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.