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The term foreign body granuloma [1-4] represents an inflammatory histiocytic/macrophagic tissue reaction pattern. It refers to one type of tissue response to exogenous (foreign) or endogenous material usually not present free in the dermis and that normally results from the direct penetration of the skin by the material itself, during surgery or by injection. Infectious granulomatous diseases should be considered in the differential diagnosis of a foreign body reaction and must be ruled out .
Causative material includes (Table I) :
– endogenous: hair shaft, keratin, calcium, cyst contents;
– exogenous: tattoo inks, sutures, hyaluronic acid, silicone, paraffin, bovine collagen and other injectable soft-tissue fillers, intralesional corticosteroids, wood, silica, talc, zirconium, beryllium, aluminum, starch, cactus, arthropod parts.
The clinical presentation depends on the tissue response to the foreign body, body site, and mode of entry, composition and quantity of the material involved. The main clinical features include erythematous brown or purple papules, nodules or plaques. Over time the lesions often become harder because of fibrosis. Some materials result in discharge even without infectious agents (e.g. paraffins and other oils) and others may produce pigmentary changes (for example, metals may result in a tattoo-like black color). As the clinical features are variable, it is essential to have a high index of suspicion and carry out a histopathological examination to confirm the diagnosis [1, 5, 6].
Histologically [1-3, 7, 8], intradermal histiocytic granulomas with giant cells (that may include foreign-body, Langhans’ and Touton types) prevail (Figure 1a, Figure 1b, Figure 2a). There are two main types of granulomas, nevertheless it may not always be easy to distinguish them and sometimes different patterns may be seen in the same section: a) the allergic type (immunologic) characterized by collections of individual histiocytes and variable numbers of lymphocytes and fewer multinucleated Langhans-type giant cells; and b) non-allergic type (“foreign body”) where the foreign body giant cells predominate in the infiltrate, which also contains histiocytes, lymphocytes and other inflammatory cells.
An optimal protocol for the identification of foreign bodies should include hematoxylin and eosin-stained sections and also special procedures, including microscopic examination with polarized light (Figure 2b), histochemical stains with Periodic Acid Schiff (PAS), silver stains (such as Grocott) or even other procedures that help in the identification of the chemical nature of the foreign material, available in some research centers, such as energy-dispersive X-ray analysis (EDXA), electron energy loss spectroscopy (EELS), laser microprobe mass analysis, and infrared spectrophotometry .
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