The histology of cotton pellet and polyvinyl sponge induced granulomas in rats (Abstract)
Sections have been taken from granulomas induced by the subcutaneous implantation of sterile cotton-wool pellets and polyvinyl sponges and these have been stained with the haematoxylin/eosin and Weigert/Van Gieson procedures. The granulomas have been removed at 9, 15 and 21 days after implantation and show a different pattern of formation in the two models. In the pellet a dense granuloma forms in and around the peripheral zone, completely encapsulating the cotton wool and barely penetrating into the centre. In the sponge, on the other hand, granuloma tissue has gradually penetrated the entire area. In the sponge random bundles of collagen fibres can be seen contrasting with the more organized fibrous sheath surrounding the pellet. Giant cells appeared in much greater frequency in the pellet, which had the characteristics of a typical foreign body granuloma, in contrast to that of the sponge, which was more characteristic of an irritant fibrosis.