Inflammatory pseudotumour of the lung. Immunohistochemical analysis on four new cases.

Inflammatory pseudotumour of the lung (I.P.) is a quite rare benign lesion, variously named by different authors. In the present report four new cases of I.P. are presented and immunohistochemically studied with a panel of antibodies. Microscopically, the most prominent histological features were the presence of interlacing bundles of elongated histiocytic-like cells, plasma cell aggregates and lymphoid follicles. Immunohistochemistry showed that plasma cells are polyclonal. The spindle cells were negative for desmin, cytokeratins, lysozyme and S-100 and immunoreactive for alpha-1-antichymotrypsin, vimentin and for smooth-muscle alpha-actin. Actin and desmin, were clearly evident in the vessels' smooth muscle layers, highlighting the angioinvasive behaviour of the lesions. Our data are in keeping with literature suggesting that I.P. is due to a mixed histiocytic-myofibroblastic-reactive proliferation and support the inflammatory nature of IP.