Discussion
Inflammatory myofibroblastic tumor (IMT) is also known as inflammatory pseudotumor, plasma cell granuloma, fibrous xanthogranuloma and myofibroblastoma.5 Histologically, it is composed of spindle cells with an inflammatory infiltrate of plasma cells, lymphocytes, and/or eosinophils. Microscopically, three histologic patterns have been previously described: Type I was characterized as loosely organized spindle cells admixed with small blood vessels and inflammatory cells in a myxoid background, namely mucous/vascular intensive; Type II is featured with dense clumps of spindle cells, scattered in a small number of inflammatory cells, called spindle cell rich type; Type III is the hypocellular fibrous pattern, usually occurs in soft tissue of limbs, showing large collagen fibers mixed with a few tumor cells and local calcification or ossification.6Immunohistochemical analyses confirmed that vimentin, muscle-specific actin, smooth muscle actin and CK were positive in IMT.7
Etiology has been linked to surgery, vascular causes, chronic inflammation, infection, trauma, immune disorders and autoimmune reaction, however, it remains unclear.8 The occasionally seen aggressive features and distant metastasis cannot be well explained by the inflammatory etiology alone. The current WHO classification of this lesion is intermediate grade malignant, with the potential of recurrence and rare metastasis.9 Many studies tried to link the aggressive behavior with certain molecular markers such as P-53 and translocations of ALK-1 gene, yet inconsistent results among these studies make a prediction of prognosis difficult.10 The fever may indicate a chronic inflammatory process in our case.
IMT frequently involves the lung and now has been reported at multiple extrapulmonary sites. In the urogenital tract, IMT mainly affects the urinary bladder , but rarely the kidney.11 Among the 8 cases of urinary IMT studied by Liang WJ, et al only 2 cases occurred in the kidney.12There’s no noteworthy distinction between sex and age. The clinical manifestations were not typical, mainly manifested as lumbago, gross hematuria and fever.13 In our case, The patient presented with abdominal pain accompanied with a fever. However, there were no significant past of infection, surgery, or immunology associated with the patient.
The imaging manifestations of renal IMT are highly variable due to pathological types, disease duration and blood supply, it is easy to be misdiagnosed as malignant tumor before surgery, almost all cases were diagnosed at the time of surgical intervention. When it occurs in children, it is difficult to differentiate IMT from the most common Wilms’ tumor. Few articles described the MRI findings of IMT. In our case, the mass presented round with clear boundary. T1WI showed low signal and patchy high signal shadow within it; On T2WI, there were mixed signals with multiple low-signal separations; DWI and ADC presents uneven mixed signals. Surrounding tissues were pushed but not obvious violated, no distant metastasis was observed. According to the characteristics of MRI signal, the area with high signal intensity in both DWI and ADC may be the mucous component in the lesion rather than the tumor parenchyma, which corresponds to scattered spindle cells and inflammatory cell infiltration in the pathological mucous background, thus, we can suggest that the case may belong to type I of pathological classification (mucous/vascular intensive). The MRI features of IMT need to be summarized by accumulating more cases. The purpose of imaging examination is to judge the location, size, invasion, relationship with surrounding structure and metastasis, so as to guide the patient management.
At present, anti-inflammatory drugs, steroids, surgery, even radiotherapy has been reported as an option to controlling kidney IMT.14 Nevertheless, total nephrectomy is still advocated due to a subset of rare metastasis and recurrence.15 In the present case, the preoperative diagnosis was Wilms’ tumor, as the mass was large and lead to hydronephrosis, a right nephrectomy was carried out.
Although IMT mimics malignancy, however, these tumors generally behave in an indolent manner and do not recur after complete surgical excision and the outcome is quite favorable. Local recurrence and malignant transformation have been reported in a small subset of patients, particularly in those cases in which complete surgical excision was not possible. Recurrence or metastasis has not yet been discovered from our case.