History
5-year-old girl with history of epigastric pain for 3 months;
fever and night sweats for 3
weeks.
Pathology
Large retroperitoneal mass at the root of the mesentery, with
loose and dense areas
displaying short fascicles of spindle cells, intimately admixed
with plasma cells and lymphocytes. Follicle-like arrangement
of lymphocytes along vessels. Immunohistochemically, the follicular
infiltrate is formed of T- and B-lymphocytes (Fig.1,2), while
the diffuse infiltrate is composed of Tlymphocytes, plasma cells
and macrophages. The spindle cells are strongly positive for
smooth muscle actin and focally positive for desmin and pancytokeratin,
as well as positive for the transcription factor ALK1. The proliferation
index (MIB-1) of the spindle cell population is less than 5%.
Mast cells are not prominent.
Discussion
Inflammatory myofibroblastic tumour (IMT) is characterized by
a mixture of myofibroblasts, fibroblasts, lymphocytes and plasma
cells, in proportions varying from one microscopic field to
another and from one tumor to another. An often used term is
“inflammatory pseudotumour”, which is correct in
certain sites and circumstances, e.g. in the bladder (postoperative
spindle cell nodule) or in the lungs of young children (plasma
cell granuloma). Most IMT will indeed regress, even after incomplete
surgery; however, there is a minority of cases which can progress
rapidly, metastasize and kill the patient; those cases have been
termed inflammatory fibrosarcoma.
Studies on a limited number of cases have demonstrated the presence
of a clonal cytogenetic abnormality and ALK-expression similar
to anaplastic large cell lymphoma. The ALK-kinase is normally
located at the inner surface of the cell membrane of neural cells.
The fusion transcript (CLTC-ALK) is a fusion oncogene that can
transform lymphoid as well as mesenchymal human cell lineages.
A recent paper reports that some cases of IMT might constitute
a reaction to the invasion of bacteria. The differential diagnosis
includes calcifying fibrous pseudotumor (this
has dystrophic, ossifying, or psammomatous calcifications; metastases
have not been reported). Inflammatory pseudotumor-like
follicular dendritic cell tumor is a subset of dendritic
cell tumours with a morphology very similar to inflammatory myofibroblastic
tumour. All reported cases were positive for CD21 and EBER. The inflammatory
type of malignant fibrous histiocytoma contains bizarre
pleomorphic and xanthomatous cells; the neoplastic cell is negative
for smooth muscle actin and may express leukocyte lineage markers.
