Oral inflammatory pseudotumour: immunohistochemical investigation of a case involving the submandibular gland and review of the literature.

Inflammatory pseudotumours (IPs) are rare lesions. Most commonly reported in the lung, they are almost ubiquitous, but few oral cases have been described. Their rapid growth, local invasiveness and recurrence, and their ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) aspects are confusing and mimic benign or malignant neoplasms. Their recognition and distinction from malignant tumors is of importance but their histopathological diagnosis may represent a challenge. In the case reported involving the submandibular gland, the spindle cells had the immunohistochemical profile of myofibroblasts, broader cells with a larger nucleus were CD68 and/or Mac387 positive and the dense plasmacytic infiltrate was polyclonal. Histopathology of IPs covers a spectrum of appearances according to the cellularity and the degree of fibrosis. The recognition of a variable mixture of three main cell types: histiocytes or macrophages, myofibroblasts or fibroblasts and abundant plasma cells, with low mitotic activity and absence of cytological abnormalities in an ill circumscribed and rather fibrous lesion is recommended for the diagnosis of oral IP.