"Inflammatory pseudotumor": what is it? How does it behave?

Inflammatory pseudotumor, as a histologic diagnosis and carrying with it the prospect of a benign clinical course, is rather firmly entrenched as a pulmonary lesion. Extrapulmonic forms, however, are farraginous and, as reported, have included lesions having few, or even none, of the histologic features of those in the lungs. For those more closely aligned with the fibroblastic or myofibroblastic phase of the lung lesions, their biologic behavior can belie their histology in that they can be locally aggressive and metastasize as sarcomas. For those tumors in the upper airway, and especially in the abdomen, pathologists should be very circumspect in the use of inflammatory pseudotumor as a diagnosis, and clinicians should not be lulled into denying the extrapulmonic forms their due respect.