IMT is the most frequent benign primary lung tumor in childhood. Due to
confusion about the histogenesis of the lesion, various synonyms have been
used (such as inflammatory, pseudotumor, plasma cell granuloma e.g.) In the
last few years, IMT with borderline biological course, has been described in
which myofibroblasts represent not only a reactive mechanism but also a true
neoplastic component. It has been regarded as a benign and reactive disorder
for a long time. Only in recent reports it has been demonstrated that, in spite of
an apparently benign morphological pattern, some cases of IMTs have a
malignant course [
3,
4,
7].
The myofibroblast was eventually recognised as the principal spindle-cell
type in this tumor, which led to the new term IMT. Myofibroblasts are spindle
cells having ultra-structural features in common with smooth muscle cells and
fibroblasts. The important function of the myofibroblast in tissue repair is
consistent with the hypothesis that an aberrant response to tissue injury is the
pathogenesis of IMT, however in most cases there is no identifiable
precipitating factor [2,6].
Evidence to support a directly infectious etiology is scanty but an
immunological pathogenesis remains possible. The role of cytokines,
particularly interleukin-6 (IL-6) in pathogenesis and the possibility for a specific
therapeutic approach has been described. Many authors postulate a post
inflammatory process; although the presence of clonal chromosomal
abnormalities suggests a neoplastic process [1,5,7].
Until 1992, a total of 21 children, predominantly female, with IMTs affecting
intra-abdominal sites have been reported in the literature. These tumors are
often large. Multi-centric lesions are rare. There are no reports of malignancy
arising in an IMT; nevertheless, the clinical, radiological and histological
features of these may cause confusion with malignant lesions. Most patients
presented with fever, anemia, trombocytosis, hyperglobulinemia and weight
loss. These systemic features resolve after tumor excision but may enable the
diagnosis to be suspected before operation. Misdiagnosis has led some
patients to be inappropriately treated with chemotherapy and radical surgery
[2,4].
In IMTs, high cellularity with large, plump, active myofibroblasts with
prominent nucleoli can cause confusion with malignancy, in particular
rhabdomyosarcoma. However the lack of atypia, hyperchromasia and abnormal
mitotic figures are pointers toward a benign lesion. IMT should be diagnosed by
routine staining because special stains and immunocytochemistry can be
misleading. Preliminary biopsy and full histological evaluation is recommended
in cases where resection may be particularly hazardous [5,6,7].
Other reasons for confusion of IMTs with malignant neoplasms include their
capacity for local tissue infiltration, occasional rapid growth and the
development of local recurrence. Mediastinal and esophageal involvement from
adjacent pulmonary pathology appears to be particularly aggressive. Their
course is complicated, which ranges from spontaneous regression through
gradual enlargement to rapid growth with local invasion. Tumor resolution or
regression has been reported after radiotherapy, chemotherapy and steroid
therapy. Local recurrences after incomplete excision are recognised, may occur
many years later and may be fatal. This underlines the importance of complete
surgical resection whenever possible [1,3].
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