opaque area in the left mid lung with a small pleural effusion. The patient was treated with antibiotics. Ten months later, she developed pleuritic chest pain, night sweats, and decreased exercise tolerance. (b) Repeat chest radiograph shows marked increase in the size of the mass and volume loss of the left lung. (c) Contrast-enhanced CT scan of the chest reveals a mildly enhancing, large left-sided mass surrounding the left bronchus and extending into the left chest wall. Analysis of the specimen obtained at CT-guided fine-needle aspiration confirmed a diagnosis of inflammatory pseudotumor. (d) Low-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) shows inflammatory cells and myofibroblasts. Because the mass was deemed unresectable, the patient was given prednisone (20 mg three times a day). The patient’s symptoms improved, and the dose of steroids was reduced to 5 mg every other night over the next 18 months and finally stopped. (e) Repeat chest CT scan, obtained with intravenous contrast material, shows resolution of the mass with some residual scarring.
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Figure 3d. Pulmonary pseudotumor in a 10-year-old girl who developed left-sided anterior chest pain after minor trauma. (a) Initial chest radiograph shows a 3-cm rounded opaque area in the left mid lung with a small pleural effusion. The patient was treated with antibiotics. Ten months later, she developed pleuritic chest pain, night sweats, and decreased exercise tolerance. (b) Repeat chest radiograph shows marked increase in the size of the mass and volume loss of the left lung. (c) Contrast-enhanced CT scan of the chest reveals a mildly enhancing, large left-sided mass surrounding the left bronchus and extending into the left chest wall. Analysis of the specimen obtained at CT-guided fine-needle aspiration confirmed a diagnosis of inflammatory pseudotumor. (d) Low-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) shows inflammatory cells and myofibroblasts. Because the mass was deemed unresectable, the patient was given prednisone (20 mg three times a day). The patient’s symptoms improved, and the dose of steroids was reduced to 5 mg every other night over the next 18 months and finally stopped. (e) Repeat chest CT scan, obtained with intravenous contrast material, shows resolution of the mass with some residual scarring.
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Figure 3e. Pulmonary pseudotumor in a 10-year-old girl who developed left-sided anterior chest pain after minor trauma. (a) Initial chest radiograph shows a 3-cm rounded opaque area in the left mid lung with a small pleural effusion. The patient was treated with antibiotics. Ten months later, she developed pleuritic chest pain, night sweats, and decreased exercise tolerance. (b) Repeat chest radiograph shows marked increase in the size of the mass and volume loss of the left lung. (c) Contrast-enhanced CT scan of the chest reveals a mildly enhancing, large left-sided mass surrounding the left bronchus and extending into the left chest wall. Analysis of the specimen obtained at CT-guided fine-needle aspiration confirmed a diagnosis of inflammatory pseudotumor. (d) Low-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) shows inflammatory cells and myofibroblasts. Because the mass was deemed unresectable, the patient was given prednisone (20 mg three times a day). The patient’s symptoms improved, and the dose of steroids was reduced to 5 mg every other night over the next 18 months and finally stopped. (e) Repeat chest CT scan, obtained with intravenous contrast material, shows resolution of the mass with some residual scarring.
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Cardiac Inflammatory Pseudotumor
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Only a small number of cases of cardiac inflammatory pseudotumor have been described in the literature, with the patients ranging in age from 3 months to 17 years. Cardiac sites involved by inflammatory pseudotumor have included the right and left atrium, right and left ventricle, pulmonary and tricuspid valves, septum, right and left coronary arteries, superior vena cava, coronary sinus, and atrioventricular groove (10,18–21).
In general, primary cardiac tumors are rare in children, with a prevalence of less than 1% seen at autopsy. More than 70% of primary cardiac tumors are benign and are either a rhabdomyoma (seen in patients with tuberous sclerosis), fibroma, or myxoma (18). Common clinical manifestations of cardiac inflammatory pseudotumor are chest pain, pallor, diaphoresis, dyspnea, decreased oral intake, and collapse.
The role of cardiac MR imaging includes confirming the presence of a mass and its size, location, and imaging characteristics. Differences in MR signal characteristics have been described as being helpful in distinguishing between fibroma, lipoma, and rhabdomyoma. Fibromas have signal intensity lower than that of normal myocardium, and lipomas typically have a T1 signal intensity higher than that of myocardium (20,22). Gradient refocused echo (GRE) imaging is more sensitive than spin-echo imaging for differentiating intracardiac thrombi from tumor. On GRE images, thrombi (except for hyperacute thrombi) have lower signal intensity than that of myocardium; tumor generally has increased signal intensity. Atrial myxomas are the exception, as they also may have lower signal intensity than that of adjacent myocardium on GRE images secondary to areas of hemorrhage, hemosiderin, and foci of calcification. Gadolinium contrast enhancement of tumors may also play an important role in distinguishing a thrombus from tumor (22).
The MR imaging characteristics of cardiac inflammatory pseudotumor are not well described and appear to be similar to those of most other tumors (20). In our case (Fig 4), the lesion was slightly hyperintense relative to cardiac muscle on T1-weighted images, moderately hyperintense on T2-weighted images, and heterogeneously enhanced after administration of contrast material.
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Figure 4a. Cardiac inflammatory pseudotumor in a 7-month-old girl with no significant medical history who presented with pallor, tachypnea, and decreased oral intake. Blood gas analysis on room air revealed a PO2 of 80. Initial echocardiogram indicated the presence of a right atrial mass. (a) Axial T1-weighted MR image shows a relatively homogenous mass (M) occupying most of the right atrium and contiguous with its inferolateral wall (arrows). The mass is slightly greater in signal intensity relative to that of muscle. (b) Axial T2-weighted image demonstrates increased signal intensity of the mass (M) relative to that of muscle. Coronal images (not shown) showed a clear plane of separation between the mass and the interatrial septum. (c) Axial T1-weighted image obtained after gadolinium injection shows heterogeneous enhancement of the mass (M) and the interatrial septum (arrows). When the mass was surgically resected, a 3 x 3-cm defect was created in the inferior wall of the right atrium and was repaired with a patch of bovine pericardium. Histopathologic examination of the resected mass showed cellular spindle cell proliferation with scattered foci of inflammatory cells. No cytologic atypia was found, and the diagnosis was inflammatory pseudotumor of the right atrium. The patient is currently doing well, and follow-up echocardiograms show no evidence of recurrence. (Fig 4a-4c reprinted, with permission, from reference 20.)
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Figure 4b. Cardiac inflammatory pseudotumor in a 7-month-old girl with no significant medical history who presented with pallor, tachypnea, and decreased oral intake. Blood gas analysis on room air revealed a PO2 of 80. Initial echocardiogram indicated the presence of a right atrial mass. (a) Axial T1-weighted MR image shows a relatively homogenous mass (M) occupying most of the right atrium and contiguous with its inferolateral wall (arrows). The mass is slightly greater in signal intensity relative to that of muscle. (b) Axial T2-weighted image demonstrates increased signal intensity of the mass (M) relative to that of muscle. Coronal images (not shown) showed a clear plane of separation between the mass and the interatrial septum. (c) Axial T1-weighted image obtained after gadolinium injection shows heterogeneous enhancement of the mass (M) and the interatrial septum (arrows). When the mass was surgically resected, a 3 x 3-cm defect was created in the inferior wall of the right atrium and was repaired with a patch of bovine pericardium. Histopathologic examination of the resected mass showed cellular spindle cell proliferation with scattered foci of inflammatory cells. No cytologic atypia was found, and the diagnosis was inflammatory pseudotumor of the right atrium. The patient is currently doing well, and follow-up echocardiograms show no evidence of recurrence. (Fig 4a-4c reprinted, with permission, from reference 20.)
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Figure 4c. Cardiac inflammatory pseudotumor in a 7-month-old girl with no significant medical history who presented with pallor, tachypnea, and decreased oral intake. Blood gas analysis on room air revealed a PO2 of 80. Initial echocardiogram indicated the presence of a right atrial mass. (a) Axial T1-weighted MR image shows a relatively homogenous mass (M) occupying most of the right atrium and contiguous with its inferolateral wall (arrows). The mass is slightly greater in signal intensity relative to that of muscle. (b) Axial T2-weighted image demonstrates increased signal intensity of the mass (M) relative to that of muscle. Coronal images (not shown) showed a clear plane of separation between the mass and the interatrial septum. (c) Axial T1-weighted image obtained after gadolinium injection shows heterogeneous enhancement of the mass (M) and the interatrial septum (arrows). When the mass was surgically resected, a 3 x 3-cm defect was created in the inferior wall of the right atrium and was repaired with a patch of bovine pericardium. Histopathologic examination of the resected mass showed cellular spindle cell proliferation with scattered foci of inflammatory cells. No cytologic atypia was found, and the diagnosis was inflammatory pseudotumor of the right atrium. The patient is currently doing well, and follow-up echocardiograms show no evidence of recurrence. (Fig 4a-4c reprinted, with permission, from reference 20.)
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Inflammatory Pseudotumor of the Abdomen
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Inflammatory pseudotumor has been reported in various sites in the abdomen, including the liver, spleen, pancreas, adrenal gland, kidney, retroperitoneum, diaphragm, mesentery, and alimentary and urinary tracts. Abdominal inflammatory pseudotumor should be considered in the differential diagnosis of any soft-tissue mass within the abdomen and viscera.
Gastrointestinal tract involvement is rare, with ileocecal and gastric tumors in young girls being the most frequently described type. Abdominal pain, a palpable mass, and iron deficiency anemia are the most common presenting symptoms and signs (8,23). Gastrointestinal inflammatory pseudotumors often have features suggestive of malignancy, including ulceration, infiltration of the wall, and extragastric extension (23).
Hepatic involvement by inflammatory pseudotumors was first described in 1953 by Pack and Baker (24). Inflammatory pseudotumor of the liver has been recognized with increased frequency, mainly in Asian countries (12). The majority of hepatic inflammatory pseudotumors occur in children and young adults. Most cases have been solitary solid tumors, mainly arising from the right hepatic lobe. In a few cases, inflammatory pseudotumor has involved the porta hepatis or bile ducts, which results in obstructive jaundice. Other symptoms include abdominal pain and weight loss. In addition, other unusual inflammatory or immune responses such as sclerosing cholangitis, phlebitis, and retroperitoneal fibrosis have been found in association with inflammatory pseudotumor (9,25). Spindle cell tumors in the liver and elsewhere have been described in immunocompromised patients after transplantation. Although these tumors occur much less commonly than posttransplantation lymphoproliferative disorder, Epstein-Barr virus has also been implicated in some of these lesions (26). Spontaneous regression of hepatic inflammatory pseudotumor has been reported (12).
The CT appearance of abdominal inflammatory pseudotumor is variable. The mass may be hypoattenuated or isoattenuated relative to muscle on unenhanced scans, and calcification has been observed within inflammatory pseudotumors of the pancreas, stomach, and liver. Enhancement with contrast material usually occurs but is not pronounced, and a variety of patterns have been noted. These patterns include early peripheral, with delayed central filling (Fig 5); heterogeneous; homogeneous; and no enhancement (12,14). Larger lesions may have central necrosis. On MR images, the appearance of these tumors is also variable; they are usually hypointense relative to skeletal muscle on T1-weighted images, hyperintense on T2-weighted images, and heterogeneously enhanced after administration of contrast material (25). The important entities included in the differential diagnosis include hepatocellular carcinoma, gastric carcinoma, and pancreatic carcinoma.
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Figure 5a. Inflammatory pseudotumor of the adrenal gland in an 8-year-old girl with a history of nonspecific fever, weight loss, and elevated platelet count. Unenhanced abdominal CT scan (not shown) revealed a right adrenal mass with no calcifications. (a) Contrast-enhanced CT scan shows an unusual pattern of early, dense, peripheral enhancement. (b) On a delayed CT image, the center of the lesion has filled in with contrast material. Findings from surgical excision and histologic analysis confirmed the diagnosis of inflammatory pseudotumor.
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Figure 5b. Inflammatory pseudotumor of the adrenal gland in an 8-year-old girl with a history of nonspecific fever, weight loss, and elevated platelet count. Unenhanced abdominal CT scan (not shown) revealed a right adrenal mass with no calcifications. (a) Contrast-enhanced CT scan shows an unusual pattern of early, dense, peripheral enhancement. (b) On a delayed CT image, the center of the lesion has filled in with contrast material. Findings from surgical excision and histologic analysis confirmed the diagnosis of inflammatory pseudotumor.
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Urinary tract involvement by inflammatory pseudotumors was first described by Roth in 1980, who reported a case of urinary bladder inflammatory pseudotumor (27). This entity is rare in children, can occur at any age (28), but typically appears in young adults with an average age of 28 years. The youngest patient described in the literature was a 7-day-old neonate. Painless gross hematuria from exophytic and ulcerated lesions is the most common initial manifestation and may result in anemia (29). Other symptoms include frequency of urination and dysuria, and urinary tract obstruction can also occur. Inflammatory pseudotumor should be considered when an enhancing tumor is surrounded by a clot, particularly in young adults. Inflammatory pseudotumor of the urinary tract is extremely difficult to distinguish from malignant tumors clinically, radiologically, and histologically and may be misdiagnosed as rhabdomyosarcoma (Fig 6). Fine-needle biopsy may fail to yield a sufficient volume of tumor tissue for making a definite diagnosis. The recognition of the benign entity is important to avoid unnecessary radical surgery (2). Spontaneous regression of inflammatory pseudotumor of the bladder has been described (31).
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Figure 6a. Inflammatory pseudotumor of the iliopsoas muscle mimicking rhabdomyosarcoma in a 20-month-old girl with a 4-week history of limping with her right leg. The patient was afebrile at presentation, and radiographs of her pelvis were normal. Sonograms (not shown) revealed a hypoechoic mass in the right pelvis that appeared to be arising from or was contiguous with the right iliopsoas muscle. (a) Axial contrast-enhanced CT scan shows a 2.5 x 3.5-cm mildly enhancing mass, contiguous with the right iliopsoas muscle (arrows), with no evidence of lymphadenopathy or bone destruction. Analysis of a fine-needle aspirate from the mass suggested a sarcoma. At surgery, the mass was found to be adherent to the pelvic vessels and was unresectable. Wedge biopsies were performed, and findings from histologic examination confirmed the diagnosis of inflammatory pseudotumor. The patient was managed conservatively, and her limp resolved spontaneously. (b) Axial contrast-enhanced CT scan obtained 6 weeks later shows resolution of the mass. (Fig 6a and 6b reprinted, with permission, from reference 30.)
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Figure 6b. Inflammatory pseudotumor of the iliopsoas muscle mimicking rhabdomyosarcoma in a 20-month-old girl with a 4-week history of limping with her right leg. The patient was afebrile at presentation, and radiographs of her pelvis were normal. Sonograms (not shown) revealed a hypoechoic mass in the right pelvis that appeared to be arising from or was contiguous with the right iliopsoas muscle. (a) Axial contrast-enhanced CT scan shows a 2.5 x 3.5-cm mildly enhancing mass, contiguous with the right iliopsoas muscle (arrows), with no evidence of lymphadenopathy or bone destruction. Analysis of a fine-needle aspirate from the mass suggested a sarcoma. At surgery, the mass was found to be adherent to the pelvic vessels and was unresectable. Wedge biopsies were performed, and findings from histologic examination confirmed the diagnosis of inflammatory pseudotumor. The patient was managed conservatively, and her limp resolved spontaneously. (b) Axial contrast-enhanced CT scan obtained 6 weeks later shows resolution of the mass. (Fig 6a and 6b reprinted, with permission, from reference 30.)
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Inflammatory Pseudotumor of the Head and Neck
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Orbital pseudotumor is the third most common primary tumor of the orbit and a common cause of unilateral proptosis in adults (32,33) (Fig 7). It constitutes about 6% of all orbital lesions. Orbital pseudotumor has no sex or race predilection and can develop in patients of any age, although it most frequently occurs in middle-aged individuals. It is usually unilateral (34), and the presence of bilateral masses suggests an underlying systemic disease (32).
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Figure 7. Orbital pseudotumor in a 48-year-old woman with a painful, proptotic left eye. Axial CT scan of the orbit shows an enlarged left medial rectus muscle. The patient was treated with high doses of corticosteroids, and the symptoms resolved.
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Uveal and scleral thickening is seen in 33% of orbital pseudotumors and is thought to be a specific sign of inflammatory pseudotumor (35). Orbital pseudotumor manifests with exophthalmos and acute pain, compared with neoplasm, in which pain develops over several months (32). Other clinical manifestations include reduced ocular motility, diplopia, ptosis, and chemosis. Severely decreased vision occurs in about 15% of cases. Bone destruction and intracranial extension are rare but have been reported (32,36). If the orbital pseudotumor extends into the anterior cranial fossa with bony alterations, this extension can occur through the anterior ethmoid foramen.
Extraorbital inflammatory pseudotumors of the head and neck can occur in the nasal cavity, nasopharynx, maxillary sinus, larynx, and trachea. Perineural spread along maxillary, mandibular, and hypoglossal nerves and a case complicated by internal carotid occlusion have been described (37). Sinonasal inflammatory pseudotumors do not affect a particular age group and cause no systemic symptoms. Characteristics include bone destruction, less response to corticosteroid treatment than orbital pseudotumors, and a good prognosis.
Both orbital and extraorbital inflammatory pseudotumors have similar imaging characteristics. On CT scans, a moderately enhancing mass is usually seen (Fig 8). Orbital tumors are commonly accompanied by fat infiltration or edema. Sinonasal pseudotumors have a more aggressive appearance than those of the orbit, with bony changes such as erosion, remodeling, and sclerosis being common (37). On MR images, inflammatory pseudotumors are usually isointense to hypointense relative to muscle on T1-weighted images, with relatively hypointense T2 signal compared with most other tumors. Variable contrast enhancement is reported (38). Orbital pseudotumors are classified into four groups on the basis of findings from orbital imaging studies (Table 3) (32).
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Figure 8. Orbital pseudotumor in a 57-year-old woman with decreased vision in her left eye. Axial contrast-enhanced CT scan of the orbit demonstrates a left orbital mass involving the optic canal, cavernous sinus, and left posterior optic nerve.
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The differential diagnosis of orbital pseudotumor is quite extensive, as outlined in Table 4. The diagnosis of orbital pseudotumor is primarily clinical, usually by exclusion.
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Treatment
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The biologic potential of inflammatory pseudotumor is highly variable, but it generally has an innocuous course, with local recurrence developing in 25% of cases. Rare cases of distant metastases (6) and spontaneous remissions have been described.
Complete surgical resection, if possible, is the treatment of choice for most inflammatory pseudotumors with the exception of orbital lesions (2,18,19,32). Surgical resection may still be successful in cases with recurrence. Several reports of spontaneous regression have been reported (Fig 6). Radiation therapy has been tried in unresectable cases. Chemotherapy in the form of cyclosporine, methotrexate, azathioprine, and cyclophosphamide has been used but generally has little role. Response to steroids is often unpredictable, but these drugs are the primary treatment method for orbital inflammatory pseudotumor (Fig 7). Antibiotics have been used in some cases.
Treatment of orbital pseudotumor usually begins with high doses of systemic steroids (Fig 7), followed by a slow reduction in the dose. Most cases show improvement within 48–72 hours. Approximately 50% of cases resolve completely with steroid treatment (19,32,36,39). For cases in which use of steroids is contraindicated, there is a poor response to steroids, or the tumor recurs during dose reduction, low-dose radiation therapy is the treatment of choice. Cyclosporine, chlorambucil, and indomethacin have all been used as alternative treatments. Surgical excision is the last resort for pseudotumor in the orbital apex. It is important to follow up patients with treated orbital pseudotumor very closely because even histologically proved cases of orbital pseudotumor have been diagnosed at a later date as meningioma, carcinoma, or lymphoma (32).
Treatment of choice for sinonasal inflammatory pseudotumor is surgery, followed by corticosteroids in cases of incomplete excision. The only cases in which radiation therapy is indicated are those patients for whom surgery or corticosteroid therapy is unsuccessful or contraindicated (40).
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Summary
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Inflammatory pseudotumors can both radiologically and clinically mimic a malignant process. They involve many anatomic sites. If this diagnosis is considered, unnecessary radical surgery may be avoided. The treatment options are varied and consist of surgery, high-dose steroids, irradiation, and chemotherapeutic agents.
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