Inflammatory myofibroblastic tumor: Description, Causes and Risk Factors:
IMT, also known as "plasma cell granuloma," "myoblastoma," or "inflammatory pseudotumor," is a lesion characterized by proliferation of myofibroblastic spindle cells with mixed inflammatory infiltrates of plasma cells, lymphocytes, eosinophils, and histocytes; the constituent inflammatory cells are mature and polyclonal. Three dominant histologic patterns have been described, and these patterns can mimic nodular fasciitis, desmoid fibromatosis, or fibrous histiocytoma. Histopathologic discrimination of these entities may require careful attention not only to the histopathologic findings but also to clinical course and to additional diagnostic tools, particularly immunocytochemistry. These lesions were once thought to be reactive in nature but have come to be considered a true soft tissue neoplasm with potential for recurrence and multifocality; however, the exact cause and pathogenesis of this spectrum of inflammatory disease is largely unknown.
IMTs have a number of appearances that may overlap, most often including orbital involvement when located in the head and neck area. Other possible areas of involvement include the larynx, paranasal sinuses, parapharyngeal space, infratemporal fossa, bony structures, and the soft tissues of the neck and esophagus. Locations outside of the head and neck include most often the lung and/or pleura, though examples have been described in the abdomen, mediastinum, skin, and soft tissues among many other sites. The occurrence of these findings at various sites throughout the body may be grouped under the general designation of multifocal fibrosclerosis.
Inflammatory myofibroblastic tumor occurs most often in the lung and conducting airways, but has also been found in other organs such as the spleen, stomach, pancreas, liver, thyroid, larynx, orbit, heart, kidney, and retroperitoneum. Intracranial and spinal cord plasma cell granulomas have also been described infrequently (a total of 38 cases). In exceptional cases, inflammatory myofibroblastic tumor have involved different organs in the same patient
The causes of inflammatory myofibroblastic tumor are unknown. Some authors believe this tumor is a low-grade fibrosarcoma with inflammatory (lymphomatous) cells. The propensity of Inflammatory myofibroblastic tumor to be locally aggressive, to frequently be multifocal, and to progress occasionally to a true malignant tumor supports this idea. 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 myofibroblastic tumor tends to exclude lymphoma.
In some cases, Inflammatory myofibroblastic tumor is thought to result from inflammation following minor trauma or surgery or to be associated with other malignancy. An immune-autoimmune mechanism has also been implicated. In one case, inflammatory myofibroblastic tumor was associated with vasculitis and inferior vena caval thrombosis, with anti-C3 and antifibrinogen deposits found in the vessel wall.
There appears to be a subset of inflammatory myofibroblastic tumor that occur secondary to infection. Organisms found in association with inflammatory myofibroblastic tumor 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. 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. It has been suggested that histiocytic cells predominate in inflammatory myofibroblastic tumor associated with infection, whereas myofibroblastic cells characterize the lesions more likely to be considered true neoplasms.
Many of the features of inflammatory myofibroblastic tumor can be related to the production of inflammatory mediators such as cytokines and particularly interleukin-1. 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 myofibroblastic tumor tend to have varying degrees of fever, growth impairment, iron deficiency anemia, thrombocytosis, and hypergammaglobulinemia.
The symptoms depend on the specific location of the tumor, which can be anywhere in the body. Most of inflammatory myofibroblastic tumors are asymptomatic at the time of presentation,but some may have symptoms like fever
, chestpain, cough, hemoptysis, airway obstructionand dysphagia
due to esophageal obstruction.
Inflammatory myofibroblastic tumours are diagnosed based on their appearance under the microscope, by pathologists.Medical imaging findings are non-specific.
The biologic potential of inflammatory myofibroblastic tumor is highly variable, but it generally has an innocuous course, with local recurrence developing in 25% of cases. Rare cases of distant metastases and spontaneous remissions have been described.
Complete surgical resection, if possible, is the treatment of choice for most inflammatory myofibroblastic tumor with the exception of orbital lesions. Surgical resection may still be successful in cases with recurrence. Several reports of spontaneous regression have been reported. 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. Antibiotics have been used in some cases.
Treatment of orbital pseudotumor usually begins with high doses of systemic steroids, 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. 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.
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.
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